climate change and human health essay

Why climate change is still the greatest threat to human health

Polluted air and steadily rising temperatures are linked to health effects ranging from increased heart attacks and strokes to the spread of infectious diseases and psychological trauma.

People around the world are witnessing firsthand how climate change can wreak havoc on the planet. Steadily rising average temperatures fuel increasingly intense wildfires, hurricanes, and other disasters that are now impossible to ignore. And while the world has been plunged into a deadly pandemic, scientists are sounding the alarm once more that climate change is still the greatest threat to human health in recorded history .

As recently as August—when wildfires raged in the United States, Europe, and Siberia—World Health Organization Director-General Tedros Adhanom Ghebreyesus said in a statement that “the risks posed by climate change could dwarf those of any single disease.”

On September 5, more than 200 medical journals released an unprecedented joint editorial that urged world leaders to act. “The science is unequivocal,” they write. “A global increase of 1.5°C above the pre-industrial average and the continued loss of biodiversity risk catastrophic harm to health that will be impossible to reverse.”

Despite the acute dangers posed by COVID-19, the authors of the joint op-ed write that world governments “cannot wait for the pandemic to pass to rapidly reduce emissions.” Instead, they argue, everyone must treat climate change with the same urgency as they have COVID-19.

Here’s a look at the ways that climate change can affect your health—including some less obvious but still insidious effects—and why scientists say it’s not too late to avert catastrophe.

Air pollution

Climate change is caused by an increase of carbon dioxide and other greenhouse gases in Earth’s atmosphere, mostly from fossil fuel emissions. But burning fossil fuels can also have direct consequences for human health. That’s because the polluted air contains small particles that can induce stroke and heart attacks by penetrating the lungs and heart and even traveling into the bloodstream. Those particles might harm the organs directly or provoke an inflammatory response from the immune system as it tries to fight them off. Estimates suggest that air pollution causes anywhere between 3.6 million and nine million premature deaths a year.

“The numbers do vary,” says Andy Haines , professor of environmental change and public health at the London School of Hygiene and Tropical Medicine and author of the recently published book Planetary Health . “But they all agree that it’s a big public health burden.”

People over the age of 65 are most susceptible to the harmful effects of air pollution, but many others are at risk too, says Kari Nadeau , director of the Sean N. Parker Center for Allergy and Asthma Research at Stanford University. People who smoke or vape are at increased risk, as are children with asthma.

Air pollution also has consequences for those with allergies. Carbon dioxide increases the acidity of the air, which then pulls more pollen out from plants. For some people, this might just mean that they face annoyingly long bouts of seasonal allergies. But for others, it could be life-threatening.

“For people who already have respiratory disease, boy is that a problem,” Nadeau says. When pollen gets into the respiratory pathway, the body creates mucus to get rid of it, which can then fill up and suffocate the lungs.

Even healthy people can have similar outcomes if pollen levels are especially intense. In 2016, in the Australian state of Victoria, a severe thunderstorm combined with high levels of pollen to induce what The Lancet has described as “the world’s largest and most catastrophic epidemic of thunderstorm asthma.” So many residents suffered asthma attacks that emergency rooms were overwhelmed—and at least 10 people died as a result.

Climate change is also causing wildfires to get worse, and wildfire smoke is especially toxic. As one recent study showed, fires can account for 25 percent of dangerous air pollution in the U.S. Nadeau explains that the smoke contains particles of everything that the fire has consumed along its path—from rubber tires to harmful chemicals. These particles are tiny and can penetrate even deeper into a person’s lungs and organs. ( Here’s how breathing wildfire smoke affects the body .)

Extreme heat

Heat waves are deadly, but researchers at first didn’t see direct links between climate change and the harmful impacts of heat waves and other extreme weather events. Haines says the evidence base has been growing. “We have now got a number of studies which has shown that we can with high confidence attribute health outcomes to climate change,” he says.

Most recently, Haines points to a study published earlier this year in Nature Climate Change that attributes more than a third of heat-related deaths to climate change. As National Geographic reported at the time , the study found that the human toll was even higher in some countries with less access to air conditioning or other factors that render people more vulnerable to heat. ( How climate change is making heat waves even deadlier .)

That’s because the human body was not designed to cope with temperatures above 98.6°F, Nadeau says. Heat can break down muscles. The body does have some ways to deal with the heat—such as sweating. “But when it’s hot outside all the time, you cannot cope with that, and your heart muscles and cells start to literally die and degrade,” she says.

If you’re exposed to extreme heat for too long and are unable to adequately release that heat, the stress can cause a cascade of problems throughout the body. The heart has to work harder to pump blood to the rest of the organs, while sweat leeches the body of necessary minerals such as sodium and potassium. The combination can result in heart attacks and strokes .

Dehydration from heat exposure can also cause serious damage to the kidneys, which rely on water to function properly. For people whose kidneys are already beginning to fail—particularly older adults—Nadeau says that extreme heat can be a death sentence. “This is happening more and more,” she says.

Studies have also drawn links between higher temperatures and preterm birth and other pregnancy complications. It’s unclear why, but Haines says that one hypothesis is that extreme heat reduces blood flow to the fetus.

Food insecurity

One of the less direct—but no less harmful—ways that climate change can affect health is by disrupting the world’s supply of food.

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Climate change both reduces the amount of food that’s available and makes it less nutritious.   According to an Intergovernmental Panel on Climate Change (IPCC) special report , crop yields have already begun to decline as a result of rising temperatures, changing precipitation patterns, and extreme weather events. Meanwhile, studies have shown that increased carbon dioxide in the atmosphere can leech plants of zinc, iron, and protein—nutrients that humans need to survive.

Malnutrition is linked to a variety of illnesses, including heart disease, cancer, and diabetes. It can also increase the risk of stunting, or impaired growth , in children, which can harm cognitive function.

Climate change also imperils what we eat from the sea. Rising ocean temperatures have led many fish species to migrate toward Earth’s poles in search of cooler waters. Haines says that the resulting decline of fish stocks in subtropic regions “has big implications for nutrition,” because many of those coastal communities depend on fish for a substantial amount of the protein in their diets.

This effect is likely to be particularly harmful for Indigenous communities, says Tiff-Annie Kenny, a professor in the faculty of medicine at Laval University in Quebec who studies climate change and food security in the Canadian Arctic. It’s much more difficult for these communities to find alternative sources of protein, she says, either because it’s not there or because it’s too expensive. “So what are people going to eat instead?” she asks.

Infectious diseases  

As the planet gets hotter, the geographic region where ticks and mosquitoes like to live is getting wider. These animals are well-known vectors of diseases such as the Zika virus, dengue fever, and malaria. As they cross the tropics of Cancer and Capricorn, Nadeau says, mosquitoes and ticks bring more opportunities for these diseases to infect greater swaths of the world.

“It used to be that they stayed in those little sectors near the Equator, but now unfortunately because of the warming of northern Europe and Canada, you can find Zika in places you wouldn’t have expected,” Nadeau says.

In addition, climate conditions such as temperature and humidity can impact the life cycle of mosquitoes. Haines says there’s particularly good evidence showing that, in some regions, climate change has altered these conditions in ways that increase the risk of mosquitos transmitting dengue .

There are also several ways in which climate change is increasing the risk of diseases that can be transmitted through water, such as cholera, typhoid fever, and parasites. Sometimes that’s fairly direct, such as when people interact with dirty floodwaters. But Haines says that drought can have indirect impacts when people, say, can’t wash their hands or are forced to drink from dodgier sources of freshwater.

Mental health

A common result of any climate-linked disaster is the toll on mental health. The distress caused by drastic environmental change is so significant that it has been given its own name— solastalgia .

Nadeau says that the effects on mental health have been apparent in her studies of emergency room visits arising from wildfires in the western U.S. People lose their homes, their jobs, and sometimes their loved ones, and that takes an immediate toll. “What’s the fastest acute issue that develops? It’s psychological,” she says. Extreme weather events such as wildfires and hurricanes cause so much stress and anxiety that they can lead to post-traumatic stress disorder and even suicide in the long run.

Another common factor is that climate change causes disproportionate harm to the world’s most vulnerable people. On September 2, the Environmental Protection Agency (EPA) released an analysis showing that racial and ethnic minority communities are particularly at risk . According to the report, if temperatures rise by 2°C (3.6°F), Black people are 40 percent more likely to live in areas with the highest projected increases in related deaths. Another 34 percent are more likely to live in areas with a rise in childhood asthma.

Further, the effects of climate change don’t occur in isolation. At any given time, a community might face air pollution, food insecurity, disease, and extreme heat all at once. Kenny says that’s particularly devastating in communities where the prevalence of food insecurity and poverty are already high. This situation hasn’t been adequately studied, she says, because “it’s difficult to capture these shocks that climate can bring.”

Why there’s reason for hope

In recent years, scientists and environmental activists have begun to push for more research into the myriad health effects of climate change. “One of the striking things is there’s been a real dearth of funding for climate change and health,” Haines says. “For that reason, some of the evidence we have is still fragmentary.”

Still, hope is not lost. In the Paris Agreement, countries around the world have pledged to limit global warming to below 2°C (3.6°F)—and preferably to 1.5°C (2.7°F)—by cutting their emissions. “When you reduce those emissions, you benefit health as well as the planet,” Haines says.

Meanwhile, scientists and environmental activists have put forward solutions that can help people adapt to the health effects of climate change. These include early heat warnings and dedicated cooling centers, more resilient supply chains, and freeing healthcare facilities from dependence on the electric grid.

Nadeau argues that the COVID-19 pandemic also presents an opportunity for world leaders to think bigger and more strategically. For example, the pandemic has laid bare problems with efficiency and equity that have many countries restructuring their healthcare facilities. In the process, she says, they can look for new ways to reduce waste and emissions, such as getting more hospitals using renewable energy.

“This is in our hands to do,” Nadeau says. “If we don’t do anything, that would be cataclysmic.”

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Impacts of Climate Change on Human Health: Emerging Evidence and Call to Action

Introduction.

It is already widely known that the climate crisis is an existential threat that is already impacting every aspect of human society and the planet. Hence, action from all sectors is not only necessary but urgent. One area that requires immediate attention is the impact of climate change on human health. For the past three decades, there have been numerous efforts from the academic and policy worlds to highlight the immutable connection between human health and climate change. However, it was only during the 26th Conference of Parties (COP26) of the United Nations Framework Convention on Climate Change, which was held in November 2021 in Glasgow, Scotland, that health started to receive an appropriate level of attention, in large part due to the still-ongoing Coronavirus disease (COVID-19) pandemic. Under the leadership of the World Health Organization (WHO) a two-week series of activities and discussions was held, bringing together health professionals, researchers, policymakers and advocates to highlight the importance of health in the climate discourse. The COP26 health programme culminated with more than 50 countries making a commitment to build climate-smart national health systems that are both resilient to the growing impacts of climate change and sustainable, so that they do no further harm to the planet through carbon emissions and other types of pollution ( 1 ). We hope that Malaysia will join in this global campaign.

Climate change affects human health in many different ways. For example, extreme weather events such as typhoons and intense flooding result in water-borne diarrheal disease outbreaks or worse forced displacement of entire communities to new locations without reliable access to food, water and other life-sustaining services. Changes in environmental conditions such as precipitation and temperature influence the behaviour of disease-carrying mosquitoes, resulting in more outbreaks and reduced crop yields leading to hunger and malnutrition. Because of the diverse ways in which climate change influences health the magnitude of its health impact is challenging to measure or estimate. For instance, the WHO previously estimated that, due to climate change alone, there will be 250,000 additional deaths annually between 2030 and 2050 resulting from climate-sensitive diseases such as undernutrition, infectious diseases and heat-related illness ( 2 ). A newer study projected that if business as usual continues, an additional 83 million people will die from exposure to extreme heat alone by the end of the century ( 3 ). One certainty is that the direction of change in negative health outcomes due to climate change is upwards—more diseases, disabilities and even deaths in the years and decades to come.

Below, we summarise some of the latest research and events that must sound the alarm bells for us in the medical sector—emerging health challenges linked to climate change that we must pay attention to and urgently act on.

Future Pandemics

The COVID-19 pandemic may not be over yet but we must already be alert to the possibility of future ones. Pandemics originate from zoonotic spillover events—when pathogens jump from animals to human beings. This means that we must tackle the major factors that tighten the animal-human interface where such spillover events do occur. One of the known drivers of infectious disease emergence is rapid and widespread urbanisation, which impinges and disturbs natural habitats where pathogen-carrying animals live. Other human activities that bring people closer to animals include wildlife consumption and trade as well as animal farming for meat production.

An added driver to all these human activities is the evolving climate crisis (which, let us remember, is also driven by human behaviour), which alters environmental conditions not only for humans and animals but also for pathogens with pandemic potential. Using machine learning, a recent study revealed that by 2070, there will be at least 15,000 cross-species transmission events of at least one novel virus that could occur between mammals, including human beings, if climate change continues to worsen and if the goals of the Paris Agreement are not achieved ( 4 ). The majority of these zoonotic spillovers will occur in Southeast Asia, which is a major biodiversity hotspot. Therefore, preventing the next pandemic in our own backyard must be a priority for Malaysia and the Association of Southeast Asian Nations (ASEAN). Currently, the WHO is negotiating a future pandemic treaty to ensure that COVID-19 does not happen again. This new treaty must, therefore, emphasise pandemic prevention through tackling the aforementioned infectious disease drivers, including climate change.

Exposure to Extreme Heat

Over the past months, we have witnessed heat wave events wreak havoc in China, Central Asia and Europe, resulting to spikes in emergency room visits and even deaths. Being in a tropical region, we in Malaysia may be feeling complacent about the potential impacts of extreme heat on our health. One analysis estimates that under one of the climate scenarios, by 2050, between 600 million and 1 billion people in Asia will be living in areas that are likely to experience lethal heat waves each year ( 5 ). In major cities in other regions such as Athens and Los Angeles, local governments are already appointing ‘Chief Heat Officers’ that will lead the development of city health plans to increase community resilience to extreme heat—a policy innovation that we can easily emulate ( 6 ).

Moreover, extreme heat not only affects people directly but also other sectors on which human survival depends. For instance, the agriculture sector is also very sensitive to climate crisis, particularly to drought which can destroy croplands and jeopardise food security. Thus, there is an increasingly urgent need to enhance the resilience of the agricultural sector to climate change impacts—while also lowering its carbon emissions and ecological footprint. One of the proposed solutions is the adoption of the Planetary Health Diet—a diet that provides nutrition for all people while also protecting the planet ( 7 ). We must investigate the feasibility of this diet in Malaysia, given our unique cultural, geographic and social context.

Climate Change and Mental Health

The physical health impacts of climate change, such as the diseases mentioned above, are much more widely known to the medical community and the broader public. What receives little attention is the impact of climate change on people’s mental and emotional wellbeing. In the disaster response and humanitarian sectors, there is some awareness of the importance of addressing post-traumatic stress experienced by victims of typhoons and other calamities. However, other indirect and subtle pathways by which climate change affects mental health are less well understood.

For instance, the concept of ‘climate anxiety,’ which includes a wide range of emotions about climate change, remains to be investigated especially in non-Western contexts ( 8 ). Particularly, vulnerable to climate anxiety are young people who are feeling increasingly concerned about their futures in a scenario of an unstable climate. One recent cross-sectional study of young people from 10 countries, revealed that the young people from the Philippines are the most climate-anxious in the world, possibly due to their direct experience of extreme weather events ( 9 ). This growing mental health pandemic driven by the climate crisis will impose an enormous additional burden on existing mental healthcare systems which are largely underdeveloped, deeply stigmatised and poorly resourced. This emerging area calls for more transdisciplinary collaborative research between psychologists, psychiatrists, social scientists and experts from other related disciplines—not only to assess the magnitude of this problem but also capture people’s lived experiences and develop interventions and policies that will enhance people’s mental resilience to the climate crisis.

With these emerging health threats driven by climate change as well as existing health problems that the climate crisis will exacerbate, we, in the medical community must embrace climate change as our own issue of concern as well as part of our healing enterprise. The Malaysian medical community can begin by coming together to declare that while we talk about climate change, we are now faced with the reality of a climate crisis which constitutes a public health emergency. This will ensure that building a national climate-resilient health system becomes an integral part of our country’s health reform agenda.

Such a declaration can also be used for our advocacy activities with other sectors and disciplines, especially those that require urgent climate mitigation and adaptation actions such as the energy and food sectors. The above-mentioned climate-related health issues must also be incorporated into the teaching of medical and other health students, as they will be the ones who will be preventing and treating these diseases in the decades to come. Finally, our medical institutes and research funders must invest in climate and health research in order to study the unknowns about the climate-health nexus and develop evidence-based solutions that will protect our citizens from the health impacts of the climate crisis.

Acknowledgements

Conflict of Interest

Authors’ Contributions

Conception and design: JM, RRG

Analysis and interpretation of the data: JM, RRG

Drafting of the article: JM, RRG

Critical revision of the article for important intellectual content: JM, RRG

Final approval of the article: JM, RRG

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Focus  10 May 2024

Climate Change and Human Health

Climate change is profoundly impacting human health, with direct and indirect effects on physical, mental and social health. In light of the growing recognition of the climate change–health intersection, here we feature a collection of recent research and opinion pieces on the theme from Nature Climate Change, and from across the Nature Portfolio.

Features and Opinions

Talking about climate change and health

The climate crisis is also an urgent and ongoing health crisis with diverse human impacts leading to physical, mental and cultural losses. Translating knowledge into action involves broad collaboration, which relies heavily on careful communication of a personal and politicized issue.

Climate change in and out of the therapy room

Climate change can have profound impacts on mental health, yet few therapists receive training on how to talk to their clients about this issue. This Comment explores strategies for therapists to best support clients in climate distress.

Considering health can drive climate action

Last December saw the inaugural Health Day at a Climate Conference of the Parties (COP) and the announcement of the COP28 UAE Declaration on Climate and Health, marking a substantial step in global recognition of the intersecting crises of climate change and health . Nature Climate Change speaks to Maria Neira, director of the Department of Environment, Climate Change and Health at the World Health Organization, about successes and next steps.

• Tegan Armarego-Marriott

Bringing health out of the clinic and into the courts

Scientists and health professionals acknowledge that climate change is also a health emergency, but responses have been slow. Now, citizens and experts are turning to the courts as a path towards accountability, action and adaptation.

• Yessenia Funes

Views on climate change and health

Climate change is a health emergency, impacting multiple facets of human well-being via direct and indirect pathways. Nature Climate Change asked experts from different health fields to share their thoughts on the urgent issues and possible paths forward.

• Jessica Fanzo
• Elizabeth Marks

Death by climate change

As deaths attributable to climate change increase, there has been a call from some scientists for the inclusion of climate-related data on death certificates. However, others argue that there are more important methods to reduce the impacts of climate extremes on people.

• Carrie Arnold

The role of the scientific community in strengthening disability-inclusive climate resilience

Despite the trajectory towards climate catastrophe, governments are failing to take disability-inclusive climate action. We discuss how the scientific community could advance and hasten the development of disability-inclusive climate resilience, and which areas should be prioritized.

• Penelope J. S. Stein
• Michael Ashley Stein

Reducing personal climate risk to reduce personal climate anxiety

Climate anxiety, reflecting concerns about the negative impacts of climate change, is growing. Planning and action on individual specific climate risks could be a way to reduce personal climate anxiety.

• Jeremy Fyke
• Andrew Weaver

Research Papers

Analysing health system capacity and preparedness for climate change

The authors perform a meta-analysis to assess current and future capacities of healthcare systems under climate change. They summarize the key focus points of current literature and highlight the need for effective policies, trained workforces and redesigned infrastructure to meet future burdens.

• Jeffrey Braithwaite
• Yvonne Zurynski

Over half of known human pathogenic diseases can be aggravated by climate change

A systematic review shows that >58% of infectious diseases confronted by humanity, via 1,006 unique pathways, have at some point been affected by climatic hazards sensitive to GHGs. These results highlight the mounting challenge for adaption and the urgent need to reduce GHG emissions.

• Camilo Mora
• Tristan McKenzie
• Erik C. Franklin

Risk factors associated with heatwave mortality in Chinese adults over 65 years

In a prospective cohort of Chinese participants aged 65 years and older, heatwaves doubled the risk of mortality, especially in adults with functional impairments and dependency on daily living activities.

Anthropogenic emissions and urbanization increase risk of compound hot extremes in cities

Heat extremes threaten the health of urban residents with particularly strong impacts from day–night sustained heat. Observation and simulation data across eastern China show increasing risks of compound events attributed to anthropogenic emissions and urbanization.

Health co-benefits of climate change mitigation depend on strategic power plant retirements and pollution controls

Climate mitigation policies often provide health co-benefits. Analysis of individual power plants under future climate–energy policy scenarios shows reducing air pollution-related deaths does not automatically align with emission reduction policies and that policy design needs to consider public health.

• Guannan Geng
• Steven J. Davis

A meta-analysis on global change drivers and the risk of infectious disease

Reducing greenhouse gas emissions, managing ecosystem health, and preventing biological invasions and biodiversity loss could help to reduce the burden of plant, animal and human diseases, especially when coupled with improvements to social and economic determinants of health.

• Michael B. Mahon
• Alexandra Sack
• Jason R. Rohr

City-level impact of extreme temperatures and mortality in Latin America

An ecological analysis of 326 cities in 9 countries across Latin America found that changes in ambient temperature have a substantial contribution to all-cause mortality, with small increases in extreme heat associated with steep increases in mortality risk.

• Josiah L. Kephart
• Brisa N. Sánchez
• Daniel A. Rodríguez

Hazardous heat exposure among incarcerated people in the United States

An increasingly warm climate can lead to more intense, frequent and longer periods of hazardous heat, increasing the risk of heat-related health concerns. This study assesses whether incarcerated people in the United States are potentially disproportionately exposed to such hazardous heat conditions.

• Cascade Tuholske
• Victoria D. Lynch
• Robbie M. Parks

Effects of global climate mitigation on regional air quality and health

More efficient and targeted climate mitigation policies require an improved understanding of how the associated air quality and health benefits will be distributed. This study assesses, at the country level, the health effects of a global carbon price under different future scenarios.

• Xinyuan Huang
• Vivek Srikrishnan

Exploratory empirical model of combined effects of COVID-19 and climate change on youth mental health

In this article, the authors use survey data from youth in three countries from the Caribbean to provide an evidence-based model of the association of climate distress and generalized anxiety and well-being more broadly.

• Quinta Seon
• Natalie Greaves
• Sandeep B. Maharaj

Impact of anthropogenic CO 2 emissions on global human nutrition

Elevated atmospheric CO 2 (550 ppm) could cause an additional 175 million people to be zinc deficient and 122 million protein deficient (assuming 2050 population and CO 2 projections) due to the reduced nutritional value of staple food crops.

• Matthew R. Smith
• Samuel S. Myers

Expanding ocean food production under climate change

Sustainable mariculture could increase seafood production under almost all climate-change scenarios analysed, but this would require substantial fisheries reforms, continued advances in feed technology and the establishment of effective mariculture governance and best practices.

• Christopher M. Free
• Reniel B. Cabral
• Steven D. Gaines

Climate change increases cross-species viral transmission risk

Changes in climate and land use will lead to species aggregating in new combinations at high elevations, in biodiversity hotspots and in areas of high human population density in Asia and Africa, driving the cross-species transmission of animal-associated viruses.

• Colin J. Carlson
• Gregory F. Albery
• Shweta Bansal

Amplified positive effects on air quality, health, and renewable energy under China’s carbon neutral target

The interaction between aerosol and meteorology amplifies the positive effects on air quality, health and renewable energy under China’s carbon neutrality target for 2060, according to an integrated modelling analysis.

Heat-related mortality in Europe during the summer of 2022

This ecological analysis using the Eurostat database estimated that summer 2022, the hottest summer on record, was associated with over 61,000 heat-related deaths across 35 countries in Europe, with the highest mortality rates in countries near the Mediterranean Sea.

• Joan Ballester
• Marcos Quijal-Zamorano
• Hicham Achebak

Stakeholder-driven transformative adaptation is needed for climate-smart nutrition security in sub-Saharan Africa

Effective solutions for food systems transformation must be designed in a participatory way. This study illustrates the application of an integrated assessment framework to explore stakeholder-driven scenarios towards climate-smart nutrition security in Malawi, South Africa, Tanzania and Zambia.

• Stewart Jennings
• Andrew Challinor

A systematic review of the effects of chronic, slow-onset climate change on mental health

Burrows, Denckla and colleagues performed a systematic review to evaluate the available evidence linking climate change to mental health outcomes.

• Kate Burrows
• Christy A. Denckla
• Sarah R. Lowe

Climate change exacerbates nutrient disparities from seafood

The authors use fisheries databases and predictive models to understand past and future changes in the availability of iron, calcium omega-3 and protein from seafood. They show disproportional loss of nutrients in tropical low-income countries, which will be exacerbated by higher levels of global warming.

• William W. L. Cheung
• Christina C. Hicks

Impact of extreme weather events on healthcare utilization and mortality in the United States

Analysis of 42 severe weather disasters (floods, storms and cyclones) in the United States between 2011 and 2016 reported associations with increased emergency department utilization and mortality in affected counties for up to 6 weeks.

• Renee N. Salas
• Laura G. Burke
• Ashish K. Jha

Reviews and Perspectives

Infectious disease in an era of global change

Global change, including climate change, urbanization and global travel and trade, has affected the emergence and spread of infectious diseases. In the Review, Baker, Metcalf and colleagues examine how global change affects infectious diseases, highlighting examples ranging from COVID-19 to Zika virus disease.

• Rachel E. Baker
• Ayesha S. Mahmud
• C. Jessica E. Metcalf

Climate change affects multiple dimensions of well-being through impacts, information and policy responses

This Review by Neil Adger and colleagues examines the multiple dimensions of human well-being that are affected by climate change. The authors propose policy and research priorities that are oriented towards supporting well-being.

• W. Neil Adger
• Jon Barnett
• Sergio Jarillo

Climate change and health: three grand challenges

This Review outlines three ‘grand challenges’ to protect and promote health in the face of climate change, and discusses the role of the health community in driving change within and beyond the health sector.

• Diarmid Campbell-Lendrum
• Tara Neville
• Maria Neira

Climate change and cardiovascular disease: implications for global health

The relationship between climate change and health outcomes is complex. In this Review, Rajagopalan and colleagues describe the environmental exposures associated with climate change and provide an overview of the consequences of climate change, including air pollution and extreme temperatures, on cardiovascular health and disease.

• Haitham Khraishah
• Barrak Alahmad
• Sanjay Rajagopalan

Environmental effects of surgical procedures and strategies for sustainable surgery

Health care contributes to the climate change burden, and measures should be taken to mitigate these effects. This Perspective discusses the carbon footprint of surgery in gastroenterology and hepatology and offers an overview of sustainable strategies.

• Miguel F. Cunha
• Gianluca Pellino

A social–ecological perspective on climate anxiety in children and adolescents

Children and adolescents may be the age cohort most vulnerable to climate anxiety. This Review uses a social–ecological theoretical framework to outline how they are uniquely susceptible to climate anxiety and identify potential protective factors.

• Tara J. Crandon
• James G. Scott
• Hannah J. Thomas

Further Reading

Climate change is also a health crisis — these 3 graphics explain why

Health is on the agenda at the COP28 climate meeting. Rising temperatures increase the spread of infectious diseases, claim lives and drive food insecurity.

• Carissa Wong

These veteran female activists are fighting a pivotal climate case with science

Research on the effects of climate change on health will be key in high-profile lawsuits being heard by Europe’s human-rights court.

• Layal Liverpool

Antibiotic resistance is a growing threat — is climate change making it worse?

Researchers are studying how extreme weather and rising temperatures can encourage the spread of drug-resistant infections.

Exploring the nurturing effects of nature on mental health

In this Q&A, we speak to Melissa Marselle, a member of the British Psychological Society’s Climate Environment Action Coordinating Group , which supports and advises on the implementation of effective climate change and environment work rooted in psychological evidence, and a lecturer of environmental psychology at the University of Surrey , UK. Her research examines the mental health benefits of contact with nature, with a specific focus on biodiversity.

• Natalia Gass

What happens when climate change and the mental-health crisis collide?

The warming planet is worsening mental illness and distress. Researchers need to work out the scale of the problem and how those who need assistance can be helped.

The rise of eco-anxiety: scientists wake up to the mental-health toll of climate change

Researchers want to unpick how climate change affects mental health around the world — from lives that are disrupted by catastrophic weather to people who are anxious about the future.

• Helen Pearson

After millions of preventable deaths, climate change must be treated like a health emergency

Health impacts from climate change have been apparent for at least 20 years, but the climate crisis is still not treated like other global public health emergencies.

Do no harm: addressing the environmental impact of health care

Planetary and human health are inseparably connected; yet, health-care systems produce considerable amounts of greenhouse gas emissions, waste and pollution. A growing movement to measure and mitigate the health sector’s own climate damage is underway, supported by national policies and clinical innovation.

• Frances Mortimer
• David Pencheon

Climate change and health: understanding mechanisms will inform mitigation and prevention strategies

The cellular and molecular mechanisms underlying the health impacts of climate change must be better understood in order to plan interventions that mitigate harm.

• Diddier Prada
• Andrea A. Baccarelli

Tackling climate change and deforestation to protect against vector-borne diseases

The spread of vector-borne infectious diseases is driven by a complex array of environmental and social drivers, including climate and land-use changes. Global and regional action is urgently needed to tackle carbon emissions and deforestation to halt future outbreaks.

• Erin A. Mordecai

Climate and health strategies must take vaccination into account

• Nidhee Jadeja
• Judy Omumbo
• Marta Tufet Bayona

Climate change-fuelled natural disasters and chronic kidney disease: a call for action

People with kidney disease are particularly vulnerable to the impacts of natural disasters and extreme weather events. As climate change is increasing the frequency and severity of these events, a robust response is needed to improve disaster preparedness and increase the resilience of these patients.

• Amir Sapkota
• Peter Kotanko

Eco-distress is not a pathology, but it still hurts

Climate change and ecological emergencies threaten life on Earth. This creates a distress that is in danger of being pathologized and dismissed. We examine how such feelings are rational and underpinned by instinctive compassion for the environment and each other. We must respond by supporting people to act with their full potential, amidst systemic and government failures.

• Caroline Hickman

Climate change and nutrition-associated diseases

Climate change has multiple negative effects on global public health; reduced quality and quantity of crops result in increased food and financial insecurities leading to malnutrition (undernutrition and obesity) and diet-related non-communicable diseases, such as diabetes mellitus and cardiovascular diseases. In addition, food systems substantially contribute to greenhouse gas emissions and a shift towards sustainability is required to preserve human and planetary health.

• Jessica C. Fanzo
• Shauna M. Downs

Climate change impacts on bird migration and highly pathogenic avian influenza

The unprecedented extent of highly pathogenic avian influenza coincides with intensifying global climate changes that alter host ecology and physiology, and could impact virus evolution and dynamics.

• Diann J. Prosser
• Claire S. Teitelbaum
• Xiangming Xiao

Global warming could drive the emergence of new fungal pathogens

Increased heat tolerance in fungi with pathogenic potential due to global warming could bring new fungal diseases.

• Arturo Casadevall

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How Climate Change Affects Health and How Countries Can Respond

• Climate Resilience
• adaptation finance
• climate change
• climatewatch-pinned

Since early 2020, the world’s attention has been on the global coronavirus pandemic. The pandemic continues to put massive stress on existing health systems, exposing their fault lines. As nations think about how to make health systems more resilient to current and future threats, one threat must not be overlooked: climate change is also impacting human health and straining heavily burdened health services everywhere.

Health-related risks linked to climate change range widely, from increased likelihood of transmitting vector-borne diseases to decreased access to services as a result of natural disasters. For example, air pollution — the sources of which are often the same as those that drive climate change — kills 4.2 million people every year and makes countless more sick and debilitated. Ground-level ozone, a key component of air pollution, is even more harmful to human health when temperatures are higher. Climate change events like hurricanes and floods can also destroy or limit access to health infrastructure and services.

Human health is a priority in 59% of countries’ national climate adaptation commitments under the Paris Agreement and close to half of countries acknowledge the negative health effects of climate change. However, countries struggle to understand specific climate risks to health, as well as how to identify and fund comprehensive health adaptation actions. Only 0.5% of multilateral climate finance targets health projects. Domestic funding for this issue is also minimal or nonexistent.

This is unacceptable considering the need for resilient and stable health systems.

A new paper by WRI showcases how countries can integrate health-related risks from climate change into their national climate and health strategies and put them into action. Doing so is essential, not only in preventing the worst impacts of climate change, but in keeping people healthy and nations prosperous.

How Does Climate Change Affect Human Health?

There are many ways health risks link to climate change, which often intersect with one another. Common risks include:

1. Increased risk of vector- and water-borne diseases.

Climate change is redistributing and increasing the optimal habitats for mosquitoes and other pathogens that carry disease. In some cases, these pathogens are bringing infectious diseases into communities that had not encountered them before. For example, warmer temperatures expand mosquito breeding ranges, causing malaria to shift upslope into new villages.

One study projects that, because of climate change, up to an additional 51.3 million people will be at risk from exposure to malaria in Western Africa by 2050. These shifts can heighten suffering, increase countries’ burdens of disease and cause epidemics. The World Health Organization (WHO) estimates that one-sixth of illness and disability suffered globally is due to vector-borne diseases, which are predicted to spread due to climate change.

Climate effects related to changing rainfall patterns, water quality and water scarcity can also trigger or worsen diseases within a country. For example, Ghana is now facing a higher prevalence of cholera, diarrhea, malaria and meningitis because flooding contaminates and exacerbates sanitation problems and water quality. Cholera outbreaks in Ghana have a high fatality rate and are particularly frequent during the rainy seasons and in coastal regions.

2. Increased risks to lives and livelihoods.

Similarly, higher temperatures and extreme events — such as intense rainfall, stronger cyclones and increased risk of landslides — can cause physical injuries, water contamination , decreased labor productivity and mental stress such as anxiety, depression and post-traumatic stress disorders. Hot weather and more intense heat waves reduce people’s ability to work and stay healthy; an environment that is too hot and humid makes it impossible for the human body to sweat and can lead to overheating and death.

Changes in the rainy seasons and other, slower-onset climate change risks like salt intrusion from rising sea levels can also negatively impact crop yields and food quality over time. This can lead to greater food insecurity and undernutrition. Bangladesh has the largest delta of any country in the world, and increasing salinity has already negatively affected its crop, fish and livestock production.

Even in places where agriculture yields may be boosted due to climate change, evidence has emerged that such increases can come at the expense of nutrition. These food security threats, in turn, affect people’s every day health, especially when it comes to child growth and development .

Environmental degradation and natural resources instability and competition exacerbated by climate impacts can also contribute to forced migration and social conflict . This can expose people to physical and mental health stressors, exacerbate existing health issues, lead to poorer living conditions and reduce access to affordable medical care.

3. Greater risk of social inequities.

The effects of climate change are especially felt by the most vulnerable , including people living in poverty, those who are marginalized or socially excluded, women, children, the elderly and those who are already ill or living with a disability. Without adequate support and funding, vulnerable groups will continue to suffer the most from the impacts of climate change on health.

The rising frequency, intensity and duration of extreme weather events will disproportionately impact the physical and economic capacities of people and households already struggling with weakened health and chronic disease. Due to their already debilitated or weakened immune systems, people with cardiovascular diseases, respiratory diseases and other pre-existing health conditions are at higher risk of injury or sickness from natural disasters and other climate-related risks.

The elderly and people who perform heavy physical labor, including agricultural laborers, are especially at risk from the effects of increasing heat and heat wave events, which stress the heart (possibly leading to cardiac arrest) and can cause severe dehydration, which damages other vital organs like the kidneys.

When combined with poorer nutrition and water stress, the result is often worse existing health problems, which can further entrench generational poverty and systemic vulnerabilities . This, in turn, contributes to heightened mortality and morbidity at a wider scale, increasing countries’ disease burdens.

What Are the Challenges to Integrating Climate Adaptation into Health Plans?

Several technical and financial challenges remain when it comes to incorporating climate-sensitive risks into health systems. Many countries and groups lack a strong understanding of the links between climate change and health. This is made more complicated when considering that cause-and-effect is difficult, and at times impossible, to prove.

While environmental health and public health officers can see the connections, policymakers may not understand them without proper training. These knowledge gaps can lead to inconsistent policies and a lack of adaptation activities in health budgets.

Many countries also have inadequate finance to implement adaptation and health activities.

As our case study illustrates, in Ghana, for instance, policymakers have limited human resources and skills available to identify and develop appropriate adaptation measures to reduce climate-sensitive health risks. As a result, it is difficult to persuade Parliament to dedicate an adequate budget for such activities. Frequent changes in administration can also make it difficult to ensure consistent allocation of public resources for adaptation in the health sector.

Despite being a priority in national policies and international commitments, technical and financial support requests to the NDC Partnership and multilateral climate funds like the Green Climate Fund often vastly underrepresent health-specific activities.

In a global review of more than 100 countries, the UN found that only one in five countries is spending enough to implement climate-related health commitments. This gap will be further exacerbated by 2030, when the direct damage costs to health are expected to be between $2 billion to $4 billion per year — even without considering indirect effects.

How Can Governments Adapt to Protect Human Health from the Effects of Climate Change?

While it can be difficult to identify, understand and reduce climate-sensitive health risks, a lack of information should not prevent action or delay no-regrets adaptation measures to strengthen health care systems. No-regrets measures include actions that protect communities whether climate impacts materialize as severely as expected or not, such as building robust food and medical supply chains, retrofitting technology and equipment, increasing training of medical staff and establishing protections against interrupted health services.

Governments can establish policy frameworks and collaboration mechanisms to provide needed guidance and support for no-regrets adaptation measures. Champions of climate and health issues inside and outside of the health sector can rally critical supporters and resources to influence policies and drive action.

Fiji, one of the most climate-vulnerable countries in the world, provides an excellent example of how to advance solutions. The nation developed and implemented its national Climate Change and Health Strategic Action Plan and integrated it into various policies and plans. The adaptation and health activities in Fiji’s plan are expected to increase the nation’s ability to provide and use reliable information on climate-sensitive health risks through an early warning system; improve capacity within health sector institutions to respond to these risks; and allow the nation to pilot disease prevention measures in higher-risk areas.

Fiji also set up a Climate Change and Health Unit within its Ministry of Health and allocated domestic funding to advance climate-health activities, like early warning systems, and build the capacity of health institutions to respond to climate threats. Health and climate change also remain on the political agenda thanks to the continuous efforts of and leadership from its Permanent Secretaries of the Ministry of Health, who encourage collaboration with other ministries.

Protecting the Health of Current and Future Generations

The links between climate change and health continue to grow in clarity and evidence. Policymakers can seize on the political momentum created by the global pandemic to strengthen their countries’ abilities to respond to a range of shocks and stressors — including the linked challenges of infectious disease and climate change. Strengthening the overall capacities and resources of health systems will increase adaptive capacity to deal with climate impacts, ensuring that current and future generations remain healthy.

Relevant Work

Key investments can build resilience to pandemics and climate change, 6 big findings from the ipcc 2022 report on climate impacts, adaptation and vulnerability, global emissions and local deforestation are combining to create dangerous levels of heat stress in the tropics, how floods in pakistan threaten global security, how you can help.

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Envision a world where everyone can enjoy clean air, walkable cities, vibrant landscapes, nutritious food and affordable energy.

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Climate change: a threat to human wellbeing and health of the planet. taking action now can secure our future.

BERLIN, Feb 28 – Human-induced climate change is causing dangerous and widespread disruption in nature and affecting the lives of billions of people around the world, despite efforts to reduce the risks. People and ecosystems least able to cope are being hardest hit, said scientists in the latest Intergovernmental Panel on Climate Change (IPCC) report, released today.

“This report is a dire warning about the consequences of inaction,” said Hoesung Lee, Chair of the IPCC. “It shows that climate change is a grave and mounting threat to our wellbeing and a healthy planet. Our actions today will shape how people adapt and nature responds to increasing climate risks.”

The world faces unavoidable multiple climate hazards over the next two decades with global warming of 1.5°C (2.7°F). Even temporarily exceeding this warming level will result in additional severe impacts, some of which will be irreversible. Risks for society will increase, including to infrastructure and low-lying coastal settlements.

The Summary for Policymakers of the IPCC Working Group II report,  Climate Change 2022: Impacts, Adaptation and Vulnerability was approved on Sunday, February 27 2022, by 195 member governments of the IPCC, through a virtual approval session that was held over two weeks starting on February 14.

Urgent action required to deal with increasing risks

Increased heatwaves, droughts and floods are already exceeding plants’ and animals’ tolerance thresholds, driving mass mortalities in species such as trees and corals. These weather extremes are occurring simultaneously, causing cascading impacts that are increasingly difficult to manage. They have exposed millions of people to acute food and water insecurity, especially in Africa, Asia, Central and South America, on Small Islands and in the Arctic.

To avoid mounting loss of life, biodiversity and infrastructure, ambitious, accelerated action is required to adapt to climate change, at the same time as making rapid, deep cuts in greenhouse gas emissions. So far, progress on adaptation is uneven and there are increasing gaps between action taken and what is needed to deal with the increasing risks, the new report finds. These gaps are largest among lower-income populations. 

The Working Group II report is the second instalment of the IPCC’s Sixth Assessment Report (AR6), which will be completed this year.

“This report recognizes the interdependence of climate, biodiversity and people and integrates natural, social and economic sciences more strongly than earlier IPCC assessments,” said Hoesung Lee. “It emphasizes the urgency of immediate and more ambitious action to address climate risks. Half measures are no longer an option.”

Safeguarding and strengthening nature is key to securing a liveable future

There are options to adapt to a changing climate. This report provides new insights into nature’s potential not only to reduce climate risks but also to improve people’s lives.

“Healthy ecosystems are more resilient to climate change and provide life-critical services such as food and clean water”, said IPCC Working Group II Co-Chair Hans-Otto Pörtner. “By restoring degraded ecosystems and effectively and equitably conserving 30 to 50 per cent of Earth’s land, freshwater and ocean habitats, society can benefit from nature’s capacity to absorb and store carbon, and we can accelerate progress towards sustainable development, but adequate finance and political support are essential.”

Scientists point out that climate change interacts with global trends such as unsustainable use of natural resources, growing urbanization, social inequalities, losses and damages from extreme events and a pandemic, jeopardizing future development.

“Our assessment clearly shows that tackling all these different challenges involves everyone – governments, the private sector, civil society – working together to prioritize risk reduction, as well as equity and justice, in decision-making and investment,” said IPCC Working Group II Co-Chair Debra Roberts.

“In this way, different interests, values and world views can be reconciled. By bringing together scientific and technological know-how as well as Indigenous and local knowledge, solutions will be more effective. Failure to achieve climate resilient and sustainable development will result in a sub-optimal future for people and nature.”

Cities: Hotspots of impacts and risks, but also a crucial part of the solution

This report provides a detailed assessment of climate change impacts, risks and adaptation in cities, where more than half the world’s population lives. People’s health, lives and livelihoods, as well as property and critical infrastructure, including energy and transportation systems, are being increasingly adversely affected by hazards from heatwaves, storms, drought and flooding as well as slow-onset changes, including sea level rise.

“Together, growing urbanization and climate change create complex risks, especially for those cities that already experience poorly planned urban growth, high levels of poverty and unemployment, and a lack of basic services,” Debra Roberts said.

“But cities also provide opportunities for climate action – green buildings, reliable supplies of clean water and renewable energy, and sustainable transport systems that connect urban and rural areas can all lead to a more inclusive, fairer society.”

There is increasing evidence of adaptation that has caused unintended consequences, for example destroying nature, putting peoples’ lives at risk or increasing greenhouse gas emissions. This can be avoided by involving everyone in planning, attention to equity and justice, and drawing on Indigenous and local knowledge.

A narrowing window for action

Climate change is a global challenge that requires local solutions and that’s why the Working Group II contribution to the IPCC’s Sixth Assessment Report (AR6) provides extensive regional information to enable Climate Resilient Development.

The report clearly states Climate Resilient Development is already challenging at current warming levels. It will become more limited if global warming exceeds 1.5°C (2.7°F). In some regions it will be impossible if global warming exceeds 2°C (3.6°F). This key finding underlines the urgency for climate action, focusing on equity and justice. Adequate funding, technology transfer, political commitment and partnership lead to more effective climate change adaptation and emissions reductions.

“The scientific evidence is unequivocal: climate change is a threat to human wellbeing and the health of the planet. Any further delay in concerted global action will miss a brief and rapidly closing window to secure a liveable future,” said Hans-Otto Pörtner.

For more information, please contact:

IPCC Press Office, Email: [email protected]   IPCC Working Group II:  Sina Löschke,  Komila Nabiyeva: [email protected]

Notes for Editors

Climate Change 2022: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change

The Working Group II report examines the impacts of climate change on nature and people around the globe. It explores future impacts at different levels of warming and the resulting risks and offers options to strengthen nature’s and society’s resilience to ongoing climate change, to fight hunger, poverty, and inequality and keep Earth a place worth living on – for current as well as for future generations. 

Working Group II introduces several new components in its latest report: One is a special section on climate change impacts, risks and options to act for cities and settlements by the sea, tropical forests, mountains, biodiversity hotspots, dryland and deserts, the Mediterranean as well as the polar regions. Another is an atlas that will present data and findings on observed and projected climate change impacts and risks from global to regional scales, thus offering even more insights for decision makers.

The Summary for Policymakers of the Working Group II contribution to the Sixth Assessment Report (AR6) as well as additional materials and information are available at https://www.ipcc.ch/report/ar6/wg2/

Note : Originally scheduled for release in September 2021, the report was delayed for several months by the COVID-19 pandemic, as work in the scientific community including the IPCC shifted online. This is the second time that the IPCC has conducted a virtual approval session for one of its reports.

AR6 Working Group II in numbers

270 authors from 67 countries

• 47 – coordinating authors
• 184 – lead authors
• 39 – review editors
• 675 – contributing authors

Over 34,000 cited references

A total of 62,418 expert and government review comments

(First Order Draft 16,348; Second Order Draft 40,293; Final Government Distribution: 5,777)

More information about the Sixth Assessment Report can be found  here .

Additional media resources

Assets available after the embargo is lifted on Media Essentials website .

Press conference recording, collection of sound bites from WGII authors, link to presentation slides, B-roll of approval session, link to launch Trello board including press release and video trailer in UN languages, a social media pack.

The website includes  outreach materials  such as videos about the IPCC and video recordings from  outreach events  conducted as webinars or live-streamed events.

Most videos published by the IPCC can be found on our  YouTube  channel. Credit for artwork

About the IPCC

The Intergovernmental Panel on Climate Change (IPCC) is the UN body for assessing the science related to climate change. It was established by the United Nations Environment Programme (UNEP) and the World Meteorological Organization (WMO) in 1988 to provide political leaders with periodic scientific assessments concerning climate change, its implications and risks, as well as to put forward adaptation and mitigation strategies. In the same year the UN General Assembly endorsed the action by the WMO and UNEP in jointly establishing the IPCC. It has 195 member states.

Thousands of people from all over the world contribute to the work of the IPCC. For the assessment reports, IPCC scientists volunteer their time to assess the thousands of scientific papers published each year to provide a comprehensive summary of what is known about the drivers of climate change, its impacts and future risks, and how adaptation and mitigation can reduce those risks.

The IPCC has three working groups:  Working Group I , dealing with the physical science basis of climate change;  Working Group II , dealing with impacts, adaptation and vulnerability; and  Working Group III , dealing with the mitigation of climate change. It also has a  Task Force on National Greenhouse Gas Inventories  that develops methodologies for measuring emissions and removals. As part of the IPCC, a Task Group on Data Support for Climate Change Assessments (TG-Data) provides guidance to the Data Distribution Centre (DDC) on curation, traceability, stability, availability and transparency of data and scenarios related to the reports of the IPCC.

IPCC assessments provide governments, at all levels, with scientific information that they can use to develop climate policies. IPCC assessments are a key input into the international negotiations to tackle climate change. IPCC reports are drafted and reviewed in several stages, thus guaranteeing objectivity and transparency. An IPCC assessment report consists of the contributions of the three working groups and a Synthesis Report. The Synthesis Report integrates the findings of the three working group reports and of any special reports prepared in that assessment cycle.

About the Sixth Assessment Cycle

At its 41st Session in February 2015, the IPCC decided to produce a Sixth Assessment Report (AR6). At its 42nd Session in October 2015 it elected a new Bureau that would oversee the work on this report and the Special Reports to be produced in the assessment cycle.

Global Warming of 1.5°C , an IPCC special report on the impacts of global warming of 1.5 degrees Celsius above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty  was launched in October 2018.

Climate Change and Land , an IPCC special report on climate change, desertification, land degradation, sustainable land management, food security, and greenhouse gas fluxes in terrestrial ecosystems  was launched in August 2019, and the  Special Report on the Ocean and Cryosphere in a Changing Climate  was released in September 2019.

In May 2019 the IPCC released the  2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories , an update to the methodology used by governments to estimate their greenhouse gas emissions and removals.

In August 2021 the IPCC released the Working Group I contribution to the AR6, Climate Change 2021, the Physical Science Basis

The Working Group III contribution to the AR6 is scheduled for early April 2022.

The Synthesis Report of the Sixth Assessment Report will be completed in the second half of 2022.

For more information go to  www.ipcc.ch

Related Content

Remarks by the ipcc chair during the press conference to present the working group ii contribution to the sixth assessment report.

Monday, 28 February 2022 Distinguished representatives of the media, WMO Secretary-General Petteri, UNEP Executive Director Andersen, We have just heard …

February 2022

Fifty-fifth session of the ipcc (ipcc-55) and twelfth session of working group ii (wgii-12), february 14, 2022, working group report, ar6 climate change 2022: impacts, adaptation and vulnerability.

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Your environment. your health., human health impacts of climate change.

Climate change impacts human health in both direct and indirect ways 1 , 2 . Extreme heat waves, rising sea level, changes in precipitation resulting in flooding and droughts, and intense hurricanes can directly cause injury, illness, and even death 3 . The effects of climate change can also indirectly affect health through alterations to the environment. For example, worsening air pollution levels can have negative impacts on respiratory and cardiovascular conditions 4 . Changes in temperature and rainfall can alter the survival, distribution, and behavior of insects and other species that can lead to changes in infectious diseases 5 . Increases in precipitation, storm surge, and sea temperature can lead to more water-related illnesses 6 . Climate change can also affect food safety, exposing people to contaminated foods that can result in foodborne illnesses 7 . In addition, climate change can affect mental health and well-being 8 , 9 .

Exposure to climate-related hazards can include biological, chemical, or physical stressors and can differ in time, locations, populations, and severity. These are referred to as exposure pathways. These threats can occur simultaneously, resulting in compounding health impacts. Climate change threats may also accumulate over time, leading to longer-term changes in resilience and health.

Climate change can affect human health by changing the severity, duration, or frequency of health problems and by creating unprecedented or unanticipated health problems or health threats in places or populations where they have not previously occurred 10 . While everyone is exposed to climate-related health threats, not everyone experiences the same harms. Individuals may experience greater risk from climate-related health effects because: they have greater exposure to climate-related hazards; they are more sensitive to the effects of climate stressors; their own present state of health and wellbeing; or they do not have sufficient capacity or resources to cope or remove themselves from harm 11 . An effective public health response to mitigate the risks of climate change is essential to preventing injuries and illnesses and enhancing overall public health preparedness.

NIEHS supports research that can be used to make decisions that can help reduce the threats of climate change. In the 2016 report by the U.S. Global Change Research Program,  The Impacts of Climate Change on Human Health: A Scientific Assessment , the Interagency Working Group on Climate Change and Health describes seven different types of health threats that help outline the major research areas. These include the following:

• Foodborne Illness and Nutrition
• Health Impacts of Air Quality
• Health Impacts of Extreme Weather Events
• Mental Health and Well-being
• People Who Are Vulnerable to Climate Change
• Temperature-Related Death and Illness
• Vector-borne Diseases
• Water-related Illnesses

• Ebi K.L, Balbus JM, Luber G, Bole A, Crimmins A, Glass G, Saha S, Shimamoto MM, Trtanj J, and White-Newsome JL. 2018: Human Health. In Impacts, Risks, and Adaptation in the United States: Fourth National Climate Assessment, Volume II [Reidmiller, D.R., C.W. Avery, D.R. Easterling, K.E. Kunkel, K.L.M. Lewis, T.K. Maycock, and B.C. Stewart (eds.)]. U.S. Global Change Research Program, Washington, DC, USA, pp. 539–571. doi: 10.7930/NCA4. 2018. CH14. [ Full Text Ebi K.L, Balbus JM, Luber G, Bole A, Crimmins A, Glass G, Saha S, Shimamoto MM, Trtanj J, and White-Newsome JL. 2018: Human Health. In Impacts, Risks, and Adaptation in the United States: Fourth National Climate Assessment, Volume II [Reidmiller, D.R., C.W. Avery, D.R. Easterling, K.E. Kunkel, K.L.M. Lewis, T.K. Maycock, and B.C. Stewart (eds.)]. U.S. Global Change Research Program, Washington, DC, USA, pp. 539–571. doi: 10.7930/NCA4. 2018. CH14. ]
• IPCC, 2022: Climate Change 2022: Impacts, Adaptation, and Vulnerability. Contribution of Working Group II to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [H.-O. Pörtner, D.C. Roberts, M. Tignor, E.S. Poloczanska, K. Mintenbeck, A. Alegría, M. Craig, S. Langsdorf, S. Löschke, V. Möller, A. Okem, B. Rama (eds.)]. Cambridge University Press. In Press. [ Full Text IPCC, 2022: Climate Change 2022: Impacts, Adaptation, and Vulnerability. Contribution of Working Group II to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [H.-O. Pörtner, D.C. Roberts, M. Tignor, E.S. Poloczanska, K. Mintenbeck, A. Alegría, M. Craig, S. Langsdorf, S. Löschke, V. Möller, A. Okem, B. Rama (eds.)]. Cambridge University Press. In Press. ]
• IPCC, 2021: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press. In Press. [ Full Text IPCC, 2021: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press. In Press. ]
• Mills, Nicholas L., et al. Adverse cardiovascular effects of air pollution. Nature Clinical Practice Cardiovascular Medicine 6.1 (2009): 36-44. [ Full Text Mills, Nicholas L., et al. Adverse cardiovascular effects of air pollution. Nature Clinical Practice Cardiovascular Medicine 6.1 (2009): 36-44. ]
• Hunter, Paul R. Climate change and waterborne and vector‐borne disease. Journal of Applied Microbiology 94 (2003): 37-46. [ Full Text Hunter, Paul R. Climate change and waterborne and vector‐borne disease. Journal of Applied Microbiology 94 (2003): 37-46. ]
• Rose, Joan B., et al. Climate variability and change in the United States: potential impacts on water-and foodborne diseases caused by microbiologic agents. Environmental Health Perspectives 109.suppl 2 (2001): 211-221. [ Full Text Rose, Joan B., et al. Climate variability and change in the United States: potential impacts on water-and foodborne diseases caused by microbiologic agents. Environmental Health Perspectives 109.suppl 2 (2001): 211-221. ]
• Lake, Iain R., et al. A re-evaluation of the impact of temperature and climate change on foodborne illness. Epidemiology & Infection 137.11 (2009): 1538-1547. [ Full Text Lake, Iain R., et al. A re-evaluation of the impact of temperature and climate change on foodborne illness. Epidemiology & Infection 137.11 (2009): 1538-1547. ]
• Cissé, G., R. McLeman, H. Adams, P. Aldunce, K. Bowen, D. Campbell-Lendrum, S. Clayton, K.L. Ebi, J. Hess, C. Huang, Q. Liu, G. McGregor, J. Semenza, and M.C. Tirado, 2022: Health, Wellbeing, and the Changing Structure of Communities. In: Climate Change 2022: Impacts, Adaptation, and Vulnerability. Contribution of Working Group II to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [H.-O. Pörtner, D.C. Roberts, M. Tignor, E.S. Poloczanska, K. Mintenbeck, A. Alegría, M. Craig, S. Langsdorf, S. Löschke, V. Möller, A. Okem, B. Rama (eds.)]. Cambridge University Press. In Press. [ Full Text Cissé, G., R. McLeman, H. Adams, P. Aldunce, K. Bowen, D. Campbell-Lendrum, S. Clayton, K.L. Ebi, J. Hess, C. Huang, Q. Liu, G. McGregor, J. Semenza, and M.C. Tirado, 2022: Health, Wellbeing, and the Changing Structure of Communities. In: Climate Change 2022: Impacts, Adaptation, and Vulnerability. Contribution of Working Group II to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [H.-O. Pörtner, D.C. Roberts, M. Tignor, E.S. Poloczanska, K. Mintenbeck, A. Alegría, M. Craig, S. Langsdorf, S. Löschke, V. Möller, A. Okem, B. Rama (eds.)]. Cambridge University Press. In Press. ]
• Cianconi P, Betrò S, and Janiri L. 2020 The impact of climate change on mental health: a systematic descriptive review. Frontiers in Psychiatry, 11 (2020): 74. [ Abstract Cianconi P, Betrò S, and Janiri L. 2020 The impact of climate change on mental health: a systematic descriptive review. Frontiers in Psychiatry, 11 (2020): 74. ] [ Full Text Cianconi P, Betrò S, and Janiri L. 2020 The impact of climate change on mental health: a systematic descriptive review. Frontiers in Psychiatry, 11 (2020): 74. ]
• Balbus J, Crimmins A, Gamble JL, Easterling DR, Kunkel KE, Saha S, Sarofim MC. 2016. Chapter 1: Introduction: Climate Change and Human Health. The Impacts of Climate Change on Human Health in the United States: A Scientific Assessment. U.S. Global Change Research Program, Washington, DC, 25–42 . [ Abstract Balbus J, Crimmins A, Gamble JL, Easterling DR, Kunkel KE, Saha S, Sarofim MC. 2016. Chapter 1: Introduction: Climate Change and Human Health. The Impacts of Climate Change on Human Health in the United States: A Scientific Assessment. U.S. Global Change Research Program, Washington, DC, 25–42. ] [ Full Text Balbus J, Crimmins A, Gamble JL, Easterling DR, Kunkel KE, Saha S, Sarofim MC. 2016. Chapter 1: Introduction: Climate Change and Human Health. The Impacts of Climate Change on Human Health in the United States: A Scientific Assessment. U.S. Global Change Research Program, Washington, DC, 25–42. ]
• Benevolenza MA, DeRigne L. 2019. The impact of climate change and natural disasters on vulnerable populations: A systematic review of literature, Journal of Human Behavior in the Social Environment. 29:2, 266-281 . [ Abstract Benevolenza MA, DeRigne L. 2019. The impact of climate change and natural disasters on vulnerable populations: A systematic review of literature, Journal of Human Behavior in the Social Environment. 29:2, 266-281. ]
• Ebi K.L, Balbus JM, Luber G, Bole A, Crimmins A, Glass G, Saha S, Shimamoto MM, Trtanj J, and White-Newsome JL. 2018: Human Health. In Impacts, Risks, and Adaptation in the United States: Fourth National Climate Assessment, Volume II [Reidmiller, D.R., C.W. Avery, D.R. Easterling, K.E. Kunkel, K.L.M. Lewis, T.K. Maycock, and B.C. Stewart (eds.)]. U.S. Global Change Research Program, Washington, DC, USA, pp. 539–571. doi: 10.7930/NCA4. 2018. CH14. [ Full Text Ebi K.L, Balbus JM, Luber G, Bole A, Crimmins A, Glass G, Saha S, Shimamoto MM, Trtanj J, and White-Newsome JL. 2018: Human Health. In Impacts, Risks, and Adaptation in the United States: Fourth National Climate Assessment, Volume II [Reidmiller, D.R., C.W. Avery, D.R. Easterling, K.E. Kunkel, K.L.M. Lewis, T.K. Maycock, and B.C. Stewart (eds.)]. U.S. Global Change Research Program, Washington, DC, USA, pp. 539–571. doi: 10.7930/NCA4. 2018. CH14. ]
• IPCC, 2022: Climate Change 2022: Impacts, Adaptation, and Vulnerability. Contribution of Working Group II to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [H.-O. Pörtner, D.C. Roberts, M. Tignor, E.S. Poloczanska, K. Mintenbeck, A. Alegría, M. Craig, S. Langsdorf, S. Löschke, V. Möller, A. Okem, B. Rama (eds.)]. Cambridge University Press. In Press. [ Full Text IPCC, 2022: Climate Change 2022: Impacts, Adaptation, and Vulnerability. Contribution of Working Group II to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [H.-O. Pörtner, D.C. Roberts, M. Tignor, E.S. Poloczanska, K. Mintenbeck, A. Alegría, M. Craig, S. Langsdorf, S. Löschke, V. Möller, A. Okem, B. Rama (eds.)]. Cambridge University Press. In Press. ]
• IPCC, 2021: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press. In Press. [ Full Text IPCC, 2021: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press. In Press. ]
• Hunter, Paul R. Climate change and waterborne and vector‐borne disease. Journal of Applied Microbiology 94 (2003): 37-46. [ Full Text Hunter, Paul R. Climate change and waterborne and vector‐borne disease. Journal of Applied Microbiology 94 (2003): 37-46. ]
• Lake, Iain R., et al. A re-evaluation of the impact of temperature and climate change on foodborne illness. Epidemiology & Infection 137.11 (2009): 1538-1547. [ Full Text Lake, Iain R., et al. A re-evaluation of the impact of temperature and climate change on foodborne illness. Epidemiology & Infection 137.11 (2009): 1538-1547. ]
• Cissé, G., R. McLeman, H. Adams, P. Aldunce, K. Bowen, D. Campbell-Lendrum, S. Clayton, K.L. Ebi, J. Hess, C. Huang, Q. Liu, G. McGregor, J. Semenza, and M.C. Tirado, 2022: Health, Wellbeing, and the Changing Structure of Communities. In: Climate Change 2022: Impacts, Adaptation, and Vulnerability. Contribution of Working Group II to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [H.-O. Pörtner, D.C. Roberts, M. Tignor, E.S. Poloczanska, K. Mintenbeck, A. Alegría, M. Craig, S. Langsdorf, S. Löschke, V. Möller, A. Okem, B. Rama (eds.)]. Cambridge University Press. In Press. [ Full Text Cissé, G., R. McLeman, H. Adams, P. Aldunce, K. Bowen, D. Campbell-Lendrum, S. Clayton, K.L. Ebi, J. Hess, C. Huang, Q. Liu, G. McGregor, J. Semenza, and M.C. Tirado, 2022: Health, Wellbeing, and the Changing Structure of Communities. In: Climate Change 2022: Impacts, Adaptation, and Vulnerability. Contribution of Working Group II to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [H.-O. Pörtner, D.C. Roberts, M. Tignor, E.S. Poloczanska, K. Mintenbeck, A. Alegría, M. Craig, S. Langsdorf, S. Löschke, V. Möller, A. Okem, B. Rama (eds.)]. Cambridge University Press. In Press. ]
• Cianconi P, Betrò S, and Janiri L. 2020 The impact of climate change on mental health: a systematic descriptive review. Frontiers in Psychiatry, 11 (2020): 74. [ Abstract Cianconi P, Betrò S, and Janiri L. 2020 The impact of climate change on mental health: a systematic descriptive review. Frontiers in Psychiatry, 11 (2020): 74. ] [ Full Text Cianconi P, Betrò S, and Janiri L. 2020 The impact of climate change on mental health: a systematic descriptive review. Frontiers in Psychiatry, 11 (2020): 74. ]
• Balbus J, Crimmins A, Gamble JL, Easterling DR, Kunkel KE, Saha S, Sarofim MC. 2016. Chapter 1: Introduction: Climate Change and Human Health. The Impacts of Climate Change on Human Health in the United States: A Scientific Assessment. U.S. Global Change Research Program, Washington, DC, 25–42 . [ Abstract Balbus J, Crimmins A, Gamble JL, Easterling DR, Kunkel KE, Saha S, Sarofim MC. 2016. Chapter 1: Introduction: Climate Change and Human Health. The Impacts of Climate Change on Human Health in the United States: A Scientific Assessment. U.S. Global Change Research Program, Washington, DC, 25–42. ] [ Full Text Balbus J, Crimmins A, Gamble JL, Easterling DR, Kunkel KE, Saha S, Sarofim MC. 2016. Chapter 1: Introduction: Climate Change and Human Health. The Impacts of Climate Change on Human Health in the United States: A Scientific Assessment. U.S. Global Change Research Program, Washington, DC, 25–42. ]

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Climate change and human health : impact and adaptation

Technical guidance

Concern for human health is one of the most compelling reasons to study the effects of global climate change. Health is a focus that will reflect the combined impacts of climate change on the physical environment, ecosystems, the economic environment and society. Long-term changes in world climate may affect many of the requisites of good health – sufficient food, safe and adequate drinking water, and secure dwellings. The current large-scale social and environmental changes mean that we must assign a much higher priority to population health in the policy debate on climate change.

WHO Health and Climate Change Survey Report: Tracking Global Progress

Soaring temperatures in New York, July 2010. Photo by Eric Thayer/Reuters

The melting brain

It’s not just the planet and not just our health – the impact of a warming climate extends deep into our cortical fissures.

by Clayton Page Aldern   + BIO

In February 1884, the English art critic and polymath John Ruskin took the lectern at the London Institution for a pair of lectures on the weather. ‘The Storm-Cloud of the Nineteenth Century’ was his invective against a particular ‘wind of darkness’ and ‘plague-cloud’ that, in his estimate, had begun to envelope Victorian cities only in recent years. He had been taking careful meteorological measurements, he told a sceptical audience. He railed against the ‘bitterness and malice’ of the new weather in question; and, perhaps more importantly, about how it mirrored a certain societal ‘moral gloom’. You could read in us what you could read in the weather, he suggested.

July Thundercloud in the Val d’Aosta (1858) by John Ruskin. Courtesy Wikipedia

It was easy that February, and perhaps easy today, to disregard any alleged winds of darkness as the ravings of a madman. Clouds are clouds: even if Ruskin’s existed – which was a question of some contemporaneous debate – it would be untoward to imagine they bore any relationship with the human psyche. As Brian Dillon observed of the cloud lectures in The Paris Review in 2019, it can be hard to tell where Ruskin’s ‘bad weather ends and his own ragged, doleful mood begins.’ In 1886, Ruskin suffered a mental breakdown while giving a talk in Oxford. By the end of his life at the turn of the century, he was widely considered insane. His ramblings on meteorology and the human spirit aren’t exactly treated with the same gravitas as his books on J M W Turner.

And yet, for Ruskin, the clouds weren’t just clouds: they were juiced up by a ‘dense manufacturing mist’, as he’d noted in a diary entry. The plague-clouds embodied the miasma of the Industrial Revolution; the moral gloom was specifically that which arose from the rapid societal and environmental changes that were afoot. Ruskin’s era had seen relentless transformation of pastoral landscapes into industrial hubs. Everything smelled like sulphur and suffering. Soot-filled air, chemical and human waste, the clamour of machinery – these were more than just physical nuisances. They were assaults on the senses, shaping moods and behaviour in ways that were not yet fully understood.

Mining Area (1852-1905) by Constantin Meunier. Courtesy Wikipedia

Ruskin believed that the relentless pace of industrialisation, with its cacophony of tools and sprawling factories and environmental destruction, undermined psychological wellbeing: that the mind, much like the body, required a healthy social and physical environment to thrive. This was actually a somewhat new idea. (Isaac Ray, a founder of the American Psychiatric Association, wouldn’t define the idea of ‘mental hygiene’, the precursor to mental health, until 1893.) Instability in the environment, for Ruskin, begot instability in the mind. One reflected the other.

M ore than a century later, as we grapple with a new suite of breakneck environmental changes, the plague-clouds are again darkly literal. Global average surface temperatures have risen by about 1.1°C (2°F) since the pre-industrial era, with most of this warming occurring in the past 40 years. Ice is melting; seas are steadily rising; storms are – well, you know this story. And yet, most frequently, it is still a story of the world out there: the world outside of us. The narrative of climate change is one of meteorological extremes, economic upheaval and biodiversity losses. But perhaps it is worth taking a maybe-mad Ruskin seriously. What of our internal clouds? As the climate crisis warps weather and acidifies oceans and shatters temperature records with frightening regularity, one is tempted to ask if our minds are changing in kind.

Here are some of the most concerning answers in the affirmative. Immigration judges are less likely to rule in favour of asylum seekers on hotter days. On such days, students behave as if they’ve lost a quarter-year of education, relative to temperate days. Warmer school years correspond to lower rates of learning. Temperature predicts the incidence of online hate speech. Domestic violence spikes with warmer weather. Suicide , too.

In baseball, pitchers are more likely to hit batters with their pitches on hot days

But you already know what this feels like. Perhaps you’re more ornery in the heat. Maybe you feel a little slow in the head. It’s harder to focus and easier to act impulsively. Tomes of cognitive neuroscience and behavioural economics research back you up, and it’s not all as dire as domestic violence. Drivers honk their horns more frequently (and lean on them longer) at higher temperatures. Heat predicts more aggressive penalties in sport. In baseball, pitchers are more likely to hit batters with their pitches on hot days – and the outdoor temperature is an even stronger predictor of their tendency to retaliate in this manner if they’ve witnessed an opposing pitcher do the same thing.

In other words: it would appear the plague-clouds are within us, too. They illustrate the interconnectedness of our inner and outer worlds. They betray a certain flimsiness of human agency, painting our decision-making in strokes of environmental influence far bolder than our intuition suggests. And they throw the climate crisis into fresh, stark relief: because, yes, as the climate changes, so do we.

T he London Institution closed in 1912. These days, when you want to inveigh against adverse environmental-mind interactions, you publish a paper in The Lancet . And so that is what 24 mostly British, mostly clinical neurologists did in May 2024, arguing that the ‘incidence, prevalence, and severity of many nervous system conditions’ can be affected by global warming. For these researchers, led by Sanjay Sisodiya, professor of neurology at University College London in the UK, the climate story is indeed one of internal clouds.

In their survey of 332 scientific studies, Sisodiya and his colleagues show that climatic influence extends far beyond behaviour and deep into cortical fissures. Aspects of migraine, stroke, seizure and multiple sclerosis all appear to be temperature dependent. In Taiwan, report the authors, the risk of schizophrenia hospitalisation increases with widening daytime temperature ranges. In California , too, ‘hospital visits for any mental health disorder, self-harm, intentional injury of another person, or homicide’ rise with broader daily temperature swings. In Switzerland , hospitalisations for psychiatric disorders increase with temperature, with the risk particularly pronounced for those with developmental disorders and schizophrenia.

Outside the hospital, climate change is extending the habitable range of disease vectors like ticks, mosquitoes and bats, causing scientists to forecast an increased incidence of vector-borne and zoonotic brain maladies like yellow fever, Zika and cerebral malaria. Outside the healthcare system writ large, a changing environment bears on sensory systems and perception, degrading both sensory information and the biological tools we use to process it. Outside the realm of the even remotely reasonable, warming freshwater brings with it an increased frequency of cyanobacterial blooms, the likes of which release neurotoxins that increase the risk of neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS, also known as Lou Gehrig’s disease).

Experiencing natural disasters in utero greatly increases children’s risk of anxiety, depression and ADHD

Indeed, recent studies suggest that climate change may be exacerbating the already substantial burden of neurodegenerative diseases like Parkinson’s and Alzheimer’s. In countries with warmer-than-average climates, more intense warming has been linked to a greater increase in Parkinson’s cases and, as Sisodiya et al note, the highest forecasted rates of increase in dementia prevalence are ‘expected to be in countries experiencing the largest effects of climate change’. Similarly, short-term exposure to high temperatures appears to drive up emergency department visits for Alzheimer’s patients. The air we breathe likely plays a complementary role: in Mexico City, for example, where residents are exposed to high levels of fine particulate matter and ozone from a young age, autopsies have revealed progressive Alzheimer’s pathology in 99 per cent of those under the age of 30.

The risks aren’t limited to those alive today. In 2022, for example, an epidemiological study revealed that heat exposure during early pregnancy is associated with a significantly increased risk of children developing schizophrenia, anorexia and other neuropsychiatric conditions. High temperatures during gestation have long been known to delay neurodevelopment in rats. Other scientists have shown that experiencing natural disasters in utero greatly increases children’s risk of anxiety, depression, attention-deficit/hyperactivity disorder and conduct disorders later in life. Such effects cast the intergenerational responsibilities of the Anthropocene in harsh new light – not least because, as Sisodiya and colleagues write, there is a tremendous ‘global disparity between regions most affected by climate change (both now and in the future) and regions in which the majority of studies are undertaken.’ We don’t know what we don’t know.

What we do know is that the brain is emerging, in study after study, as one of climate change’s most vulnerable landscapes.

It is a useful reorientation. Return to the horn-honking and the baseball pitchers for a moment. A focus on the brain sheds some potential mechanistic light on the case studies and allows us to avoid phrases like ‘wind of darkness’. Higher temperatures, for example, appear to shift functional brain networks – the coordinated behaviour of various regions – toward randomised activity. In extreme heat, scientists have taken note of an overworked dorsolateral prefrontal cortex (dlPFC), the evolutionarily new brain region that the neuroendocrinologist Robert M Sapolsky at Stanford University in the US calls ‘the definitive rational decider in the frontal cortex’. The dlPFC limits the degree to which people make impulsive decisions; disrupted dlPFC activity tends to imply a relatively heightened influence of limbic structures (like the emotionally attuned amygdala) on behaviour. More heat, less rational decision-making.

When extreme heat reaches into your mind and tips your scales toward violence, it is constraining your choices

The physicality of environmental influence on the brain is more widespread than the dlPFC – and spans multiple spatial scales. Heat stress in zebrafish, for example, down-regulates the expression of proteins relevant to synapse construction and neurotransmitter release. In mice, heat also triggers inflammation in the hippocampus, a brain region necessary for memory formation and storage. While neuroinflammation often plays an initially protective role, chronic activation of immune cells – like microglia and astrocytes – can turn poisonous, since pro-inflammatory molecules can damage brain cells in the long run. In people, hyperthermia is associated with decreased blood flow to this region. Psychologists’ observations of waning cognition and waxing aggression at higher temperatures makes a world of sense in the context of such findings.

The nascent field of environmental neuroscience seeks to ‘understand the qualitative and quantitative relationships between the external environment, neurobiology, psychology and behaviour’. Searching for a more specific neologism – since that particular phrase also encompasses environmental exposures like noise, urban development, lighting and crime – we might refer to our budding, integrative field as climatological neuroepidemiology. Or, I don’t know, maybe we need something snappier for TikTok. Neuroclimatology? Ecological neurodynamics?

I tend to prefer: the weight of nature.

The weight forces our hands, as in the case of the behavioural effects highlighted above. When extreme heat reaches into your mind and tips your scales toward violence, it is constraining your choices. By definition, impulsive decisions are rooted in comparatively less reflection than considered decisions: to the extent that a changing climate influences our reactions and decision-making, we should understand it as compromising our perceived free will. The weight of nature is heavy. It displaces us.

It is also a heavy psychological burden to carry. You are likely familiar with the notion of climate anxiety . The phrase, which tends to refer to a near-pathological state of worry and fear of impending environmental destruction, has never sat particularly well with me. Anxiety, as defined by the Diagnostic and Statistical Manual , is usually couched in terms of ‘excessive’ worry. I’m not convinced there’s anything excessive about seeing the climatic writing on the wall and feeling a sense of doom. Perhaps we ought to consider the climate-anxious as having more developed brains than the rest of the litter – that the Cassandras are the only sane ones left.

I ’m not exactly joking. Neuroscience has begun to study the brains in question, and not for nothing. The midcingulate cortex, a central hub in the brain’s threat-detection circuitry, may hold some clues to the condition’s biological basis: in one 2024 study , for example, researchers at Northern Michigan University in the US found that people who reported higher levels of anxiety about climate change showed distinct patterns of brain structure and function in this region, relative to those with lower levels of climate anxiety – and irrespective of base levels of anxiety writ large. In particular, the climate-anxious brain appears to play host to a smaller midcingulate (in terms of grey matter), but one that’s functionally more connected to other key hubs in the brain’s salience network, a system understood to constantly scan the environment for emotionally relevant information. In the salience network, the midcingulate cortex works hand in hand with limbic structures like the amygdala and insula to prepare the body to respond appropriately to this type of information. In people with climate anxiety, this network may be especially attuned to signals of climate-related threats.

Rather than indicating a deficiency, then, a diminutive midcingulate might reflect a more efficient, finely honed threat-detection system. The brain is well known to prune redundant connections over time, preserving only the most useful neural pathways. Selective sculpting, suggest the Michigan researchers, may allow the climate-anxious brain to process worrisome information more effectively, facilitating rapid communication between the midcingulate and other regions involved in threat anticipation and response. In other words, they write, the climate-anxious midcingulate might be characterised by ‘more efficient wiring’.

This neural sensitivity to potential dangers could be both a blessing and a curse. On one hand, it may attune some people to the very real perils of the future. The midcingulate is critical for anticipating future threats, and meta-analyses have found the region to be consistently activated when people contemplate unpredictable negative outcomes. Given the looming spectre of climate catastrophe, a hair-trigger threat-detection system could be an adaptive asset.

Climate anxiety is not just a sociocultural phenomenon. It has a theoretically identifiable neural correlate

On the other hand, argue the researchers:

[T]he complexity, uncertainty, as well as temporal and geographical distance of the climate crisis, in addition to its global nature, may lead individuals to deprioritising the risks associated with climate change, or becoming overwhelmed and disengaged – a state sometimes referred to as ‘eco-paralysis’.

An overactive midcingulate has been implicated in clinical anxiety disorders, and the new findings suggest that climate anxiety shares some of the same neural underpinnings. (It’s important to recall that climate anxiety seems to be distinct from generalised anxiety, though, as the brain differences observed in the Michigan study couldn’t be explained by overall anxiety levels.)

Ultimately, while speculative, these findings suggest that climate anxiety is not merely a sociocultural phenomenon, but one with theoretically identifiable neural correlates. They provide a potential biological framework for understanding why some people may be more psychologically impacted by climate change than others. And they raise intriguing questions about whether the brains of the climate anxious are particularly well-suited for confronting the existential threat of a warming world – or whether they are vulnerable to becoming overwhelmed by it. In all cases, though, they illustrate that world reaching inward.

T here is perhaps a flipside to be realised here. A changing climate is seeping into our very neurobiology. What might it mean to orient our neurobiology toward climate change?

Such is the premise of a 2023 article in Nature Climate Change by the neuroscientist Kimberly Doell at the University of Vienna in Austria and her colleagues, who argue that the field is well positioned to inform our understanding of climate-adaptation responses and pro-environmental decision-making. In the decades since Ruskin shook his fists at the sky, environmental neuroscience has begun to probe the reciprocal dance between organisms and their ecological niches. We know now that the textures of modern environments – green spaces, urban sprawl, socioeconomic strata – all leave their mark on the brain. Climate change is no different.

Accordingly, argue Doell et al, scientists and advocates alike can integrate findings from neuroscience to improve communications strategies aimed at spurring climate action. They want to turn the tables, taking advantage of insights from neurobiology and cognitive neuroscience to more effectively design climate solutions – both within ourselves and for society as a whole.

The Anthropocene’s fever dream is already warping our wetware

We have models for this type of approach. Poverty research, for instance, has long implicated socioeconomic conditions with subpar health. In more recent years, neuroscience has reverse-engineered the pathways by which poverty’s various insults – understimulation, toxic exposures, chronic stress – can erode neural architecture and derail cognitive development. Brain science alone won’t solve poverty, yet even a limited understanding of these mechanisms has spurred research in programmes like Head Start, a family-based preschool curriculum that has been shown to boost selective attention (as evident in electrophysiological recordings) and cognitive test scores. While the hydra of structural inequity is not easily slain, neuroscientists have managed to shine some light on poverty’s neural correlates, flag its reversible harms, and design precision remedies accordingly. This same potential, argue Doell and her colleagues, extends to the neuroscience of climate change.

To realise this potential, though, we need to further understand how the Anthropocene’s fever dream is already warping our wetware. Social and behavioural science have begun cataloguing the psychological fallout of a planet in flux, but a neural taxonomy of climate change awaits. The field’s methodological and conceptual arsenal is primed for the challenge, but honing it will demand alliances with climate science, medicine, psychology, political science and beyond.

Some are trying. For example, the Kavli Foundation in Los Angeles, US, recognising a need for answers, last year put out a call for scientists to investigate how neural systems are responding to ecological upheaval. With a trial $5 million, the foundation aims to illuminate how habitat loss, light pollution and other environmental insults may be influencing the molecular, cellular and circuit-level machinery of brains, human and otherwise. The central question is: in a biosphere where change is the only constant, are neural systems plastic enough to keep pace, or will they be left struggling to adapt?

The first wave of researchers to take up Kavli’s challenge are studying a diverse array of creatures, each uniquely positioned to reveal insights about the brain’s resilience in the face of planetary disruption. Wolfgang Stein at Illinois State University in the US and Steffen Harzsch at University of Greifswald in Germany, for example, focus on crustaceans, seeking to understand how their neural thermal regulators cope with rising temperatures in shallow and deep waters. Another group has targeted the brains of cephalopods, whose RNA-editing prowess may be key to their ability to tolerate plummeting oxygen levels in their increasingly suffocating aquatic habitats. A third Kavli cohort, led by Florence Kermen at University of Copenhagen in Denmark, is subjecting zebrafish to extreme temperatures, scouring their neurons and glial cells for the molecular signatures that allow them to thrive – even as their watery world heats up.

These initial investments have sparked federal curiosity. In December 2023, the US National Science Foundation joined forces with Kavli, inviting researchers to submit research proposals that seek to probe the ‘modulatory, homeostatic, adaptive, and/or evolutionary mechanisms that impact neurophysiology in response to anthropogenic environmental influence’. We may not be in arms-race territory yet, but at least there’s a suggestion that we’re beginning to walk in the right direction.

T he brain, that spongy command centre perched atop our spinal cord, has always been a black box. As the climate crisis tightens its grip, and the ecological ground beneath our feet grows ever more unsteady, the imperative to pry it open and peer inside grows more urgent by the day. Already, we’ve begun to glimpse the outlines of a new neural cartography, sketched in broad strokes by the likes of Sisodiya and his colleagues. We know now that the brain is less a static lump of self-regulating tissue than it is a dynamic, living landscape, its hills and valleys shaped by the contours of our environment. Just as the Greenland ice sheet groans and buckles under the heat of a changing climate, so too do our synapses wither and our neurons wink out as the mercury rises. Just as rising seas swallow coastlines, and forests succumb to drought and flame, the anatomical borders of our brains are redrawn by each new onslaught of environmental insult.

But the dialogue between brain and biosphere is not a one-way street. The choices we make, the behaviours we pursue, the ways in which we navigate a world in crisis – all of these decisions are reflected back onto the environment, for good or for ill. So, I offer: in seeking to understand how a changing climate moulds the contours of our minds, we must also reckon with how the architecture of our thoughts might be renovated in service of sustainability.

Bit by bit, synapse by synapse, we can chart a course through the gathering plague-cloud

The cartographers of the Anthropocene mind have their work cut out for them. But in the hands of neuroscience – with its shimmering brain scans and humming electrodes, its gene-editing precision and algorithmic might – there is something approaching a starting point. By tracing the pathways of environmental impact to their neural roots, and by following the cascading consequences of our mental processes back out into the world, we might yet begin to parse the tangled web that binds the fates of mind and planet.

This much is clear: as the gears of the climate crisis grind on, our brains will be swept along for the ride. The question is whether we’ll be mere passengers, or whether we’ll seize the controls and steer towards something resembling a liveable future. The weight of nature – the immensity of the crisis we face – is daunting. But it need not be paralysing. Bit by bit, synapse by synapse, we can chart a course through the gathering plague-clouds. It was Ruskin, at a slightly more legible moment in his life, who offered: ‘To banish imperfection is to destroy expression, to check exertion, to paralyse vitality.’ Even if we somehow could, we ought not banish the alleged imperfections of environmental influence on the mind. Instead, we ought to read in them an intimate, vital relationship between self and world.

In this, climatological neuroepidemiology – young and untested though it may be – is poised to play an outsized role. In gazing into the black box of the climate-altered mind, in illuminating the neural circuitry of our planetary predicament, the field offers something precious: a flicker of agency in a world that often feels as if it’s spinning out of control. It whispers that the levers of change are within reach, lodged in the squishy confines of our crania, waiting to be grasped. And it suggests that, even as the weight of nature presses down upon us, we might yet find a way to press back.

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• Research article
• Open access
• Published: 01 June 2010

Reframing climate change as a public health issue: an exploratory study of public reactions

• Edward W Maibach 1 ,
• Matthew Nisbet 1 , 2 ,
• Paula Baldwin 1 ,
• Karen Akerlof 1 &
• Guoqing Diao 3  

BMC Public Health volume  10 , Article number:  299 ( 2010 ) Cite this article

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Climate change is taking a toll on human health, and some leaders in the public health community have urged their colleagues to give voice to its health implications. Previous research has shown that Americans are only dimly aware of the health implications of climate change, yet the literature on issue framing suggests that providing a novel frame - such as human health - may be potentially useful in enhancing public engagement. We conducted an exploratory study in the United States of people's reactions to a public health-framed short essay on climate change.

U.S. adult respondents (n = 70), stratified by six previously identified audience segments, read the essay and were asked to highlight in green or pink any portions of the essay they found "especially clear and helpful" or alternatively "especially confusing or unhelpful." Two dependent measures were created: a composite sentence-specific score based on reactions to all 18 sentences in the essay; and respondents' general reactions to the essay that were coded for valence (positive, neutral, or negative). We tested the hypothesis that five of the six audience segments would respond positively to the essay on both dependent measures.

There was clear evidence that two of the five segments responded positively to the public health essay, and mixed evidence that two other responded positively. There was limited evidence that the fifth segment responded positively. Post-hoc analysis showed that five of the six segments responded more positively to information about the health benefits associated with mitigation-related policy actions than to information about the health risks of climate change.

Conclusions

Presentations about climate change that encourage people to consider its human health relevance appear likely to provide many Americans with a useful and engaging new frame of reference. Information about the potential health benefits of specific mitigation-related policy actions appears to be particularly compelling. We believe that the public health community has an important perspective to share about climate change, a perspective that makes the problem more personally relevant, significant, and understandable to members of the public.

Peer Review reports

Climate change is already taking a toll on human health in the United States [ 1 ] and other nations worldwide [ 2 ]. Unless greenhouse gas emissions worldwide are sharply curtailed - and significant actions taken to help communities adapt to changes in their climate that are unavoidable - the human toll of climate change is likely to become dramatically worse over the next several decades and beyond [ 3 ]. Globally, the human health impacts of climate change will continue to differentially affect the world's poorest nations, where populations endemically suffer myriad health burdens associated with extreme poverty that are being exacerbated by the changing climate. As stated in a recent British Medical Journal editorial, failure of the world's nations to successfully curtail emissions will likely lead to a "global health catastrophe" [ 4 ]. In developed countries such as the United States, the segments of the population most at risk are the poor, the very young, the elderly, those already in poor health, the disabled, individuals living alone, those with inadequate housing or basic services, and/or individuals who lack access to affordable health care or who live in areas with weak public health systems. These population segments disproportionately include racial, ethnic, and indigenous minorities [ 5 ].

While legislation to reduce U.S. greenhouse gas (GHG) emissions has stalled in Congress, in December 2009 the Environmental Protection Agency (EPA) moved toward regulating carbon dioxide and five other of the gases under the Clean Air Act, citing its authority to protect public health and welfare from the impacts of global warming [ 5 ]. The agency found that global warming poses public health risks - including increased morbidity and mortality - due to declining air quality, rising temperatures, increased frequency of extreme weather events, and higher incidences of food- and water-borne pathogens and allergens.

This finding comes as a relatively small group of public health professionals are working rapidly to better comprehend and quantify the nature and magnitude of these threats to human health and wellbeing [ 6 ]. This new but rapidly advancing public health focus has received minimal news media attention, even at internationally leading news organizations such as the New York Times [unpublished data]. It is not surprising therefore that the public also has yet to fully comprehend the public health implications of climate change. Recent surveys of Americans [ 7 ], Canadians [ 8 ], and Maltese [ 9 ] demonstrate that the human health consequences of climate change are seriously underestimated and/or poorly understood, if grasped at all. About half of American survey respondents, for example, selected "don't know" (rather than "none," "hundreds," "thousands," or "millions") when asked the estimated number of current and future (i.e. 50 years hence) injuries and illnesses, and death due to climate change. An earlier survey of Americans [ 10 ] demonstrated that most people see climate change as a geographically and temporally distant threat to the non-human environment. Notably, not a single survey respondent freely associated climate change as representing a threat to people. Similarly, few Canadians, without prompting, can name any specific human health threat linked to climate change impacts in their country [ 8 ].

Cognitive research over the past several decades has shown that how people "frame" an issue - i.e., how they mentally organize and discuss with others the issue's central ideas - greatly influences how they understand the nature of the problem, who or what they see as being responsible for the problem, and what they feel should be done to address the problem [ 11 , 12 ]. The polling data cited above [ 7 – 9 ] suggests that the dominant mental frame used by most members of the public to organize their conceptions about climate change is that of "climate change as an environmental problem." However, when climate change is framed as an environmental problem, this interpretation likely distances many people from the issue and contributes to a lack of serious and sustained public engagement necessary to develop solutions. This focus is also susceptible to a dominant counter frame that the best solution is to continue to grow the economy - paying for adaptive measures in the future when, theoretically, society will be wealthier and better able to afford them - rather than focus on the root causes of the environmental problem [ 13 ]. This economic frame likely leaves the public ambivalent about policy action and works to the advantage of industries that are reluctant to reduce their carbon intensity. Indeed, it is precisely the lack of a countervailing populist movement on climate change that has made policy solutions so difficult to enact [ 13 , 14 ].

Significant efforts have been made over the past several years by public health organizations to raise awareness of the public health implications of climate change and prepare the public health workforce to respond, although as noted above, it is not clear the extent to which public health professionals, journalists, or most importantly, the public and policy makers have taken notice. In the United States, National Public Health Week 2008 was themed "Climate Change: Our Health in the Balance," the Centers for Disease Control and Prevention created a Climate Change and Public Health program, and several professional associations assessed the public health system's readiness to respond to the emerging threat [ 15 – 17 ]. Globally, World Health Day 2008 was themed "Protecting Health from Climate Change," and the World Health Organization has developed a climate change and health work plan, the first objective of which is "raising awareness of the effects of climate change on health, in order to prompt action for public health measures" [ 18 ]. Several prominent medical journals have released special issues on climate change and health [ 19 – 21 ], and these and other medical journals [ 4 ] have issued strongly worded editorials urging health professionals to give voice to the health implications of climate change.

An important assumption in these calls to action is that there may be considerable value in introducing a public health frame into the ongoing public - and policy - dialogue about climate change. While there is indeed solid theoretical basis for this assumption, to the best of our knowledge there is not yet empirical evidence to support the validity of the assumption [ 22 ].

The purpose of this study therefore was to explore how American adults respond to an essay about climate change framed as a public health issue. Our hypothesis was that a public health-framed explanation of climate change would be perceived as useful and personally relevant by readers, with the exception of members of one small segment of Americans who dismiss the notion that human-induced climate change is happening. We used two dependent measures in this hypothesis: a composite score based on respondent reactions to each sentence in the essay, and the overall valence of respondents' general comments made after reading the essay.

Our study builds on previous research that identified six distinct segments of Americans, termed Global Warming's Six Americas [ 7 ]. These six segments of Americans - the Alarmed (18% of the adult population), the Concerned (33%), the Cautious (19%), the Disengaged (12%), the Doubtful (11%), and the Dismissive (7%) - fall along a continuum from those who are engaged on the issue and looking for ways to take appropriate actions (the Alarmed) to those who actively deny its reality and are looking for ways to oppose societal action (the Dismissive; see Figure 1 ). The four segments in the middle of the continuum are likely to benefit most from a reframing of climate change as a human health problem because, to a greater or lesser degree, they are not yet sure that they fully understand the issue and are still, if motivated to do so, relatively open to learning about new perspectives.

Global Warming's Six Americas . A nationally representative sample of American adults classified into six unique audience segments based on their climate change-related beliefs, behaviors and policy preferences.

Between May and August 2009, 74 adults were recruited to participate in semi-structured in-depth elicitation interviews that lasted an average of 43 minutes (ranging from 16 to 124 minutes) and included the presentation of a public health framed essay on climate change. The recruitment process was designed to yield completed interviews with a demographically and geographically diverse group of at least 10 people from each of the previously identified "Six Americas" [ 7 ]. Four respondents were dropped from this study due to incomplete data, leaving a sample size of 70. Audience segment status (i.e., which one of the "Six Americas" a person belonged) was assessed with a previously developed 15-item screening questionnaire that identifies segment status with 80% accuracy [unpublished data].

To achieve demographic diversity in the sample, we recruited an approximately balanced number of men and women, and an approximately balanced number of younger (18 to 30), middle-aged (31 to 50), and older (51 and older) adults (see Table 1 ). We did not set recruitment quotas for racial/ethnic groups, but did make an effort to recruit a mix of people from various racial/ethnic backgrounds.

To achieve geographic diversity, we recruited participants in one of two ways. The majority of participants (n = 56) were recruited - and then interviewed - face-to-face in one of two locations: out-of-town visitors were interviewed at a central location on the National Mall in Washington, DC (a national park situated between the U.S. Capitol, the Smithsonian Museum buildings, and the Lincoln Memorial); and shoppers were interviewed at an "outlet" mall (i.e., discount branded merchandise shopping mall) adjacent to an interstate freeway in Hagerstown, MD. The outlet mall is more than an hour driving distance outside of Washington, DC and attracts shoppers from Maryland, Pennsylvania, and West Virginia, as well as visitors from further away who are driving the interstate freeway. The remaining study participants were recruited via email from among participants to a nationally representative survey that we conducted in Fall 2008 [ 7 ]. They were interviewed subsequently by telephone, after being mailed a copy of the test "public health essay" - described below - in a sealed envelope marked "do not open until asked to do so by the interviewer." As an incentive to participate, all respondents were given a $50 gift card upon completion of their interview. George Mason University Human Subjects Review Board provided approval for the study protocol (reference #6161); all potential respondents received written consent information prior to participation.

The 70 study participants resided in 29 states. Using U.S. Census Bureau classifications, 14% (n = 10) were from the Northeast region, 21% (n = 15) were from the Midwest, 40% (n = 28) from the South, and 23% (n = 16) were from the West; state and region were unknown for one participant. In 2006, the geographic distribution of the overall U.S. population was 18%, 22%, 36% and 23% in the Northeast, Midwest, South and West, respectively [ 23 ].

Data Collection and Coding

The majority of the interview was devoted to open-ended questions intended to establish the respondent's emotions, attitudes, beliefs, knowledge and behavior relative to global warming's causes and consequences. For example, respective open-ended questions asked alternatively if, how, and for whom global warming was a problem; how global warming is caused; if and how global warming can be stopped or limited; and what, if anything, an individual could do to help limit global warming. Toward the end of the interview, respondents were asked to read "a brief essay about global warming" (see Appendix 1), which was designed to frame climate change as a human health issue. Respondents were also given a green and a pink highlighting pen and asked to "use the green highlighter pen to mark any portions of the essay that you feel are especially clear or helpful, and use the pink highlighter pen to mark any portions of the essay that are particularly confusing or unhelpful."

As shown in Appendix 1, the one page essay was organized into four sections: an opening paragraph that introduced the public health frame (5 total sentences); a paragraph that emphasized how human health will be harmed if action is not taken to stop, limit, and/or protect against global warming (i.e., a description of the threat; 7 sentences); a paragraph that discussed several mitigation-focused policy actions and their human health-related benefits if adopted (4 sentences); and a brief concluding paragraph intended to reinforce the public health frame (2 sentences).

When respondents finished the reading, they were asked to describe in an open-ended format their "general reaction to this essay." (Note: This question was inadvertently not asked of one respondent, therefore the sample size for analysis of this data is 69.) For each portion of the essay they marked in green, they were subsequently asked: "What about each of these sentences was especially clear or helpful to you?" For each portion of the essay they marked in pink, they were also asked: "What about each of these sentences was especially confusing or unhelpful to you?"

To evaluate the respondent's general reactions to the essay we reviewed their individual statements (n = 193), defined as discrete thoughts or concepts. Based on this review, we iteratively developed eight thematic categories that captured the range of statements made by respondents. Table 2 defines and describe these themes.

Two graduate student coders were then trained to code each statement into one of the thematic categories. The coders were also instructed to assess the overall valence of each respondent's statements - the first of our dependent measures - rating them as: -1 (entirely negative comments); 0 (mixed, including both positive and negative comments); or 1 (entirely positive comments). Following standard content analysis procedures, we tested inter-coder agreement on approximately 50 statements, making sure that a full range of possible types of coding decisions were required of the coders. To assess reliability, we used Krippendorff's alpha [ 24 , 25 ], a conservative measure that corrects for chance agreement among coders; a K-alpha of .70 or higher is considered sufficient and .80 or higher is considered excellent. For 7 of the 8 thematic categories, we achieved a reliability of .80 or higher; "Lack of Evidence or Stylistically Confusing" was the exception, with an inter-coder reliability of .70. After establishing reliability, the two coders then went on to categorize the rest of the remaining statements from the sample of respondents.

To code the respondent's sentence-specific reactions made with the highlighting pens, sentences marked with only green on at least one word were scored +1 (i.e. indicating "especially clear or useful"), sentences marked with only pink on at least one word were scored -1 (i.e. indicating "especially confusing or unhelpful), and sentences with either no highlighting, or both green and pink, were scored 0. Composite scores were created for each of the four sections of the essay - the opening, the threat section, the benefit section, and the conclusion - by summing the sentence-specific scores in the section and dividing by the number of sentences. A composite score for the entire essay - the second of the dependent measures in our hypothesis - was created by summing the sentence scores across each segment and dividing by the number of respondents per segment. Population estimates, which can be taken solely as preliminary indicators given the non-probabilistic nature of our sampling, were estimated by weighting the mean values for each of the six segments according to its prevalence in the U.S. population (see Figure 1 ).

Data Analysis

To test the between-segment differences in our dependent measures - overall reactions to the essay (i.e., valence) and composite sentence-specific reactions to the entire essay - we used the nonparametric Kruskal-Wallis test (see Figures 2 , 3 ). To test if the median response to the essay on each dependent measure was greater than zero (i.e., a positive reaction) for our full sample, we used the Wilcoxon signed rank test. Lastly, for both dependent measures, we used the Wilcoxon signed rank test to test our hypothesis that five of the six segments (the Dismissive being the one exception) would respond positively to the essay; the null hypothesis was that the median score for each of the five segments did not differ from zero. The Wilcoxon signed rank test is appropriate for small sample sizes and non-normal distributions, both of which are the case for at least some segments in our data.

Average valence of respondents' general essay comments . The mean valence of respondent comments when asked their general reactions to the public health essay by audience segment and by a national population estimate. Note: 1 = (entirely positive comments); 0 = (mixed, including both positive and negative comments); and -1 = (entirely negative comments).

Composite essay scores by segment . Scores reflect respondent average values by segment for the difference between the number of times each of 18 sentences were marked "especially clear or helpful" and "especially confusing or unhelpful" with a full range of possible values between 18 and -18. The scores are adjusted for unequal numbers of respondents within each segment by re-weighting values to represent n = 10.

Post-hoc - after examining the visualized data (see Figures 4 , 5 and 6 ) - we decided to test for two possible main effects in the data. To examine the possibility that the essay's later focus on the public health benefits of mitigation-related policy actions was seen by respondents as clearer and more useful than the essay's earlier focus on public health-related threats, we calculated the difference between the re-scaled (by a factor of 10) average response to both the benefit and the threat sections and then used the Wilcoxon signed rank test to test, by segment, whether the median of these differences was greater than zero. We then evaluated the overall main effect of the essay - across all segments - using the weighted t-test on the differences with weights corresponding to the frequencies of the segments in the population.

Essay evaluations by sentence: Alarmed, Concerned and Cautious segments . Sentence-specific evaluations of the public health essay by respondents in the Alarmed, Concerned and Cautious segments and by a national population estimate. Note: Scores reflect the difference between the number of times a sentence was marked as "especially clear or helpful" and the number of times it was marked as "especially confusing or unhelpful," adjusting for unequal numbers of respondents within each segment by re-weighting values to represent n = 10. Sentence abbreviations correspond to O = opening section (5 sentences); T = climate change health threat related section (7 sentences); B = mitigation-related policy actions and their health benefits (4 sentences); and C = concluding section (2 sentences). The national population estimate was created by weighting the values for each of the six segments according to their relative proportion of American adults.

Essay evaluations by sentence: Disengaged, Doubtful and Dismissive segments . Sentence-specific evaluations of the public health essay by respondents in the Disengaged, Doubtful and Dismissive segments and by a national population estimate. Note: Scores reflect the difference between the number of times within a sentence was marked as "especially clear or helpful" and the number of times it was marked as "especially confusing or unhelpful," adjusting for unequal numbers of respondents within each segment by re-weighting values to represent n = 10. Sentence abbreviations correspond to O = opening section (5 sentences); T = climate change health threat related section (7 sentences); B = mitigation-related policy actions and their health benefits (4 sentences); and C = concluding section (2 sentences). The national population estimate was created by weighting the values for each of the six segments according to their relative proportion of American adults.

Essay evaluations by section (opening, threat, benefits, closing) . Average section-specific evaluations of the public health essay by respondents in each of the six audience segments and by a national population estimate. Note: Scores reflect the difference between the number of sentences within each section marked by a respondent as "especially clear or helpful" and those marked as "especially confusing or unhelpful" with those values averaged across the number of sentences per section and rescaled by a factor of 10. Section abbreviations correspond to O = opening section (5 sentences); T = climate change health threat related section (7 sentences); B = mitigation-related policy actions and their health benefits (4 sentences); and C = concluding section (2 sentences). The national population estimate was created by weighting the mean values for each of the six segments according to their relative proportion of American adults.

Lastly, to examine for the possibility that the concluding framing section of the essay was perceived by respondents as clearer and more useful than the opening framing section, we calculated the difference between the re-scaled average response to both the opening and the concluding sections and then used the Wilcoxon signed rank test to test, by segment, whether the median of these differences was greater than zero. We then evaluated the overall main effect - across all segments - using the weighted t-test on the differences with weights corresponding to the frequencies of the segments in the population.

Overall Sample Response and Between-Group Differences

The results of non-parametric Kruskal-Wallis tests indicate that there are significant between-group differences for both dependent measures: valence ( p = .001)and the composite sentence-specific score ( p < .0001). For the overall sample, the Wilcoxon signed rank tests indicated a positive response on the sentence-specific composite score ( p < .001) but not on the valence score ( p = .12). The average valence scores - on a scale of 1 to -1 - spanned from .55 (Alarmed) to -.7 (Dismissive) (see Figure 2 ). The average sentence-specific composite scores - on a scale of 18 to -18 - ranged from 9.27 (Alarmed) to -4.64 (Dismissive) (see Figure 3 ).

Hypothesis Test

The Wilcoxon signed rank tests indicated only partial support for our hypothesis. Using valence as the dependent measure, the null hypothesis can be rejected only for the Alarmed ( p = .04) and Concerned ( p = .02) segments, but not for the Cautious ( p = .50), Disengaged ( p = .36) or Doubtful segments ( p = .50). Using the composite sentence-specific score as the dependent measure, the null hypothesis can be rejected for the Alarmed ( p = .001), Concerned ( p < .01) and Cautious ( p = .01) segments, and marginally rejected for the Disengaged segment ( p = .06), but not for the Doubtful segment ( p = .61) segment.

In sum, there was clear evidence that the Alarmed and Concerned segments responded positively to the public health essay, and mixed evidence that the Cautious and Disengaged responded positively. There was no evidence that the Doubtful responded positively. It is worthy of note, however, that all six segments agreed with the essay's opening frame device (O1) that "good health is a great blessing," suggesting that human health and wellbeing is a widely shared value.

Table 3 summarizes the thematic content of the statements made by respondents when they were asked to discuss their general reactions to the public health essay. Across segments, not surprisingly, a substantial proportion of comments focused on the presentation of evidence or the stylistic tone of the essay. For the Alarmed and Concerned segments, roughly a third of their statements reflected personal agreement with the essay. In contrast, among the Dismissive, roughly a third of their statements characterized the essay as biased or alarmist. Relative to other possible reactions, substantial proportions of the statements made by the Concerned (18%), Cautious (19%), Disengaged (13%); and Doubtful (16%) indicated that the essay was informative and/or thought provoking.

Benefit versus Threat Statements

The Wilcoxon signed rank tests used to compare segments on the perceived clarity and helpfulness of the threat statements in the first part of the essay against the health benefits of mitigation-related policy actions in the second part of the essay showed a significant main effect ( p ≤ .05) for all segments except the Alarmed ( p = .17). The Dismissive segment showed the largest difference between the sections of the essay (6.10), followed by the Doubtful (3.69), the Cautious (3.57), the Concerned (3.13), and the Disengaged (2.12). Using a weighted t-test, the estimated gain from the Threat to Benefits sections across all segments was 3.17 ( p < .0001), with a 95% confidence interval of 1.85 to 4.49. In short, the health benefits associated with mitigation-related policy actions were seen as clearer and more useful than the preceding threat statements in the essay.

Also worthy of note, as Figures 4 and 5 indicate, is that all six segments reacted positively to the following statements focusing on specific mitigation-related policy actions that lead to human health benefits:

"Taking actions to limit global warming - by making our energy sources cleaner and our cars and appliances more efficient, by making our cities and towns friendlier to trains, buses, and bikers and walkers, and by improving the quality and safety of our food - will improve the health of almost every American."

"Cleaner energy sources and more efficient use of energy will lead to healthier air for children and adults to breathe."

"Improving the design of our cities and towns in ways that make it easier to get around on foot, by bike and on mass transit will reduce the number of cars and help people become more physically active, lose weight."

Conversely, respondents in all segments responded less positively to the statement:

"Increasing our consumption of fruits and vegetables, and reducing our intake of meat - especially beef - will help people maintain a healthy weight, will help prevent heart disease and cancer, and will play an important role in limiting global warming."

Opening versus Concluding Framing Statements

The Wilcoxon signed rank test used to compare segments on their reactions to the opening versus concluding framing statements for each segment showed a significant or marginally significant main effect in the Alarmed ( p = .07), Concerned ( p < .01), Cautious ( p = .05), Disengaged ( p = .03) and Dismissive ( p < .01) segments; the trend was not significant in the Doubtful ( p = .14) segment. The largest differences were seen in the Concerned segment (4.31), followed by the Dismissive (4.09), Disengaged (3.8), Cautious (2.54) and the Alarmed segment (2.45). Again using a weighted t-test, the estimated increase from the Opening to Concluding sections across all segments was 3.30 ( p < .0001), with a 95% confidence interval of 2.14 to 4.47.

On the whole, people who read our public health-framed essay about climate change reacted positively to the information. People in the Alarmed and the Concerned segments demonstrated consistent positive response to the information, while people in the Cautious, Disengaged, and Doubtful segments were less consistent. Although we did not treat it as a dependent measure per se, many of the respondents in all five segments made open-ended comments about the essay that demonstrated a positive engagement with the material. For example, nearly half (44%) of the comments made by the Disengaged segment indicated that the essay reflected their personal point of view, was informative or thought-provoking, or offered valuable prescriptive information on how to take action relative to the climate problem. Similarly, 39% of the comments made by respondents in the Doubtful segment reflected one of these three themes. Moreover, the ascending sentence-specific evaluations between the opening and concluding sections of the essay, for the sample overall and for all of the segments (excluding the Dismissive), suggest that the value of the public health frame may not be immediate, but rather may manifest more fully after people have had time to consider the evidence, especially when this evidence is presented with specific mitigation-related policy actions that are likely to have human health benefits.

One of the most intriguing findings in the study - albeit not definitive due to the order effect of the information in the essay - is the robustness of the response across all six segments to information about the health benefits of taking action to address global warming.

Overall, we interpret these collective findings as providing partial support for our hypothesis that information about climate change framed in ways that encourage people to consider its human health context provides many Americans with a useful and engaging new frame of reference and that this new interpretation may broaden the personal significance and relevance of the issue. Our methods were exploratory, however, and additional research on this question is needed. To that end, we are further analyzing the data already collected to determine more systematically which specific ideas are most and also least resonant with members of each segment. We are also planning an experimental test of climate education material framed in various ways, including a public health frame. Additional research is needed to determine if these findings generalize across nations and other populations.

In the U.S., these findings are especially relevant given the "issue fatigue" that appears to be developing with regard to climate change among at least certain segments of the American public [ 26 ]. Recent public opinion polls in the U.S. have shown a marked decline in the proportion of adults who are worried about global warming, and even relative to the proportion who are convinced that global warming is happening [ 27 – 29 ]. The public health voice may offer an important hedge against such issue fatigue.

Suggesting a novel frame for climate change - i.e., a frame that people had not previously considered - is potentially useful when it helps people understand the issue more clearly by providing additional personal and societal relevance [ 30 , 31 ]. Re-defining climate change in public health terms should help people make connections to already familiar problems such as asthma, allergies, and infectious diseases experienced in their communities, while shifting the visualization of the issue away from remote Arctic regions, and distant peoples and animals. In the process, giving climate change a public health focus suggests that there is a need to both mitigate (i.e. reduce greenhouse gas emissions) and adapt to the problem (i.e. protect communities and people from current and future health related impacts). The frame also presents the opportunity to involve additional trusted communication partners on the issue, notably public health experts and local community leaders [ 13 ].

In conclusion, we believe that the public health community has an important perspective to share about climate change, a perspective that potentially offers the public a more salient way to comprehend an issue that has proven deeply difficult for many people to fully comprehend. Moreover, the public health perspective offers a vision of a better, healthier future - not just a vision of environmental disaster averted, and it focuses on a range of possible policy actions that offer local as well as global benefits. Many leading experts in climate change communication, including the present authors, have suggested that a positive vision for the future and a localization of the issue is precisely what has been missing from the public dialogue on climate change thus far [ 13 , 22 , 32 ].

Not all aspects of the public health implications, however, may be engaging. Certain key recommendations, such as eating less meat, tended to elicit counter-arguments among people in many of the segments in our research. Our research provides clues about specific public health messages that might not be helpful, and suggests the need in future research to look carefully for examples or associations that trigger counter-arguments and negative reactions.

There is an urgent need for the public health community to successfully educate the public and policy makers about the serious human health implications of climate change, and to engage those publics in appropriate preventive and adaptive responses. As a point of strategy, however, our findings may suggest that continuing to communicate about the problem of climate change is not likely to generate wider public engagement. Instead public health voices may be wise to focus their communication on the solutions and the many co-benefits that matter most to people.

Global Warming is a Threat to Peoples' Health & Wellbeing

Most people agree with the sentiment that "good health is a great blessing." Although not yet widely known, global warming poses a very real threat to the health and wellbeing of Americans and other people around the world. Experts at the World Health Organization say that global warming is already leading to an increase in the rate of some diseases and is causing many deaths. If our government and other governments around the world do not soon take steps to limit global warming, a growing number of people in the United States will likely be harmed and killed. Conversely, if our government does take steps to limit global warming, our health and wellbeing will likely improve in a number of important ways.

Our health will suffer if we don't take action

Global warming can harm people both directly and indirectly. Directly, global warming causes more extreme weather patterns including more frequent heat waves, more violent storms, and rising sea-levels - all of which can lead to people being harmed or killed. Indirectly, global warming harms the quality of our water, air and food, and our ecosystems, all of which can lead to increasing rates of disease and death. If we do not act now to limit global warming, experts at the U.S. Centers for Disease Control and Prevention say that global warming will harm people in every region of the United States. As a result of the poor air quality caused by global warming, children will become more likely to develop asthma, and the asthma they suffer from will be more severe; adults who have heart and lung diseases will become more likely to be hospitalized or die from their illness. An increasing number of extreme heat waves, floods, storms, fires and droughts caused by the changes in our climate will lead to more people being injured or killed. New infectious diseases (such as West Nile Virus) and old infectious diseases that we had previously eradicated from the United States (such as malaria and Dengue Fever) are likely to become an increasing problem for us as our climate warms.

Our health will benefit if we do take action

According to a recent study published in the medical journal Lancet, taking actions to limit global warming - by making our energy sources cleaner and our cars and appliances more efficient, by making our cities and towns friendlier to trains, buses, and bikers and walkers, and by improving the quality and safety of our food - will improve the health of almost every American. Cleaner energy sources and more efficient use of energy will lead to healthier air for children and adults to breathe. Improving the design of our cities and towns in ways that make it easier and safer to get around on foot, by bike and on mass transit will reduce the number of cars on our roads and will help people become more physically active and lose weight. Increasing our consumption of fruits and vegetables, and reducing our intake of meat - especially beef - will help people maintain a healthy weight, will help prevent heart disease and cancer, and will play an important role in limiting global warming.

Peoples' health is dependent on the health of the environment in which we live. Global warming offers America an opportunity to make choices that are healthier for us, and for our climate.

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Acknowledgements

This research was supported by a Robert Wood Johnson Foundation Health Policy Investigator Award.

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Edward W Maibach, Matthew Nisbet, Paula Baldwin & Karen Akerlof

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EWM and MN developed the research question, participated in all aspects of the research, and wrote the first draft of the paper. PB coded and conducted preliminary data analysis. KA managed the data collection, conducted data analysis and prepared all figures and tables. GD conducted the final data analysis. All authors contributed to the final draft of the paper.

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Maibach, E.W., Nisbet, M., Baldwin, P. et al. Reframing climate change as a public health issue: an exploratory study of public reactions. BMC Public Health 10 , 299 (2010). https://doi.org/10.1186/1471-2458-10-299

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• Volume 11, Issue 6
• Health effects of climate change: an overview of systematic reviews
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• http://orcid.org/0000-0003-4548-2229 Rhea J Rocque 1 ,
• Caroline Beaudoin 2 ,
• http://orcid.org/0000-0002-4716-6505 Ruth Ndjaboue 2 , 3 ,
• Laura Cameron 1 ,
• Louann Poirier-Bergeron 2 ,
• Rose-Alice Poulin-Rheault 2 ,
• Catherine Fallon 2 , 4 ,
• http://orcid.org/0000-0002-4114-8971 Andrea C Tricco 5 , 6 ,
• http://orcid.org/0000-0003-4192-0682 Holly O Witteman 2 , 3
• 1 Prairie Climate Centre , The University of Winnipeg , Winnipeg , Manitoba , Canada
• 2 Faculty of Medicine , Université Laval , Quebec , QC , Canada
• 3 VITAM Research Centre for Sustainable Health , Quebec , QC , Canada
• 4 CHUQ Research Centre , Quebec , QC , Canada
• 5 Li Ka Shing Knowledge Institute , Toronto , Ontario , Canada
• 6 Dalla Lana School of Public Health , University of Toronto , Toronto , Ontario , Canada
• Correspondence to Dr Rhea J Rocque; rhea.rocque{at}gmail.com

Objectives We aimed to develop a systematic synthesis of systematic reviews of health impacts of climate change, by synthesising studies’ characteristics, climate impacts, health outcomes and key findings.

Design We conducted an overview of systematic reviews of health impacts of climate change. We registered our review in PROSPERO (CRD42019145972). No ethical approval was required since we used secondary data. Additional data are not available.

Data sources On 22 June 2019, we searched Medline, Cumulative Index to Nursing and Allied Health Literature (CINAHL), Embase, Cochrane and Web of Science.

Eligibility criteria We included systematic reviews that explored at least one health impact of climate change.

Data extraction and synthesis We organised systematic reviews according to their key characteristics, including geographical regions, year of publication and authors’ affiliations. We mapped the climate effects and health outcomes being studied and synthesised major findings. We used a modified version of A MeaSurement Tool to Assess systematic Reviews-2 (AMSTAR-2) to assess the quality of studies.

Results We included 94 systematic reviews. Most were published after 2015 and approximately one-fifth contained meta-analyses. Reviews synthesised evidence about five categories of climate impacts; the two most common were meteorological and extreme weather events. Reviews covered 10 health outcome categories; the 3 most common were (1) infectious diseases, (2) mortality and (3) respiratory, cardiovascular or neurological outcomes. Most reviews suggested a deleterious impact of climate change on multiple adverse health outcomes, although the majority also called for more research.

Conclusions Most systematic reviews suggest that climate change is associated with worse human health. This study provides a comprehensive higher order summary of research on health impacts of climate change. Study limitations include possible missed relevant reviews, no meta-meta-analyses, and no assessment of overlap. Future research could explore the potential explanations between these associations to propose adaptation and mitigation strategies and could include broader sociopsychological health impacts of climate change.

• public health
• social medicine

Data availability statement

Data sharing not applicable as no datasets generated and/or analysed for this study. All data relevant to the study are included in the article or uploaded as supplementary information. Additional data are not available.

This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited, appropriate credit is given, any changes made indicated, and the use is non-commercial. See:  http://creativecommons.org/licenses/by-nc/4.0/ .

https://doi.org/10.1136/bmjopen-2020-046333

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Strengths and limitations of this study

A strength of this study is that it provides the first broad overview of previous systematic reviews exploring the health impacts of climate change. By targeting systematic reviews, we achieve a higher order summary of findings than what would have been possible by consulting individual original studies.

By synthesising findings across all included studies and according to the combination of climate impact and health outcome, we offer a clear, detailed and unique summary of the current state of evidence and knowledge gaps about how climate change may influence human health.

A limitation of this study is that we were unable to access some full texts and therefore some studies were excluded, even though we deemed them potentially relevant after title and abstract inspection.

Another limitation is that we could not conduct meta-meta-analyses of findings across reviews, due to the heterogeneity of the included systematic reviews and the relatively small proportion of studies reporting meta-analytic findings.

Finally, the date of the systematic search is a limitation, as we conducted the search in June 2019.

Introduction

The environmental consequences of climate change such as sea-level rise, increasing temperatures, more extreme weather events, increased droughts, flooding and wildfires are impacting human health and lives. 1 2 Previous studies and reviews have documented the multiple health impacts of climate change, including an increase in infectious diseases, respiratory disorders, heat-related morbidity and mortality, undernutrition due to food insecurity, and adverse health outcomes ensuing from increased sociopolitical tension and conflicts. 2–5 Indeed, the most recent Lancet Countdown report, 2 which investigates 43 indicators of the relationship between climate change and human health, arrived at their most worrisome findings since the beginning of their on-going annual work. This report underlines that the health impacts of climate change continue to worsen and are being felt on every continent, although they are having a disproportionate and unequal impact on populations. 2 Authors caution that these health impacts will continue to worsen unless we see an immediate international response to limiting climate change.

To guide future research and action to mitigate and adapt to the health impacts of climate change and its environmental consequences, we need a complete and thorough overview of the research already conducted regarding the health impacts of climate change. Although the number of original studies researching the health impacts of climate change has greatly increased in the recent decade, 2 these do not allow for an in-depth overview of the current literature on the topic. Systematic reviews, on the other hand, allow a higher order overview of the literature. Although previous systematic reviews have been conducted on the health impacts of climate change, these tend to focus on specific climate effects (eg, impact of wildfires on health), 6 7 health impacts (eg, occupational health outcomes), 8 9 countries, 10–12 or are no longer up to date, 13 14 thus limiting our global understanding of what is currently known about the multiple health impacts of climate change across the world.

In this study, we aimed to develop such a complete overview by synthesising systematic reviews of health impacts of climate change. This higher order overview of the literature will allow us to better prepare for the worsening health impacts of climate change, by identifying and describing the diversity and range of health impacts studied, as well as by identifying gaps in previous research. Our research objectives were to synthesise studies’ characteristics such as geographical regions, years of publication, and authors’ affiliations, to map the climate impacts, health outcomes, and combinations of these that have been studied, and to synthesise key findings.

We applied the Cochrane method for overviews of reviews. 15 This method is designed to systematically map the themes of studies on a topic and synthesise findings to achieve a broader overview of the available literature on the topic.

Research questions

Our research questions were the following: (1) What is known about the relationship between climate change and health, as shown in previous systematic reviews? (2) What are the characteristics of these studies? We registered our plan (CRD42019145972 16 ) in PROSPERO, an international prospective register of systematic reviews and followed Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 17 to report our findings, as a reporting guideline for overviews is still in development. 18

Search strategy and selection criteria

To identify relevant studies, we used a systematic search strategy. There were two inclusion criteria. We included studies in this review if they (1) were systematic reviews of original research and (2) reported at least one health impact as it related (directly or indirectly) to climate change.

We defined a systematic review, based on Cochrane’s definition, as a review of the literature in which one ‘attempts to identify, appraise and synthesize all the empirical evidence that meets pre-specified eligibility criteria to answer a specific research question [by] us[ing] explicit, systematic methods that are selected with a view aimed at minimizing bias, to produce more reliable findings to inform decision making’. 19 We included systematic reviews of original research, with or without meta-analyses. We excluded narrative reviews, non-systematic literature reviews and systematic reviews of materials that were not original research (eg, systematic reviews of guidelines.)

We based our definition of health impacts on the WHO’s definition of health as, ‘a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity’. 20 Therefore, health impacts included, among others, morbidity, mortality, new conditions, worsening/improving conditions, injuries and psychological well-being. Included studies could refer to climate change or global warming directly or indirectly, for instance, by synthesising the direct or indirect health effects of temperature rises or of natural conditions/disasters made more likely by climate change (eg, floods, wildfires, temperature variability, droughts.) Although climate change and global warming are not equivalent terms, in an effort to avoid missing relevant literature, we included studies using either term. We included systematic reviews whose main focus was not the health impacts of climate change, providing they reported at least one result regarding health effects related to climate change (or consequences of climate change.) We excluded studies if they did not report at least one health effect of climate change. For instance, we excluded studies which reported on existing measures of health impacts of climate change (and not the health impact itself) and studies which reported on certain health impacts without a mention of climate change, global warming or environmental consequences made more likely by climate change.

On 22 June 2019, we retrieved systematic reviews regarding the health effects of climate change by searching from inception the electronic databases Medline, CINAHL, Embase, Cochrane, Web of Science using a structured search (see online supplemental appendix 1 for final search strategy developed by a librarian.) We did not apply language restrictions. After removing duplicates, we imported references into Covidence. 21

Supplemental material

Screening process and data extraction.

To select studies, two trained analysts first screened independently titles and abstracts to eliminate articles that did not meet our inclusion criteria. Next, the two analysts independently screened the full text of each article. A senior analyst resolved any conflict or disagreement.

Next, we decided on key information that needed to be extracted from studies. We extracted the first author’s name, year of publication, number of studies included, time frame (in years) of the studies included in the article, first author’s institution’s country affiliation, whether the systematic review included a meta-analysis, geographical focus, population focus, the climate impact(s) and the health outcome(s) as well as the main findings and limitations of each systematic review.

Two or more trained analysts (RR, CB, RN, LC, LPB, RAPR) independently extracted data, using Covidence and spreadsheet software (Google Sheets). An additional trained analyst from the group or senior research team member resolved disagreements between individual judgments.

Coding and data mapping

To summarise findings from previous reviews, we first mapped articles according to climate impacts and health outcomes. To develop the categories of climate impacts and health outcomes, two researchers (RR and LC) consulted the titles and abstracts of each article. We started by identifying categories directly based on our data and finalised our categories by consulting previous conceptual frameworks of climate impacts and health outcomes. 1 22 23 The same two researchers independently coded each article according to their climate impact and health outcome. We then compared coding and resolved disagreements through discussion.

Next, using spreadsheet software, we created a matrix to map articles according to their combination of climate impacts and health outcomes. Each health outcome occupied one row, whereas climate impacts each occupied one column. We placed each article in the matrix according to the combination(s) of their climate impact(s) and health outcome(s). For instance, if we coded an article as ‘extreme weather’ for climate and ‘mental health’ for health impact, we noted the reference of this article in the cell at the intersection of these two codes. We calculated frequencies for each cell to identify frequent combinations and gaps in literature. Because one study could investigate more than one climate impact and health outcome, the frequency counts for each category could exceed the number of studies included in this review.

Finally, we re-read the Results and Discussion sections of each article to summarise findings of the studies. We first wrote an individual summary for each study, then we collated the summaries of all studies exploring the same combination of categories to develop an overall summary of findings for each combination of categories.

Quality assessment

We used a modified version of AMSTAR-2 to assess the quality of the included systematic reviews ( online supplemental appendix 2 ). The purpose of this assessment was to evaluate the quality of the included studies as a whole to get a sense of the overall quality of evidence in this field. Therefore, individual quality scores were not compiled for each article, but scores were aggregated according to items. Since AMSTAR-2 was developed for syntheses of systematic reviews of randomised controlled trials, working with a team member with expertise in knowledge synthesis (AT), we adapted it to suit a research context that is not amenable to randomised controlled trials. For instance, we changed assessing and accounting for risk of bias in studies’ included randomised controlled trials to assessing and accounting for limitations in studies’ included articles. Complete modifications are presented in online supplemental appendix 2 .

Patient and public involvement

Patients and members of the public were not involved in this study.

Articles identified

As shown in the PRISMA diagram in figure 1 , from an initial set of 2619 references, we retained 94 for inclusion. More precisely, following screening of titles and abstracts, 146 studies remained for full-text inspection. During full-text inspection, we excluded 52 studies, as they did not report a direct health effect of climate change (n=17), did not relate to climate change (n=15), were not systematic reviews (n=10), or we could not retrieve the full text (n=10).

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The flow chart for included articles in this review.

Study descriptions

A detailed table of all articles and their characteristics can be found in online supplemental appendix 3 . Publication years ranged from 2007 to 2019 (year of data extraction), with the great majority of included articles (n=69; 73%) published since 2015 ( figure 2 ). A median of 30 studies had been included in the systematic reviews (mean=60; SD=49; range 7–722). Approximately one-fifth of the systematic reviews included meta-analyses of their included studies (n=18; 19%). The majority of included systematic reviews’ first authors had affiliations in high-income countries, with the largest representations by continent in Europe (n=30) and Australia (n=24) ( figure 3 ). Countries of origin by continents include (from highest to lowest frequency, then by alphabetical order): Europe (30); UK (9), Germany (6), Italy (4), Sweden (4), Denmark (2), France (2), Georgia (1), Greece (1) and Finland (1); Australia (24); Asia (21); China (11), Iran (4), India (1), Jordan (1), Korea (1), Nepal (1), Philippines (1), Taiwan (1); North America (16); USA (15), Canada (1); Africa (2); Ethiopia (1), Ghana (1), and South America (1); Brazil (1).

Number of included systematic reviews by year of publication.

Number of publications according to geographical affiliation of the first author.

Regarding the geographical focus of systematic reviews, most of the included studies (n=68; 72%) had a global focus or no specified geographical limitations and therefore included studies published anywhere in the world. The remaining systematic reviews either targeted certain countries (n=12) (1 for each Australia, Germany, Iran, India, Ethiopia, Malaysia, Nepal, New Zealand and 2 reviews focused on China and the USA), continents (n=5) (3 focused on Europe and 2 on Asia), or regions according to geographical location (n=6) (1 focused on Sub-Saharan Africa, 1 on Eastern Mediterranean countries, 1 on Tropical countries, and 3 focused on the Arctic), or according to the country’s level of income (n=3) (2 on low to middle income countries, 1 on high income countries).

Regarding specific populations of interest, most of the systematic reviews did not define a specific population of interest (n=69; 73%). For the studies that specified a population of interest (n=25; 26.6%), the most frequent populations were children (n=7) and workers (n=6), followed by vulnerable or susceptible populations more generally (n=4), the elderly (n=3), pregnant people (n=2), people with disabilities or chronic illnesses (n=2) and rural populations (n=1).

We assessed studies for quality according to our revised AMSTAR-2. Complete scores for each article and each item are available in online supplemental appendix 4 . Out of 94 systematic reviews, the most commonly fully satisfied criterion was #1 (Population, Intervention, Comparator, Outcome (PICO) components) with 81/94 (86%) of included systematic reviews fully satisfying this criterion. The next most commonly satisfied criteria were #16 (potential sources of conflict of interest reported) (78/94=83% fully), #13 (account for limitations in individual studies) (70/94=75% fully and 2/94=2% partially), #7 (explain both inclusion and exclusion criteria) (64/94=68% fully and 19/94=20% partially), #8 (description of included studies in adequate detail) (36/94=38% fully and 41/94=44% partially), and #4 (use of a comprehensive literature search strategy) (0/94=0% fully and 80/94=85% partially). For criteria #11, #12, and #15, which only applied to reviews including meta-analyses, 17/18 (94%) fully satisfied criterion #11 (use of an appropriate methods for statistical combination of results), 12/18 (67%) fully satisfied criterion #12 (assessment of the potential impact of Risk of Bias (RoB) in individual studies) (1/18=6% partially), and 11/18 (61%) fully satisfied criterion #15 (an adequate investigation of publication bias, small study bias).

Climate impacts and health outcomes

Regarding climate impacts, we identified 5 mutually exclusive categories, with 13 publications targeting more than one category of climate impacts: (1) meteorological (n=71 papers) (eg, temperature, heat waves, humidity, precipitation, sunlight, wind, air pressure), (2) extreme weather (n=24) (eg, water-related, floods, cyclones, hurricanes, drought), (3) air quality (n=7) (eg, air pollution and wildfire smoke exposure), (4) general (n=5), and (5) other (n=3). Although heat waves could be considered an extreme weather event, papers investigating heat waves’ impact on health were classified in the meteorological impact category, since some of these studies treated them with high temperature. ‘General’ climate impacts included articles that did not specify climate change impacts but stated general climate change as their focus. ‘Other’ climate impacts included studies investigating other effects indirectly related to climate change (eg, impact of environmental contaminants) or general environmental risk factors (eg, environmental hazards, sanitation and access to clean water.)

We identified 10 categories to describe the health outcomes studied by the systematic reviews, and 29 publications targeted more than one category of health outcomes: (1) infectious diseases (n=41 papers) (vector borne, food borne and water borne), (2) mortality (n=32), (3) respiratory, cardiovascular and neurological (n=23), (4) healthcare systems (n=16), 5) mental health (n=13), (6) pregnancy and birth (n=11), 7) nutritional (n=9), (8) skin diseases and allergies (n=8), (9) occupational health and injuries (n=6) and (10) other health outcomes (n=17) (eg, sleep, arthritis, disability-adjusted life years, non-occupational injuries, etc)

Figure 4 depicts the combinations of climate impact and health outcome for each study, with online supplemental appendix 5 offering further details. The five most common combinations are studies investigating the (1) meteorological impacts on infectious diseases (n=35), (2) mortality (n=24) and (3) respiratory, cardiovascular and neurological outcomes (n=17), (4) extreme weather events’ impacts on infectious diseases (n=14), and (5) meteorological impacts on health systems (n=11).

Summary of the combination of climate impact and health outcome (frequencies). The total frequency for one category of health outcome could exceed the number of publications included in this health outcome, since one publication could explore the health impact according to more than one climate factor (eg, one publication could explore both the impact of extreme weather events and temperature on mental health).

For studies investigating meteorological impacts on health, the three most common health outcomes studied were impacts on (1) infectious diseases (n=35), (2) mortality (n=24) and (3) respiratory, cardiovascular and neurological outcomes (n=17). Extreme weather event studies most commonly reported health outcomes related to (1) infectious diseases (n=14), (2) mental health outcomes (n=9) and (3) nutritional outcomes (n=6) and other health outcomes (eg, injuries, sleep) (n=6). Studies focused on the impact of air quality were less frequent and explored mostly health outcomes linked to (1) respiratory, cardiovascular and neurological outcomes (n=6), (2) mortality (n=5) and (3) pregnancy and birth outcomes (n=3).

Summary of findings

Most reviews suggest a deleterious impact of climate change on multiple adverse health outcomes, with some associations being explored and/or supported with consistent findings more often than others. Some reviews also report conflicting findings or an absence of association between the climate impact and health outcome studied (see table 1 for a detailed summary of findings according to health outcomes).

• View inline

Summary of findings from systematic reviews according to health outcome and climate impact

Notable findings of health outcomes according to climate impact include the following. For meteorological factors (n=71), temperature and humidity are the variables most often studied and report the most consistent associations with infectious diseases and respiratory, cardiovascular, and neurological outcomes. Temperature is also consistently associated with mortality and healthcare service use. Some associations are less frequently studied, but remain consistent, including the association between some meteorological factors (eg, temperature and heat) and some adverse mental health outcomes (eg, hospital admissions for mental health reasons, suicide, exacerbation of previous mental health conditions), and the association between heat and adverse occupational outcomes and some adverse birth outcomes. Temperature is also associated with adverse nutritional outcomes (likely via crop production and food insecurity) and temperature and humidity are associated with some skin diseases and allergies. Some health outcomes are less frequently studied, but studies suggest an association between temperature and diabetes, impaired sleep, cataracts, heat stress, heat exhaustion and renal diseases.

Extreme weather events (n=24) are consistently associated with mortality, some mental health outcomes (eg, distress, anxiety, depression) and adverse nutritional outcomes (likely via crop production and food insecurity). Some associations are explored less frequently, but these studies suggest an association between drought and respiratory and cardiovascular outcomes (likely via air quality), between extreme weather events and an increased use of healthcare services and some adverse birth outcomes (likely due to indirect causes, such as experiencing stress). Some health outcomes are less frequently studied, but studies suggest an association between extreme weather events and injuries, impaired sleep, oesophageal cancer and exacerbation of chronic illnesses. There are limited and conflicting findings for the association between extreme weather events and infectious diseases, as well as for certain mental health outcomes (eg, suicide and substance abuse). At times, different types of extreme weather events (eg, drought vs flood) led to conflicting findings for some health outcomes (eg, mental health outcomes, infectious diseases), but for other health outcomes, the association was consistent independently of the extreme weather event studied (eg, mortality, healthcare service use and nutritional outcomes).

The impact of air quality on health (n=7) was less frequently studied, but the few studies exploring this association report consistent findings regarding an association with respiratory-specific mortality, adverse respiratory outcomes and an increase in healthcare service use. There is limited evidence regarding the association between air quality and cardiovascular outcomes, limited and inconsistent evidence between wildfire smoke exposure and adverse birth outcomes, and no association is found between exposure to wildfire smoke and increase in use of health services for mental health reasons. Only one review explored the impact of wildfire smoke exposure on ophthalmic outcomes, and it suggests that it may be associated with eye irritation and cataracts.

Reviews which stated climate change as their general focus and did not specify the climate impact(s) under study were less frequent (n=5), but they suggest an association between climate change and pollen allergies in Europe, increased use of healthcare services, obesity, skin diseases and allergies and an association with disability-adjusted life years. Reviews investigating the impact of other climate-related factors (n=3) show inconsistent findings concerning the association between environmental pollutant and adverse birth outcomes, and two reviews suggest an association between environmental risk factors and pollutants and childhood stunting and occupational diseases.

Most reviews concluded by calling for more research, noting the limitations observed among the studies included in their reviews, as well as limitations in their reviews themselves. These limitations included, among others, some systematic reviews having a small number of publications, 24 25 language restrictions such as including only papers in English, 26 27 arriving at conflicting evidence, 28 difficulty concluding a strong association due to the heterogeneity in methods and measurements or the limited equipment and access to quality data in certain contexts, 24 29–31 and most studies included were conducted in high-income countries. 32 33

Previous authors also discussed the important challenge related to exploring the relationship between climate change and health. Not only is it difficult to explore the potential causal relationship between climate change and health, mostly due to methodological challenges, but there are also a wide variety of complex causal factors that may interact to determine health outcomes. Therefore, the possible causal mechanisms underlying these associations were at times still unknown or uncertain and the impacts of some climate factors were different according to geographical location and specificities of the context. Nonetheless, some reviews offered potential explanations for the climate-health association, with the climate factor at times, having a direct impact on health (eg, flooding causing injuries, heat causing dehydration) and in other cases, having an indirect impact (eg, flooding causing stress which in turn may cause adverse birth outcomes, heat causing difficulty concentrating leading to occupational injuries.)

Principal results

In this overview of systematic reviews, we aimed to develop a synthesis of systematic reviews of health impacts of climate change by mapping the characteristics and findings of studies exploring the relationship between climate change and health. We identified four key findings.

First, meteorological impacts, mostly related to temperature and humidity, were the most common impacts studied by included publications, which aligns with findings from a previous scoping review on the health impacts of climate change in the Philippines. 10 Indeed, meteorological factors’ impact on all health outcomes identified in this review are explored, although some health outcomes are more rarely explored (eg, mental health and nutritional outcomes). Although this may not be surprising given that a key implication of climate change is the long-term meteorological impact of temperature rise, this finding suggests we also need to undertake research focused on other climate impacts on health, including potential direct and indirect effects of temperature rise, such as the impact of droughts and wildfire smoke. This will allow us to better prepare for the health crises that arise from these ever-increasing climate-related impacts. For instance, the impacts of extreme weather events and air quality on certain health outcomes are not explored (eg, skin diseases and allergies, occupational health) or only rarely explored (eg, pregnancy outcomes).

Second, systematic reviews primarily focus on physical health outcomes, such as infectious diseases, mortality, and respiratory, cardiovascular and neurological outcomes, which also aligns with the country-specific previous scoping review. 10 Regarding mortality, we support Campbell and colleagues’ 34 suggestion that we should expand our focus to include other types of health outcomes. This will provide better support for mitigation policies and allow us to adapt to the full range of threats of climate change.

Moreover, it is unclear whether the distribution of frequencies of health outcomes reflects the actual burden of health impacts of climate change. The most commonly studied health outcomes do not necessarily reflect the definition of health presented by the WHO as, ‘a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity’. 20 This suggests that future studies should investigate in greater depth the impacts of climate change on mental and broader social well-being. Indeed, some reviews suggested that climate change impacts psychological and social well-being, via broader consequences, such as political instability, health system capacity, migration, and crime, 3 4 35 36 thus illustrating how our personal health is determined not only by biological and environmental factors but also by social and health systems. The importance of expanding our scope of health in this field is also recognised in the most recent Lancet report, which states that future reports will include a new mental health indicator. 2

Interestingly, the reviews that explored the mental health impacts of climate change were focused mostly on the direct and immediate impacts of experiencing extreme weather events. However, psychologists are also warning about the long-term indirect mental health impacts of climate change, which are becoming more prevalent for children and adults alike (eg, eco-anxiety, climate depression). 37 38 Even people who do not experience direct climate impacts, such as extreme weather events, report experiencing distressing emotions when thinking of the destruction of our environment or when worrying about one’s uncertain future and the lack of actions being taken. To foster emotional resilience in the face of climate change, these mental health impacts of climate change need to be further explored. Humanity’s ability to adapt to and mitigate climate change ultimately depends on our emotional capacity to face this threat.

Third, there is a notable geographical difference in the country affiliations of first authors, with three quarters of systematic reviews having been led by first authors affiliated to institutions in Europe, Australia, or North America, which aligns with the findings of the most recent Lancet report. 2 While perhaps unsurprising given the inequalities in research funding and institutions concentrated in Western countries, this is of critical importance given the significant health impacts that are currently faced (and will remain) in other parts of the world. Research funding organisations should seek to provide more resources to authors in low-income to middle-income countries to ensure their expertise and perspectives are better represented in the literature.

Fourth, overall, most reviews suggest an association between climate change and the deterioration of health in various ways, illustrating the interdependence of our health and well-being with the well-being of our environment. This interdependence may be direct (eg, heat’s impact on dehydration and exhaustion) or indirect (eg, via behaviour change due to heat.) The most frequently explored and consistently supported associations include an association between temperature and humidity with infectious diseases, mortality and adverse respiratory, cardiovascular and neurological outcomes. Other less frequently studied but consistent associations include associations between climate impacts and increased use of healthcare services, some adverse mental health outcomes, adverse nutritional outcomes and adverse occupational health outcomes. These associations support key findings of the most recent Lancet report, in which authors report, among others, increasing heat exposure being associated with increasing morbidities and mortality, climate change leading to food insecurity and undernutrition, and to an increase in infectious disease transmission. 2

That said, a number of reviews included in this study reported limited, conflicting and/or an absence of evidence regarding the association between the climate impact and health outcome. For instance, there was conflicting or limited evidence concerning the association between extreme weather events and infectious diseases, cardiorespiratory outcomes and some mental health outcomes and the association between air quality and cardiovascular-specific mortality and adverse birth outcomes. These conflicting and limited findings highlight the need for further research. These associations are complex and there exist important methodological challenges inherent to exploring the causal relationship between climate change and health outcomes. This relationship may at times be indirect and likely determined by multiple interacting factors.

The climate-health link has been the target of more research in recent years and it is also receiving increasing attention from the public and in both public health and climate communication literature. 2 39–41 However, the health framing of climate change information is still underused in climate communications, and researchers suggest we should be doing more to make the link between human health and climate change more explicit to increase engagement with the climate crisis. 2 41–43 The health framing of climate communication also has implications for healthcare professionals 44 and policy-makers, as these actors could play a key part in climate communication, adaptation and mitigation. 41 42 45 These key stakeholders’ perspectives on the climate-health link, as well as their perceived role in climate adaptation and mitigation could be explored, 46 since research suggests that health professionals are important voices in climate communications 44 and especially since, ultimately, these adverse health outcomes will engender pressure on and cost to our health systems and health workers.

Strengths and limitations

To the best of our knowledge, the current study provides the first broad overview of previous systematic reviews exploring the health impacts of climate change. Our review has three main strengths. First, by targeting systematic reviews, we achieve a higher order summary of findings than what would have been possible by consulting individual original studies. Second, by synthesising findings across all included studies and according to the combination of climate impact and health outcome, we offer a clear, detailed and unique summary of the current state of evidence and knowledge gaps about how climate change may influence human health. This summary may be of use to researchers, policy-makers and communities. Third, we included studies published in all languages about any climate impact and any health outcome. In doing so, we provide a comprehensive and robust overview.

Our work has four main limitations. First, we were unable to access some full texts and therefore some studies were excluded, even though we deemed them potentially relevant after title and abstract inspection. Other potentially relevant systematic reviews may be missing due to unseen flaws in our systematic search. Second, due to the heterogeneity of the included systematic reviews and the relatively small proportion of studies reporting meta-analytic findings, we could not conduct meta-meta-analyses of findings across reviews. Future research is needed to quantify the climate and health links described in this review, as well as to investigate the causal relationship and other interacting factors. Third, due to limited resources, we did not assess overlap between the included reviews concerning the studies they included. Frequencies and findings should be interpreted with potential overlap in mind. Fourth, we conducted the systematic search of the literature in June 2019, and it is therefore likely that some recent systematic reviews are not included in this study.

Conclusions

Overall, most systematic reviews of the health impacts of climate change suggest an association between climate change and the deterioration of health in multiple ways, generally in the direction that climate change is associated with adverse human health outcomes. This is worrisome since these outcomes are predicted to rise in the near future, due to the rise in temperature and increase in climate-change-related events such as extreme weather events and worsened air quality. Most studies included in this review focused on meteorological impacts of climate change on adverse physical health outcomes. Future studies could fill knowledge gaps by exploring other climate-related impacts and broader psychosocial health outcomes. Moreover, studies on health impacts of climate change have mostly been conducted by first authors affiliated with institutions in high-income countries. This inequity needs to be addressed, considering that the impacts of climate change are and will continue to predominantly impact lower income countries. Finally, although most reviews also recommend more research to better understand and quantify these associations, to adapt to and mitigate climate change’s impacts on health, it will also be important to unpack the ‘what, how, and where’ of these effects. Health effects of climate change are unlikely to be distributed equally or randomly through populations. It will be important to mitigate the changing climate’s potential to exacerbate health inequities.

Ethics statements

Patient consent for publication.

Not required.

Acknowledgments

The authors gratefully acknowledge the contributions of Selma Chipenda Dansokho, as research associate, and Thierry Provencher, as research assistant, to this project, and of Frederic Bergeron, for assistance with search strategy, screening and selection of articles for the systematic review.

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Supplementary materials

Supplementary data.

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• Data supplement 1
• Data supplement 2
• Data supplement 3
• Data supplement 4
• Data supplement 5

Twitter @RutNdjab, @ATricco, @hwitteman

Contributors RN, CF, ACT, HOW contributed to the design of the study. CB, RN, LPB, RAPR and HOW contributed to the systematic search of the literature and selection of studies. RR, HOW, LC conducted data analysis and interpretation. RR and HOW drafted the first version of the article with early revision by CB, LC and RN. All authors critically revised the article and approved the final version for submission for publication. RR and HOW had full access to all the data in the study and had final responsibility for the decision to submit for publication.

Funding This study was funded by the Canadian Institutes of Health Research (CIHR) FDN-148426. The CIHR had no role in determining the study design, the plans for data collection or analysis, the decision to publish, nor the preparation of this manuscript. ACT is funded by a Tier 2 Canada Research Chair in Knowledge Synthesis. HOW is funded by a Tier 2 Canada Research Chair in Human-Centred Digital Health.

Competing interests None declared.

Provenance and peer review Not commissioned; externally peer reviewed.

Supplemental material This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise.

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Climate change and human health

Affiliation.

• 1 Global Climate Change, Division of Environmental Hazards and Health Effects, National Center for Environmental Health, CDC, 4770 Buford Highway, NE, MS F-57, Atlanta, Georgia 30341, USA. [email protected]
• PMID: 19768168
• PMCID: PMC2744549

Climate change science points to an increase in sea surface temperature, increases in the severity of extreme weather events, declining air quality, and destabilizing natural systems due to increases in greenhouse gas emissions. The direct and indirect health results of such a global imbalance include excessive heat-related illnesses, vector- and waterborne diseases, increased exposure to environmental toxins, exacerbation of cardiovascular and respiratory diseases due to declining air quality, and mental health stress among others. Vulnerability to these health effects will increase as elderly and urban populations increase and are less able to adapt to climate change. In addition, the level of vulnerability to certain health impacts will vary by location. As a result, strategies to address climate change must include health as a strategic component on a regional level. The co-benefits of improving health while addressing climate change will improve public health infrastructure today, while mitigating the negative consequences of a changing climate for future generations.

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Potential Conflicts of Interest: None disclosed

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Exploring the health impacts of climate change

In a new study, published in Nature Reviews Endocrinology , endocrinologists and researchers from the Nuffield Department of Women’s & Reproductive Health (NDWRH) at the University of Oxford, the London School of Hygiene & Tropical Medicine, the William Harvey Research Institute (WHRI) at Queen Mary University of London and the National University of Singapore have emphasised the critical need for further research into the effects of heat exposure on the endocrine system. 

With climate change increasing seasonal temperatures and causing more frequent heatwaves, understanding these effects has become more crucial than ever.

Hormones play a role in nearly all biological functions, yet the influence of environmental factors on hormone release and action is not well characterised. Researchers from the University of Oxford, the London School of Hygiene & Tropical Medicine, the William Harvey Research Institute at Queen Mary University of London, and the National University of Singapore have highlighted the urgent need for more research into the effects of heat exposure, particularly in the context of climate change increasing seasonal temperatures and causing more heatwaves.

Hormones influence how we adapt to changes in environmental temperature by controlling processes such as conservation of body water, sweating, and heat generation from cell metabolism. A review of studies published from the 1940s onwards indicates that heat exposure affects hormones involved in processes ranging from the stress response, blood glucose control, fertility, and breast milk production. However, many of these studies involved short-term heat exposure in non-human animal models or in healthy human volunteers such as military recruits.

Our review highlights the gap in evidence regarding the impact of sustained heat exposure on the endocrine system, which is particularly relevant to the increasing numbers of people living with endocrine conditions such as diabetes mellitus or thyroid disorders, who may have limited tolerance to higher temperatures. Heatwaves increase the risk of hospitalisation for these patients, which also increases the burden of heat on the health system.

Lead author, Professor Fadil Hannan from the Nuffield Department of Women’s & Reproductive Health at the University of Oxford, stated: 'We know very little about whether increased heat exposure due to climate change could affect endocrine health. We require research involving both the endocrine and global health research communities to assess the impact of rising temperatures and heatwaves on endocrine patients. This is particularly important for patients living in hot climates, who may have inadequate access to cooled environments. A better understanding of these effects will enable interventions to be developed for endocrine patients most at risk from heat extremes.'

Certain hormonal disorders can disrupt the body's ability to regulate temperature, making it harder to cool down and increasing the risk of heat-related illnesses. Co-author, Professor Jason Lee , at the National University of Singapore, adds: 'As the world grapples with the escalating threats of climate change, unravelling the intricate relationships between heat exposure, endocrine function, and human health is not only a scientific imperative but a moral obligation to protect the vulnerable and ensure the well-being of generations to come.'

The management of heat risks is becoming increasingly important and this review highlights the need to educate health professionals about environmental hazards. Co-author, Associate Professor Sari Kovats at the NIHR Health Protection Research Unit in Environmental Change and Health at LSHTM, adds: 'We need to do better to manage heat risks in patients with diabetes and other endocrine disorders.'

Heatwaves are increasing in frequency and severity with major impacts on health, Co-author, Professor Rajesh Thakker from the University of Oxford and Queen Mary’s William Harvey Research Institute states: 'Climate change with increasing heat exposure are major global challenges confronting us, yet we know little about their effects on health, and identifying these gaps in our knowledge is important for planning strategies and future research for the benefit of humankind.' The study, ' Endocrine effects of heat exposure and relevance to climate change ,' is published in  Nature Reviews Endocrinology .

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Exploring the health impacts of climate change on the endocrine system

by University of Oxford

In a new study, endocrinologists and researchers from the Nuffield Department of Women's & Reproductive Health (NDWRH) at the University of Oxford, the London School of Hygiene & Tropical Medicine, the William Harvey Research Institute (WHRI) at Queen Mary University of London and the National University of Singapore have emphasized the critical need for further research into the effects of heat exposure on the endocrine system.

The study, " Endocrine effects of heat exposure and relevance to climate change ," is published in Nature Reviews Endocrinology .

With climate change increasing seasonal temperatures and causing more frequent heat waves, understanding these effects has become more crucial than ever.

Hormones play a role in nearly all biological functions , yet the influence of environmental factors on hormone release and action is not well characterized. Researchers from the University of Oxford, the London School of Hygiene & Tropical Medicine, the William Harvey Research Institute at Queen Mary University of London, and the National University of Singapore have highlighted the urgent need for more research into the effects of heat exposure, particularly in the context of climate change increasing seasonal temperatures and causing more heat waves.

Hormones influence how we adapt to changes in environmental temperature by controlling processes such as conservation of body water, sweating, and heat generation from cell metabolism. A review of studies published from the 1940s onwards indicates that heat exposure affects hormones involved in processes ranging from the stress response, blood glucose control, fertility, and breast milk production. However, many of these studies involved short-term heat exposure in non-human animal models or in healthy human volunteers such as military recruits.

Our review highlights the gap in evidence regarding the impact of sustained heat exposure on the endocrine system , which is particularly relevant to the increasing numbers of people living with endocrine conditions such as diabetes mellitus or thyroid disorders, who may have limited tolerance to higher temperatures. Heat waves increase the risk of hospitalization for these patients, which also increases the burden of heat on the health system.

Lead author, Professor Fadil Hannan from the Nuffield Department of Women's & Reproductive Health at the University of Oxford, stated, "We know very little about whether increased heat exposure due to climate change could affect endocrine health. We require research involving both the endocrine and global health research communities to assess the impact of rising temperatures and heat waves on endocrine patients.

"This is particularly important for patients living in hot climates, who may have inadequate access to cooled environments. A better understanding of these effects will enable interventions to be developed for endocrine patients most at risk from heat extremes."

Certain hormonal disorders can disrupt the body's ability to regulate temperature, making it harder to cool down and increasing the risk of heat-related illnesses. Co-author, Professor Jason Lee, at the National University of Singapore, adds, "As the world grapples with the escalating threats of climate change, unraveling the intricate relationships between heat exposure, endocrine function, and human health is not only a scientific imperative but a moral obligation to protect the vulnerable and ensure the well-being of generations to come."

The management of heat risks is becoming increasingly important and this review highlights the need to educate health professionals about environmental hazards. Co-author, Associate Professor Sari Kovats at the NIHR Health Protection Research Unit in Environmental Change and Health at LSHTM, adds, "We need to do better to manage heat risks in patients with diabetes and other endocrine disorders."

Heat waves are increasing in frequency and severity with major impacts on health, Co-author, Professor Rajesh Thakker from the University of Oxford and Queen Mary's William Harvey Research Institute states, "Climate change with increasing heat exposure are major global challenges confronting us, yet we know little about their effects on health, and identifying these gaps in our knowledge is important for planning strategies and future research for the benefit of humankind."

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