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How does global warming work?

Where does global warming occur in the atmosphere, why is global warming a social problem, where does global warming affect polar bears.

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• U.S. Department of Transportation - Global Warming: A Science Overview
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Human activity affects global surface temperatures by changing Earth ’s radiative balance—the “give and take” between what comes in during the day and what Earth emits at night. Increases in greenhouse gases —i.e., trace gases such as carbon dioxide and methane that absorb heat energy emitted from Earth’s surface and reradiate it back—generated by industry and transportation cause the atmosphere to retain more heat, which increases temperatures and alters precipitation patterns.

Global warming, the phenomenon of increasing average air temperatures near Earth’s surface over the past one to two centuries, happens mostly in the troposphere , the lowest level of the atmosphere, which extends from Earth’s surface up to a height of 6–11 miles. This layer contains most of Earth’s clouds and is where living things and their habitats and weather primarily occur.

Continued global warming is expected to impact everything from energy use to water availability to crop productivity throughout the world. Poor countries and communities with limited abilities to adapt to these changes are expected to suffer disproportionately. Global warming is already being associated with increases in the incidence of severe and extreme weather, heavy flooding , and wildfires —phenomena that threaten homes, dams, transportation networks, and other facets of human infrastructure. Learn more about how the IPCC’s Sixth Assessment Report, released in 2021, describes the social impacts of global warming.

Polar bears live in the Arctic , where they use the region’s ice floes as they hunt seals and other marine mammals . Temperature increases related to global warming have been the most pronounced at the poles, where they often make the difference between frozen and melted ice. Polar bears rely on small gaps in the ice to hunt their prey. As these gaps widen because of continued melting, prey capture has become more challenging for these animals.

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global warming , the phenomenon of increasing average air temperatures near the surface of Earth over the past one to two centuries. Climate scientists have since the mid-20th century gathered detailed observations of various weather phenomena (such as temperatures, precipitation , and storms) and of related influences on climate (such as ocean currents and the atmosphere’s chemical composition). These data indicate that Earth’s climate has changed over almost every conceivable timescale since the beginning of geologic time and that human activities since at least the beginning of the Industrial Revolution have a growing influence over the pace and extent of present-day climate change .

Giving voice to a growing conviction of most of the scientific community , the Intergovernmental Panel on Climate Change (IPCC) was formed in 1988 by the World Meteorological Organization (WMO) and the United Nations Environment Program (UNEP). The IPCC’s Sixth Assessment Report (AR6), published in 2021, noted that the best estimate of the increase in global average surface temperature between 1850 and 2019 was 1.07 °C (1.9 °F). An IPCC special report produced in 2018 noted that human beings and their activities have been responsible for a worldwide average temperature increase between 0.8 and 1.2 °C (1.4 and 2.2 °F) since preindustrial times, and most of the warming over the second half of the 20th century could be attributed to human activities.

AR6 produced a series of global climate predictions based on modeling five greenhouse gas emission scenarios that accounted for future emissions, mitigation (severity reduction) measures, and uncertainties in the model projections. Some of the main uncertainties include the precise role of feedback processes and the impacts of industrial pollutants known as aerosols , which may offset some warming. The lowest-emissions scenario, which assumed steep cuts in greenhouse gas emissions beginning in 2015, predicted that the global mean surface temperature would increase between 1.0 and 1.8 °C (1.8 and 3.2 °F) by 2100 relative to the 1850–1900 average. This range stood in stark contrast to the highest-emissions scenario, which predicted that the mean surface temperature would rise between 3.3 and 5.7 °C (5.9 and 10.2 °F) by 2100 based on the assumption that greenhouse gas emissions would continue to increase throughout the 21st century. The intermediate-emissions scenario, which assumed that emissions would stabilize by 2050 before declining gradually, projected an increase of between 2.1 and 3.5 °C (3.8 and 6.3 °F) by 2100.

Many climate scientists agree that significant societal, economic, and ecological damage would result if the global average temperature rose by more than 2 °C (3.6 °F) in such a short time. Such damage would include increased extinction of many plant and animal species, shifts in patterns of agriculture , and rising sea levels. By 2015 all but a few national governments had begun the process of instituting carbon reduction plans as part of the Paris Agreement , a treaty designed to help countries keep global warming to 1.5 °C (2.7 °F) above preindustrial levels in order to avoid the worst of the predicted effects. Whereas authors of the 2018 special report noted that should carbon emissions continue at their present rate, the increase in average near-surface air temperature would reach 1.5 °C sometime between 2030 and 2052, authors of the AR6 report suggested that this threshold would be reached by 2041 at the latest.

The AR6 report also noted that the global average sea level had risen by some 20 cm (7.9 inches) between 1901 and 2018 and that sea level rose faster in the second half of the 20th century than in the first half. It also predicted, again depending on a wide range of scenarios, that the global average sea level would rise by different amounts by 2100 relative to the 1995–2014 average. Under the report’s lowest-emission scenario, sea level would rise by 28–55 cm (11–21.7 inches), whereas, under the intermediate emissions scenario, sea level would rise by 44–76 cm (17.3–29.9 inches). The highest-emissions scenario suggested that sea level would rise by 63–101 cm (24.8–39.8 inches) by 2100.

The scenarios referred to above depend mainly on future concentrations of certain trace gases, called greenhouse gases , that have been injected into the lower atmosphere in increasing amounts through the burning of fossil fuels for industry, transportation , and residential uses. Modern global warming is the result of an increase in magnitude of the so-called greenhouse effect , a warming of Earth’s surface and lower atmosphere caused by the presence of water vapour , carbon dioxide , methane , nitrous oxides , and other greenhouse gases. In 2014 the IPCC first reported that concentrations of carbon dioxide, methane, and nitrous oxides in the atmosphere surpassed those found in ice cores dating back 800,000 years.

Of all these gases, carbon dioxide is the most important, both for its role in the greenhouse effect and for its role in the human economy. It has been estimated that, at the beginning of the industrial age in the mid-18th century, carbon dioxide concentrations in the atmosphere were roughly 280 parts per million (ppm). By the end of 2022 they had risen to 419 ppm, and, if fossil fuels continue to be burned at current rates, they are projected to reach 550 ppm by the mid-21st century—essentially, a doubling of carbon dioxide concentrations in 300 years.

A vigorous debate is in progress over the extent and seriousness of rising surface temperatures, the effects of past and future warming on human life, and the need for action to reduce future warming and deal with its consequences. This article provides an overview of the scientific background related to the subject of global warming. It considers the causes of rising near-surface air temperatures, the influencing factors, the process of climate research and forecasting, and the possible ecological and social impacts of rising temperatures. For an overview of the public policy developments related to global warming occurring since the mid-20th century, see global warming policy . For a detailed description of Earth’s climate, its processes, and the responses of living things to its changing nature, see climate . For additional background on how Earth’s climate has changed throughout geologic time , see climatic variation and change . For a full description of Earth’s gaseous envelope, within which climate change and global warming occur, see atmosphere .

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What is global warming?

What causes global warming, how is global warming linked to extreme weather, what are the other effects of global warming, where does the united states stand in terms of global-warming contributors, is the united states doing anything to prevent global warming, is global warming too big a problem for me to help tackle.

A: Since the Industrial Revolution, the global annual temperature has increased in total by a little more than 1 degree Celsius, or about 2 degrees Fahrenheit. Between 1880—the year that accurate recordkeeping began—and 1980, it rose on average by 0.07 degrees Celsius (0.13 degrees Fahrenheit) every 10 years. Since 1981, however, the rate of increase has more than doubled: For the last 40 years, we’ve seen the global annual temperature rise by 0.18 degrees Celsius, or 0.32 degrees Fahrenheit, per decade.

The result? A planet that has never been hotter . Nine of the 10 warmest years since 1880 have occurred since 2005—and the 5 warmest years on record have all occurred since 2015. Climate change deniers have argued that there has been a “pause” or a “slowdown” in rising global temperatures, but numerous studies, including a 2018 paper published in the journal Environmental Research Letters , have disproved this claim. The impacts of global warming are already harming people around the world.

Now climate scientists have concluded that we must limit global warming to 1.5 degrees Celsius by 2040 if we are to avoid a future in which everyday life around the world is marked by its worst, most devastating effects: the extreme droughts, wildfires, floods, tropical storms, and other disasters that we refer to collectively as climate change . These effects are felt by all people in one way or another but are experienced most acutely by the underprivileged, the economically marginalized, and people of color, for whom climate change is often a key driver of poverty, displacement, hunger, and social unrest.

A: Global warming occurs when carbon dioxide (CO 2 ) and other air pollutants collect in the atmosphere and absorb sunlight and solar radiation that have bounced off the earth’s surface. Normally this radiation would escape into space, but these pollutants, which can last for years to centuries in the atmosphere, trap the heat and cause the planet to get hotter. These heat-trapping pollutants—specifically carbon dioxide, methane, nitrous oxide, water vapor, and synthetic fluorinated gases—are known as greenhouse gases, and their impact is called the greenhouse effect.

Though natural cycles and fluctuations have caused the earth’s climate to change several times over the last 800,000 years, our current era of global warming is directly attributable to human activity—specifically to our burning of fossil fuels such as coal, oil, gasoline, and natural gas, which results in the greenhouse effect. In the United States, the largest source of greenhouse gases is transportation (29 percent), followed closely by electricity production (28 percent) and industrial activity (22 percent). Learn about the natural and human causes of climate change .

Curbing dangerous climate change requires very deep cuts in emissions, as well as the use of alternatives to fossil fuels worldwide. The good news is that countries around the globe have formally committed—as part of the 2015 Paris Climate Agreement —to lower their emissions by setting new standards and crafting new policies to meet or even exceed those standards. The not-so-good news is that we’re not working fast enough. To avoid the worst impacts of climate change, scientists tell us that we need to reduce global carbon emissions by as much as 40 percent by 2030. For that to happen, the global community must take immediate, concrete steps: to decarbonize electricity generation by equitably transitioning from fossil fuel–based production to renewable energy sources like wind and solar; to electrify our cars and trucks; and to maximize energy efficiency in our buildings, appliances, and industries.

A: Scientists agree that the earth’s rising temperatures are fueling longer and hotter heat waves , more frequent droughts , heavier rainfall , and more powerful hurricanes .

In 2015, for example, scientists concluded that a lengthy drought in California—the state’s worst water shortage in 1,200 years —had been intensified by 15 to 20 percent by global warming. They also said the odds of similar droughts happening in the future had roughly doubled over the past century. And in 2016, the National Academies of Science, Engineering, and Medicine announced that we can now confidently attribute some extreme weather events, like heat waves, droughts, and heavy precipitation, directly to climate change.

The earth’s ocean temperatures are getting warmer, too—which means that tropical storms can pick up more energy. In other words, global warming has the ability to turn a category 3 storm into a more dangerous category 4 storm. In fact, scientists have found that the frequency of North Atlantic hurricanes has increased since the early 1980s, as has the number of storms that reach categories 4 and 5. The 2020 Atlantic hurricane season included a record-breaking 30 tropical storms, 6 major hurricanes, and 13 hurricanes altogether. With increased intensity come increased damage and death. The United States saw an unprecedented 22 weather and climate disasters that caused at least a billion dollars’ worth of damage in 2020, but, according to NOAA, 2017 was the costliest on record and among the deadliest as well: Taken together, that year's tropical storms (including Hurricanes Harvey, Irma, and Maria) caused nearly $300 billion in damage and led to more than 3,300 fatalities.

The impacts of global warming are being felt everywhere. Extreme heat waves have caused tens of thousands of deaths around the world in recent years. And in an alarming sign of events to come, Antarctica has lost nearly four trillion metric tons of ice since the 1990s. The rate of loss could speed up if we keep burning fossil fuels at our current pace, some experts say, causing sea levels to rise several meters in the next 50 to 150 years and wreaking havoc on coastal communities worldwide.

A: Each year scientists learn more about the consequences of global warming , and each year we also gain new evidence of its devastating impact on people and the planet. As the heat waves, droughts, and floods associated with climate change become more frequent and more intense, communities suffer and death tolls rise. If we’re unable to reduce our emissions, scientists believe that climate change could lead to the deaths of more than 250,000 people around the globe every year and force 100 million people into poverty by 2030.

Global warming is already taking a toll on the United States. And if we aren’t able to get a handle on our emissions, here’s just a smattering of what we can look forward to:

• Disappearing glaciers, early snowmelt, and severe droughts will cause more dramatic water shortages and continue to increase the risk of wildfires in the American West.
• Rising sea levels will lead to even more coastal flooding on the Eastern Seaboard, especially in Florida, and in other areas such as the Gulf of Mexico.
• Forests, farms, and cities will face troublesome new pests , heat waves, heavy downpours, and increased flooding . All of these can damage or destroy agriculture and fisheries.
• Disruption of habitats such as coral reefs and alpine meadows could drive many plant and animal species to extinction.
• Allergies, asthma, and infectious disease outbreaks will become more common due to increased growth of pollen-producing ragweed , higher levels of air pollution , and the spread of conditions favorable to pathogens and mosquitoes.

Though everyone is affected by climate change, not everyone is affected equally. Indigenous people, people of color, and the economically marginalized are typically hit the hardest. Inequities built into our housing , health care , and labor systems make these communities more vulnerable to the worst impacts of climate change—even though these same communities have done the least to contribute to it.

A: In recent years, China has taken the lead in global-warming pollution , producing about 26 percent of all CO2 emissions. The United States comes in second. Despite making up just 4 percent of the world’s population, our nation produces a sobering 13 percent of all global CO2 emissions—nearly as much as the European Union and India (third and fourth place) combined. And America is still number one, by far, in cumulative emissions over the past 150 years. As a top contributor to global warming, the United States has an obligation to help propel the world to a cleaner, safer, and more equitable future. Our responsibility matters to other countries, and it should matter to us, too.

A: We’ve started. But in order to avoid the worsening effects of climate change, we need to do a lot more—together with other countries—to reduce our dependence on fossil fuels and transition to clean energy sources.

Under the administration of President Donald Trump (a man who falsely referred to global warming as a “hoax”), the United States withdrew from the Paris Climate Agreement, rolled back or eliminated dozens of clean air protections, and opened up federally managed lands, including culturally sacred national monuments, to fossil fuel development. Although President Biden has pledged to get the country back on track, years of inaction during and before the Trump administration—and our increased understanding of global warming’s serious impacts—mean we must accelerate our efforts to reduce greenhouse gas emissions.

Despite the lack of cooperation from the Trump administration, local and state governments made great strides during this period through efforts like the American Cities Climate Challenge and ongoing collaborations like the Regional Greenhouse Gas Initiative . Meanwhile, industry and business leaders have been working with the public sector, creating and adopting new clean-energy technologies and increasing energy efficiency in buildings, appliances, and industrial processes. 

Today the American automotive industry is finding new ways to produce cars and trucks that are more fuel efficient and is committing itself to putting more and more zero-emission electric vehicles on the road. Developers, cities, and community advocates are coming together to make sure that new affordable housing is built with efficiency in mind , reducing energy consumption and lowering electric and heating bills for residents. And renewable energy continues to surge as the costs associated with its production and distribution keep falling. In 2020 renewable energy sources such as wind and solar provided more electricity than coal for the very first time in U.S. history.

President Biden has made action on global warming a high priority. On his first day in office, he recommitted the United States to the Paris Climate Agreement, sending the world community a strong signal that we were determined to join other nations in cutting our carbon pollution to support the shared goal of preventing the average global temperature from rising more than 1.5 degrees Celsius above preindustrial levels. (Scientists say we must stay below a 2-degree increase to avoid catastrophic climate impacts.) And significantly, the president has assembled a climate team of experts and advocates who have been tasked with pursuing action both abroad and at home while furthering the cause of environmental justice and investing in nature-based solutions.

A: No! While we can’t win the fight without large-scale government action at the national level , we also can’t do it without the help of individuals who are willing to use their voices, hold government and industry leaders to account, and make changes in their daily habits.

Wondering how you can be a part of the fight against global warming? Reduce your own carbon footprint by taking a few easy steps: Make conserving energy a part of your daily routine and your decisions as a consumer. When you shop for new appliances like refrigerators, washers, and dryers, look for products with the government’s ENERGY STAR ® label; they meet a higher standard for energy efficiency than the minimum federal requirements. When you buy a car, look for one with the highest gas mileage and lowest emissions. You can also reduce your emissions by taking public transportation or carpooling when possible.

And while new federal and state standards are a step in the right direction, much more needs to be done. Voice your support of climate-friendly and climate change preparedness policies, and tell your representatives that equitably transitioning from dirty fossil fuels to clean power should be a top priority—because it’s vital to building healthy, more secure communities.

You don’t have to go it alone, either. Movements across the country are showing how climate action can build community , be led by those on the front lines of its impacts, and create a future that’s equitable and just for all .

This story was originally published on March 11, 2016 and has been updated with new information and links.

This NRDC.org story is available for online republication by news media outlets or nonprofits under these conditions: The writer(s) must be credited with a byline; you must note prominently that the story was originally published by NRDC.org and link to the original; the story cannot be edited (beyond simple things such as grammar); you can’t resell the story in any form or grant republishing rights to other outlets; you can’t republish our material wholesale or automatically—you need to select stories individually; you can’t republish the photos or graphics on our site without specific permission; you should drop us a note to let us know when you’ve used one of our stories.

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A Lesson Plan About Climate Change and the People Already Harmed by It

Climate refugees: bolivia, the disappearance of lake poopó has not only destroyed the livelihoods of hundreds of fishing families, but also added to a new category of climate refugees..

The disappearance of Lake Poopó has not just meant a loss of livelihood for hundreds of fishing families, it is adding to the new category of climate refugees.

By Sara Rust and Michael Gonchar

• March 22, 2017

Students might see climate change as a future threat — a prediction about what may happen in the distant future. But do they know that scientific data shows that the Earth’s climate is already changing? And do they know that people and communities are already being affected by these changes?

In this lesson, students use the Times’s series Carbon’s Casualties to learn about how climate change is displacing people around the world. They then practice the important skill of explaining the science to a skeptical public that sometimes doubts what it doesn’t see with its own eyes.

Warm-Up and Background

To get the most out of the main activities in this lesson, students should have a familiarity with the science of climate change. Teachers may want to do part of this Warm-Up as a brief refresher, or they might choose to do the entire Warm-Up as an extended background lesson before tackling the more in-depth articles.

Warm-Up: Ask students to engage in a free write for five minutes in response to the term “climate change.” This practice of informal writing can encourage them to activate prior knowledge and to explore questions that they have in a nonthreatening, non-evaluative way. They can write what they know, what they think they know, what they’ve heard, what they’re confused or unsure about, or what they want to know.

After students are done writing, ask them to turn and read their writing to a partner. After they have heard each other’s writings, ask them to work together to write a collaborative summary in which they combine their ideas.

As a class, discuss what students noticed as they went through this process. What did they know? What did they learn from their peers? What was it like to engage in this process? What questions do they have? Were there disagreements?

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What Is Climate Change?

In this educational video, learn why the climate is changing, how it affects us, and what we can do about it.

Climate Change Causes and Effects

Climate change is rapidly altering our world in profound ways. Human activity has already increased the earth’s temperature by about 2°F since 1880. As the planet continues to get hotter, through a process known as global warming, the dangers intensify. Millions of people could be displaced and vital infrastructure could be destroyed. Climate change’s effects are far-reaching and varied and touch virtually every aspect of life on the earth: extreme heat events, rising sea levels, deeper droughts, desertification, bigger wildfires, and more intense storms.

Because climate change poses such an extraordinary threat to the planet, it needs to be addressed. There are no clear-cut answers to this global challenge, but it is not insurmountable. Countries are already taking steps to adapt to climate change and mitigate its effects. Blueprints exist, but they need to be used more widely and more effectively, because the longer action is delayed, the worse climate change becomes—and the more difficult it will be to endure.

Essay on Global Warming – Causes and Solutions

500+ words essay on global warming.

Global Warming is a term almost everyone is familiar with. But, its meaning is still not clear to most of us. So, Global warming refers to the gradual rise in the overall temperature of the atmosphere of the Earth. There are various activities taking place which have been increasing the temperature gradually. Global warming is melting our ice glaciers rapidly. This is extremely harmful to the earth as well as humans. It is quite challenging to control global warming; however, it is not unmanageable. The first step in solving any problem is identifying the cause of the problem. Therefore, we need to first understand the causes of global warming that will help us proceed further in solving it. In this essay on Global Warming, we will see the causes and solutions of Global Warming.

Causes of Global Warming

Global warming has become a grave problem which needs undivided attention. It is not happening because of a single cause but several causes. These causes are both natural as well as manmade. The natural causes include the release of greenhouses gases which are not able to escape from earth, causing the temperature to increase.

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Further, volcanic eruptions are also responsible for global warming. That is to say, these eruptions release tons of carbon dioxide which contributes to global warming. Similarly, methane is also one big issue responsible for global warming.

So, when one of the biggest sources of absorption of carbon dioxide will only disappear, there will be nothing left to regulate the gas. Thus, it will result in global warming. Steps must be taken immediately to stop global warming and make the earth better again.

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Global Warming Solutions

As stated earlier, it might be challenging but it is not entirely impossible. Global warming can be stopped when combined efforts are put in. For that, individuals and governments, both have to take steps towards achieving it. We must begin with the reduction of greenhouse gas.

Furthermore, they need to monitor the consumption of gasoline. Switch to a hybrid car and reduce the release of carbon dioxide. Moreover, citizens can choose public transport or carpool together. Subsequently, recycling must also be encouraged.

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For instance, when you go shopping, carry your own cloth bag. Another step you can take is to limit the use of electricity which will prevent the release of carbon dioxide. On the government’s part, they must regulate industrial waste and ban them from emitting harmful gases in the air. Deforestation must be stopped immediately and planting of trees must be encouraged.

In short, all of us must realize the fact that our earth is not well. It needs to treatment and we can help it heal. The present generation must take up the responsibility of stopping global warming in order to prevent the suffering of future generations. Therefore, every little step, no matter how small carries a lot of weight and is quite significant in stopping global warming.

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FAQs on Global Warming

Q.1 List the causes of Global Warming.

A.1 There are various causes of global warming both natural and manmade. The natural one includes a greenhouse gas, volcanic eruption, methane gas and more. Next up, manmade causes are deforestation, mining, cattle rearing, fossil fuel burning and more.

Q.2 How can one stop Global Warming?

A.2 Global warming can be stopped by a joint effort by the individuals and the government. Deforestation must be banned and trees should be planted more. The use of automobiles must be limited and recycling must be encouraged.

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Global Warming Definition, Causes, Effects, Impacts, Solutions

Global Warming is a long-term increase in average global temperature. Read about Global Warming Definition, Causes, Effects, Impact on Climate Change & Solutions for the UPSC exam.

Table of Contents

What is Global Warming?

Global Warming is a long-term increase in average global temperature. It is considered a natural phenomenon, but anthropogenic activities on earth, particularly post Industrial Revolution , have led to an increase in the rate of this temperature increase. Various Reports published by the International Panel on Climate Change (IPCC) have time and again highlighted that since 1850 human activities have led to an increase of about 1 degree Celsius in average global temperature. Most of this warming has taken place in the second half of the 20th century. The fact that 5 of the hottest recorded year have occurred since 2015 can help us better understand the calamitous impact of anthropogenic activities.

Global Warming Causes

Green House Gases also known as GHGs in the atmosphere trap the solar radiations that are reflected by the earth’s surface. Under normal circumstances, most of these radiations escape into outer space. However, the release of GHGs by anthropogenic activities has increased their concentration in the atmosphere. Thus, the earth is getting hotter and hotter. 

Some of the common GHGs include carbon dioxide, methane, nitrous oxide, chlorofluorocarbons, and water vapour, among others. The global warming potential of each GHG is different. For example, methane has a 25-time warming potential than carbon dioxide. Similarly, nitrous oxide has more than 250 times the warming potential than carbon dioxide. The top  anthropogenic activities that are responsible for the release of GHGs are shown below.

Global Warming and Green House Effect

Both phenomena are related to each other. Green House Gases also known as GHGs in the atmosphere trap the solar radiations that are reflected by the earth’s surface. Under normal circumstances, most of these radiations escape into outer space. However, the release of GHGs by anthropogenic activities has increased their concentration in the atmosphere. This is the primary cause of Global Warming . 

Global Warming Effects

Increase in the average temperature of the earth.

According to IPCC reports, human-induced global warming is responsible for nearly 1 degree Celsius temperature rise vis a vis pre-industrial level. Data from NASA suggest that 2016 has been the hottest year on record.

Frequency of Extreme Weather Events is Increasing

Across the globe, extreme weather events have increased in occurrence. For example, forest fires in California have become an annual event. Also, it is increasing in frequency each year. Most recently, we have recorded the phenomena of heat waves in Antarctica. The intensity of cyclones in the Bay of Bengal region has increased. Similarly, the frequency of occurrence of El Niño and La Niña has reduced from once in 8–10 years to once in 3–4 years now. More frequent episodes of floods and drought are being recorded every year across the world.

Melting of Ice

According to IPCC, there is 10% less permafrost in North Hemisphere at present compared to the 1900s. Remote sensing data suggest Arctic ice is melting fast. Experts suggest that not only will the sea level rise with the melting of glaciers, but there is also a danger of new bacteria and viruses being released into the environment which has so far been trapped in ice sheets. This may lead to outbreaks of disease and pandemics which are beyond the control of human medical sciences.

Sea Level Rise and Acidification of Ocean

A report published by WMO, suggests that the rate of sea level rise has doubled for the period between 2013 and 2021 compared to the rate for the period between 1993 and 2002. Earth scientists are suggesting that if this phenomenon continues, many human-inhabited coastal areas will be submerged into the sea in the coming decades. Also, with the concentration of carbon dioxide rising in the atmosphere, oceans are absorbing more of it. This is leading to ocean acidification. The impact of this phenomenon can be disastrous for ocean biodiversity, particularly the coral reefs. 

Adverse Impact on Terrestrial Ecosystems of the Earth

It has been recorded that many flora and fauna species are heading northwards in Northern Hemisphere. Significant changes have been observed in the migratory movements of birds across the world. Early arrival to their summer feeding and breeding grounds is quite evident. Expert biologists suggest that rising temperatures in the tropical and subtropical regions may lead to an outbreak of new diseases, which in turn may render many floral and faunal species extinct.

Social and Economic Impact

A rising number of extreme weather events will have an adverse impact on agriculture and fisheries. Rising global temperatures will have a negative impact on the productivity of human beings, particularly in tropical and subtropical regions of the earth. The impact on life and livelihoods of indigenous people across the world will be even more pronounced. 

Global Warming Solutions

Global cooperation for reduction of emissions.

It is time that the target of containing the global average temperature rise within 1.5 degrees Celsius of pre-industrial levels is taken seriously. Also, global efforts should be based on a spirit of Common But Differentiated Responsibility. This will ensure that historical injustices done to the global south are duly acknowledged, and they have an equal chance to transform themselves into developed countries. Countries must act proactively to achieve Net Zero Emission status at the earliest. 

Transition to Cleaner and Greener Forms of Energy

Thermal power plants based on coal should be made more efficient and inefficient ones should be phased off. Also, mass adoption of renewable forms of energy like solar should be promoted. Similarly, avenues for using hydrogen as energy fuel should be looked into. We must also explore the possibility of Nuclear fusion for energy generation, in addition to making nuclear fission-based energy generation safer.

Changes in Agricultural Practices and Land Use

Agriculture based on the use of nitrogenous fertilizers must be replaced with organic farming techniques. Also, methane gas released from agricultural and cattle waste must be trapped as biogas for domestic usage. Massive afforestation drives must be organized. Urban governments must make it a point to include green spaces in urban planning.

Improving Transportation System

The advent of E-vehicles is a welcome change, but we need to make the batteries used in these vehicles more efficient. Urban planners must make public transportation systems inherent as a benchmark of good urban planning. Also, urban planning should be such that it promotes more walking and cycling habits among the residents. 

Behavioural Changes

All the above discussions will have no meaning if we as individuals are not sensitive enough. We need to make reducing, reusing and recycling a mantra of our living. It should be our civic duty to save water, and wildlife and raise awareness among others. 

Solar Geoengineering

Solar geoengineering, a proposed climate intervention method, aims to counteract global warming by reflecting a portion of the sun’s rays back into space. One prominent approach involves injecting substances like sulphur dioxide into the upper atmosphere to create reflective aerosols. These particles can scatter sunlight, reducing the Earth’s temperature. However, solar geoengineering is a topic of debate, with concerns about its side effects, such as disrupted weather patterns and potential geopolitical risks. Research in this field is ongoing, but it remains a theoretical concept with limited practical implementation.

Can Solar Geoengineering Halt Global Warming?

Solar geoengineering, specifically solar radiation management (SRM), is under scrutiny as a potential method to mitigate global warming. SRM involves reflecting sunlight away from Earth, often by injecting substances like sulphur dioxide into the upper atmosphere to create reflective aerosols. However, its effectiveness remains a subject of debate, with concerns about potential side effects and ethical implications. While research in this field is ongoing, solar geoengineering is currently in a theoretical stage, with limited practical implementation.

Global Warming Conclusion

It is rightly said that “Charity begins at home.” Climate action will be more efficient if we go by this spirit. To begin with, each individual can make sure that what is happening in their house and immediate surroundings is in harmony with the environment. If this can happen, all the policies we are making at the local, national, regional and global levels will give far better results. 

Global Warming UPSC

Each year, we read about rising global temperatures. Also, catching the headlines is the news related to disasters caused by events like cyclones, forest fires, floods and drought. All these phenomena can be attributed to one single cause which is global warming. 

Global Warming is a long-term increase in average global temperature. It is considered a natural phenomenon, but anthropogenic activities on earth, particularly post-Industrial Revolution, have led to an increase in the rate of this temperature increase.

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Why is global warming a problem?

Global Warming at present rate can lead to disastrous impacts like rising sea level, out break of new diseases, extreme weather events among others.

What are 3 causes of global warming?

Human induced green house gas emission due to activities like agriculture, industrial emissions, transportation are the top 3 causes of global warming.

What are 5 effects of global warming?

Rising sea level, out break of new diseases, extreme weather events, changes in biodiversity and melting of glaciers are top 5 effects of global warming.

Why global warming is important?

Global warming at its natural rate is important to keep up the temperature of earth within the range that makes it habitable. This makes global warming important.

Can we control global warming?

Number of mitigation measures like shifting to cleaning forms of energy and transportation can be taken to control global warming.

Who help with global warming?

Global Warming is a collective challenge for entire humanity. Citizens, civil societies, governments and businesses must act in unison to address it.

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Global Warming

Miss Parson – Allerton Grange School

Aims and objectives

• To be able to define and understand the process of Global Warming.
• Be able to describe the effects of Global Warming on a global and local scale.
• Be able to recognise how the effects of Global Warming can be reduced.

What is�Global Warming ?

Global warming is the increase in the world’s average temperature, believed to be the result from the release of carbon dioxide and other gases into the atmosphere by burning fossil fuels.

This increase in greenhouse gases is causing an increase in the rate of the greenhouse effect .

The Greenhouse�Effect

The earth is warming rather like the inside of a greenhouse. On a basic level the sun’s rays enter the earths atmosphere and are prevented from escaping by the greenhouse gases. This results in higher world temperatures.

In more detail………

Energy from the sun drives the earth's weather and climate, and heats the earth's surface; in turn, the earth radiates energy back into space. Atmospheric greenhouse gases (water vapor, carbon dioxide, and other gases) trap some of the outgoing energy, retaining heat somewhat like the glass panels of a greenhouse.�

Without this natural "greenhouse effect," temperatures would be much lower than they are now, and life as known today would not be possible. Instead, thanks to greenhouse gases, the earth's average temperature is a more hospitable 60°F. However, problems may arise when the atmospheric concentration of greenhouse gases increases. �

What are the�greenhouse gases?

Since the beginning of the industrial revolution, atmospheric concentrations of carbon dioxide have increased nearly 30%, methane concentrations have more than doubled, and nitrous oxide concentrations have risen by about 15%. Why are greenhouse gas concentrations increasing?

Burning of fossil fuels and other human activities are the primary reason for the increased concentration of carbon dioxide.

CFC’s from aerosols, air conditioners, foam packaging and refrigerators most damaging (approx 6%).

Methane is released from decaying organic matter, waste dumps, animal dung, swamps and peat bogs (approx 19%).

Nitrous Oxide is emitted from car exhausts, power stations and agricultural fertiliser (approx 6%).

The major contributor is Carbon Dioxide (approx 64%).

Task 1:The �Greenhouse Effect

Complete your worksheet by cutting and labeling the diagram and answering the questions

Task 2 : Effects of global warming

You are about to see a series of pictures which show some of the effects of global warming.

Draw a rough sketch then write down the effects or titles for the pictures you've drawn

I’m thinking !

What are the consequences of Global Warming?

What are the pictures showing, what are the effects of global warming?

How did�you do?

Hurricanes –extreme weather

Flooding of coastal areas

Desertification

Ice caps melt

Rise in temperatures

Loss of wildlife habitats and species

Sea level rise

Extreme storms

There are also some positive effects of global warming

• Decrease in death and disease
• Healthier, faster growing forests due to excess CO2
• Longer growing seasons
• Warmer temperatures (UK Mediterranean climate!!)
• Plants and shrubs will be able to grow further north and in present desert conditions
• Heavier rainfall in certain locations will give higher agricultural production (Rice in India, Wheat in Africa).

How can Global Warming be reduced?

• Reduce the use of fossil fuels. A major impact would be to find alternatives to coal, oil and gas power stations.
• Afforest areas, trees use up the CO2, reduce deforestation.
• Reduce the reliance on the car (promote shared public transport).
• Try to use energy efficiently (turn off lights and not use as much!).
• Reduce, Reuse, Recycle.
• Careful long term planning to reduce the impact of global warming.
• Global Warming is the increase in global temperatures due to the increased rate of the Greenhouse Effect.
• Greenhouse gases trap the incoming solar radiation, these gases include Carbon Dioxide, CFCs, Methane, Nitrous Oxides and other Halocarbons. These are released by human activity.
• We need the Greenhouse effect to maintain life on earth as we know it…however if we keep adding to the Greenhouse gases there will be many changes.
• Consequences can be negative ( ice caps melt, sea level rise, extreme weather conditions) or positive (more rain in drought areas, longer growing season).

Re do diagram slide 7

http://www.flickr.com/photos/wwworks/2222523486/ - slide 1

http://www.flickr.com/photos/dzwjedziak/375723120/ - slide 8 and 1

http://www.flickr.com/photos/bratan/452189020/ - slide 4

http://www.flickr.com/photos/hogbard/412932972/- slide 6

http://www.flickr.com/photos/tiger_empress/467671978/ - slide 8

http://www.flickr.com/photos/48135670@N00/97951579/ - slide 9,12

http://www.flickr.com/photos/60158441@N00/177929708/ - slide 9,12

http://www.flickr.com/photos/andzer/1480068258/ - slide 9,12

http://www.flickr.com/photos/nickrussill/146743082/ - slide 9,12

http://www.flickr.com/photos/dasha/443747644/ - slide 10,13

http://www.flickr.com/photos/11371618@N00/469788104/ - slide 10,13

http://www.flickr.com/photos/mikebaird/2087879492/ - slide 10,13

http://www.flickr.com/photos/7471118@N02/432453250/ - slide 10,13

http://www.flickr.com/photos/madron/2595909135/ - slide 11

http://www.flickr.com/photos/chi-liu/491412087/ - slide 12,13

http://www.flickr.com/photos/fabbriciuse/2073789872/ - slide 16

http://www.flickr.com/photos/algo/92463787/ - slide 16

http://www.flickr.com/photos/nickwheeleroz/2295584401/ - slide 16

http://www.flickr.com/photos/andidfl/229169559/ - slide 16

• ENVIRONMENT

How global warming is disrupting life on Earth

The signs of global warming are everywhere, and are more complex than just climbing temperatures.

Our planet is getting hotter. Since the Industrial Revolution—an event that spurred the use of fossil fuels in everything from power plants to transportation—Earth has warmed by 1 degree Celsius, about 2 degrees Fahrenheit.  

That may sound insignificant, but 2023 was the hottest year on record , and all 10 of the hottest years on record have occurred in the past decade.  

Global warming and climate change are often used interchangeably as synonyms, but scientists prefer to use “climate change” when describing the complex shifts now affecting our planet’s weather and climate systems.  

Climate change encompasses not only rising average temperatures but also natural disasters, shifting wildlife habitats, rising seas , and a range of other impacts. All of these changes are emerging as humans continue to add heat-trapping greenhouse gases , like carbon dioxide and methane, to the atmosphere.

What causes global warming?

When fossil fuel emissions are pumped into the atmosphere, they change the chemistry of our atmosphere, allowing sunlight to reach the Earth but preventing heat from being released into space. This keeps Earth warm, like a greenhouse, and this warming is known as the greenhouse effect .  

Carbon dioxide is the most commonly found greenhouse gas and about 75 percent of all the climate warming pollution in the atmosphere. This gas is a product of producing and burning oil, gas, and coal. About a quarter of Carbon dioxide also results from land cleared for timber or agriculture.  

Methane is another common greenhouse gas. Although it makes up only about 16 percent of emissions, it's roughly 25 times more potent than carbon dioxide and dissipates more quickly. That means methane can cause a large spark in warming, but ending methane pollution can also quickly limit the amount of atmospheric warming. Sources of this gas include agriculture (mostly livestock), leaks from oil and gas production, and waste from landfills.  

What are the effects of global warming?  

One of the most concerning impacts of global warming is the effect warmer temperatures will have on Earth's polar regions and mountain glaciers. The Arctic is warming four times faster than the rest of the planet. This warming reduces critical ice habitat and it disrupts the flow of the jet stream, creating more unpredictable weather patterns around the globe.  

( Learn more about the jet stream. )

A warmer planet doesn't just raise temperatures. Precipitation is becoming more extreme as the planet heats. For every degree your thermometer rises, the air holds about seven percent more moisture. This increase in moisture in the atmosphere can produce flash floods, more destructive hurricanes, and even paradoxically, stronger snow storms.  

The world's leading scientists regularly gather to review the latest research on how the planet is changing. The results of this review is synthesized in regularly published reports known as the Intergovernmental Panel on Climate Change (IPCC) reports.  

A recent report outlines how disruptive a global rise in temperature can be:

• Coral reefs are now a highly endangered ecosystem. When corals face environmental stress, such as high heat, they expel their colorful algae and turn a ghostly white, an effect known as coral bleaching . In this weakened state, they more easily die.  
• Trees are increasingly dying from drought , and this mass mortality is reshaping forest ecosystems.
• Rising temperatures and changing precipitation patterns are making wildfires more common and more widespread. Research shows they're even moving into the eastern U.S. where fires have historically been less common.
• Hurricanes are growing more destructive and dumping more rain, an effect that will result in more damage. Some scientists say we even need to be preparing for Cat 6 storms . (The current ranking system ends at Cat 5.)

How can we limit global warming?  

Limiting the rising in global warming is theoretically achievable, but politically, socially, and economically difficult.  

Those same sources of greenhouse gas emissions must be limited to reduce warming. For example, oil and gas used to generate electricity or power industrial manufacturing will need to be replaced by net zero emission technology like wind and solar power. Transportation, another major source of emissions, will need to integrate more electric vehicles, public transportation, and innovative urban design, such as safe bike lanes and walkable cities.  

( Learn more about solutions to limit global warming. )

One global warming solution that was once considered far fetched is now being taken more seriously: geoengineering. This type of technology relies on manipulating the Earth's atmosphere to physically block the warming rays of the sun or by sucking carbon dioxide straight out of the sky.

Restoring nature may also help limit warming. Trees, oceans, wetlands, and other ecosystems help absorb excess carbon—but when they're lost, so too is their potential to fight climate change.  

Ultimately, we'll need to adapt to warming temperatures, building homes to withstand sea level rise for example, or more efficiently cooling homes during heat waves.  

Related Topics

• CLIMATE CHANGE
• ENVIRONMENT AND CONSERVATION
• POLAR REGIONS

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ENCYCLOPEDIC ENTRY

Climate change.

Climate change is a long-term shift in global or regional climate patterns. Often climate change refers specifically to the rise in global temperatures from the mid-20th century to present.

Earth Science, Climatology

Fracking tower

Fracking is a controversial form of drilling that uses high-pressure liquid to create cracks in underground shale to extract natural gas and petroleum. Carbon emissions from fossils fuels like these have been linked to global warming and climate change.

Photograph by Mark Thiessen / National Geographic

Climate is sometimes mistaken for weather. But climate is different from weather because it is measured over a long period of time, whereas weather can change from day to day, or from year to year. The climate of an area includes seasonal temperature and rainfall averages, and wind patterns. Different places have different climates. A desert, for example, is referred to as an arid climate because little water falls, as rain or snow, during the year. Other types of climate include tropical climates, which are hot and humid , and temperate climates, which have warm summers and cooler winters.

Climate change is the long-term alteration of temperature and typical weather patterns in a place. Climate change could refer to a particular location or the planet as a whole. Climate change may cause weather patterns to be less predictable. These unexpected weather patterns can make it difficult to maintain and grow crops in regions that rely on farming because expected temperature and rainfall levels can no longer be relied on. Climate change has also been connected with other damaging weather events such as more frequent and more intense hurricanes, floods, downpours, and winter storms.

In polar regions, the warming global temperatures associated with climate change have meant ice sheets and glaciers are melting at an accelerated rate from season to season. This contributes to sea levels rising in different regions of the planet. Together with expanding ocean waters due to rising temperatures, the resulting rise in sea level has begun to damage coastlines as a result of increased flooding and erosion.

The cause of current climate change is largely human activity, like burning fossil fuels , like natural gas, oil, and coal. Burning these materials releases what are called greenhouse gases into Earth’s atmosphere . There, these gases trap heat from the sun’s rays inside the atmosphere causing Earth’s average temperature to rise. This rise in the planet's temperature is called global warming. The warming of the planet impacts local and regional climates. Throughout Earth's history, climate has continually changed. When occuring naturally, this is a slow process that has taken place over hundreds and thousands of years. The human influenced climate change that is happening now is occuring at a much faster rate.

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Related Resources

Special Report

Global warming of 1.5 ºc.

An IPCC special report on the impacts of global warming of 1.5 °C 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. The translations of the SPM and other material can be downloaded from this  link  

” Pour ce qui est de l’avenir, il ne s’agit pas de le prévoir, mais de le rendre possible. “  – Antoine de Saint Exupéry , Citadelle, 1948

Summary for Policymakers

• Explore Graphics

Understanding the impacts of 1.5°C global warming above pre-industrial levels and related global emission pathways in the context of strengthening the response to the threat of climate change, sustainable development and efforts to eradicate poverty.

Executive Summary

This chapter frames the context, knowledge-base and assessment approaches used to understand the impacts of 1.5°C global warming above pre-industrial levels and related global greenhouse gas emission pathways, building on the IPCC Fifth Assessment Report (AR5), in the context of strengthening the global response to the threat of climate change, sustainable development and efforts to eradicate poverty.

Human-induced warming reached approximately 1°C ( likely between 0.8°C and 1.2°C) above pre-industrial levels in 2017, increasing at 0.2°C ( likely between 0.1°C and 0.3°C) per decade ( high confidence ). Global warming is defined in this report as an increase in combined surface air and sea surface temperatures averaged over the globe and over a 30-year period. Unless otherwise specified, warming is expressed relative to the period 1850–1900, used as an approximation of pre-industrial temperatures in AR5. For periods shorter than 30 years, warming refers to the estimated average temperature over the 30 years centred on that shorter period, accounting for the impact of any temperature fluctuations or trend within those 30 years. Accordingly, warming from pre- industrial levels to the decade 2006–2015 is assessed to be 0.87°C ( likely between 0.75°C and 0.99°C). Since 2000, the estimated level of human-induced warming has been equal to the level of observed warming with a likely range of ±20% accounting for uncertainty due to contributions from solar and volcanic activity over the historical period ( high confidence ). {1.2.1}

Warming greater than the global average has already been experienced in many regions and seasons, with higher average warming over land than over the ocean ( high confidence ). Most land regions are experiencing greater warming than the global average, while most ocean regions are warming at a slower rate. Depending on the temperature dataset considered, 20–40% of the global human population live in regions that, by the decade 2006–2015, had already experienced warming of more than 1.5°C above pre-industrial in at least one season ( medium confidence ). {1.2.1, 1.2.2}

Past emissions alone are unlikely to raise global-mean temperature to 1.5°C above pre-industrial levels ( medium confidence ) , but past emissions do commit to other changes, such as further sea level rise ( high confidence ). If all anthropogenic emissions (including aerosol-related) were reduced to zero immediately, any further warming beyond the 1°C already experienced would likely be less than 0.5°C over the next two to three decades ( high confidence ), and likely less than 0.5°C on a century time scale ( medium confidence ), due to the opposing effects of different climate processes and drivers. A warming greater than 1.5°C is therefore not geophysically unavoidable: whether it will occur depends on future rates of emission reductions. {1.2.3, 1.2.4}

1.5°C emission pathways are defined as those that, given current knowledge of the climate response, provide a one- in-two to two-in-three chance of warming either remaining below 1.5°C or returning to 1.5°C by around 2100 following an overshoot. Overshoot pathways are characterized by the peak magnitude of the overshoot, which may have implications for impacts. All 1.5°C pathways involve limiting cumulative emissions of long-lived greenhouse gases, including carbon dioxide and nitrous oxide, and substantial reductions in other climate forcers ( high confidence ). Limiting cumulative emissions requires either reducing net global emissions of long-lived greenhouse gases to zero before the cumulative limit is reached, or net negative global emissions (anthropogenic removals) after the limit is exceeded. {1.2.3, 1.2.4, Cross-Chapter Boxes 1 and 2}

This report assesses projected impacts at a global average warming of 1.5°C and higher levels of warming. Global warming of 1.5°C is associated with global average surface temperatures fluctuating naturally on either side of 1.5°C, together with warming substantially greater than 1.5°C in many regions and seasons ( high confidence ), all of which must be considered in the assessment of impacts. Impacts at 1.5°C of warming also depend on the emission pathway to 1.5°C. Very different impacts result from pathways that remain below 1.5°C versus pathways that return to 1.5°C after a substantial overshoot, and when temperatures stabilize at 1.5°C versus a transient warming past 1.5°C ( medium confidence ). {1.2.3, 1.3}

Ethical considerations, and the principle of equity in particular, are central to this report, recognizing that many of the impacts of warming up to and beyond 1.5°C, and some potential impacts of mitigation actions required to limit warming to 1.5°C, fall disproportionately on the poor and vulnerable ( high confidence ). Equity has procedural and distributive dimensions and requires fairness in burden sharing both between generations and between and within nations. In framing the objective of holding the increase in the global average temperature rise to well below 2°C above pre-industrial levels, and to pursue efforts to limit warming to 1.5°C, the Paris Agreement associates the principle of equity with the broader goals of poverty eradication and sustainable development, recognising that effective responses to climate change require a global collective effort that may be guided by the 2015 United Nations Sustainable Development Goals. {1.1.1}

Climate adaptation refers to the actions taken to manage impacts of climate change by reducing vulnerability and exposure to its harmful effects and exploiting any potential benefits. Adaptation takes place at international, national and local levels. Subnational jurisdictions and entities, including urban and rural municipalities, are key to developing and reinforcing measures for reducing weather- and climate-related risks. Adaptation implementation faces several barriers including lack of up-to-date and locally relevant information, lack of finance and technology, social values and attitudes, and institutional constraints ( high confidence ). Adaptation is more likely to contribute to sustainable development when policies align with mitigation and poverty eradication goals ( medium confidence ). {1.1, 1.4}

Ambitious mitigation actions are indispensable to limit warming to 1.5°C while achieving sustainable development and poverty eradication ( high confidence ). Ill-designed responses, however, could pose challenges especially – but not exclusively – for countries and regions contending with poverty and those requiring significant transformation of their energy systems. This report focuses on ‘climate-resilient development pathways’, which aim to meet the goals of sustainable development, including climate adaptation and mitigation, poverty eradication and reducing inequalities. But any feasible pathway that remains within 1.5°C involves synergies and trade-offs ( high confidence ). Significant uncertainty remains as to which pathways are more consistent with the principle of equity. {1.1.1, 1.4}

Multiple forms of knowledge, including scientific evidence, narrative scenarios and prospective pathways, inform the understanding of 1.5°C. This report is informed by traditional evidence of the physical climate system and associated impacts and vulnerabilities of climate change, together with knowledge drawn from the perceptions of risk and the experiences of climate impacts and governance systems. Scenarios and pathways are used to explore conditions enabling goal-oriented futures while recognizing the significance of ethical considerations, the principle of equity, and the societal transformation needed. {1.2.3, 1.5.2}

There is no single answer to the question of whether it is feasible to limit warming to 1.5°C and adapt to the consequences. Feasibility is considered in this report as the capacity of a system as a whole to achieve a specific outcome. The global transformation that would be needed to limit warming to 1.5°C requires enabling conditions that reflect the links, synergies and trade-offs between mitigation, adaptation and sustainable development. These enabling conditions are assessed across many dimensions of feasibility – geophysical, environmental-ecological, technological, economic, socio-cultural and institutional – that may be considered through the unifying lens of the Anthropocene, acknowledging profound, differential but increasingly geologically significant human influences on the Earth system as a whole. This framing also emphasises the global interconnectivity of past, present and future human–environment relations, highlighting the need and opportunities for integrated responses to achieve the goals of the Paris Agreement. {1.1, Cross-Chapter Box 1}

Showing how emissions can be brought to zero by mid-century stay within the small remaining carbon budget for limiting global warming to 1.5°C.

This chapter assesses mitigation pathways consistent with limiting warming to 1.5°C above pre-industrial levels. In doing so, it explores the following key questions: What role do CO 2 and non-CO 2 emissions play? {2.2, 2.3, 2.4, 2.6} To what extent do 1.5°C pathways involve overshooting and returning below 1.5°C during the 21st century? {2.2, 2.3} What are the implications for transitions in energy, land use and sustainable development? {2.3, 2.4, 2.5} How do policy frameworks affect the ability to limit warming to 1.5°C? {2.3, 2.5} What are the associated knowledge gaps? {2.6}

The assessed pathways describe integrated, quantitative evolutions of all emissions over the 21st century associated with global energy and land use and the world economy. The assessment is contingent upon available integrated assessment literature and model assumptions, and is complemented by other studies with different scope, for example, those focusing on individual sectors. In recent years, integrated mitigation studies have improved the characterizations of mitigation pathways. However, limitations remain, as climate damages, avoided impacts, or societal co-benefits of the modelled transformations remain largely unaccounted for, while concurrent rapid technological changes, behavioural aspects, and uncertainties about input data present continuous challenges. ( high confidence ) {2.1.3, 2.3, 2.5.1, 2.6, Technical Annex 2}

The Chances of Limiting Warming to 1.5°C and the Requirements for Urgent Action

Pathways consistent with 1.5°C of warming above pre-industrial levels can be identified under a range of assumptions about economic growth, technology developments and lifestyles. However, lack of global cooperation, lack of governance of the required energy and land transformation, and increases in resource-intensive consumption are key impediments to achieving 1.5°C pathways. Governance challenges have been related to scenarios with high inequality and high population growth in the 1.5°C pathway literature. {2.3.1, 2.3.2, 2.5}

Under emissions in line with current pledges under the Paris Agreement (known as Nationally Determined Contributions, or NDCs), global warming is expected to surpass 1.5°C above pre-industrial levels, even if these pledges are supplemented with very challenging increases in the scale and ambition of mitigation after 2030 ( high confidence ). This increased action would need to achieve net zero CO 2 emissions in less than 15 years. Even if this is achieved, temperatures would only be expected to remain below the 1.5°C threshold if the actual geophysical response ends up being towards the low end of the currently estimated uncertainty range. Transition challenges as well as identified trade-offs can be reduced if global emissions peak before 2030 and marked emissions reductions compared to today are already achieved by 2030 {2.2, 2.3.5, Cross-Chapter Box 11 in Chapter 4}.

Limiting warming to 1.5°C depends on greenhouse gas (GHG) emissions over the next decades, where lower GHG emissions in 2030 lead to a higher chance of keeping peak warming to 1.5°C ( high confidence ). Available pathways that aim for no or limited (less than 0.1°C) overshoot of 1.5°C keep GHG emissions in 2030 to 25–30 GtCO 2 e yr −1 in 2030 (interquartile range). This contrasts with median estimates for current unconditional NDCs of 52–58 GtCO 2 e yr −1 in 2030. Pathways that aim for limiting warming to 1.5°C by 2100 after a temporary temperature overshoot rely on large-scale deployment of carbon dioxide removal (CDR) measures, which are uncertain and entail clear risks. In model pathways with no or limited overshoot of 1.5°C, global net anthropogenic CO 2 emissions decline by about 45% from 2010 levels by 2030 (40–60% interquartile range), reaching net zero around 2050 (2045–2055 interquartile range). 1 For limiting global warming to below 2°C with at least 66% probability CO 2 emissions are projected to decline by about 25% by 2030 in most pathways (10–30% interquartile range) and reach net zero around 2070 (2065–2080 interquartile range). {2.2, 2.3.3, 2.3.5, 2.5.3, Cross-Chapter Boxes 6 in Chapter 3 and 9 in Chapter 4, 4.3.7}

Limiting warming to 1.5°C implies reaching net zero CO 2 emissions globally around 2050 and concurrent deep reductions in emissions of non- CO 2 forcers, particularly methane ( high confidence ). Such mitigation pathways are characterized by energy-demand reductions, decarbonization of electricity and other fuels, electrification of energy end use, deep reductions in agricultural emissions, and some form of CDR with carbon storage on land or sequestration in geological reservoirs. Low energy demand and low demand for land- and GHG-intensive consumption goods facilitate limiting warming to as close as possible to 1.5°C. {2.2.2, 2.3.1, 2.3.5, 2.5.1, Cross-Chapter Box 9 in Chapter 4}.

In comparison to a 2°C limit, the transformations required to limit warming to 1.5°C are qualitatively similar but more pronounced and rapid over the next decades ( high confidence ). 1.5°C implies very ambitious, internationally cooperative policy environments that transform both supply and demand ( high confidence ). {2.3, 2.4, 2.5}

Policies reflecting a high price on emissions are necessary in models to achieve cost-effective 1.5°C pathways ( high confidence ). Other things being equal, modelling studies suggest the global average discounted marginal abatement costs for limiting warming to 1.5°C being about 3–4 times higher compared to 2°C over the 21st century, with large variations across models and socio-economic and policy assumptions. Carbon pricing can be imposed directly or implicitly by regulatory policies. Policy instruments, like technology policies or performance standards, can complement explicit carbon pricing in specific areas. {2.5.1, 2.5.2, 4.4.5}

Limiting warming to 1.5°C requires a marked shift in investment patterns ( medium confidence ). Additional annual average energy-related investments for the period 2016 to 2050 in pathways limiting warming to 1.5°C compared to pathways without new climate policies beyond those in place today (i.e., baseline) are estimated to be around 830 billion USD2010 (range of 150 billion to 1700 billion USD2010 across six models). Total energy-related investments increase by about 12% (range of 3% to 24%) in 1.5°C pathways relative to 2°C pathways. Average annual investment in low-carbon energy technologies and energy efficiency are upscaled by roughly a factor of six (range of factor of 4 to 10) by 2050 compared to 2015, overtaking fossil investments globally by around 2025 ( medium confidence ). Uncertainties and strategic mitigation portfolio choices affect the magnitude and focus of required investments. {2.5.2}

Future Emissions in 1.5°C Pathways  

Mitigation requirements can be quantified using carbon budget approaches that relate cumulative CO 2 emissions to global mean temperature increase. Robust physical understanding underpins this relationship, but uncertainties become increasingly relevant as a specific temperature limit is approached. These uncertainties relate to the transient climate response to cumulative carbon emissions (TCRE), non-CO 2 emissions, radiative forcing and response, potential additional Earth system feedbacks (such as permafrost thawing), and historical emissions and temperature. {2.2.2, 2.6.1}

Cumulative CO 2 emissions are kept within a budget by reducing global annual CO 2 emissions to net zero. This assessment suggests a remaining budget of about 420 GtCO 2 for a two-thirds chance of limiting warming to 1.5°C, and of about 580 GtCO 2 for an even chance ( medium confidence ). The remaining carbon budget is defined here as cumulative CO 2 emissions from the start of 2018 until the time of net zero global emissions for global warming defined as a change in global near-surface air temperatures. Remaining budgets applicable to 2100 would be approximately 100 GtCO 2 lower than this to account for permafrost thawing and potential methane release from wetlands in the future, and more thereafter. These estimates come with an additional geophysical uncertainty of at least ±400 GtCO 2 , related to non-CO 2 response and TCRE distribution. Uncertainties in the level of historic warming contribute ±250 GtCO 2 . In addition, these estimates can vary by ±250 GtCO 2 depending on non-CO 2 mitigation strategies as found in available pathways. {2.2.2, 2.6.1}

Staying within a remaining carbon budget of 580 GtCO 2 implies that CO 2 emissions reach carbon neutrality in about 30 years, reduced to 20 years for a 420 GtCO 2 remaining carbon budget ( high confidence ). The ±400 GtCO 2 geophysical uncertainty range surrounding a carbon budget translates into a variation of this timing of carbon neutrality of roughly ±15–20 years. If emissions do not start declining in the next decade, the point of carbon neutrality would need to be reached at least two decades earlier to remain within the same carbon budget. {2.2.2, 2.3.5}

Non- CO 2 emissions contribute to peak warming and thus affect the remaining carbon budget. The evolution of methane and sulphur dioxide emissions strongly influences the chances of limiting warming to 1.5°C. In the near-term, a weakening of aerosol cooling would add to future warming, but can be tempered by reductions in methane emissions ( high confidence ). Uncertainty in radiative forcing estimates (particularly aerosol) affects carbon budgets and the certainty of pathway categorizations. Some non-CO 2 forcers are emitted alongside CO 2 , particularly in the energy and transport sectors, and can be largely addressed through CO 2 mitigation. Others require specific measures, for example, to target agricultural nitrous oxide (N 2 O) and methane (CH 4 ), some sources of black carbon, or hydrofluorocarbons ( high confidence ) . In many cases, non-CO 2 emissions reductions are similar in 2°C pathways, indicating reductions near their assumed maximum potential by integrated assessment models. Emissions of N 2 O and NH 3 increase in some pathways with strongly increased bioenergy demand. {2.2.2, 2.3.1, 2.4.2, 2.5.3}  

The Role of Carbon Dioxide Removal (CDR)

All analysed pathways limiting warming to 1.5°C with no or limited overshoot use CDR to some extent to neutralize emissions from sources for which no mitigation measures have been identified and, in most cases, also to achieve net negative emissions to return global warming to 1.5°C following a peak ( high confidence ). The longer the delay in reducing CO 2 emissions towards zero, the larger the likelihood of exceeding 1.5°C, and the heavier the implied reliance on net negative emissions after mid-century to return warming to 1.5°C ( high confidence ). The faster reduction of net CO 2 emissions in 1.5°C compared to 2°C pathways is predominantly achieved by measures that result in less CO 2 being produced and emitted, and only to a smaller degree through additional CDR. Limitations on the speed, scale and societal acceptability of CDR deployment also limit the conceivable extent of temperature overshoot. Limits to our understanding of how the carbon cycle responds to net negative emissions increase the uncertainty about the effectiveness of CDR to decline temperatures after a peak. {2.2, 2.3, 2.6, 4.3.7}

CDR deployed at scale is unproven, and reliance on such technology is a major risk in the ability to limit warming to 1.5°C. CDR is needed less in pathways with particularly strong emphasis on energy efficiency and low demand. The scale and type of CDR deployment varies widely across 1.5°C pathways, with different consequences for achieving sustainable development objectives ( high confidence ). Some pathways rely more on bioenergy with carbon capture and storage (BECCS), while others rely more on afforestation, which are the two CDR methods most often included in integrated pathways. Trade-offs with other sustainability objectives occur predominantly through increased land, energy, water and investment demand. Bioenergy use is substantial in 1.5°C pathways with or without BECCS due to its multiple roles in decarbonizing energy use. {2.3.1, 2.5.3, 2.6.3, 4.3.7}  

Properties of Energy and Land Transitions in 1.5°C Pathways

The share of primary energy from renewables increases while coal usage decreases across pathways limiting warming to 1.5°C with no or limited overshoot ( high confidence ). By 2050, renewables (including bioenergy, hydro, wind, and solar, with direct-equivalence method) supply a share of 52–67% (interquartile range) of primary energy in 1.5°C pathways with no or limited overshoot; while the share from coal decreases to 1–7% (interquartile range), with a large fraction of this coal use combined with carbon capture and storage (CCS). From 2020 to 2050 the primary energy supplied by oil declines in most pathways (−39 to −77% interquartile range). Natural gas changes by −13% to −62% (interquartile range), but some pathways show a marked increase albeit with widespread deployment of CCS. The overall deployment of CCS varies widely across 1.5°C pathways with no or limited overshoot, with cumulative CO 2 stored through 2050 ranging from zero up to 300 GtCO 2 (minimum–maximum range), of which zero up to 140 GtCO 2 is stored from biomass. Primary energy supplied by bioenergy ranges from 40–310 EJ yr −1 in 2050 (minimum-maximum range), and nuclear from 3–66 EJ yr −1 (minimum–maximum range). These ranges reflect both uncertainties in technological development and strategic mitigation portfolio choices. {2.4.2}

1.5°C pathways with no or limited overshoot include a rapid decline in the carbon intensity of electricity and an increase in electrification of energy end use ( high confidence ). By 2050, the carbon intensity of electricity decreases to −92 to +11 gCO 2 MJ −1 (minimum–maximum range) from about 140 gCO 2 MJ −1 in 2020, and electricity covers 34–71% (minimum–maximum range) of final energy across 1.5°C pathways with no or limited overshoot from about 20% in 2020. By 2050, the share of electricity supplied by renewables increases to 59–97% (minimum-maximum range) across 1.5°C pathways with no or limited overshoot. Pathways with higher chances of holding warming to below 1.5°C generally show a faster decline in the carbon intensity of electricity by 2030 than pathways that temporarily overshoot 1.5°C. {2.4.1, 2.4.2, 2.4.3}

Transitions in global and regional land use are found in all pathways limiting global warming to 1.5°C with no or limited overshoot, but their scale depends on the pursued mitigation portfolio ( high confidence ) . Pathways that limit global warming to 1.5°C with no or limited overshoot project a 4 million km 2 reduction to a 2.5 million km 2 increase of non-pasture agricultural land for food and feed crops and a 0.5–11 million km 2 reduction of pasture land, to be converted into 0-6 million km 2 of agricultural land for energy crops and a 2 million km 2 reduction to 9.5 million km 2 increase in forests by 2050 relative to 2010 ( medium confidence ). Land-use transitions of similar magnitude can be observed in modelled 2°C pathways ( medium confidence ). Such large transitions pose profound challenges for sustainable management of the various demands on land for human settlements, food, livestock feed, fibre, bioenergy, carbon storage, biodiversity and other ecosystem services ( high confidence ). {2.3.4, 2.4.4}  

Demand-Side Mitigation and Behavioural Changes

Demand-side measures are key elements of 1.5°C pathways. Lifestyle choices lowering energy demand and the land- and GHG-intensity of food consumption can further support achievement of 1.5°C pathways ( high confidence ). By 2030 and 2050, all end-use sectors (including building, transport, and industry) show marked energy demand reductions in modelled 1.5°C pathways, comparable and beyond those projected in 2°C pathways. Sectoral models support the scale of these reductions. {2.3.4, 2.4.3, 2.5.1}  

Links between 1.5 ° C Pathways and Sustainable Development

Choices about mitigation portfolios for limiting warming to 1.5°C can positively or negatively impact the achievement of other societal objectives, such as sustainable development ( high confidence ). In particular, demand-side and efficiency measures, and lifestyle choices that limit energy, resource, and GHG-intensive food demand support sustainable development ( medium confidence ). Limiting warming to 1.5°C can be achieved synergistically with poverty alleviation and improved energy security and can provide large public health benefits through improved air quality, preventing millions of premature deaths . However, specific mitigation measures, such as bioenergy, may result in trade-offs that require consideration. {2.5.1, 2.5.2, 2.5.3}

Why is it necessary and even vital to maintain the global temperature increase below 1.5°C versus higher levels? Adaptation will be less difficult. Our world will suffer less negative impacts on intensity and frequency of extreme events, on resources, ecosystems, biodiversity, food security, cities, tourism, and carbon removal.

This chapter builds on findings of AR5 and assesses new scientific evidence of changes in the climate system and the associated impacts on natural and human systems, with a specific focus on the magnitude and pattern of risks linked for global warming of 1.5°C above temperatures in the pre-industrial period. Chapter 3 explores observed impacts and projected risks to a range of natural and human systems, with a focus on how risk levels change from 1.5°C to 2°C of global warming. The chapter also revisits major categories of risk (Reasons for Concern, RFC) based on the assessment of new knowledge that has become available since AR5.

 1.5°C and 2°C Warmer Worlds

The global climate has changed relative to the pre-industrial period, and there are multiple lines of evidence that these changes have had impacts on organisms and ecosystems, as well as on human systems and well-being ( high confidence ). The increase in global mean surface temperature (GMST), which reached 0.87°C in 2006–2015 relative to 1850–1900, has increased the frequency and magnitude of impacts ( high confidence ), strengthening evidence of how an increase in GMST of 1.5°C or more could impact natural and human systems (1.5°C versus 2°C). {3.3, 3.4, 3.5, 3.6, Cross-Chapter Boxes 6, 7 and 8 in this chapter}

Human-induced global warming has already caused multiple observed changes in the climate system ( high confidence ). Changes include increases in both land and ocean temperatures, as well as more frequent heatwaves in most land regions ( high confidence ). There is also ( high confidence ) global warming has resulted in an increase in the frequency and duration of marine heatwaves. Further, there is substantial evidence that human-induced global warming has led to an increase in the frequency, intensity and/or amount of heavy precipitation events at the global scale ( medium confidence ), as well as an increased risk of drought in the Mediterranean region ( medium confidence ). {3.3.1, 3.3.2, 3.3.3, 3.3.4, Box 3.4}

Trends in intensity and frequency of some climate and weather extremes have been detected over time spans during which about 0.5°C of global warming occurred ( medium confidence ). This assessment is based on several lines of evidence, including attribution studies for changes in extremes since 1950. {3.2, 3.3.1, 3.3.2, 3.3.3, 3.3.4}

Several regional changes in climate are assessed to occur with global warming up to 1.5°C as compared to pre-industrial levels, including warming of extreme temperatures in many regions ( high confidence ), increases in frequency, intensity and/or amount of heavy precipitation in several regions ( high confidence ), and an increase in intensity or frequency of droughts in some regions ( medium confidence ). {3.3.1, 3.3.2, 3.3.3, 3.3.4, Table 3.2}

There is no single ‘1.5°C warmer world’ ( high confidence ). In addition to the overall increase in GMST, it is important to consider the size and duration of potential overshoots in temperature. Furthermore, there are questions on how the stabilization of an increase in GMST of 1.5°C can be achieved, and how policies might be able to influence the resilience of human and natural systems, and the nature of regional and subregional risks. Overshooting poses large risks for natural and human systems, especially if the temperature at peak warming is high, because some risks may be long-lasting and irreversible, such as the loss of some ecosystems ( high confidence ). The rate of change for several types of risks may also have relevance, with potentially large risks in the case of a rapid rise to overshooting temperatures, even if a decrease to 1.5°C can be achieved at the end of the 21st century or later ( medium confidence ). If overshoot is to be minimized, the remaining equivalent CO 2 budget available for emissions is very small, which implies that large, immediate and unprecedented global efforts to mitigate greenhouse gases are required ( high confidence ). {3.2, 3.6.2, Cross-Chapter Box 8 in this chapter}

Robust 1   global differences in temperature means and extremes are expected if global warming reaches 1.5°C versus 2°C above the pre-industrial levels ( high confidence) . For oceans, regional surface temperature means and extremes are projected to be higher at 2°C compared to 1.5°C of global warming ( high confidence ). Temperature means and extremes are also projected to be higher at 2°C compared to 1.5°C in most land regions, with increases being 2–3 times greater than the increase in GMST projected for some regions ( high confidence ). Robust increases in temperature means and extremes are also projected at 1.5°C compared to present-day values ( high confidence ) {3.3.1, 3.3.2}. There are decreases in the occurrence of cold extremes, but substantial increases in their temperature, in particular in regions with snow or ice cover ( high confidence ) {3.3.1}.

Climate models project robust 2 differences in regional climate between present-day and global warming up to 1.5°C 3 , and between 1.5°C and 2°C 4 ( high confidence ), depending on the variable and region in question ( high confidence ). Large, robust and widespread differences are expected for temperature extremes ( high confidence ). Regarding hot extremes, the strongest warming is expected to occur at mid-latitudes in the warm season (with increases of up to 3°C for 1.5°C of global warming, i.e., a factor of two) and at high latitudes in the cold season (with increases of up to 4.5°C at 1.5°C of global warming, i.e., a factor of three) ( high confidence ). The strongest warming of hot extremes is projected to occur in central and eastern North America, central and southern Europe, the Mediterranean region (including southern Europe, northern Africa and the Near East), western and central Asia, and southern Africa ( medium confidence ). The number of exceptionally hot days are expected to increase the most in the tropics, where interannual temperature variability is lowest; extreme heatwaves are thus projected to emerge earliest in these regions, and they are expected to already become widespread there at 1.5°C global warming ( high confidence ). Limiting global warming to 1.5°C instead of 2°C could result in around 420 million fewer people being frequently exposed to extreme heatwaves, and about 65 million fewer people being exposed to exceptional heatwaves, assuming constant vulnerability ( medium confidence ). {3.3.1, 3.3.2, Cross-Chapter Box 8 in this chapter}

Limiting global warming to 1.5°C would limit risks of increases in heavy precipitation events on a global scale and in several regions compared to conditions at 2°C global warming ( medium confidence ). The regions with the largest increases in heavy precipitation events for 1.5°C to 2°C global warming include: several high-latitude regions (e.g. Alaska/western Canada, eastern Canada/ Greenland/Iceland, northern Europe and northern Asia); mountainous regions (e.g.,Tibetan Plateau); eastern Asia (including China and Japan); and eastern North America ( medium confidence ). Tropical cyclones are projected to decrease in frequency but with an increase in the number of very intense cyclones ( limited evidence , low confidence ). Heavy precipitation associated with tropical cyclones is projected to be higher at 2°C compared to 1.5°C of global warming ( medium confidence ). Heavy precipitation, when aggregated at a global scale, is projected to be higher at 2°C than at 1.5°C of global warming ( medium confidence ) {3.3.3, 3.3.6}

Limiting global warming to 1.5°C is expected to substantially reduce the probability of extreme drought, precipitation deficits, and risks associated with water availability (i.e., water stress) in some regions ( medium confidence ). In particular, risks associated with increases in drought frequency and magnitude are projected to be substantially larger at 2°C than at 1.5°C in the Mediterranean region (including southern Europe, northern Africa and the Near East) and southern Africa ( medium confidence ). {3.3.3, 3.3.4, Box 3.1, Box 3.2}

Risks to natural and human systems are expected to be lower at 1.5°C than at 2°C of global warming ( high confidence ). This difference is due to the smaller rates and magnitudes of climate change associated with a 1.5°C temperature increase, including lower frequencies and intensities of temperature-related extremes. Lower rates of change enhance the ability of natural and human systems to adapt, with substantial benefits for a wide range of terrestrial, freshwater, wetland, coastal and ocean ecosystems (including coral reefs) ( high confidence ), as well as food production systems, human health, and tourism ( medium confidence ), together with energy systems and transportation ( low confidence) . {3.3.1, 3.4}

Exposure to multiple and compound climate-related risks is projected to increase between 1.5°C and 2°C of global warming with greater proportions of people both exposed and susceptible to poverty in Africa and Asia ( high confidence ). For global warming from 1.5°C to 2°C, risks across energy, food, and water sectors could overlap spatially and temporally, creating new – and exacerbating current – hazards, exposures, and vulnerabilities that could affect increasing numbers of people and regions ( medium confidence ). Small island states and economically disadvantaged populations are particularly at risk ( high confidence ). {3.3.1, 3.4.5.3, 3.4.5.6, 3.4.11, 3.5.4.9, Box 3.5}

Global warming of 2°C would lead to an expansion of areas with significant increases in runoff, as well as those affected by flood hazard, compared to conditions at 1.5°C ( medium confidence ). Global warming of 1.5°C would also lead to an expansion of the global land area with significant increases in runoff ( medium confidence ) and an increase in flood hazard in some regions ( medium confidence ) compared to present-day conditions. {3.3.5}

The probability of a sea-ice-free Arctic Ocean 5   during summer is substantially higher at 2°C compared to 1.5°C of global warming ( medium confidence ) . Model simulations suggest that at least one sea-ice-free Arctic summer is expected every 10 years for global warming of 2°C, with the frequency decreasing to one sea-ice-free Arctic summer every 100 years under 1.5°C ( medium confidence ). An intermediate temperature overshoot will have no long- term consequences for Arctic sea ice coverage, and hysteresis is not expected ( high confidence ). {3.3.8, 3.4.4.7}

Global mean sea level rise (GMSLR) is projected to be around 0.1 m (0.04 – 0.16 m) less by the end of the 21st century in a 1.5°C warmer world compared to a 2°C warmer world ( medium confidence ). Projected GMSLR for 1.5°C of global warming has an indicative range of 0.26 – 0.77m, relative to 1986–2005, ( medium confidence ). A smaller sea level rise could mean that up to 10.4 million fewer people (based on the 2010 global population and assuming no adaptation) would be exposed to the impacts of sea level rise globally in 2100 at 1.5°C compared to at 2°C. A slower rate of sea level rise enables greater opportunities for adaptation ( medium confidence ). There is high confidence that sea level rise will continue beyond 2100. Instabilities exist for both the Greenland and Antarctic ice sheets, which could result in multi-meter rises in sea level on time scales of century to millennia. There is ( medium confidence ) that these instabilities could be triggered at around 1.5°C to 2°C of global warming. {3.3.9, 3.4.5, 3.6.3}

The ocean has absorbed about 30% of the anthropogenic carbon dioxide, resulting in ocean acidification and changes to carbonate chemistry that are unprecedented for at least the last 65 million years ( high confidence ). Risks have been identified for the survival, calcification, growth, development and abundance of a broad range of marine taxonomic groups, ranging from algae to fish, with substantial evidence of predictable trait-based sensitivities ( high confidence ). There are multiple lines of evidence that ocean warming and acidification corresponding to 1.5°C of global warming would impact a wide range of marine organisms and ecosystems, as well as sectors such as aquaculture and fisheries ( high confidence ). {3.3.10, 3.4.4}

Larger risks are expected for many regions and systems for global warming at 1.5°C, as compared to today, with adaptation required now and up to 1.5°C. However, risks would be larger at 2°C of warming and an even greater effort would be needed for adaptation to a temperature increase of that magnitude ( high confidence ). {3.4, Box 3.4, Box 3.5, Cross-Chapter Box 6 in this chapter}

Future risks at 1.5°C of global warming will depend on the mitigation pathway and on the possible occurrence of a transient overshoot ( high confidence ). The impacts on natural and human systems would be greater if mitigation pathways temporarily overshoot 1.5°C and return to 1.5°C later in the century, as compared to pathways that stabilize at 1.5°C without an overshoot ( high confidence ). The size and duration of an overshoot would also affect future impacts (e.g., irreversible loss of some ecosystems) ( high confidence ). Changes in land use resulting from mitigation choices could have impacts on food production and ecosystem diversity. {3.6.1, 3.6.2, Cross-Chapter Boxes 7 and 8 in this chapter}

Climate Change Risks for Natural and Human systems

Terrestrial and Wetland Ecosystems

Risks of local species losses and, consequently, risks of extinction are much less in a 1.5°C versus a 2°C warmer world ( high confidence ). The number of species projected to lose over half of their climatically determined geographic range at 2°C global warming (18% of insects, 16% of plants, 8% of vertebrates) is projected to be reduced to 6% of insects, 8% of plants and 4% of vertebrates at 1.5°C warming ( medium confidence ). Risks associated with other biodiversity-related factors, such as forest fires, extreme weather events, and the spread of invasive species, pests and diseases, would also be lower at 1.5°C than at 2°C of warming ( high confidence ), supporting a greater persistence of ecosystem services. {3.4.3, 3.5.2}

Constraining global warming to 1.5°C, rather than to 2°C and higher, is projected to have many benefits for terrestrial and wetland ecosystems and for the preservation of their services to humans ( high confidence ). Risks for natural and managed ecosystems are higher on drylands compared to humid lands. The global terrestrial land area projected to be affected by ecosystem transformations (13%, interquartile range 8–20%) at 2°C is approximately halved at 1.5°C global warming to 4% (interquartile range 2–7%) ( medium confidence ). Above 1.5°C, an expansion of desert terrain and vegetation would occur in the Mediterranean biome ( medium confidence ), causing changes unparalleled in the last 10,000 years ( medium confidence ). {3.3.2.2, 3.4.3.2, 3.4.3.5, 3.4.6.1, 3.5.5.10, Box 4.2}

Many impacts are projected to be larger at higher latitudes, owing to mean and cold-season warming rates above the global average ( medium confidence ). High-latitude tundra and boreal forest are particularly at risk, and woody shrubs are already encroaching into tundra ( high confidence ) and will proceed with further warming. Constraining warming to 1.5°C would prevent the thawing of an estimated permafrost area of 1.5 to 2.5 million km 2 over centuries compared to thawing under 2°C ( medium confidence ). {3.3.2, 3.4.3, 3.4.4}

Ocean Ecosystems

Ocean ecosystems are already experiencing large-scale changes, and critical thresholds are expected to be reached at 1.5°C and higher levels of global warming ( high confidence ). In the transition to 1.5°C of warming, changes to water temperatures are expected to drive some species (e.g., plankton, fish) to relocate to higher latitudes and cause novel ecosystems to assemble ( high confidence ). Other ecosystems (e.g., kelp forests, coral reefs) are relatively less able to move, however, and are projected to experience high rates of mortality and loss ( very high confidence ). For example, multiple lines of evidence indicate that the majority (70–90%) of warm water (tropical) coral reefs that exist today will disappear even if global warming is constrained to 1.5°C (very high confidence ). {3.4.4, Box 3.4}

Current ecosystem services from the ocean are expected to be reduced at 1.5°C of global warming, with losses being even greater at 2°C of global warming ( high confidence ) . The risks of declining ocean productivity, shifts of species to higher latitudes, damage to ecosystems (e.g., coral reefs, and mangroves, seagrass and other wetland ecosystems), loss of fisheries productivity (at low latitudes), and changes to ocean chemistry (e.g., acidification, hypoxia and dead zones) are projected to be substantially lower when global warming is limited to 1.5°C ( high confidence ). {3.4.4, Box 3.4}

Water Resources

The projected frequency and magnitude of floods and droughts in some regions are smaller under 1.5°C than under 2°C of warming ( medium confidence ). Human exposure to increased flooding is projected to be substantially lower at 1.5°C compared to 2°C of global warming, although projected changes create regionally differentiated risks ( medium confidence ). The differences in the risks among regions are strongly influenced by local socio-economic conditions ( medium confidence ). {3.3.4, 3.3.5, 3.4.2}

Risks of water scarcity are projected to be greater at 2°C than at 1.5°C of global warming in some regions ( medium confidence ). Depending on future socio-economic conditions, limiting global warming to 1.5°C, compared to 2°C, may reduce the proportion of the world population exposed to a climate change-induced increase in water stress by up to 50%, although there is considerable variability between regions ( medium confidence ). Regions with particularly large benefits could include the Mediterranean and the Caribbean ( medium confidence ). Socio-economic drivers, however, are expected to have a greater influence on these risks than the changes in climate ( medium confidence ). {3.3.5, 3.4.2, Box 3.5}

Land Use, Food Security and Food Production Systems

Limiting global warming to 1.5°C, compared with 2°C, is projected to result in smaller net reductions in yields of maize, rice, wheat, and potentially other cereal crops, particularly in sub-Saharan Africa, Southeast Asia, and Central and South America; and in the CO 2 -dependent nutritional quality of rice and wheat ( high confidence ). A loss of 7–10% of rangeland livestock globally is projected for approximately 2°C of warming, with considerable economic consequences for many communities and regions ( medium confidence ). {3.4.6, 3.6, Box 3.1, Cross-Chapter Box 6 in this chapter}

Reductions in projected food availability are larger at 2°C than at 1.5°C of global warming in the Sahel, southern Africa, the Mediterranean, central Europe and the Amazon ( medium confidence ). This suggests a transition from medium to high risk of regionally differentiated impacts on food security between 1.5°C and 2°C (medium confidence ). Future economic and trade environments and their response to changing food availability ( medium confidence ) are important potential adaptation options for reducing hunger risk in low- and middle-income countries. {Cross-Chapter Box 6 in this chapter}

Fisheries and aquaculture are important to global food security but are already facing increasing risks from ocean warming and acidification ( medium confidence ). These risks are projected to increase at 1.5°C of global warming and impact key organisms such as fin fish and bivalves (e.g., oysters), especially at low latitudes ( medium confidence ). Small-scale fisheries in tropical regions, which are very dependent on habitat provided by coastal ecosystems such as coral reefs, mangroves, seagrass and kelp forests, are expected to face growing risks at 1.5°C of warming because of loss of habitat ( medium confidence ). Risks of impacts and decreasing food security are projected to become greater as global warming reaches beyond 1.5°C and both ocean warming and acidification increase, with substantial losses likely for coastal livelihoods and industries (e.g., fisheries and aquaculture) ( medium to high confidence ). {3.4.4, 3.4.5, 3.4.6, Box 3.1, Box 3.4, Box 3.5, Cross-Chapter Box 6 in this chapter}

Land use and land-use change emerge as critical features of virtually all mitigation pathways that seek to limit global warming to 1.5°C ( high confidence ). Most least-cost mitigation pathways to limit peak or end-of-century warming to 1.5°C make use of carbon dioxide removal (CDR), predominantly employing significant levels of bioenergy with carbon capture and storage (BECCS) and/or afforestation and reforestation (AR) in their portfolio of mitigation measures ( high confidence ). {Cross-Chapter Box 7 in this chapter}

Large-scale deployment of BECCS and/or AR would have a far-reaching land and water footprint ( high confidence ). Whether this footprint would result in adverse impacts, for example on biodiversity or food production, depends on the existence and effectiveness of measures to conserve land carbon stocks, measures to limit agricultural expansion in order to protect natural ecosystems, and the potential to increase agricultural productivity ( medium agreement ). In addition, BECCS and/or AR would have substantial direct effects on regional climate through biophysical feedbacks, which are generally not included in Integrated Assessments Models ( high confidence ). {3.6.2, Cross-Chapter Boxes 7 and 8 in this chapter}

The impacts of large-scale CDR deployment could be greatly reduced if a wider portfolio of CDR options were deployed, if a holistic policy for sustainable land management were adopted, and if increased mitigation efforts were employed to strongly limit the demand for land, energy and material resources, including through lifestyle and dietary changes ( medium confidence ). In particular, reforestation could be associated with significant co-benefits if implemented in a manner than helps restore natural ecosystems ( high confidence ). {Cross-Chapter Box 7 in this chapter}

Human Health, Well-Being, Cities and Poverty

Any increase in global temperature (e.g., +0.5°C) is projected to affect human health, with primarily negative consequences ( high confidence ). Lower risks are projected at 1.5°C than at 2°C for heat-related morbidity and mortality ( very high confidence ), and for ozone-related mortality if emissions needed for ozone formation remain high ( high confidence ). Urban heat islands often amplify the impacts of heatwaves in cities ( high confidence ). Risks for some vector-borne diseases, such as malaria and dengue fever are projected to increase with warming from 1.5°C to 2°C, including potential shifts in their geographic range ( high confidence ). Overall for vector- borne diseases, whether projections are positive or negative depends on the disease, region and extent of change ( high confidence ). Lower risks of undernutrition are projected at 1.5°C than at 2°C ( medium confidence ). Incorporating estimates of adaptation into projections reduces the magnitude of risks ( high confidence ). {3.4.7, 3.4.7.1, 3.4.8, 3.5.5.8}

Global warming of 2°C is expected to pose greater risks to urban areas than global warming of 1.5°C ( medium confidence ) . The extent of risk depends on human vulnerability and the effectiveness of adaptation for regions (coastal and non-coastal), informal settlements and infrastructure sectors (such as energy, water and transport) ( high confidence ). {3.4.5, 3.4.8}

Poverty and disadvantage have increased with recent warming (about 1°C) and are expected to increase for many populations as average global temperatures increase from 1°C to 1.5°C and higher ( medium confidence ). Outmigration in agricultural- dependent communities is positively and statistically significantly associated with global temperature ( medium confidence ). Our understanding of the links of 1.5°C and 2°C of global warming to human migration are limited and represent an important knowledge gap. {3.4.10, 3.4.11, 5.2.2, Table 3.5}

Key Economic Sectors and Services

Risks to global aggregated economic growth due to climate change impacts are projected to be lower at 1.5°C than at 2°C by the end of this century ( medium confidence ). {3.5.2, 3.5.3} The largest reductions in economic growth at 2°C compared to 1.5°C of warming are projected for low- and middle-income countries and regions (the African continent, Southeast Asia, India, Brazil and Mexico) ( low to medium confidence ). Countries in the tropics and Southern Hemisphere subtropics are projected to experience the largest impacts on economic growth due to climate change should global warming increase from 1.5°C to 2°C ( medium confidence ). {3.5} Global warming has already affected tourism, with increased risks projected under 1.5°C of warming in specific geographic regions and for seasonal tourism including sun, beach and snow sports destinations ( very high confidence ). Risks will be lower for tourism markets that are less climate sensitive, such as gaming and large hotel-based activities ( high confidence ). Risks for coastal tourism, particularly in subtropical and tropical regions, will increase with temperature-related degradation (e.g., heat extremes, storms) or loss of beach and coral reef assets ( high confidence ). {3.3.6, 3.4.4.12, 3.4.9.1, Box 3.4}

Small Islands, and Coastal and Low-lying areas

Small islands are projected to experience multiple inter- related risks at 1.5°C of global warming that will increase with warming of 2°C and higher levels ( high confidence ). Climate hazards at 1.5°C are projected to be lower compared to those at 2°C ( high confidence ). Long-term risks of coastal flooding and impacts on populations, infrastructures and assets ( high confidence ), freshwater stress ( medium confidenc e), and risks across marine ecosystems ( high confidence ) and critical sectors ( medium confidence ) are projected to increase at 1.5°C compared to present-day levels and increase further at 2°C, limiting adaptation opportunities and increasing loss and damage ( medium confidence ). Migration in small islands (internally and internationally) occurs for multiple reasons and purposes, mostly for better livelihood opportunities ( high confidence ) and increasingly owing to sea level rise ( medium confidence ). {3.3.2.2, 3.3.6–9, 3.4.3.2, 3.4.4.2, 3.4.4.5, 3.4.4.12, 3.4.5.3, 3.4.7.1, 3.4.9.1, 3.5.4.9, Box 3.4, Box 3.5}

Impacts associated with sea level rise and changes to the salinity of coastal groundwater, increased flooding and damage to infrastructure, are projected to be critically important in vulnerable environments, such as small islands, low-lying coasts and deltas, at global warming of 1.5°C and 2°C ( high confidence ). Localized subsidence and changes to river discharge can potentially exacerbate these effects. Adaptation is already happening ( high confidence ) and will remain important over multi-centennial time scales. {3.4.5.3, 3.4.5.4, 3.4.5.7, 5.4.5.4, Box 3.5}

Existing and restored natural coastal ecosystems may be effective in reducing the adverse impacts of rising sea levels and intensifying storms by protecting coastal and deltaic regions ( medium confidence ). Natural sedimentation rates are expected to be able to offset the effect of rising sea levels, given the slower rates of sea level rise associated with 1.5°C of warming ( medium confidence ). Other feedbacks, such as landward migration of wetlands and the adaptation of infrastructure, remain important ( medium confidence ). {3.4.4.12, 3.4.5.4, 3.4.5.7}

Increased Reasons for Concern

There are multiple lines of evidence that since AR5 the assessed levels of risk increased for four of the five Reasons for Concern (RFCs) for global warming levels of up to 2°C ( high confidence ). The risk transitions by degrees of global warming are now: from high to very high between 1.5°C and 2°C for RFC1 (Unique and threatened systems) ( high confidence ); from moderate to high risk between 1°C and 1.5°C for RFC2 (Extreme weather events) ( medium confidence ); from moderate to high risk between 1.5°C and 2°C for RFC3 (Distribution of impacts) ( high confidence ); from moderate to high risk between 1.5°C and 2.5°C for RFC4 (Global aggregate impacts) ( medium confidence ); and from moderate to high risk between 1°C and 2.5°C for RFC5 (Large-scale singular events) ( medium confidence ). {3.5.2}

• The category ‘Unique and threatened systems’ (RFC1) display a transition from high to very high risk which is now located between 1.5°C and 2°C of global warming as opposed to at 2.6°C of global warming in AR5, owing to new and multiple lines of evidence for changing risks for coral reefs, the Arctic and biodiversity in general ( high confidence ). {3.5.2.1}
• In ‘Extreme weather events’ (RFC2), the transition from moderate to high risk is now located between 1.0°C and 1.5°C of global warming, which is very similar to the AR5 assessment but is projected with greater confidence ( medium confidence ). The impact literature contains little information about the potential for human society to adapt to extreme weather events, and hence it has not been possible to locate the transition from ‘high’ to ‘very high’ risk within the context of assessing impacts at 1.5°C versus 2°C of global warming. There is thus low confidence in the level at which global warming could lead to very high risks associated with extreme weather events in the context of this report. {3.5}
• With respect to the ‘Distribution of impacts’ (RFC3) a transition from moderate to high risk is now located between 1.5°C and 2°C of global warming, compared with between 1.6°C and 2.6°C global warming in AR5, owing to new evidence about regionally differentiated risks to food security, water resources, drought, heat exposure and coastal submergence ( high confidence ). {3.5}
• In ‘global aggregate impacts’ (RFC4) a transition from moderate to high levels of risk is now located between 1.5°C and 2 .5°C of global warming, as opposed to at 3.6°C of warming in AR5, owing to new evidence about global aggregate economic impacts and risks to Earth’s biodiversity ( medium confidence ). {3.5}
• Finally, ‘large-scale singular events’ (RFC5), moderate risk is now located at 1°C of global warming and high risk is located at 2.5°C of global warming, as opposed to at 1.6°C (moderate risk) and around 4°C (high risk) in AR5, because of new observations and models of the West Antarctic ice sheet ( medium confidence ). {3.3.9, 3.5.2, 3.6.3}

The global response to warming of 1.5°C comprises transitions in land and ecosystem, energy, urban and infrastructure, and industrial systems. The feasibility of mitigation and adaptation options, and the enabling conditions for strengthening and implementing the systemic changes, are assessed in this chapter.

Limiting warming to 1.5°C above pre-industrial levels would require transformative systemic change, integrated with sustainable development. Such change would require the upscaling and acceleration of the implementation of far- reaching, multilevel and cross-sectoral climate mitigation and addressing barriers. Such systemic change would need to be linked to complementary adaptation actions, including transformational adaptation, especially for pathways that temporarily overshoot 1.5°C ( medium evidence,high agreement ) {Chapter 2, Chapter 3, 4.2.1, 4.4.5, 4.5}. Current national pledges on mitigation and adaptation are not enough to stay below the Paris Agreement temperature limits and achieve its adaptation goals. While transitions in energy efficiency, carbon intensity of fuels, electrification and land-use change are underway in various countries, limiting warming to 1.5°C will require a greater scale and pace of change to transform energy, land, urban and industrial systems globally. {4.3, 4.4, Cross-Chapter Box 9 in this Chapter}

Although multiple communities around the world are demonstrating the possibility of implementation consistent with 1.5°C pathways {Boxes 4.1-4.10}, very few countries, regions, cities, communities or businesses can currently make such a claim ( high confidence ). To strengthen the global response, almost all countries would need to significantly raise their level of ambition. Implementation of this raised ambition would require enhanced institutional capabilities in all countries, including building the capability to utilize indigenous and local knowledge ( medium evidence, high agreement ). In developing countries and for poor and vulnerable people, implementing the response would require financial, technological and other forms of support to build capacity, for which additional local, national and international resources would need to be mobilized ( high confidence ). However, public, financial, institutional and innovation capabilities currently fall short of implementing far-reaching measures at scale in all countries ( high confidence ). Transnational networks that support multilevel climate action are growing, but challenges in their scale-up remain. {4.4.1, 4.4.2, 4.4.4, 4.4.5, Box 4.1, Box 4.2, Box 4.7}

Adaptation needs will be lower in a 1.5°C world compared to a 2°C world ( high confidence ) {Chapter 3; Cross-Chapter Box 11 in this chapter}. Learning from current adaptation practices and strengthening them through adaptive governance {4.4.1}, lifestyle and behavioural change {4.4.3} and innovative financing mechanisms {4.4.5} can help their mainstreaming within sustainable development practices.Preventing maladaptation,drawing on bottom-up approaches {Box 4.6} and using indigenous knowledge {Box 4.3} would effectively engage and protect vulnerable people and communities. While adaptation finance has increased quantitatively, significant further expansion would be needed to adapt to 1.5°C. Qualitative gaps in the distribution of adaptation finance, readiness to absorb resources, and monitoring mechanisms undermine the potential of adaptation finance to reduce impacts. {Chapter 3, 4.4.2, 4.4.5, 4.6}

System Transitions

The energy system transition that would be required to limit global warming to 1.5°C above pre-industrial conditions is underway in many sectors and regions around the world ( medium evidence, high agreement ). The political, economic, social and technical feasibility of solar energy, wind energy and electricity storage technologies has improved dramatically over the past few years, while that of nuclear energy and carbon dioxide capture and storage (CCS) in the electricity sector have not shown similar improvements. {4.3.1}

Electrification, hydrogen, bio-based feedstocks and substitution, and, in several cases, carbon dioxide capture, utilization and storage (CCUS), would lead to the deep emissions reductions required in energy-intensive industries to limit warming to 1.5°C. However, those options are limited by institutional, economic and technical constraints, which increase financial risks to many incumbent firms ( medium evidence, high agreement ). Energy efficiency in industry is more economically feasible and helps enable industrial system transitions but would have to be complemented with greenhouse gas (GHG)-neutral processes or carbon dioxide removal (CDR) to make energy-intensive industries consistent with 1.5°C ( high confidence ). {4.3.1, 4.3.4}

Global and regional land-use and ecosystems transitions and associated changes in behaviour that would be required to limit warming to 1.5°C can enhance future adaptation and land-based agricultural and forestry mitigation potential. Such transitions could, however, carry consequences for livelihoods that depend on agriculture and natural resources {4.3.2, Cross- Chapter Box 6 in Chapter 3}. Alterations of agriculture and forest systems to achieve mitigation goals could affect current ecosystems and their services and potentially threaten food, water and livelihood security. While this could limit the social and environmental feasibility of land-based mitigation options, careful design and implementation could enhance their acceptability and support sustainable development objectives ( medium evidence, medium agreement ). {4.3.2, 4.5.3}

Changing agricultural practices can be an effective climate adaptation strategy. A diversity of adaptation options exists, including mixed crop-livestock production systems which can be a cost-effective adaptation strategy in many global agriculture systems ( robust evidence, medium agreement ). Improving irrigation efficiency could effectively deal with changing global water endowments, especially if achieved via farmers adopting new behaviours and water- efficient practices rather than through large-scale infrastructural interventions ( medium evidence, medium agreement ). Well-designed adaptation processes such as community-based adaptation can be effective depending upon context and levels of vulnerability. {4.3.2, 4.5.3}

Improving the efficiency of food production and closing yield gaps have the potential to reduce emissions from agriculture, reduce pressure on land, and enhance food security and future mitigation potential ( high confidence ). Improving productivity of existing agricultural systems generally reduces the emissions intensity of food production and offers strong synergies with rural development, poverty reduction and food security objectives, but options to reduce absolute emissions are limited unless paired with demand-side measures. Technological innovation including biotechnology, with adequate safeguards, could contribute to resolving current feasibility constraints and expand the future mitigation potential of agriculture. {4.3.2, 4.4.4}

Shifts in dietary choices towards foods with lower emissions and requirements for land, along with reduced food loss and waste, could reduce emissions and increase adaptation options ( high confidence ). Decreasing food loss and waste and changing dietary behaviour could result in mitigation and adaptation ( high confidence ) by reducing both emissions and pressure on land, with significant co-benefits for food security, human health and sustainable development {4.3.2, 4.4.5, 4.5.2, 4.5.3, 5.4.2}, but evidence of successful policies to modify dietary choices remains limited.

Mitigation and Adaptation Options and Other Measures

A mix of mitigation and adaptation options implemented in a participatory and integrated manner can enable rapid, systemic transitions – in urban and rural areas – that are necessary elements of an accelerated transition consistent with limiting warming to 1.5°C. Such options and changes are most effective when aligned with economic and sustainable development, and when local and regional governments are supported by national governments {4.3.3, 4.4.1, 4.4.3}. Various mitigation options are expanding rapidly across many geographies. Although many have development synergies, not all income groups have so far benefited from them. Electrification, end-use energy efficiency and increased share of renewables, amongst other options, are lowering energy use and decarbonizing energy supply in the built environment, especially in buildings. Other rapid changes needed in urban environments include demotorization and decarbonization of transport, including the expansion of electric vehicles, and greater use of energy-efficient appliances ( medium evidence, high agreement ). Technological and social innovations can contribute to limiting warming to 1.5°C, for example, by enabling the use of smart grids, energy storage technologies and general-purpose technologies, such as information and communication technology (ICT) that can be deployed to help reduce emissions. Feasible adaptation options include green infrastructure, resilient water and urban ecosystem services, urban and peri-urban agriculture, and adapting buildings and land use through regulation and planning ( medium evidence, medium to high agreement ). {4.3.3, 4.4.3, 4.4.4}

Synergies can be achieved across systemic transitions through several overarching adaptation options in rural and urban areas. Investments in health, social security and risk sharing and spreading are cost-effective adaptation measures with high potential for scaling up ( medium evidence, medium to high agreement ). Disaster risk management and education-based adaptation have lower prospects of scalability and cost-effectiveness ( medium evidence, high agreement ) but are critical for building adaptive capacity. {4.3.5, 4.5.3}

Converging adaptation and mitigation options can lead to synergies and potentially increase cost-effectiveness, but multiple trade-offs can limit the speed of and potential for scaling up. Many examples of synergies and trade-offs exist in all sectors and system transitions. For instance, sustainable water management ( high evidence, medium agreement ) and investment in green infrastructure ( medium evidence, high agreement ) to deliver sustainable water and environmental services and to support urban agriculture are less cost-effective than other adaptation options but can help build climate resilience. Achieving the governance, finance and social support required to enable these synergies and to avoid trade-offs is often challenging, especially when addressing multiple objectives, and attempting appropriate sequencing and timing of interventions. {4.3.2, 4.3.4, 4.4.1, 4.5.2, 4.5.3, 4.5.4}

Though CO 2 dominates long-term warming, the reduction of warming short-lived climate forcers (SLCFs), such as methane and black carbon, can in the short term contribute significantly to limiting warming to 1.5°C above pre-industrial levels. Reductions of black carbon and methane would have substantial co-benefits ( high confidence ), including improved health due to reduced air pollution. This, in turn, enhances the institutional and socio- cultural feasibility of such actions. Reductions of several warming SLCFs are constrained by economic and social feasibility ( low evidence, high agreement ). As they are often co-emitted with CO 2 , achieving the energy, land and urban transitions necessary to limit warming to 1.5°C would see emissions of warming SLCFs greatly reduced. {2.3.3.2, 4.3.6}

Most CDR options face multiple feasibility constraints, which differ between options, limiting the potential for any single option to sustainably achieve the large-scale deployment required in the 1.5°C-consistent pathways described in Chapter 2 ( high confidence ) . Those 1.5°C pathways typically rely on bioenergy with carbon capture and storage (BECCS), afforestation and reforestation (AR), or both, to neutralize emissions that are expensive to avoid, or to draw down CO 2 emissions in excess of the carbon budget {Chapter 2}. Though BECCS and AR may be technically and geophysically feasible, they face partially overlapping yet different constraints related to land use. The land footprint per tonne of CO 2 removed is higher for AR than for BECCS, but given the low levels of current deployment, the speed and scales required for limiting warming to 1.5°C pose a considerable implementation challenge, even if the issues of public acceptance and absence of economic incentives were to be resolved ( high agreement, medium evidence ). The large potential of afforestation and the co-benefits if implemented appropriately (e.g., on biodiversity and soil quality) will diminish over time, as forests saturate ( high confidence ). The energy requirements and economic costs of direct air carbon capture and storage (DACCS) and enhanced weathering remain high ( medium evidence, medium agreement ).At the local scale, soil carbon sequestration has co-benefits with agriculture and is cost-effective even without climate policy ( high confidence ). Its potential feasibility and cost-effectiveness at the global scale appears to be more limited. {4.3.7}

Uncertainties surrounding solar radiation modification (SRM) measures constrain their potential deployment. These uncertainties include: technological immaturity; limited physical understanding about their effectiveness to limit global warming; and a weak capacity to govern, legitimize, and scale such measures. Some recent model-based analysis suggests SRM would be effective but that it is too early to evaluate its feasibility. Even in the uncertain case that the most adverse side-effects of SRM can be avoided, public resistance, ethical concerns and potential impacts on sustainable development could render SRM economically, socially and institutionally undesirable ( low agreement, medium evidence ). {4.3.8, Cross-Chapter Box 10 in this chapter}

Enabling Rapid and Far-Reaching Change

The speed of transitions and of technological change required to limit warming to 1.5°C above pre-industrial levels has been observed in the past within specific sectors and technologies {4.2.2.1}. But the geographical and economic scales at which the required rates of change in the energy, land, urban, infrastructure and industrial systems would need to take place are larger and have no documented historic precedent ( limited evidence, medium agreement ). To reduce inequality and alleviate poverty, such transformations would require more planning and stronger institutions (including inclusive markets) than observed in the past, as well as stronger coordination and disruptive innovation across actors and scales of governance. {4.3, 4.4}

Governance consistent with limiting warming to 1.5°C and the political economy of adaptation and mitigation can enable and accelerate systems transitions,behavioural change,innovation and technology deployment ( medium evidence, medium agreement ) . For 1.5°C-consistent actions, an effective governance framework would include: accountable multilevel governance that includes non- state actors, such as industry, civil society and scientific institutions; coordinated sectoral and cross-sectoral policies that enable collaborative multi-stakeholder partnerships; strengthened global-to-local financial architecture that enables greater access to finance and technology; addressing climate-related trade barriers; improved climate education and greater public awareness; arrangements to enable accelerated behaviour change; strengthened climate monitoring and evaluation systems; and reciprocal international agreements that are sensitive to equity and the Sustainable Development Goals (SDGs). System transitions can be enabled by enhancing the capacities of public, private and financial institutions to accelerate climate change policy planning and implementation, along with accelerated technological innovation, deployment and upkeep. {4.4.1, 4.4.2, 4.4.3, 4.4.4}

Behaviour change and demand-side management can significantly reduce emissions, substantially limiting the reliance on CDR to limit warming to 1.5°C {Chapter 2, 4.4.3}. Political and financial stakeholders may find climate actions more cost- effective and socially acceptable if multiple factors affecting behaviour are considered, including aligning these actions with people’s core values ( medium evidence, high agreement ). Behaviour- and lifestyle- related measures and demand-side management have already led to emission reductions around the world and can enable significant future reductions ( high confidence ). Social innovation through bottom-up initiatives can result in greater participation in the governance of systems transitions and increase support for technologies, practices and policies that are part of the global response to limit warming to 1.5°C . {Chapter 2, 4.4.1, 4.4.3, Figure 4.3}

This rapid and far-reaching response required to keep warming below 1.5°C and enhance the capacity to adapt to climate risks would require large increases of investments in low-emission infrastructure and buildings, along with a redirection of financial flows towards low-emission investments ( robust evidence, high agreement) . An estimated mean annual incremental investment of around 1.5% of global gross fixed capital formation (GFCF) for the energy sector is indicated between 2016 and 2035, as well as about 2.5% of global GFCF for other development infrastructure that could also address SDG implementation. Though quality policy design and effective implementation may enhance efficiency, they cannot fully substitute for these investments. {2.5.2, 4.2.1, 4.4.5}

Enabling this investment requires the mobilization and better integration of a range of policy instruments that include the reduction of socially inefficient fossil fuel subsidy regimes and innovative price and non-price national and international policy instruments. These would need to be complemented by de-risking financial instruments and the emergence of long-term low-emission assets.These instruments would aim to reduce the demand for carbon-intensive services and shift market preferences away from fossil fuel-based technology. Evidence and theory suggest that carbon pricing alone, in the absence of sufficient transfers to compensate their unintended distributional cross- sector, cross-nation effects, cannot reach the incentive levels needed to trigger system transitions ( robust evidence, medium agreement ). But, embedded in consistent policy packages, they can help mobilize incremental resources and provide flexible mechanisms that help reduce the social and economic costs of the triggering phase of the transition ( robust evidence, medium agreement ). {4.4.3, 4.4.4, 4.4.5}

Increasing evidence suggests that a climate-sensitive realignment of savings and expenditure towards low-emission, climate-resilient infrastructure and services requires an evolution of global and national financial systems. Estimates suggest that, in addition to climate-friendly allocation of public investments, a potential redirection of 5% to 10% of the annual capital revenues 1 is necessary for limiting warming to 1.5°C {4.4.5, Table 1 in Box 4.8}. This could be facilitated by a change of incentives for private day-to-day expenditure and the redirection of savings from speculative and precautionary investments towards long- term productive low-emission assets and services. This implies the mobilization of institutional investors and mainstreaming of climate finance within financial and banking system regulation. Access by developing countries to low-risk and low-interest finance through multilateral and national development banks would have to be facilitated ( medium evidence, high agreement ). New forms of public– private partnerships may be needed with multilateral, sovereign and sub-sovereign guarantees to de-risk climate-friendly investments, support new business models for small-scale enterprises and help households with limited access to capital. Ultimately, the aim is to promote a portfolio shift towards long-term low-emission assets that would help redirect capital away from potentially stranded assets ( medium evidence, medium agreement ). {4.4.5}

Knowledge gaps around implementing and strengthening the global response to climate change would need to be urgently resolved if the transition to a 1.5°C world is to become reality. Remaining questions include: how much can be realistically expected from innovation and behavioural and systemic political and economic changes in improving resilience, enhancing adaptation and reducing GHG emissions? How can rates of changes be accelerated and scaled up? What is the outcome of realistic assessments of mitigation and adaptation land transitions that are compliant with sustainable development, poverty eradication and addressing inequality? What are life-cycle emissions and prospects of early-stage CDR options? How can climate and sustainable development policies converge, and how can they be organised within a global governance framework and financial system, based on principles of justice and ethics (including ‘common but differentiated responsibilities and respective capabilities’ (CBDR-RC)), reciprocity and partnership? To what extent would limiting warming to 1.5°C require a harmonization of macro-financial and fiscal policies, which could include financial regulators such as central banks? How can different actors and processes in climate governance reinforce each other, and hedge against the fragmentation of initiatives? {4.1, 4.3.7, 4.4.1, 4.4.5, 4.6}

The interactions of climate change and climate responses with sustainable development including sustainable development impacts at 1.5°C and 2°C, the synergies and tradeoffs of mitigation and adaptation with the Sustainable Development Goals/SDGs, and the possibilities for sustainable and equitable low carbon, climate-resilient development pathways,

This chapter takes sustainable development as the starting point and focus for analysis. It considers the broad and multifaceted bi-directional interplay between sustainable development, including its focus on eradicating poverty and reducing inequality in their multidimensional aspects, and climate actions in a 1.5°C warmer world. These fundamental connections are embedded in the Sustainable Development Goals (SDGs). The chapter also examines synergies and trade-offs of adaptation and mitigation options with sustainable development and the SDGs and offers insights into possible pathways, especially climate-resilient development pathways towards a 1.5°C warmer world.

Sustainable Development, Poverty and Inequality in a 1.5°C Warmer World

Limiting global warming to 1.5°C rather than 2°C above pre- industrial levels would make it markedly easier to achieve many aspects of sustainable development, with greater potential to eradicate poverty and reduce inequalities ( medium evidence, high agreement ) . Impacts avoided with the lower temperature limit could reduce the number of people exposed to climate risks and vulnerable to poverty by 62 to 457 million, and lessen the risks of poor people to experience food and water insecurity, adverse health impacts, and economic losses, particularly in regions that already face development challenges ( medium evidence, medium agreement ). {5.2.2, 5.2.3} Avoided impacts expected to occur between 1.5°C and 2°C warming would also make it easier to achieve certain SDGs, such as those that relate to poverty, hunger, health, water and sanitation, cities and ecosystems (SDGs 1, 2, 3, 6, 11, 14 and 15) ( medium evidence, high agreement ). {5.2.3, Table 5.2 available at the end of the chapter}

Compared to current conditions, 1.5°C of global warming would nonetheless pose heightened risks to eradicating poverty, reducing inequalities and ensuring human and ecosystem well- being ( medium evidence, high agreement ). Warming of 1.5°C is not considered ‘safe’ for most nations, communities, ecosystems and sectors and poses significant risks to natural and human systems as compared to the current warming of 1°C ( high confidence ). {Cross- Chapter Box 12 in Chapter 5} The impacts of 1.5°C of warming would disproportionately affect disadvantaged and vulnerable populations through food insecurity, higher food prices, income losses, lost livelihood opportunities, adverse health impacts and population displacements ( medium evidence, high agreement ). {5.2.1} Some of the worst impacts on sustainable development are expected to be felt among agricultural and coastal dependent livelihoods, indigenous people, children and the elderly, poor labourers, poor urban dwellers in African cities, and people and ecosystems in the Arctic and Small Island Developing States (SIDS) ( medium evidence, high agreement ). {5.2.1, Box 5.3, Chapter 3, Box 3.5, Cross-Chapter Box 9 in Chapter 4}

Climate Adaptation and Sustainable Development

Prioritization of sustainable development and meeting the SDGs is consistent with efforts to adapt to climate change ( high  confidence ). Many strategies for sustainable development enable transformational adaptation for a 1.5°C warmer world, provided attention is paid to reducing poverty in all its forms and to promoting equity and participation in decision-making ( medium evidence, high agreement ). As such, sustainable development has the potential to significantly reduce systemic vulnerability, enhance adaptive capacity, and promote livelihood security for poor and disadvantaged populations ( high confidence ). {5.3.1}

Synergies between adaptation strategies and the SDGs are expected to hold true in a 1.5°C warmer world, across sectors  and contexts ( medium evidence, medium agreement ). Synergies between adaptation and sustainable development are significant for agriculture and health, advancing SDGs 1 (extreme poverty), 2 (hunger), 3 (healthy lives and well-being) and 6 (clean water) ( robust evidence, medium agreement ). {5.3.2} Ecosystem- and community- based adaptation, along with the incorporation of indigenous and local knowledge, advances synergies with SDGs 5 (gender equality), 10 (reducing inequalities) and 16 (inclusive societies), as exemplified in drylands and the Arctic ( high evidence, medium agreement ). {5.3.2, Box 5.1, Cross-Chapter Box 10 in Chapter 4}

Adaptation  strategies  can  result in   trade-offs   with   and among the SDGs ( medium evidence, high agreement ). Strategies that advance one SDG may create negative consequences for other SDGs, for instance SDGs 3 (health) versus 7 (energy consumption) and agricultural adaptation and SDG 2 (food security) versus SDGs 3 (health), 5 (gender equality), 6 (clean water), 10 (reducing inequalities), 14 (life below water) and 15 (life on the land) ( medium evidence, medium agreement ). {5.3.2}

Pursuing  place-specific  adaptation  pathways   towards   a   1.5°C warmer world has the potential for significant positive outcomes for well-being in countries at all levels of development ( medium evidence, high agreement ). Positive outcomes emerge when adaptation pathways (i) ensure a diversity of adaptation options based on people’s values and the trade-offs they consider acceptable, (ii) maximize synergies with sustainable development through inclusive, participatory and deliberative processes, and (iii) facilitate equitable transformation. Yet such pathways would be difficult to achieve without redistributive measures to overcome path dependencies, uneven power structures, and entrenched social inequalities ( medium evidence, high agreement ). {5.3.3}

Mitigation and Sustainable Development

The deployment of mitigation options consistent with 1.5°C pathways leads to multiple synergies across a range of sustainable development dimensions. At  the  same  time,  the rapid pace and magnitude of change that would be required to limit warming to 1.5°C, if not carefully managed, would lead to trade-offs with some sustainable development dimensions ( high confidence ). The number of synergies between mitigation response options and sustainable development exceeds the number of trade- offs in energy demand and supply sectors; agriculture, forestry and other land use (AFOLU); and for oceans ( very high confidence ). {Figure 5.2, Table 5.2 available at the end of the chapter} The 1.5°C pathways indicate robust synergies, particularly for the SDGs 3 (health), 7 (energy), 12 (responsible consumption and production) and 14 (oceans) ( very high confidence ). {5.4.2, Figure 5.3} For SDGs 1 (poverty), 2 (hunger), 6 (water) and 7 (energy), there is a risk of trade-offs or negative side effects from stringent mitigation actions compatible with 1.5°C of warming ( medium evidence, high agreement ). {5.4.2}

Appropriately designed mitigation actions to reduce energy demand can advance multiple SDGs simultaneously. Pathways compatible with 1.5°C that feature low energy demand show the most pronounced synergies and the lowest number of trade-offs with respect to sustainable development and the SDGs ( very high confidence ). Accelerating energy efficiency in all sectors has synergies with SDGs 7 (energy), 9 (industry, innovation and infrastructure), 11 (sustainable cities and communities), 12 (responsible consumption and production), 16 (peace, justice and strong institutions), and 17 (partnerships for the goals) ( robust evidence, high agreement ). {5.4.1, Figure 5.2, Table 5.2} Low-demand pathways, which would reduce or completely avoid the reliance on bioenergy with carbon capture and storage (BECCS) in 1.5°C pathways, would result in significantly reduced pressure on food security, lower food prices and fewer people at risk of hunger ( medium evidence, high agreement ). {5.4.2, Figure 5.3}

The impacts of carbon dioxide removal options on SDGs depend on the type of options and the scale of deployment ( high confidence ). If poorly implemented, carbon dioxide removal (CDR) options such as bioenergy, BECCS and AFOLU would lead to trade- offs. Appropriate design and implementation requires considering local people’s needs, biodiversity and other sustainable development dimensions ( very high confidence ). {5.4.1.3, Cross-Chapter Box 7 in Chapter 3}

The design of the mitigation portfolios and policy instruments     to limit warming to 1.5°C will largely determine the overall synergies and trade-offs between mitigation and sustainable development ( very high confidence ). Redistributive policies that shield the poor and vulnerable can resolve trade-offs for a range of SDGs ( medium evidence, high agreement ). Individual mitigation options are associated with both positive and negative interactions with the SDGs ( very high confidence ). {5.4.1} However, appropriate choices across the mitigation portfolio can help to maximize positive side effects while minimizing negative side effects ( high confidence ). {5.4.2, 5.5.2} Investment needs for complementary policies resolving trade-offs with a range of SDGs are only a small fraction of the overall mitigation investments in 1.5°C pathways ( medium evidence, high agreement ). {5.4.2, Figure 5.4} Integration of mitigation with adaptation and sustainable development compatible with 1.5°C warming requires a systems perspective ( high confidence ). {5.4.2, 5.5.2}

Mitigation consistent with 1.5°C of warming  create  high  risks  for sustainable development in countries with high dependency  on fossil fuels for revenue and employment generation ( high confidence ). These risks are caused by the reduction of global demand affecting mining activity and export revenues and challenges to rapidly decrease high carbon intensity of the domestic economy ( robust evidence, high agreement ). {5.4.1.2, Box 5.2} Targeted policies that promote diversification of the economy and the energy sector could ease this transition ( medium evidence, high agreement ). {5.4.1.2, Box 5.2}

Sustainable Development Pathways to 1.5°C

Sustainable development broadly supports and often  enables  the fundamental societal and systems  transformations that  would be required for limiting warming to 1.5°C above pre- industrial levels ( high confidence ). Simulated pathways that feature the most sustainable worlds (e.g., Shared Socio-Economic Pathways (SSP) 1) are associated with relatively lower mitigation and adaptation challenges and limit warming to 1.5°C at comparatively lower mitigation costs. In contrast, development pathways with high fragmentation, inequality and poverty (e.g., SSP3) are associated with comparatively higher mitigation and adaptation challenges. In such pathways, it is not possible to limit warming to 1.5°C for the vast majority of the integrated assessment models ( medium evidence, high agreement ). {5.5.2} In all SSPs, mitigation costs substantially increase in 1.5°C pathways compared to 2°C pathways. No pathway in the literature integrates or achieves all 17 SDGs ( high confidence ). {5.5.2} Real-world experiences at the project level show that the actual integration between adaptation, mitigation and sustainable development is challenging as it requires reconciling trade-offs across sectors and spatial scales ( very high confidence ). {5.5.1}

Without   societal   transformation   and    rapid    implementation of  ambitious  greenhouse  gas   reduction   measures,  pathways to limiting warming to 1.5°C and achieving sustainable development  will  be  exceedingly  difficult,  if   not   impossible, to achieve ( high confidence ). The potential for pursuing such pathways differs between and within nations and regions, due to different development trajectories, opportunities and challenges ( very high confidence ). {5.5.3.2, Figure 5.1} Limiting warming to 1.5°C would require all countries and non-state actors to strengthen their contributions without delay. This could be achieved through sharing efforts based on bolder and more committed cooperation, with support for those with the least capacity to adapt, mitigate and transform ( medium evidence, high agreement ). {5.5.3.1, 5.5.3.2} Current efforts towards reconciling low-carbon trajectories and reducing inequalities, including those that avoid difficult trade-offs associated with transformation, are partially successful yet demonstrate notable obstacles ( medium evidence, medium agreement ). {5.5.3.3, Box 5.3, Cross-Chapter Box 13 in this chapter}

Social justice and equity are core aspects of climate-resilient development pathways for transformational social change. Addressing challenges  and  widening  opportunities  between and  within  countries  and  communities  would  be  necessary   to achieve sustainable  development  and  limit  warming  to  1.5°C, without making the poor and disadvantaged worse  off ( high confidence ). Identifying and navigating inclusive and socially acceptable pathways towards low-carbon, climate-resilient futures is a challenging yet important endeavour, fraught with moral, practical and political difficulties and inevitable trade-offs ( very high confidence ). {5.5.2, 5.5.3.3, Box 5.3} It entails deliberation and  problem-solving processes to negotiate societal values, well-being, risks and resilience and to determine what is desirable and fair, and to whom ( medium evidence, high agreement ). Pathways that encompass joint, iterative planning and transformative visions, for instance in Pacific SIDS like Vanuatu and in urban contexts, show potential for liveable and sustainable futures ( high confidence ). {5.5.3.1, 5.5.3.3, Figure 5.5, Box 5.3, Cross-Chapter Box 13 in this chapter}

The fundamental societal and systemic changes to achieve sustainable development, eradicate poverty and reduce inequalities while limiting warming to 1.5°C would require  meeting a set of institutional, social, cultural, economic and technological conditions ( high confidence ). The  coordination and monitoring of policy actions across sectors and spatial scales is essential to support sustainable development in 1.5°C warmer conditions ( very high confidence ). {5.6.2, Box 5.3} External funding and technology transfer better support these efforts when they consider recipients’ context-specific needs ( medium evidence, high agreement ). {5.6.1} Inclusive processes can facilitate transformations by ensuring participation, transparency, capacity building and iterative social learning ( high confidence ). {5.5.3.3, Cross-Chapter Box 13, 5.6.3} Attention to power asymmetries and unequal opportunities for development, among and within countries, is key to adopting 1.5°C-compatible development pathways that benefit all populations ( high confidence ). {5.5.3, 5.6.4, Box 5.3} Re-examining individual and collective values could help spur urgent, ambitious and cooperative change ( medium evidence, high agreement ). {5.5.3, 5.6.5}

This glossary defines some specific terms as the Lead Authors intend them to be interpreted in the context of this report. Blue, italicized words indicate that the term is defined in the Glossary.

Note that subterms are in italics beneath main terms.

• I Introduction
• A Understanding Global Warming of 1.5°C*
• B Projected Climate Change, Potential Impacts and Associated Risks
• C Emission Pathways and System Transitions Consistent with 1.5°C Global Warming
• D Strengthening the Global Response in the Context of Sustainable Development and Efforts to Eradicate Poverty
• + Core Concepts Central to this Special Report
• + Acknowledgements
• SD SPM Downloads

Framing and Context

• ES Executive Summary
• 1.1.1 Equity and a 1.5°C Warmer World
• 1.1.2 Eradication of Poverty
• 1.1.3 Sustainable Development and a 1.5°C Warmer World
• 1.2.1.1 Definition of global average temperature
• 1.2.1.2 Choice of reference period
• 1.2.1.3 Total versus human-induced warming and warming rates
• 1.2.2 Global versus Regional and Seasonal Warming
• 1.2.3.1 Pathways remaining below 1.5°C
• 1.2.3.2 Pathways temporarily exceeding 1.5°C
• 1.2.3.3 Impacts at 1.5°C warming associated with different pathways: transience versus stabilisation
• 1.2.4 Geophysical Warming Commitment
• 1.3.1 Definitions
• 1.3.2 Drivers of Impacts
• 1.3.3 Uncertainty and Non-Linearity of Impacts
• 1.4.1 Classifying Response Options
• 1.4.2 Governance, Implementation and Policies
• 1.4.3 Transformation, Transformation Pathways, and Transition: Evaluating Trade-Offs and Synergies Between Mitigation, Adaptation and Sustainable Development Goals
• 1.5.1 Knowledge Sources and Evidence Used in the Report
• 1.5.2 Assessment Frameworks and Methodologies
• 1.6 Confidence, Uncertainty and Risk
• 1.7 Storyline of the Report
• FAQs Frequently Asked Questions
• SM Supplementary Material
• CD Chapter Downloads

Mitigation pathways compatible with 1.5°C in the context of sustainable development

• 2.1.1 Mitigation Pathways Consistent with 1.5°C
• 2.1.2 The Use of Scenarios
• 2.1.3 New Scenario Information since AR5
• 2.1.4 Utility of Integrated Assessment Models (IAMs) in the Context of this Report
• 2.2.1.1 Geophysical uncertainties: non-CO 2 forcing agents
• 2.2.1.2 Geophysical uncertainties: climate and Earth system feedbacks
• 2.2.2.1 Carbon budget estimates
• 2.2.2.2 CO 2 and non-CO 2 contributions to the remaining carbon budget
• 2.3.1.1 Socio-economic drivers and the demand for energy and land in 1.5°C pathways
• 2.3.1.2 Mitigation options in 1.5°C pathways
• 2.3.1.3 Policy assumptions in 1.5°C pathways
• 2.3.2.1 Variation in system transformations underlying 1.5°C pathways
• 2.3.2.2 Pathways keeping warming below 1.5°C or temporarily overshooting it
• 2.3.3.1 Emissions of long-lived climate forcers
• 2.3.3.2 Emissions of short-lived climate forcers and fluorinated gases
• 2.3.4.1 CDR technologies and deployment levels in 1.5°C pathways
• 2.3.4.2 Sustainability implications of CDR deployment in 1.5°C pathways
• 2.3.5 Implications of Near-Term Action in 1.5°C Pathways
• 2.4.1 Energy System Transformation
• 2.4.2.1 Evolution of primary energy contributions over time
• 2.4.2.2 Evolution of electricity supply over time
• 2.4.2.3 Deployment of carbon capture and storage
• 2.4.3.1 Industry
• 2.4.3.2 Buildings
• 2.4.3.3 Transport
• 2.4.4 Land-Use Transitions and Changes in the Agricultural Sector
• 2.5.1 Policy Frameworks and Enabling Conditions
• 2.5.2.1 Price of carbon emissions
• 2.5.2.2 Investments
• 2.5.3 Sustainable Development Features of 1.5°C Pathways
• 2.6.1 Geophysical Understanding
• 2.6.2 Integrated Assessment Approaches
• 2.6.3 Carbon Dioxide Removal (CDR)

Impacts of 1.5ºC global warming on natural and human systems

• 3.1 About the Chapter
• 3.2.1 How are Changes in Climate and Weather at 1.5°C versus Higher Levels of Warming Assessed?
• 3.2.2 How are Potential Impacts on Ecosystems Assessed at 1.5°C versus Higher Levels of Warming?
• 3.3.1 Global Changes in Climate
• 3.3.2.1 Observed and attributed changes in regional temperature means and extremes
• 3.3.2.2 Projected changes in regional temperature means and extremes at 1.5°C versus 2°C of global warming
• 3.3.3.1 Observed and attributed changes in regional precipitation
• 3.3.3.2 Projected changes in regional precipitation at 1.5°C versus 2°C of global warming
• 3.3.4.1 Observed and attributed changes
• 3.3.4.2 Projected changes in drought and dryness at 1.5°C versus 2°C
• 3.3.5.1 Observed and attributed changes in runoff and river flooding
• 3.3.5.2 Projected changes in runoff and river flooding at 1.5°C versus 2°C of global warming
• 3.3.6 Tropical Cyclones and Extratropical Storms
• 3.3.7 Ocean Circulation and Temperature
• 3.3.8 Sea Ice
• 3.3.9 Sea Level
• 3.3.10 Ocean Chemistry
• 3.3.11 Global Synthesis
• 3.4.1 Introduction
• 3.4.2.1 Water availability
• 3.4.2.2 Extreme hydrological events (floods and droughts)
• 3.4.2.3 Groundwater
• 3.4.2.4 Water quality
• 3.4.2.5 Soil erosion and sediment load
• 3.4.3.1 Biome shifts
• 3.4.3.2 Changes in phenology
• 3.4.3.3 Changes in species range, abundance and extinction
• 3.4.3.4 Changes in ecosystem function, biomass and carbon stocks
• 3.4.3.5 Regional and ecosystem-specific risks
• 3.4.3.6 Summary of implications for ecosystem services
• 3.4.4.1 Observed impacts
• 3.4.4.2 Warming and stratification of the surface ocean
• 3.4.4.3 Storms and coastal runoff
• 3.4.4.4 Ocean circulation
• 3.4.4.5 Ocean acidification
• 3.4.4.6 Deoxygenation
• 3.4.4.7 Loss of sea ice
• 3.4.4.8 Sea level rise
• 3.4.4.9 Projected risks and adaptation options for oceans under global warming of 1.5°C or 2°C above pre-industrial levels
• 3.4.4.10 Framework organisms (tropical corals, mangroves and seagrass)
• 3.4.4.11 Ocean foodwebs (pteropods, bivalves, krill and fin fish)
• 3.4.4.12 Key ecosystem services (e.g., carbon uptake, coastal protection, and tropical coral reef recreation)
• 3.4.5.1 Global / sub-global scale
• 3.4.5.2 Cities
• 3.4.5.3 Small islands
• 3.4.5.4 Deltas and estuaries
• 3.4.5.5 Wetlands
• 3.4.5.6 Other coastal settings
• 3.4.5.7 Adapting to coastal change
• 3.4.6.1 Crop production
• 3.4.6.2 Livestock production
• 3.4.6.3 Fisheries and aquaculture production
• 3.4.7.1 Projected risk at 1.5°C and 2°C of global warming
• 3.4.8 Urban Areas
• 3.4.9.1 Tourism
• 3.4.9.2 Energy systems
• 3.4.9.3 Transportation
• 3.4.10.1 Livelihoods and poverty
• 3.4.10.2 The changing structure of communities: migration, displacement and conflict
• 3.4.11 Interacting and Cascading Risks
• 3.4.12 Summary of Projected Risks at 1.5°C and 2°C of Global Warming
• 3.4.13 Synthesis of Key Elements of Risk
• 3.5.1 Introduction
• 3.5.2.1 RFC 1 – Unique and threatened systems
• 3.5.2.2 RFC 2 – Extreme weather events
• 3.5.2.3 RFC 3 – Distribution of impacts
• 3.5.2.4 RFC 4 – Global aggregate impacts
• 3.5.2.5 RFC 5 – Large-scale singular events
• 3.5.3 Regional Economic Benefit Analysis for the 1.5°C versus 2°C Global Goals
• 3.5.4.1 Arctic sea ice
• 3.5.4.2 Arctic land regions
• 3.5.4.3 Alpine regions
• 3.5.4.4 Southeast Asia
• 3.5.4.5 Southern Europe and the Mediterranean
• 3.5.4.6 West Africa and the Sahel
• 3.5.4.7 Southern Africa
• 3.5.4.8 Tropics
• 3.5.4.9 Small islands
• 3.5.4.10 Fynbos and shrub biomes
• 3.5.5.1 Arctic sea ice
• 3.5.5.2 Tundra
• 3.5.5.3 Permafrost
• 3.5.5.4 Asian monsoon
• 3.5.5.5 West African monsoon and the Sahel
• 3.5.5.6 Rainforests
• 3.5.5.7 Boreal forests
• 3.5.5.8 Heatwaves, unprecedented heat and human health
• 3.5.5.9 Agricultural systems: key staple crops
• 3.5.5.10 Agricultural systems: livestock in the tropics and subtropics
• 3.6.1 Gradual versus Overshoot in 1.5°C Scenarios
• 3.6.2.1 Risks arising from land-use changes in mitigation pathways
• 3.6.2.2 Biophysical feedbacks on regional climate associated with land-use changes
• 3.6.2.3 Atmospheric compounds (aerosols and methane)
• 3.6.3.1 Sea ice
• 3.6.3.2 Sea level
• 3.6.3.3 Permafrost
• 3.7.1 Gaps in Methods and Tools
• 3.7.2.1 Earth systems and 1.5°C of global warming
• 3.7.2.2 Physical and chemical characteristics of a 1.5°C warmer world
• 3.7.2.3 Terrestrial and freshwater systems
• 3.7.2.4 Ocean Systems
• 3.7.2.5 Human systems

Strengthening and implementing the global response

• 4.1 Accelerating the Global Response to Climate Change
• 4.2.1.1 Challenges and Opportunities for Mitigation Along the Reviewed Pathways
• 4.2.1.2 Implications for Adaptation Along the Reviewed Pathways
• 4.2.2.1 Mitigation: historical rates of change and state of decoupling
• 4.2.2.2 Transformational adaptation
• 4.2.2.3 Disruptive innovation
• 4.3.1.1 Renewable electricity: solar and wind
• 4.3.1.2 Bioenergy and biofuels
• 4.3.1.3 Nuclear energy
• 4.3.1.4 Energy storage
• 4.3.1.5 Options for adapting electricity systems to 1.5°C
• 4.3.1.6 Carbon dioxide capture and storage in the power sector
• 4.3.2.1 Agriculture and food
• 4.3.2.2 Forests and other ecosystems
• 4.3.2.3 Coastal systems
• 4.3.3.1 Urban energy systems
• 4.3.3.2 Urban infrastructure, buildings and appliances
• 4.3.3.3 Urban transport and urban planning
• 4.3.3.4 Electrification of cities and transport
• 4.3.3.5 Shipping, freight and aviation
• 4.3.3.6 Climate-resilient land use
• 4.3.3.8 Sustainable urban water and environmental services
• 4.3.3.7 Green urban infrastructure and ecosystem services
• 4.3.4.1 Energy efficiency
• 4.3.4.2 Substitution and circularity
• 4.3.4.3 Bio-based feedstocks
• 4.3.4.4 Electrification and hydrogen
• 4.3.4.5 CO2 capture, utilization and storage in industry
• 4.3.5.1 Disaster risk management (DRM)
• 4.3.5.2 Risk sharing and spreading
• 4.3.5.3 Education and learning
• 4.3.5.4 Population health and health system adaptation options
• 4.3.5.5 Indigenous knowledge
• 4.3.5.6 Human migration
• 4.3.5.7 Climate services
• 4.3.6 Short-Lived Climate Forcers
• 4.3.7.1 Bioenergy with carbon capture and storage (BECCS)
• 4.3.7.2 Afforestation and reforestation (AR)
• 4.3.7.3 Soil carbon sequestration and biochar
• 4.3.7.4 Enhanced weathering (EW) and ocean alkalinization
• 4.3.7.5 Direct air carbon dioxide capture and storage (DACCS)
• 4.3.7.6 Ocean fertilization
• 4.3.8.1 Governance and institutional feasibility
• 4.3.8.2 Economic and technological feasibility
• 4.3.8.3 Social acceptability and ethics
• 4.4.1.1 Institutions and their capacity to invoke far-reaching and rapid change
• 4.4.1.2 International governance
• 4.4.1.3 Sub-national governance
• 4.4.1.4 Interactions and processes for multilevel governance
• 4.4.2.1 Capacity for policy design and implementation
• 4.4.2.2 Monitoring, reporting, and review institutions
• 4.4.2.3 Financial institutions
• 4.4.2.4 Co-operative institutions and social safety nets
• 4.4.3.1 Factors related to climate actions
• 4.4.3.2 Strategies and policies to promote actions on climate change
• 4.4.3.3 Acceptability of policy and system changes
• 4.4.4.1 The nature of technological innovations
• 4.4.4.2 Technologies as enablers of climate action
• 4.4.4.3 The role of government in 1.5°C-consistent climate technology policy
• 4.4.4.4 Technology transfer in the Paris Agreement
• 4.4.5.1 The core challenge: cost-efficiency, coordination of expectations and distributive effects
• 4.4.5.2 Carbon pricing: necessity and constraints
• 4.4.5.3 Regulatory measures and information flows
• 4.4.5.4 Scaling up climate finance and de-risking low-emission investments
• 4.4.5.5 Financial challenge for basic needs and adaptation finance
• 4.4.5.6 Towards integrated policy packages and innovative forms of financial cooperation
• 4.5.1 Assessing Feasibility of Options for Accelerated Transitions
• 4.5.2.1 Assessing mitigation options for limiting warming to 1.5˚C against feasibility dimensions
• Enabling conditions for implementation of mitigation options towards 1.5˚C
• 4.5.3.1 Feasible adaptation options
• 4.5.3.2 Monitoring and evaluation
• 4.5.4 Synergies and Trade-Offs between Adaptation and Mitigation
• 4.6 Knowledge Gaps and Key Uncertainties

Sustainable Development, Poverty Eradication and Reducing Inequalities

• 5.1.1 Sustainable Development, SDGs, Poverty Eradication and Reducing Inequalities
• 5.1.2 Pathways to 1.5°C
• 5.1.3 Types of Evidence
• 5.2.1 Impacts and Risks of a 1.5°C Warmer World: Implications for Poverty and Livelihoods
• 5.2.2 Avoided Impacts of 1.5°C versus 2°C Warming for Poverty and Inequality
• 5.2.3 Risks from 1.5°C versus 2°C Global Warming and the Sustainable Development Goals
• 5.3.1 Sustainable Development in Support of Climate Adaptation
• 5.3.2 Synergies and Trade-Offs between Adaptation Options and Sustainable Development
• 5.3.3 Adaptation Pathways towards a 1.5°C Warmer World and Implications for Inequalities
• 5.4.1.1 Energy Demand: Mitigation Options to Accelerate Reduction in Energy Use and Fuel Switch
• 5.4.1.2 Energy Supply: Accelerated Decarbonization
• 5.4.1.3 Land-based agriculture, forestry and ocean: mitigation response options and carbon dioxide removal
• 5.4.2.1 Air pollution and health
• 5.4.2.2 Food security and hunger
• 5.4.2.3 Lack of energy access/energy poverty
• 5.4.2.4 Water security
• 5.5.1 Integration of Adaptation, Mitigation and Sustainable Development
• 5.5.2 Pathways for Adaptation, Mitigation and Sustainable Development
• 5.5.3.1 Transformations, equity and well-being
• 5.5.3.2 Development trajectories, sharing of efforts and cooperation
• 5.5.3.3 Country and community strategies and experiences
• 5.6.1 Finance and Technology Aligned with Local Needs
• 5.6.2 Integration of Institutions
• 5.6.3 Inclusive Processes
• 5.6.4 Attention to Issues of Power and Inequality
• 5.6.5 Reconsidering Values
• 5.7 Synthesis and Research Gaps
• GD Glossary Downloads

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Global Warming: A Very Short Introduction (2nd edn)

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Global warming is arguably the most critical and controversial issue facing the world in the twenty-first century. Global Warming: A Very Short Introduction provides a concise and accessible explanation of the key topics in the debate: how and why changes are occurring, setting these changes in the context of past global climate change, looking at the predicted impact of climate change, exploring the political controversies of recent years, and explaining the proposed solutions. Recent developments from US policy to the UK Climate Change Bill, and where we now stand with the Kyoto Protocol are described.

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UN climate report: It’s ‘now or never’ to limit global warming to 1.5 degrees

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A new flagship UN report on climate change out Monday indicating that harmful carbon emissions from 2010-2019 have never been higher in human history, is proof that the world is on a “fast track” to disaster, António Guterres has warned , with scientists arguing that it’s ‘now or never’ to limit global warming to 1.5 degrees.

Reacting to the latest findings of the Intergovernmental Panel on Climate Change ( IPCC ), the UN Secretary-General insisted that unless governments everywhere reassess their energy policies, the world will be uninhabitable.

His comments reflected the IPCC’s insistence that all countries must reduce their fossil fuel use substantially, extend access to electricity, improve energy efficiency and increase the use of alternative fuels, such as hydrogen.

Unless action is taken soon, some major cities will be under water, Mr. Guterres said in a video message, which also forecast “unprecedented heatwaves, terrifying storms, widespread water shortages and the extinction of a million species of plants and animals”.

Horror story

The UN chief added: “This is not fiction or exaggeration. It is what science tells us will result from our current energy policies. We are on a pathway to global warming of more than double the 1.5-degree (Celsius, or 2.7-degrees Fahreinheit) limit ” that was agreed in Paris in 2015.

Providing the scientific proof to back up that damning assessment, the IPCC report – written by hundreds of leading scientists and agreed by 195 countries - noted that greenhouse gas emissions generated by human activity, have increased since 2010 “across all major sectors globally”.

In an op-ed article penned for the Washington Post, Mr. Guterres described the latest IPCC report as "a litany of broken climate promises ", which revealed a "yawning gap between climate pledges, and reality."

He wrote that high-emitting governments and corporations, were not just turning a blind eye, "they are adding fuel to the flames by continuing to invest in climate-choking industries. Scientists warn that we are already perilously close to tipping points that could lead to cascading and irreversible climate effects."

Urban issue

An increasing share of emissions can be attributed to towns and cities , the report’s authors continued, adding just as worryingly, that emissions reductions clawed back in the last decade or so “have been less than emissions increases, from rising global activity levels in industry, energy supply, transport, agriculture and buildings”.

Striking a more positive note - and insisting that it is still possible to halve emissions by 2030 - the IPCC urged governments to ramp up action to curb emissions.

The UN body also welcomed the significant decrease in the cost of renewable energy sources since 2010, by as much as 85 per cent for solar and wind energy, and batteries.

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Encouraging climate action

“We are at a crossroads. The decisions we make now can secure a liveable future,” said IPCC Chair Hoesung Lee. “ I am encouraged by climate action being taken in many countries . There are policies, regulations and market instruments that are proving effective. If these are scaled up and applied more widely and equitably, they can support deep emissions reductions and stimulate innovation.”

To limit global warming to around 1.5C (2.7°F), the IPCC report insisted that global greenhouse gas emissions would have to peak “before 2025 at the latest, and be reduced by 43 per cent by 2030”.

Methane would also need to be reduced by about a third, the report’s authors continued, adding that even if this was achieved, it was “almost inevitable that we will temporarily exceed this temperature threshold”, although the world “could  return to below it by the end of the century”.

Now or never

“ It’s now or never, if we want to limit global warming to 1.5°C (2.7°F); without immediate and deep emissions reductions across all sectors, it will be impossible ,” said Jim Skea, Co-Chair of IPCC Working Group III, which released the latest report.

Global temperatures will stabilise when carbon dioxide emissions reach net zero. For 1.5C (2.7F), this means achieving net zero carbon dioxide emissions globally in the early 2050s; for 2C (3.6°F), it is in the early 2070s, the IPCC report states.

“This assessment shows that limiting warming to around 2C (3.6F) still requires global greenhouse gas emissions to peak before 2025 at the latest, and be reduced by a quarter by 2030.”

Policy base

A great deal of importance is attached to IPCC assessments because they provide governments with scientific information that they can use to develop climate policies.

They also play a key role in international negotiations to tackle climate change.

Among the sustainable and emissions-busting solutions that are available to governments, the IPCC report emphasised that rethinking how cities and other urban areas function in future could help significantly in mitigating the worst effects of climate change.

“These (reductions) can be achieved through lower energy consumption (such as by creating compact, walkable cities), electrification of transport in combination with low-emission energy sources, and enhanced carbon uptake and storage using nature,” the report suggested. “There are options for established, rapidly growing and new cities,” it said.

Echoing that message, IPCC Working Group III Co-Chair, Priyadarshi Shukla, insisted that “the right policies, infrastructure and technology…to enable changes to our lifestyles and behaviour, can result in a 40 to 70 per cent reduction in greenhouse gas emissions by 2050. “The evidence also shows that these lifestyle changes can improve our health and wellbeing.”

• climate action
• Intergovernmental Panel on Climate Change (IPCC)