quantitative research title about global warming

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• Published: 04 January 2021

Climate change and health in North America: literature review protocol

• Sherilee L. Harper   ORCID: orcid.org/0000-0001-7298-8765 1 ,
• Ashlee Cunsolo 2 ,
• Amreen Babujee 1 ,
• Shaugn Coggins 1 ,
• Mauricio Domínguez Aguilar 3 &
• Carlee J. Wright 1  

Systematic Reviews volume  10 , Article number:  3 ( 2021 ) Cite this article

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Climate change is a defining issue and grand challenge for the health sector in North America. Synthesizing evidence on climate change impacts, climate-health adaptation, and climate-health mitigation is crucial for health practitioners and decision-makers to effectively understand, prepare for, and respond to climate change impacts on human health. This protocol paper outlines our process to systematically conduct a literature review to investigate the climate-health evidence base in North America.

A search string will be used to search CINAHL®, Web of Science™, Scopus®, Embase® via Ovid, and MEDLINE® via Ovid aggregator databases. Articles will be screened using inclusion/exclusion criteria by two independent reviewers. First, the inclusion/exclusion criteria will be applied to article titles and abstracts, and then to the full articles. Included articles will be analyzed using quantitative and qualitative methods.

This protocol describes review methods that will be used to systematically and transparently create a database of articles published in academic journals that examine climate-health in North America.

Peer Review reports

The direct and indirect impacts of climate change on human health continue to be observed globally, and these wide-ranging impacts are projected to continue to increase and intensify this century [ 1 , 2 ]. The direct climate change effects on health include rising temperatures, which increase heat-related mortality and morbidity [ 3 , 4 , 5 ], and increased frequency and intensity of storms, resulting in increased injury, death, and psychological stressors [ 2 , 6 , 7 , 8 ]. Indirect climate change impacts on health occur via altered environmental conditions, such as climate change impacts on water quality and quantity, which increase waterborne disease [ 9 , 10 , 11 , 12 , 13 ]; shifting ecosystems, which increase the risk of foodborne disease [ 14 , 15 , 16 ], exacerbate food and nutritional security [ 17 , 18 ], and change the range and distribution of vectors that cause vectorborne disease [ 19 , 20 ]; and place-based connections and identities, leading to psycho-social stressors and potential increases in negative mental health outcomes and suicide [ 6 , 8 ]. These wide-ranging impacts are not uniformly or equitably distributed: children, the elderly, those with pre-existing health conditions, those experiencing lower socio-economic conditions, women, and those with close connections to and reliance upon the local environment (e.g. Indigenous Peoples, farmers, fishers) often experience higher burdens of climate-health impacts [ 1 , 2 , 21 ]. Indeed, climate change impacts on human health not only are dependent on exposure to climatic and environmental changes, but also depend on climate change sensitivity and adaptive capacity—both of which are underpinned by the social determinants of health [ 1 , 22 , 23 ].

The inherent complexity, great magnitude, and widespread, inequitable, and intersectional distribution of climate change impacts on health present an urgent and grand challenge for the health sector this century [ 2 , 24 , 25 ]. Climate-health research and evidence is critical for informing effective, equitable, and timely adaptation responses and strategies. For instance, research continues to inform local to international climate change and health vulnerability and adaptation assessments [ 26 ]. However, to create evidence-based climate-health adaptation strategies, health practitioners, researchers, and policy makers must sift and sort through vast and often unmanageable amounts of information. Indeed, the global climate-health evidence base has seen exponential growth in recent years, with tens of thousands of articles published globally this century [ 22 , 25 , 27 , 28 ]. Even when resources are available to parse through the evidence base, the available research evidence may not be locally pertinent to decision-makers, may provide poor quality of evidence, may exclude factors important to decision-makers, may overlook temporal and geographical scales over which decision-makers have impact, and/or may not produce information in a timely manner [ 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 ].

Literature reviews that utilize systematic methods present a tool to efficiently and effectively integrate climate-health information and provide data to support evidence-based decision-making. Furthermore, literature reviews that use systematic methods are replicable and transparent, reduce bias, and are ultimately intended to improve reliability and accuracy of conclusions. As such, systematic approaches to identify, explore, evaluate, and synthesize literature separates insignificant, less rigorous, or redundant literature from the critical and noteworthy studies that are worthy of exploration and consideration [ 38 ]. As such, a systematic approach to synthesizing the climate-health literature provides invaluable information and adds value to the climate-health evidence base from which decision-makers can draw from. Therefore, we aim to systematically and transparently create a database of articles published in academic journals that examine climate-health in North America. As such, we outline our protocol that will be used to systematically identify and characterize literature at the climate-health nexus in North America.

This protocol was designed in accordance with the Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA) Guidelines [ 39 , 40 ] and presented in accordance with the PRISMA-P checklist.

Research questions

Research on climate change and human health encompasses a diverse range of health outcomes, climate change exposures, populations, and study designs. Given the breadth and depth of information needed by health practitioners and decision-makers, a variety of research questions will be examined (Table 1 ).

Search strategy

The search strategy, including the search string development and selection of databases, was developed in consultation with a research librarian and members of the research team (SLH, AC, and MDA). The search string contains terms related to climate change [ 41 , 42 ], human health outcomes [ 1 , 25 , 43 , 44 ], and study location (Table 2 ). Given the interdisciplinary nature of the climate-health nexus and to ensure that our search is comprehensive, the search string will be used to search five academic databases:

CINAHL® will be searched to capture unique literature not found in other databases on common disease and injury conditions, as well as other health topics;

Web of Science™ will be searched to capture a wide range of multi-disciplinary literature;

Scopus® will be searched to capture literature related to medicine, technology, science, and social sciences;

Embase® via Ovid will be searched to capture a vast range of biomedical sciences journals; and

MEDLINE® via Ovid will be searched to capture literature on biomedical and health sciences.

No language restrictions will be placed on the search. Date restrictions will be applied to capture literature published on or after 01 January 2013, in order to capture literature published after the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (which assessed literature accepted for publication prior to 31 August 2013). An initial test search was conducted on June 10, 2019, and updated on February 14, 2020; however, the search will be updated to include literature published within the most recent full calendar year prior to publication.

To explore the sensitivity of our search and capture any missed articles, (1) a snowball search will be conducted on the reference lists of all the literature that meet the inclusion criteria and (2) a hand search of three relevant disciplinary journals will be conducted:

Environmental Health Perspectives , an open access peer-reviewed journal that is a leading disciplinary journal within environmental health sciences;

The Lancet , a peer-reviewed journal that is the leading disciplinary journal within public health sciences; and

Climatic Change , a peer-reviewed journal covering cross-disciplinary literature that is a leading disciplinary journal for climate change research.

Citations will be downloaded from the databases and uploaded into Mendeley™ reference management software to facilitate reference management, article retrieval, and removal of duplicate citations. Then, de-duplicated citations will be uploaded into DistillerSR® to facilitate screening.

Article selection

Inclusion and exclusion criteria.

To be included, articles must evaluate or examine the intersection of climate change and human health in North America (Fig. 1 ). Health is defined to include physical, mental, emotional, and social health and wellness [ 1 , 25 , 43 , 44 ] (Fig. 1 ). This broad definition will be used to examine the nuanced and complex direct and indirect impacts of climate change on human health. To examine the depth and breadth of climate change impacts on health, climate change contexts are defined to include seasonality, weather parameters, extreme weather events, climate, climate change, climate variability, and climate hazards [ 41 , 42 ] (Fig. 1 ). However, articles that discuss climate in terms of indoor work environments, non-climate hazards due to geologic events (e.g. earthquakes), and non-anthropogenic climate change (e.g. due to volcanic eruptions) will be excluded. This broad definition of climate change contexts will be used in order to examine the wide range and complexity of climate change impacts on human health. To be included, articles need to explicitly link health outcomes to climate change in the goal statement, methods section, and/or results section of the article. Therefore, articles that discuss both human health and climate change—but do not link the two together—will be excluded. The climate-health research has to take place in North America to be included. North America is defined to include Canada, the USA, and Mexico in order to be consistent with the IPCC geographical classifications; that is, in the Fifth Assessment Report, the IPCC began confining North America to include Canada, Mexico, and the USA [ 45 ] (Fig. 1 ). Articles published in any language will be eligible for inclusion. Articles need to be published online on or after 01 January 2013 to be included. No restrictions will be placed on population type (i.e. all human studies will be eligible for inclusion).

Inclusion and exclusion criteria to review climate change and health literature in North America

Level 1 screening

The title and abstract of each citation will be examined for relevance. A stacked questionnaire will be used to screen the titles and abstracts; that is, when a criterion is not met, the subsequent criteria will not be assessed. When all inclusion criteria are met and/or it is unclear whether or not an inclusion criterion is met (e.g. “unsure”), the article will proceed to Level 2 screening. If the article meets any exclusion criteria, it will not proceed to Level 2 screening. Level 1 screening will be completed by two independent reviewers, who will meet to resolve any conflicts via discussion. The level of agreement between reviewers will be evaluated by dividing the total number of conflicts by the total number of articles screened for Level 1.

Level 2 screening

The full text of all potentially relevant articles will be screened for relevance. A stacked questionnaire will also be used to screen the full texts. In Level 2 screening, only articles that meet all the inclusion criteria will be included in the review (i.e. “unsure” will not be an option). Level 2 screening will be completed by two independent reviewers, who will meet to resolve any conflicts via discussion. The level of agreement between reviewers will be evaluated by dividing the total number of conflicts by the total number of articles screened for Level 2 (Fig. 2 ).

Flow chart of screening questions for the literature review on climate change and health in North America

Data extraction and analysis

A data extraction form will be created in DistillerSR® ( Appendix 2 ) and will be tested by three data extractors on a sample of articles to allow for calibration on the extraction process (i.e. 5% of articles if greater than 50 articles, 10% of articles if less than or equal to 50 articles). After completing the calibration process, the form will be adapted based on feedback from the extractors to improve usability and accuracy. The data extractors will then use the data extraction form to complete data extraction. Reviewers will meet regularly to discuss and resolve any further issues in data extraction, in order to ensure the data extraction process remains consistent across reviewers.

Data will be extracted from original research papers (i.e. articles containing data collection and analysis) and review articles that reported a systematic methodology. This data extraction will focus on study characteristics, including the country that the data were collected in, focus of the study (i.e. climate change impact, adaptation, and/or mitigation), weather variables, climatic hazards, health outcomes, social characteristics, and future projections. The categories within each study characteristic will not be mutually exclusive, allowing more than one response/category to be selected under each study characteristic. For the country of study, Canada, the USA, and/or Mexico will be selected if the article describes data collection in each country respectively. Non-North American regions will be selected if the article not only collects data external to North America, but also includes data collection within Canada, the USA, and/or Mexico. For the study focus, data will be extracted on whether the article focuses on climate change impacts, adaptation, and/or mitigation within the goals, methods, and/or results sections of the article. Temperature, precipitation, and/or UV radiation will be selected for weather variables if the article utilizes these data in the goal, methods, and/or results sections. Data will be extracted on the following climatic hazards if the article addresses them in the goal, methods, and/or results sections: heat events (e.g. extreme heat, heat waves), cold events (e.g. extreme cold, winter storms), air quality (e.g. pollution, parts per million (PPM) data, greenhouse gas emissions), droughts, flooding, wildfires, hurricanes, wildlife changes (including changes in disease vectors such as ticks or mosquitos), vegetation changes (including changes in pollen), freshwater (including drinking water), ocean conditions (including sea level rise and ocean acidity/salinity/temperature changes), ice extent/stability/duration (including sea ice and freshwater ice), coastal erosion, permafrost changes, and/or environmental hazards (e.g. exposure to sewage, reduced crop productivity).

Data will be extracted on the following health outcomes if the article focuses on them within the goal, methods, and/or results sections: heat-related morbidity and/or mortality, respiratory outcomes (including asthma, chronic obstructive pulmonary disease), cardiovascular outcomes (including heart attacks or stroke), urinary outcomes (e.g. urinary tract infections, renal failure), dermatologic concerns, mental health and wellness (e.g. suicide, emotional health), fetal health/birth outcomes and/or maternal health, cold exposure, allergies, nutrition (including nutrient deficiency), waterborne disease, foodborne disease, vectorborne disease, injuries (including accidents), and general morbidity and/or mortality. Data on the following social characteristics will also be extracted from the articles if they are included in the goal, methods, and/or results sections of the article: access to healthcare, sex and/or gender, age, income, livelihood (including data on employment, occupation), ethnicity, culture, Indigenous Peoples, rural/remote communities (“rural”, “remote”, or similar terminology must be explicitly mentioned), urban communities (“urban”, “city”, “metropolitan”, or similar terminology must be explicitly used), coastal communities (use of “coastal”, or similar terms must be explicitly mentioned), residence location (zipcode/postal code, neighbourhood, etc.), level of education, and housing (e.g. data on size, age, number of windows, air conditioning). Finally, data will be collected on future projections, including projections that employ qualitative and/or quantitative methods that are included in the goal, methods, and/or results sections of the article.

Descriptive statistics and regression modelling will be used to examine publication trends. Data will be visualized through the use of maps, graphs, and other visualization techniques as appropriate. To enable replicability and transparency, a PRISMA flowchart will be created to illustrate the article selection process and reasons for exclusion. Additionally, qualitative thematic analyses will be conducted. These analyses will utilize constant-comparative approaches to identify patterns across articles through the identification, development, and refinement of codes and themes. Article excerpts will be grouped under thematic categories in order to explore connections in article characteristics, methodologies, and findings.

Quality appraisal of studies included in the systematic scoping review will be performed using a framework based on the Mixed Methods Appraisal Tool (MMAT) [ 46 ] and the Confidence in the Evidence from Reviews of Qualitative Research (CERQual) tool [ 47 ]. This will enable appraisal of evidence in reviews that contain qualitative, quantitative, and mixed methods studies, as well as appraisal of methodological limitations in included qualitative studies. These tools may be adapted to include additional questions as required in order to fit the scope and objectives of the review. A minimum of two reviewers will independently appraise the included articles and discuss judgements as needed. The findings will be made available as supplementary material for the review.

Climate-health literature reviews using systematic methods will be increasingly critical in the health sector, given the depth and breadth of the growing body of climate change and health literature, as well as the urgent need for evidence to inform climate-health adaptation and mitigation strategies. To support and encourage the systematic and transparent identification and synthesis of climate-health information, this protocol describes our approach to systematically and transparently create a database of articles published in academic journals that examine climate-health in North America.

Availability of data and materials

Not applicable.

Abbreviations

Confidence in the Evidence from Reviews of Qualitative Research

Intergovernmental Panel on Climate Change

Mixed Methods Appraisal Tool

Parts per million

Preferred Reporting Items for Systematic review and Meta-Analyses

Preferred Reporting Items for Systematic review and Meta-Analyses, Protocol Extension

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Ultraviolet

Smith KR, Woodward A, Campbell-Lendrum D, Chadee DD, Honda Y, Liu Q, et al. Human health: impacts, adaptation, and co-benefits. In: Field CB, Barros VR, Dokken DJ, Mach KJ, Mastrandrea MD, Bilir TE, et al., editors. Climate Change 2014: impacts, adaptation, and vulnerability part A: global and sectoral aspects contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge, UK and New York, USA: Cambridge University Press; 2014. p. 709–54.

Google Scholar  

Watts N, Amann M, Ayeb-Karlsson S, Belesova K, Bouley T, Boykoff M, et al. The Lancet Countdown on health and climate change: from 25 years of inaction to a global transformation for public health. Lancet. 2018;391(10120):581–630.

Article   Google Scholar  

Son JY, Liu JC, Bell ML. Temperature-related mortality: a systematic review and investigation of effect modifiers. Environ Res Lett. 2019;14:073004.

Campbell S, Remenyi TA, White CJ, Johnston FH. Heatwave and health impact research: a global review. Heal Place. 2018;53:210–8.

Sanderson M, Arbuthnott K, Kovats S, Hajat S, Falloon P. The use of climate information to estimate future mortality from high ambient temperature: a systematic literature review. PLoS One. 2017: e0180369.

Rataj E, Kunzweiler K, Garthus-Niegel S. Extreme weather events in developing countries and related injuries and mental health disorders - a systematic review. BMC Public Health. 2016;16:1020.

Saulnier DD, Brolin Ribacke K, von Schreeb J. No Calm after the storm: a systematic review of human health following flood and storm disasters. Prehosp Disaster Med. 2017;32(5):568–79.

Cunsolo A, Neville E. Ecological grief as a mental health response to climate change-related loss. Nat Clim Chang. 2018;8:275–81.

Levy K, Woster AP, Goldstein RS, Carlton EJ. Untangling the impacts of climate change on waterborne diseases: a systematic review of relationships between diarrheal diseases and temperature, rainfall, flooding, and drought. Environ Sci Technol. 2016;50:4905–22.

Article   CAS   Google Scholar  

Semenza JC, Herbst S, Rechenburg A, Suk JE, Höser C, Schreiber C, et al. Climate change impact assessment of food- and waterborne diseases. Crit Rev Environ Sci Technol. 2012;42(8):857–90.

Cann K, Thomas D, Salmon R, W-J AP, Kay D. Extreme water-related weather events and waterborne disease. Epidemiol Infect. 2013;141:671–86.

Andrade L, O’Dwyer J, O’Neill E, Hynds P. Surface water flooding, groundwater contamination, and enteric disease in developed countries: a scoping review of connections and consequences. Environ Pollut. 2018;236:540–9.

Harper SL, Wright C, Masina S, Coggins S. Climate change, water, and human health research in the Arctic. Water Secur. 2020;10:100062.

Park MS, Park KH, Bahk GJ. Interrelationships between multiple climatic factors and incidence of foodborne diseases. Int J Environ Res Public Health. 2018;15:2482.

Lake IR, Barker GC. Climate change, foodborne pathogens and illness in higher-income countries. Curr Environ Heal Rep. 2018;5(1):187–96.

Lake IR, Gillespie IA, Bentham G, Nichols GL, Lane C, Adak GK, et al. A re-evaluation of the impact of temperature and climate change on foodborne illness. Epidemiol Infect. 2009;137(11):1538–47.

Lake IR, Hooper L, Abdelhamid A, Bentham G, Boxall AB. a. A, Draper A, et al. Climate change and food security: health impacts in developed countries. Environ Health Perspect. 2012;120(11):1520–6.

Springmann M, Mason-D’Croz D, Robinson S, Garnett T, Godfray HCJ, Gollin D, et al. Global and regional health effects of future food production under climate change: a modelling study. Lancet. 2016;387(10031):1937–46.

Campbell-Lendrum D, Manga L, Bagayoko M, Sommerfeld J. Climate change and vector-borne diseases: what are the implications for public health research and policy? Philos Trans R Soc London. 2015;370:20130552.

Sweileh WM. Bibliometric analysis of peer-reviewed literature on climate change and human health with an emphasis on infectious diseases. Glob Health. 2020;16(1):1–17.

Ford J. Indigenous health and climate change. Am J Public Health. 2012;102(7):1260–6.

Butler CD. Climate change, health and existential risks to civilization: a comprehensive review (1989–2013). Int J Environ Res Public Health. 2018;15(10):2266.

Tong S, Ebi K. Preventing and mitigating health risks of climate change. Environ Res. 2019;174:9–13.

Ebi KL, Hess JJ. The past and future in understanding the health risks of and responses to climate variability and change. Int J Biometeorol. 2017;61(S1):71–80.

Hosking J, Campbell-Lendrum D. How well does climate change and human health research match the demands of policymakers? A scoping review. Environ Health Perspect. 2012;120(8):1076–82.

Berry P, Enright PM, Shumake-Guillemot J, Villalobos Prats E, Campbell-Lendrum D. Assessing health vulnerabilities and adaptation to climate change: a review of international progress. Int J Environ Res Public Health. 2018;15(12):2626.

Verner G, Schütte S, Knop J, Sankoh O, Sauerborn R. Health in climate change research from 1990 to 2014: positive trend, but still underperforming. Glob Health Action. 2016;9:30723.

Ebi KL, Hasegawa T, Hayes K, Monaghan A, Paz S, Berry P. Health risks of warming of 1.5 °C, 2 °C, and higher, above pre-industrial temperatures. Environ Res Lett. 2018;13(6):063007.

Bäckstrand K. Civic science for sustainability: reframing the role of experts, policy-makers and citizens in environmental governance. Glob Environ Polit. 2003;3(4):24–41.

Susskind L, Jain R, Martyniuk A. Better environmental policy studies: how to design and conduct more effective analyses. Washington, DC: Island Press; 2001. p. 256.

Holmes J, Clark R. Enhancing the use of science in environmental policy-making and regulation. Environ Sci Policy. 2008;11(8):702–11.

Pearce T, Ford J, Duerden F, Smit B, Andrachuk M, Berrang-Ford L, et al. Advancing adaptation planning for climate change in the Inuvialuit Settlement Region (ISR): a review and critique. Reg Environ Chang. 2011;11(1):1–17.

Gearheard S, Shirley J. Challenges in community-research relationships: learning from natural science in Nunavut. Arctic. 2007;60(1):62–74.

Brownson R, Royer C, Ewing R, McBride T. Researchers and policymakers: travelers in parallel universes. Am J Prev Med. 2006;30(2):164–72.

Feldman P. Improving communication between researchers and policy makers in long-term care or, researchers are from Mars; policy makers are from Venus. Gerontologist. 2001;41(3):312–21.

Pearce TD, Ford JD, Laidler GJ, Smit B, Duerden F, Allarut M, et al. Community collaboration and climate change research in the Canadian Arctic. Polar Res. 2009;28(1):10–27.

Duerden F, Beasley E, Riewe R, Oakes J. Assessing community vulnerabilities to environmental change in the Inuvialuit region. Climate Change: Linking Traditional and Scientific Knowledge. Winnipeg, MB: Aboriginal Issues Press; 2006.

Mulrow CD. Rationale for systematic reviews. BMJ. 1994;309(6954):597–9.

Tricco A, Lillie E, Zarin W, O’Brien KK, Colquhoun H, Levac D. PRISMA extension for scoping reviews (PRISMA-ScR): checklist and explanation. Ann Intern Med. 2018;169:467–73.

Moher D, Liberati A, Tetzlaff J, Altman D. The Prisma Group. Preferred reporting items for systematic reviews and meta-analyses: the PRISMA statement. Ann Intern Med. 2009;151(4):264–9.

IPCC. In: Stocker TF, Qin D, Plattner G-K, Tignor M, Allen SK, Boschung J, et al., editors. Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge: Cambridge University Press; 2013. 1535 pp.

IPCC. Managing the risks of extreme events and disasters to advance climate change adaptation. A special report of Working Groups I and II of the Intergovernmental Panel on Climate Change. In: Field CB, Barros V, Stocker TF, Qin D, Dokken DJ, Ebi KL, et al., editors. Cambridge: Cambridge University Press; 2012. p. 582.

Woodward A, Smith KR, Campbell-Lendrum D, Chadee DD, Honda Y, Liu Q, et al. Climate change and health: on the latest IPCC report. Lancet. 2014;383(9924):1185–9.

Confalonieri U, Menne B, Akhtar R, Ebi KL, Hauengue M, Kovats RS, et al. Human Health. In: Parry ML, Canziani OF, Palutikof JP, van der Linden PJ, Hanson CE, editors. Climate change 2007: impacts, adaptation and vulnerability contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge: Cambridge University Press; 2007. p. 391–431.

IPCC. Climate Change 2014: Impacts, adaptation, and vulnerability. Part B: regional aspects. Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. In: Barros VR, Field CB, Dokken DJ, Mastrandrea MD, Mach KJ, Bilir TE, et al., editors. Climate change 2014 impacts, adaptation and vulnerability: part A: global and sectoral aspects. Cambridge, UK and New York, USA: Cambridge University Press; 2014. p. 688.

Hong Q, Pluye P, Fàbregues S, Bartlett G, Boardman F, Cargo M, et al. Mixed Methods Appraisal Tool (MMAT), Version 2018. Registration of copyright (#1148552), Canadian Intellectual Property Office, Industry Canada; 2018. p. 1–11.

Lewin S, Glenton C, Munthe-Kaas H, Carlsen B, Colvin CJ, Gülmezoglu M, et al. Using qualitative evidence in decision making for health and social interventions: an approach to assess confidence in findings from qualitative evidence syntheses (GRADE-CERQual). PLoS Med. 2015;12(10):1001895.

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Acknowledgements

We would like to thank Maria Tan at the University of Alberta Library for the advice, expertise and guidance provided in developing the search strategy for this protocol. Special thanks to those who assisted with methodology refinement, including Etienne de Jongh, Katharine Neale, and Tianna Rusnak.

Funding was provided by the Canadian Institutes for Health Research (to SLH and AC). The funding body had no role in the design of the study and collection, analysis, and interpretation of data and in writing the manuscript.

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Ashlee Cunsolo

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SLH, AC, and MDA contributed to the conceptualization, methodology, writing, and editing of the manuscript. AB contributed to the methodology, writing, and editing of the manuscript. SC contributed to the writing and editing of the manuscript. CJW contributed to visualization, writing, and editing of the manuscript. The authors have read and approved the final manuscript.

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Additional file 1..

Search strategy for CINAHL®, Web of Science™, Scopus®, Embase® via Ovid, and MEDLINE® via Ovid.

Data extraction form

• *Categories were not mutually exclusive; that is, more than one category could be selected

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Harper, S.L., Cunsolo, A., Babujee, A. et al. Climate change and health in North America: literature review protocol. Syst Rev 10 , 3 (2021). https://doi.org/10.1186/s13643-020-01543-y

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Research Article

Climate Change Research in View of Bibliometrics

* E-mail: [email protected]

Affiliation Max Planck Institute for Solid State Research, Stuttgart, Germany

Affiliation Division for Science and Innovation Studies, Administrative Headquarters of the Max Planck Society, Munich, Germany

• Robin Haunschild, 
• Lutz Bornmann, 
• Werner Marx

• Published: July 29, 2016
• https://doi.org/10.1371/journal.pone.0160393
• Reader Comments

This bibliometric study of a large publication set dealing with research on climate change aims at mapping the relevant literature from a bibliometric perspective and presents a multitude of quantitative data: (1) The growth of the overall publication output as well as (2) of some major subfields, (3) the contributing journals and countries as well as their citation impact, and (4) a title word analysis aiming to illustrate the time evolution and relative importance of specific research topics. The study is based on 222,060 papers (articles and reviews only) published between 1980 and 2014. The total number of papers shows a strong increase with a doubling every 5–6 years. Continental biomass related research is the major subfield, closely followed by climate modeling. Research dealing with adaptation, mitigation, risks, and vulnerability of global warming is comparatively small, but their share of papers increased exponentially since 2005. Research on vulnerability and on adaptation published the largest proportion of very important papers (in terms of citation impact). Climate change research has become an issue also for disciplines beyond the natural sciences. The categories Engineering and Social Sciences show the strongest field-specific relative increase. The Journal of Geophysical Research , the Journal of Climate , the Geophysical Research Letters , and Climatic Change appear at the top positions in terms of the total number of papers published. Research on climate change is quantitatively dominated by the USA, followed by the UK, Germany, and Canada. The citation-based indicators exhibit consistently that the UK has produced the largest proportion of high impact papers compared to the other countries (having published more than 10,000 papers). Also, Switzerland, Denmark and also The Netherlands (with a publication output between around 3,000 and 6,000 papers) perform top—the impact of their contributions is on a high level. The title word analysis shows that the term climate change comes forward with time. Furthermore, the term impact arises and points to research dealing with the various effects of climate change. The discussion of the question of human induced climate change towards a clear fact (for the majority of the scientific community) stimulated research on future pathways for adaptation and mitigation. Finally, the term model and related terms prominently appear independent of time, indicating the high relevance of climate modeling.

Citation: Haunschild R, Bornmann L, Marx W (2016) Climate Change Research in View of Bibliometrics. PLoS ONE 11(7): e0160393. https://doi.org/10.1371/journal.pone.0160393

Editor: Wolfgang Glanzel, Katholieke Universiteit Leuven, BELGIUM

Received: May 30, 2016; Accepted: July 18, 2016; Published: July 29, 2016

Copyright: © 2016 Haunschild et al. This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Data Availability: The data have been obtained from Thomson Reuters’ Web of Science database. Readers can contact Thomson Reuters to obtain the data ( http://thomsonreuters.com/thomson-reuters-web-of-science/ ). Readers that do not have access to the Web of Science database can contact Thomson Reuters to obtain a license. Relevant information can be found at http://thomsonreuters.com/en/products-services/scholarlyscientific-reaserch/scholarly-search-and-discovery/web-of-science.html .

Funding: The authors have no support or funding to report.

Competing interests: The authors have declared that no competing interests exist.

Introduction

Climate change is a change in the statistical distribution of weather patterns during an extended period of time (from decades to millions of years). Meanwhile, climate change and global warming are terms for the observed century-scale rise in the average temperature of the earth's surface. From the perspective of large time periods, climate change is caused by a multitude of factors like variations in solar radiation (changing parameters of the earth’s orbit, variations of the solar activity observed via sunspot number), drifting continents (see plate tectonics), volcanic eruptions (producing large amounts of sulfate-based aerosols), and possibly others. During the last decades, human activities (in particular burning of fossil fuel and pollution as the main consequences of the growth of population and industrialization) have been identified as significant causes of recent climate change, often referred to as global warming . The Intergovernmental Panel on Climate Change (IPCC) reports in its foreword that “the IPCC is now 95 percent certain that humans are the main cause of current global warming [ 1 , 2 ]. The report states in its Summary for Policymakers that “human influence on the climate system is clear, and recent anthropogenic emissions of greenhouse gases are the highest in history. Recent climate changes have had widespread impacts on human and natural systems” [ 3 ].

Climate change has gained strongly increasing attention in the natural sciences and more recently also in the social and political sciences. Scientists actively work to understand the past climate and to predict the future climate by using observations and theoretical models. Various subfields from physics, chemistry, meteorology, and geosciences (atmospheric chemistry and physics, geochemistry and geophysics, oceanography, paleoclimatology etc.) are interlinked. Climate change has also become a major political, economic, and environmental issue during the last decade and a central theme in many political and public debates. How to address, mitigate and adapt to climate change has become a hot issue. The scientific community has contributed extensively to these debates with various data, discussions, and projections on the future climate as well as on the effects and risks of the expected climatic change.

The large and strongly growing amount of climate change research literature has brought about that scientists working within this research field experience increasingly problems to maintain a view over their discipline. Modern information systems could possibly offer databases and analysis tools providing a better overview on the entire research field. However, due to lack of access and experience concerning suitable databases and analysis tools, many experts do not take advantage of them. But meanwhile, a series of bibliometrics analyses have been published by scientometricians, stimulated by the growing scientific, political, and public attention of research on climate change. These publications appeared both in subject specific journals in the field of climate change research as well as in bibliometrics journals:

Based on a sample of 113,468 publications on environmental assessment from the past 20 years, Li and Zhao [ 4 ] “used a bibliometric analysis to study the literature in terms of trends of growth, subject categories and journals, international collaboration, geographic distribution of publications, and scientific research issues” (p. 158). The h index was used to evaluate global environmental assessment research quality among countries. According to this study, the USA and UK have the highest h index among the contributing countries. Stanhill [ 5 ] discussed the growth of climate change science and found a doubling of the related publications every 11 years. Li et al. [ 6 ] analyzed the scientific output of climate change research since 1992 “to assess the characteristics of research patterns, tendencies, and methods in the papers… It was concluded that the items ‘temperature’, ‘environment’, ‘precipitation’, ‘greenhouse gas’, ‘risk’, and ‘biodiversity’ will be the foci of climate change research in the 21st century, while ‘model’, ‘monitoring’, and ‘remote sensing’ will continue to be the leading research methods” (p. 13).

Based on co-citation analysis, Schwechheimer and Winterhager [ 7 ] identified highly dynamic, rapidly developing research fronts of climate research. ENSO (El Nino Southern Oscillation) irregularity, vegetation & ice-age climate, and climate-change & health were found as the research fields with the highest immediacy values.

Other bibliometric studies deal with more specific topics within the field of climate research: Ji et al. [ 8 ] analyzed research on Antarctica, Wang et al. [ 9 ] discussed the vulnerability of climate change, and Pasgaard and Strange [ 10 ] presented a quantitative analysis of around 15,000 scientific publications from the time period 1999–2010, discussing the distribution of climate change research throughout the contributing countries and the potential causes of this distribution. Vasileiadou [ 11 ] have explored the impact of the IPCC Assessment Reports on science. Bjurström and Polk [ 12 , 13 ] analyzed the interdisciplinarity of climate change research based on the referenced journals in the IPCC Third Assessment Report [ 14 ] via co-citation analysis. Hellsten and Leydesdorff [ 15 ] analyzed the development of the knowledge base and programmatic focus of the journal Climatic Change . Most interesting and in contrast to substantial public doubt are the findings of Anderegg et al. [ 2 ]. They conclusively revealed the striking agreement among climate research scientists on the anthropogenic cause of climate change based on the publications of 1,372 top climate experts. Janko et al. [ 16 ] analyzed the controversies about climate change through comparison of references in and citations of contrarian reports.

Most of the studies in the past focused on specific topics within climate change research and do not present an analysis of the complete research field. The few comprehensive studies mentioned above used search queries for the literature search which are more or less inappropriate: They are mostly based on queries for literature retrieval, using somewhat arbitrary items for selecting subfields. The corresponding publication sets are therefore limited with regard to completeness: Stanhill [ 5 ] has analyzed the growth of climate change relevant literature using exclusively the abstract journal of the American Meteorological Society as publication set. Li et al. [ 6 ] analyzed trends in research on global climate change: “‘Climate change’, ‘climate changes’, ‘climatic change’, and ‘climatic changes’ were used as the keyword to search titles, abstracts, and keywords from 1992 to 2009” (p. 14). Pasgaard and Strange [ 10 ] used “the search phrases climat* AND change* and global warming (with asterisk wildcards)” (p. 1685). Only Wang et al. [ 9 ] applied a more sophisticated method (see below) but his analysis deals exclusively with the climate change vulnerability.

The analysis presented here extends to the time period of the publications relevant for climate change research from 1980 (the time when climate change emerged as a new research field) to the present (end of 2014). We developed a sophisticated search query to cover the relevant literature as completely as possible and to exclude (climate) research not relevant for the global warming issue. Based on a carefully selected publication set of 222,060 papers (including 10,932,050 references cited therein), we firstly analyzed the growth of the overall publication output and of major subfields between 1980 and 2014. Secondly, we examined the topical shifting of the climate change relevant research by title word analysis. Finally, we identified the most contributing journals and countries and their overall citation impact. The previous papers either did not consult any citation based impact data, or they present citation counts which are not normalized with regard to the publication year and the specific research field of the cited publication (e.g. Li and Zhao [ 4 ]).

Search for the literature and description of the dataset

It is not an easy task to select all papers (to avoid confusion with the document type “article,” the term “paper” rather than “article” is used throughout this manuscript for any kind of journal-based publication) related to a specific research field or research topic using literature databases as information source. Completeness or recall ( all relevant papers) and high precision ( only relevant papers) are inversely related and mutually exclusive [ 17 ]. This basic connection between completeness and precision precludes a much “cleaner” publication set (i.e. more hits and concurrently less non-relevant papers). In particular, a broad research field like climate change research is not clearly defined and there is no sufficient categorization by keywords, index terms or thesauri. Since the beginning of climate change research, a lot of (neighboring) disciplines tend to relate their research topics on climate research but their papers often deal primarily with other topics.

Wang et al. [ 9 ] who gave an overview of climate change vulnerability, applied a more sophisticated method which they called a four step backward searching. This strategy comprises a preliminary search for key papers and a renewed search based on the synonyms revealed by the keyword analysis of the key papers. This kind of strategy has been called “interactive query formulation” and was discussed extensively by Wacholder [ 18 ]: “Iterative query reformulation involves creation of a new variant (reformulation) of a previous query … In the flow-of-information model, query reformulation is treated as a subprocess of the broader QF process” (p. 161). In the present analysis we applied a similar approach for the data retrieval. We have used the Web of Science (WoS) custom data (1980–2015) of the database producer Thomson Reuters (Philadelphia, USA) derived from the Science Citation Index Expanded (SCI-E), Social Sciences Citation Index (SSCI), and Arts and Humanities Citation Index (AHCI), allowing more advanced retrieval options than the online version of the WoS. Due to the more advanced retrieval options the number of publications might differ slightly compared to the online version of the WoS. However, this does not affect our analysis significantly.

Step 1: We searched for the term “*climat* chang*” (to include in particular the following phrases: climate/climatic change/changes/changing) within the titles only to establish a publication set of key papers (n = 29,396) with publication years between 1980 and 2015. Out of this publication set the keywords have been selected and ranked according to their frequency of occurrence. Based on the most frequently appearing more complex keywords within the selected set of key papers we looked for climate change synonyms and established the following list of search terms (with asterisk wildcards for truncation to cover in particular the terms given in parentheses):

• *climat* chang* (climate/climatic change/changes/changing)
• *climat* warming* (climate/climatic)
• *global temperature* (temperature/temperatures)
• *global warming*
• *greenhouse gas* (gas/gases)
• *greenhouse effect* (effect/effects)
• *greenhouse warming*

During selection of these search terms we had to distinguish between “classical” climate research (not referring to global warming) and climate change research (although no clear differentiation is possible). Classical climate research deals for example with the modification of landscapes through glacial periods (ice ages) or with basic topics in meteorology. The keywords have been selected here against the climate change research background. For example, terms like “climate variability” are not included in our search term list, because they appear also in biological and medical studies far from research on climate change. We may assume, however, that papers on climate variability, which are actually relevant for climate change research, are covered by the other search terms.

Step 2: We searched the more complex search terms derived from step 1 listed above and in addition the short term “*climat*” each within the titles only. The left truncation in addition to the right truncation of the term “climat” was used to include also terms such as “pal(a)eoclimate”. We found only one single term covered by this left and right truncation which is not closely related to climate change research: “acclimation” or “acclimatization”, respectively. Papers with “*acclimat*” in the title were removed unless they contain the term “climat*” (with right truncation but without left truncation) in the title.

Searching titles for the term “*climat* retrieves a certain amount of papers with limited relevance for the climate change topic, but also many papers which mention unforeseeable terms around climate change (e.g. climate cycle, climate model, climate policy, and past climate). Considering the strongly increasing number of publications dealing with research on climate change (see below), we may assume (at least for the more recent publications) a high probability that a paper is related to climate change research, if the term “*climat*” does appear in the title.

Step 3: We searched the more complex terms from step 1 within the abstracts only. Although searching in abstracts only is not possible in the WoS, it is possible in our in-house database derived from the WoS data. Abstract searching based on short terms like “climat*” results in too many papers which are not closely related to climate change research. Note that abstracts are generally included in WoS since 1991 for the SCI-E and 1992 for the SSCI only. A few papers have been indexed with abstracts prior to 1991 in WoS.

Step 4: In addition to the title word searching of step 2, we also executed a keyword-based search with the same terms as for the titles. Again, papers with the keywords “acclimation” or “acclimatization” were removed from the publication set unless the keyword section also contained “climat*” (with right but without left truncation).

Step 5: The results from steps 2–4 were combined with a logical OR and refined to articles and reviews as document types (i.e. only substantial contributions to the field are considered). The search as described above was restricted to the time period from 1980 to 2014 and eventually resulted in a publication set of 222,060 papers (articles and reviews only). This is definitely not the complete publication set covering any research paper relevant for the climate change research topic. However, we may assume that we have included by far most of the relevant papers, in particular the key papers dealing with research on climate change. Previous studies dealing with overall climate change research and extending to more recent publication years are based on substantially smaller publication sets (e.g. Li et al. [ 6 ]: around 30,000 papers).

For the growth analysis of some major research fields, the publication set resulting from step 5 has been combined with a logical AND using the additional search terms or phrases, respectively, shown in Table 1 .

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https://doi.org/10.1371/journal.pone.0160393.t001

These terms were searched in the title and keyword fields. The left and right truncations of these search terms are expected to yield no unwanted hits because each of them is combined via a logical AND with our primary climate change publication set.

Statistics for the data analysis

Normalization of citation impact..

The publication set has been analyzed with regard to the most perceived sub-fields, journals and countries by analyzing the overall citation impact of the publications. Thus, we used citation counts to measure the impact publications from certain sub-fields, journals, and countries have on science. Since the total citation impact of the publications is used in this study, not only the impact of the publications on the climate change research is measured, but also the impact on science in general. However, most of the citation impact will fall on the climate change research itself and can thus be interpreted accordingly.

Pure citation counts of papers are not meaningful, because they depend not only on the importance of research (for the research of other researchers than the authors), but also on the subject category and the publication year of the papers [ 19 ]. For example, one can expect more citations on average for papers in biology than for papers in the social sciences (using citation data from WoS). Therefore, we present citation impact scores in this study which are normalized concerning the particular publication year and WoS subject category [ 20 ]. The normalization is done in our in-house database as follows: The proportion of papers of a given publication set A (e.g. a journal or a country) which belong to the most frequently cited papers in the corresponding WoS subject categories and publication years has emerged as the most robust normalized impact score [ 21 , 22 ]. In order to ascertain the proportion of papers, for every paper in A the reference set with comparable papers is composed. The comparable papers consist of papers belonging to the same subject category and publication year as the paper from A. The papers in the reference sets are sorted in descending order by their citation counts and the most frequently cited papers are identified. Then, either a paper from A belongs to the most frequently cited papers in the corresponding reference set (P Ai = 1) or not (P Ai = 0). Only some papers from A are fractionally assigned to the most frequently cited papers, if their citation counts position them at the threshold which is used to separate the most frequently cited papers from the rest in the reference set [ 23 ]. Based on this value for every paper i in A (0, …, 1), the proportion of papers in A is calculated which belongs to the most frequently cited papers in their set of comparable papers. In the case that a paper belongs to multiple subject categories, impact values are calculated for such papers in each subject category and average values are used for impact values on a paper basis.

The indicator PP top 50% is the proportion of papers in A which belongs to the 50% most frequently cited papers. Thus, this is the proportion of papers which is cited equal to or more frequently than “an average paper” in the corresponding reference sets. PP top 50% is the basic citation impact indicator in bibliometrics which indicates above average perceptions of literature with PP top 50% >50 and below average perceptions with PP top 50% <50 (50 is the expected value indicating an average impact). Besides PP top 50% , two further indicators are frequently used in bibliometric studies (e.g. in the Leiden Ranking), which focus on the excellence level: PP top 10% and PP top 1% , respectively, specifies the papers which belong to the 10% and 1%, respectively, most frequently cited papers. The expected values for an average paper set are 10 for PP top 10% and 1 for PP top 1% . These indicators show, e.g., whether a given country B was able to publish more papers in the excellence area than a given country C. With more papers in this area, country B would have contributed more important papers to the climate change research than country C.

As citations accumulate rather slowly over time, we restrict the citation impact analyses to the time period 1980–2012 whenever impact indicators are performed. Citations were gathered until May 15 th 2015 which allows for a citation window of at least three years.

Mapping of research topics.

Bibliometrics aims to quantify the outcome and interconnection of scientific activity. The number of publications is the most popular measure of output, while the number of citations is the most popular indicator of impact, which is one (measurable) aspect of quality. Text searching (data mining) is another tool which may be used to quantify content. A simple method for revealing the hot topics of a research field is based on an analysis of the title words (or alternatively: the keywords) of the literature published so far. In our study we used the VOSviewer software package [ 24 ] for mapping the title words of the climate research literature of our publication set (see www.vosviewer.com )

The maps created by VOSviewer and used in this study are based on bibliographic coupling as a technique to position nodes (in our case: the corresponding title words). The distance between the nodes is proportional to the similarity (relatedness) with regard to the cited references. Hence, title words of papers that cite similar literature are found closer to each other. The automatically performed arrangement of the nodes is highly sensitive and might change significantly if rather few papers are added or removed. However, the size of the nodes (the larger the number of papers with a specific title word, the larger the node) and the distances between each other are hardly affected. The nodes on a map are also assigned by VOSviewer to clusters (they are highlighted in different colors). These clusters identify closely related nodes, where each node is assigned to only one cluster [ 25 ]. VOSviewer uses a modularity-based clustering technique, which is closely related to the multidimensional scaling technique [ 26 ] and is based on the smart local moving algorithm [ 27 ].

Overall growth and growth in terms of disciplines and subfields

As a first step to provide an overview of the development of the entire research dealing with climate change, the time evolution of the publication productivity (output) of this research field (measured as number of papers published per year) has been analyzed. Fig 1 shows the annual number of papers published within the time period 1980–2014 and covered by the WoS database.

The distinct step from 1990 to 1991 does not signal a sudden increase in productivity but solely the fact that the WoS does not include abstracts before 1991. As a consequence, searches using the WoS field tag “topic” in combination with publication years prior to 1991 yield significantly lower hit numbers (frequently one order of magnitude).

https://doi.org/10.1371/journal.pone.0160393.g001

According to Fig 1 , the total number of papers dealing with climate change shows a strong increase: Within the time period 1991 to 2010, the number of climate change papers published per year increased by a factor of ten, whereas in the same time period the overall number of papers covered by the WoS databases increased “only” by a factor of around two. The data row of Fig 1 exhibits a doubling of the climate change papers every 5–6 years. The exponential growth of climate change literature is possibly induced by the increasing influence of the IPCC Assessment Reports, which eventually made climate change research a hot topic. These reports revealed the strong need of further research for a better understanding of the earth’s climate system and for improved predictions of the future climate. Furthermore, the effects, impacts and risks of climate change became more and more concrete. The discussion of the question of human induced climate change towards a clear fact (at least for the majority of the scientific community, see Anderegg [ 2 ] stimulated research on future pathways for adaptation and mitigation.

The literature growth is roughly in accordance with the results of Grieneisen and Zhang [ 28 ], who report that the number of publications on climate change and global warming has doubled with a rate of approximately every 4 years. As mentioned above, Stanhill [ 5 ] found a doubling rate of 11 years for the time period 1951–1997. To put this into perspective, we compare our results with the growth rate of the overall science: According to Bornmann and Mutz [ 29 ] the total volume of publications covered by the WoS between 1980 and 2012 doubled approximately every 24 years. Hence, the growth rate of climate change related publications is extraordinarily high. The bend down around 2012 is presumably caused by still incomplete coverage of the recent publication years through WoS and is no sign of decline.

The results of the analysis of the climate change related papers with regard to their disciplines of origin are shown in Figs 2 and 3 . The figures are based on the main OECD categories assigned. Compared to the WoS research areas and subject categories, the main OECD categories are broader grained and therefore better suitable for an overview.

Papers which are assigned to more than one main OECD category are multiply counted.

https://doi.org/10.1371/journal.pone.0160393.g002

https://doi.org/10.1371/journal.pone.0160393.g003

As expected, climate change research is dominated by the natural sciences. Further analyses of our data with regard to the specific research areas show that the earth sciences (meteorology and atmospheric sciences), the biological, the agricultural sciences, and the environmental sciences are predominant.

Fig 3 shows the relative increase of papers since 1980 assigned to the main OECD categories. The paper share is presented in percent increase based on the numbers from 1980 (thus, the number of papers published in the year 1980 in each case equals 100%).

According to Fig 4 , climate change research has become an issue also for disciplines beyond the natural sciences (e.g. engineering, history, law, management, sociology etc.). The categories Engineering and Social Sciences show the strongest increase since around 2005. Since around 2009 the relative increase of the Natural Sciences and the Social Sciences is almost identical. Obviously, climate change is increasingly seen as a fact to be considered for the near future: The need to limit fuel combustion and to adapt to global warming apparently is a huge stimulation for various technological developments and research on the implications of climate change. For example, sociologists analyzed the public understanding and the discussion of climate change in science, politics, and the mass media [ 30 , 31 ]. Furthermore, the Humanities have discovered climate change as a research topic. Historians for example reconstructed climate extremes in medieval history [ 32 ].

These research topics comprise 182,594 papers (82.2%) of our publication set (n = 222,060).

https://doi.org/10.1371/journal.pone.0160393.g004

Climate change affects agriculture in a number of ways (changes in average temperatures, rainfall, climate extremes) and therefore has become an important field of investigation within climate change research. Climate change will likely affect food production and probably increases the risk of food shortage [ 3 ]. Although climate change is increasingly relevant also for medicine, the portion of output of this field of study is comparatively low.

The OECD categories are very broad and imply a classification of journals and not of the specific papers published therein. Also, many journals publish papers from different research fields and are assigned to more than one category which causes a certain amount of impreciseness. In order to differentiate our publication set with regard to the major subfields of climate change research we applied a different method: We parsed our paper set by combining with carefully selected further search terms which are based (1) on the title word analysis from step 1 of our literature search procedure and (2) on the major topics of climate change research as indicated by various summarizing publications (e.g. the IPCC Synthesis Report 2014, table of contents [ 1 ]).

As a first category of search terms, we selected the papers dealing with the main climate subsystems: the atmosphere, the oceanic water, the continental water, the ice sheets and glaciers, and the continental biomass. Additionally, we selected the literature specifically dealing with the various forms of atmospheric and oceanographic circulation or oscillation phenomena. All these search terms mark the kind of basic research in climatology, atmospheric- and geosciences, meteorology, and oceanography, which is undertaken to better understand the earth’s climate system. We completed this category by separately searching for the more theoretical publications dealing with climate modeling and the prediction of future climate. As a second category, we searched for papers dealing with the adaptation to climate change or its mitigation as well as papers focusing on effects, impacts, and risks of climate change. Such research takes climate change more or less as a matter of fact and discusses possible consequences and reactions. The corresponding terms were searched in titles and keywords only, because a search in abstracts might have resulted in too many false positives. For more detailed information of the search procedure, see the search terms in Table 1 . Fig 4 shows the time evolution of the papers of the major subfields within climate change research.

According to Fig 4 , continental biomass related research is the largest subfield within climate change research, closely followed by climate modeling, which demonstrates the importance of theoretical investigations (admittedly, these two subfields are rather broad). Next come research dealing with oceanic water, with impacts and effects of climate change, and with continental water (lakes, rivers, rainfall). Due to the radiative imbalance of the earth, less energy leaves the atmosphere than enters it. By far most of this extra energy has been absorbed by the oceans, which makes the oceans a major climate factor. The term “*sea*” was searched in addition to the terms “*ocean*” and “*marin*” to include papers dealing for example with changing sea surface temperatures or the rise of the sea levels into the answer set. Another major subfield is represented by the topic ice and snow (e.g. ice cores, ice sheets, glaciers, shelf ice). Ice cores are most important for the dating and reconstruction of the earth’s past climate as well as for the prediction of the future climate.

The next major subfield is related to the atmosphere as another important climate subsystem (beside the ice and water related subsystems). This subfield includes research on clouds, on wind and storms (i.e. the key topics of meteorology), but also on aerosols (see volcanic eruptions). In contrast to impacts and effects of climate change, which appear as a major field of interest, research dealing with the adaptation to and the mitigation of climate change as well as with the risks and the vulnerability of global warming are comparatively small. Both were next to insignificant until 2004, but their share of papers increased exponentially since 2005, showing the strongly increasing research activity in this field. Global warming also affects ocean currents and thereby periodical climate changes like ENSO (El Nino Southern Oscillation) and NAO (North Atlantic Oscillation). As a more specific research topic and a subset of the atmospheric and oceanic water subfields, this research represents the smallest topic within our publication set, thereby masking somewhat the importance of these research activities. In Table 2 , the total number of papers as well as the bibliometric indicators PP Top 50% , PP Top 10% , and PP Top 1% of the papers belonging to the specific subfields are given.

In addition, the bibliometric indicators PP Top 50% , PP Top 10% , and PP Top 1% of the papers belonging to the specific subfields are given.

https://doi.org/10.1371/journal.pone.0160393.t002

According to Table 2 , all subfields together comprise more than 81% of the total climate change papers published within the time period 1980–2012 (note that we have restricted all citation impact analyses to 2012 as the most recent publication year). The PP Top 50% values of all subfields are above the proportion of the total climate change literature (PP Top 50% = 63.43%). Research on vulnerability (PP Top 1% = 3.51) and on adaptation (PP Top 1% = 3.47) can be seen as the subfields within climate change research publishing the largest proportion of very important papers.

Contributing journals

In accordance with the publication practice in the core natural sciences, we assume that research results from climate change research are mainly published as journal (or conference) articles which are predominantly covered by literature databases like WoS. Thus, the number of papers published in a specific journal can be seen as a measure of the importance or “weight” of that journal for a specific research topic or field. In so far, it is interesting to find out, which journals are dominating quantitatively as publication medium for researchers active in the field of climate change research. Table 3 shows the distribution of the climate change research papers included in our data set throughout the journals which have published at least 1000 papers. Again, the bibliometric indicators PP Top 50% , PP Top 10% , and PP Top 1% have been calculated.

In addition, the bibliometric indicators PP Top 50% , PP Top 10% , and PP Top 1% of the journals are given.

https://doi.org/10.1371/journal.pone.0160393.t003

Most important are the Journal of Geophysical Research , the Journal of Climate , and the Geophysical Research Letters in terms of the total number of papers published. The journal Climatic Change , which has been founded specifically for research papers on climate change, appears on rank four. Nature as one of the most prominent multidisciplinary journals appears on lower ranks but shows the highest PP Top 50% : Nearly all papers published in Nature belong to the 50% most frequently cited papers. Most journals show a comparatively high citation impact. The proportion of highly received papers (PP Top 1% ) is very large for the journals Global Change Biology (PP Top 1% = 5.83%) and Quaternary Science Reviews (PP Top 1% = 4.53%).

Contributing countries

Climate change research is not only a highly multidisciplinary undertaking but also a research area with many countries being active and cooperating with each other. The number of papers of each country and their citation impact based on the PP Top 50% values are shown in Table 4 , together with the percentage of excellent papers (i.e. PP Top 10% and PP Top 1% ). The PP TopX% values in columns 2 are relative to the countries’ overall impact of all papers between 1980 and 2012. A value of 200 for example corresponds to twice the impact of the countries’ climate change papers compared to all the countries’ papers in the aforementioned time frame.

All contributing authors are considered; this implies a substantial overlap, since the cooperating authors of a specific paper often work in different countries. In addition, the bibliometric indicators PP Top 50% , PP Top 10% , and PP Top 1% of the countries are included: Column (1) includes the impact of climate change papers, and column (2) displays the impact of climate change papers relative to the overall impact of the countries’ papers published between 1980 and 2012.

https://doi.org/10.1371/journal.pone.0160393.t004

According to Table 4 , research on climate change is quantitatively dominated by the USA, followed by the UK, Germany, and Canada. China appears on rank five, followed by France and Australia. PP Top 50% of these seven countries (with more than 10,000 papers in total) extends between 56.98% (China) and 74.59% (UK). PP Top 1% ranges from 1.6% (China) to 4.13% (UK). PP Top 10% ranges from 14.58% (China) to 26.13% (UK). Hence, the three citation-based indicators exhibit consistently that the UK has produced papers in climate change research with the largest reception compared to the other countries (with more than 10,000 papers). However, the other top countries rank nearby (with the exception of China, which nevertheless ranks above average). Switzerland, Denmark and also The Netherlands (with a publication output between around 3,000 and 6,000 papers) perform top with regard to all three bibliometric indicators–the impact of their contributions to climate change research is impressive. The citation impact of the climate change papers of all countries is above or far above the overall impact of the countries’ papers each.

Li et al. [ 6 ] presented a comparison of publication trends of the top seven most productive countries and found a quite similar ranking concerning the publication numbers (with only one exception: Australia appears on rank 5 compared to rank 7 in our publication output ranking).

Visualization of the time evolution of research topics

The maps presented in Fig 5 and Fig 6 show the title word clusters (clouds) of the climate change papers of the overall publication set (1980–2014) and of the papers from three specific publication time periods (1980–1990, 2003, and 2014). We have chosen these specific time periods in order to compare the papers of the most recent (complete) publication year (2014) with early publication years (1980–1990) and a publication year in between (2003). Due to the low number of papers per year before 1990 (caused by both the low publication output at that time and the lack of abstracts in WoS prior to 1991) we had to accumulate the early papers from a publication time period of about a decade (1980–1990). All title words of the same cluster appear as circles with the same color. The distance between the circles relates to the distance (or closeness) in terms of bibliographic coupling. The size of the circle is proportional to the number of papers found with these terms in the titles.

The minimum number of papers containing a specific title word is 20. Readers interested in an in-depth analysis of our publication set can use VOSviewer interactively and zoom into the clusters. The NET and MAP files for the time period 1980–2014 for VOSviewer can be found at http://www.fkf.mpg.de/CC4_TI_20.zip and a Java-based web-runnable version can be started at http://www.vosviewer.com/vosviewer.php?map=http://www.fkf.mpg.de/CC4_TI_20_map&network=http://www.fkf.mpg.de/CC4_TI_20_net .

https://doi.org/10.1371/journal.pone.0160393.g005

Title words from bibliographic coupling of climate change papers published a) 1980–1990, b) 2003, and c) 2014. The minimum number of papers containing a specific title word is 10. The coloring of the clusters automatically performed by VOSviewer is different for each map of the three selected publication times. Readers interested in an in-depth analysis of our publication set can use VOSviewer interactively and zoom into the clusters. The NET and MAP files for the three time periods 1980–1990, 2003, and 2014 for VOSviewer can be found at http://www.fkf.mpg.de/CC4_TI_10_time_periods.zip and Java-based web-runnable versions can be started at http://www.vosviewer.com/vosviewer.php?map=http://www.fkf.mpg.de/CC4_TI_10_early_map&network=http://www.fkf.mpg.de/CC4_TI_10_early_net for 1980–1990, http://www.vosviewer.com/vosviewer.php?map=http://www.fkf.mpg.de/CC4_TI_10_middle_map&network=http://www.fkf.mpg.de/CC4_TI_10_middle_net for 2003, and http://www.vosviewer.com/vosviewer.php?map=http://www.fkf.mpg.de/CC4_TI_10_late_map&network=http://www.fkf.mpg.de/CC4_TI_10_late_net for 2014.

https://doi.org/10.1371/journal.pone.0160393.g006

The most pronounced title words of the papers published within the overall time period 1980–2014 are climate change , effect , and impact (center). The red cluster (center right) includes papers related to energy and policy topics. Major title words are: climate change , adaptation , emission , framework , uncertainty , cost , technology , and policy (in the order of decreasing frequency). The blue cluster (center left) combines the papers around paleoclimate. Major title words are: record , year , variation , lake , sediment , and event . The green cluster (bottom left) contains theoretical publications. Major title words are: ( climate ) model , data , parametrization , and simulation (but also variability , which often appears in combination with climate modeling). The yellow cluster (center top) illustrates the importance of biological effects of global warming. Major title words are: effect , forest , soil , and plant . And finally, the magenta cluster (top) marks papers concerning acclimatization and survival of species.

If we analyze and compare the maps based on the three selected time spans (c.f. Fig 6 ) we find some remarkable changes: The title word map of the first decade (1980–1990, Fig 6A ) shows the term climate as the most pronounced title word. The terms effect and influence appear secondarily. The term climatic change and the related terms appear third-rated (i.e. as small circles). The title word map constructed from papers published in the year 2003 ( Fig 6B ) for the first time accentuates the term change . The 2014 map ( Fig 6C ) is quite similar to the map of the overall publication set ( Fig 5 ) with climate change and effect as the most pronounced terms. The reader might miss the term impact , but it is hidden behind climate change .

The changing title words based on the maps of the three specific publication times exhibit that the term climate change comes forward with time. Obviously, the authors increasingly use a term which implies global warming (and therewith anthropogenic causes) as a matter of fact. Furthermore, the term impact arises and points to research dealing with the various effects and risks of climate change–see also the IPCC Synthesis Report 2014, Summary for Policymakers [ 3 ]. The term model and related terms (e.g. simulation ) appear independently of time. This indicates the high relevance of climate modeling since the beginning of the time period analyzed here.

This bibliometric study of a large and carefully selected publication set of papers dealing with research on climate change presents a multitude of quantitative data: (1) The growth of the overall publication output of climate change research as well as (2) of some major subfields, (3) the contributing journals and countries and their citation impact, and (4) a title word analysis aiming to illustrate the time evolution and relative importance of specific research topics.

The total number of papers dealing with climate change shows a strong increase: Within the time period 1991 to 2010, the number of climate change papers increased by a factor of ten and exhibits a doubling every 5–6 years. The exponential growth of climate change literature is possibly induced by the increasing influence of the IPCC Assessment Reports, which underlined risks of global warming and eventually made climate change research a hot topic. These reports revealed the strong need of further research for a better understanding of the earth’s climate system and for improved predictions of the future climate. Our findings are in rough accordance with Grieneisen and Zhang [ 28 ], who reported that the number of publications on climate change and global warming has doubled with a rate of approximately every 4 years. In contrast, Stanhill [ 5 ] had found a doubling rate of 11 years. But his publication set is based only on the abstract journal of the American Meteorological Society from the (earlier) time period 1951–1997. Compared with the growth of the overall science, the growth rate of climate change related publications is extraordinarily high: The total volume of publications covered by the WoS between 1980 and 2012 doubled approximately only every 24 years [ 29 ].

According to our subfield analysis, continental biomass related research is the major subfield within climate change research, closely followed by climate modeling. Next come research dealing with oceanic water, with impacts and effects of climate change, and with continental water (lakes, rivers, rainfall). Another major subfield is represented by the topics ice and snow (ice cores are most important for the dating and reconstruction of the earth’s past climate). The next major subfield is related to the atmosphere as another important climate subsystem (including research on clouds, wind, and storms). Research dealing with adaptation, mitigation, risks, and vulnerability of global warming is comparatively small, but their share of papers increased exponentially since 2005. As a more specific research topic and a subset of the oceanic water subfield, research on ocean currents represents the smallest topic within our publication set. The normalized citation impact of all subfields measured in terms of the proportion of most frequently cited papers is significantly above the expected values (50%, 10%, and 1%) and also above the proportions of the total climate change literature. Research on vulnerability (PP Top 1% = 3.51) and on adaptation (PP Top 1% = 3.47) published the largest proportion of very important papers for climate change research.

The journal analysis of our publication set revealed that the Journal of Geophysical Research , the Journal of Climate , and the Geophysical Research Letters appear at the top positions of the publication output ranking (in this order). The journal Climatic Change , which has been founded specifically for research papers on climate change, appears on rank four. Nature as one of the most prominent multidisciplinary journals appears on a lower rank but shows a very high citation impact.

Research on climate change is quantitatively dominated by the USA followed by the UK, Germany, and Canada. China appears on rank five, followed by France and Australia. The PP Top 50% values of these seven countries (with more than 10,000 papers in total) are between 56.98 (China) and 74.59 (UK). The three citation-based indicators exhibit consistently that the UK has produced papers in climate change research with the largest reception compared to the other countries (with more than 10,000 papers). Also, Switzerland, Denmark, and The Netherlands (with a publication output between around 3,000 and 6,000 papers) perform on a high level with regard to the three bibliometric indicators.

We mention here that the literature output can be seen as a combined measure of the size of a specific subfield as well as the amount of research activity and that it is no measure of research performance. For example, research dealing with ice is sometimes connected with highly specific research methods like ice core dating, which can be executed by only a few drilling teams. Although most important for the reconstruction of the earth’s past climate, the publication volume of such research is comparatively low.

The title word analysis shows that the term climate change comes forward with time. Obviously, the authors increasingly use a term which implies global warming (and therewith anthropogenic causes) as a matter of fact. Furthermore, the term impact arises and points to research dealing with the various effects of climate change. The discussion of the question of human induced climate change towards a clear fact (for the majority of the scientific community) stimulated research on future pathways for adaptation and mitigation. Finally, the term model and related terms (e.g. simulation ) appear independently of time, indicating the high relevance of climate modeling also revealed by the subfield analysis.

This study is a first attempt to a mapping of the complete climate change literature. However, more bibliometric research is needed to analyze and overview the research field from a quantitative perspective. Future research should focus on in-depth analyses of more specific topics like the impact of global warming on agriculture, fishery, forestry, and viniculture (winegrowing). Such studies can contribute to an understanding of the evolution, structure, and knowledge base of climate change research.

Like most bibliometric analyses this study has some limitations to be mentioned here: (1) The completeness of our data set is limited by the fact that abstracts are not searchable in WoS prior to 1991. (2) Title words are sometimes multi-meaning and not sufficiently specific for detailed interpretations. Therefore, one should avoid over-interpretation of title word analyses via VOSviewer.

Acknowledgments

The bibliometric data used in this paper are from an in-house database developed and maintained by the Max Planck Digital Library (MPDL, Munich) and derived from the Science Citation Index Expanded (SCI-E), Social Sciences Citation Index (SSCI), Arts and Humanities Citation Index (AHCI) prepared by Thomson Reuters (Philadelphia, Pennsylvania, USA).

Author Contributions

Conceptualization: WM RH. Data curation: WM RH LB. Formal analysis: RH. Investigation: WM RH LB. Methodology: WM RH LB. Validation: WM RH LB. Visualization: RH WM. Writing - original draft: WM RH LB. Writing - review & editing: WM RH LB.

• 1. Climate Change 2014 –IPCC Synthesis Report 2014. Available from: http://www.ipcc.ch/report/ar5/syr/ .
• View Article
• PubMed/NCBI
• Google Scholar
• 3. Climate Change 2014 –IPCC Synthesis Report. Summary for policymakers 2014. Available from: https://www.ipcc.ch/pdf/assessment-report/ar5/syr/AR5_SYR_FINAL_SPM.pdf .
• 14. Climate Change 2001—IPCC Third Assessment Report 2001. Available from: http://www.ipcc.ch/ipccreports/tar/ .
• 22. Wouters P, Thelwall M, Kousha K, Waltman L, de Rijcke S, Rushforth A, et al. The Metric Tide: Literature Review (Supplementary Report I to the Independent Review of the Role of Metrics in Research Assessment and Management). London, UK: Higher Education Funding Council for England (HEFCE), 2015.
• 25. Van Eck NJ, Waltman L. Visualizing Bibliometric Networks. In: Ding Y, Rousseau R, Wolfram D, editors. Measuring Scholarly Impact Springer International Publishing; 2014. p. 285–320.

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Heat waves: a hot topic in climate change research

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• Published: 03 September 2021
• Volume 146 , pages 781–800, ( 2021 )

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• Werner Marx   ORCID: orcid.org/0000-0002-1763-5753 1 ,
• Robin Haunschild   ORCID: orcid.org/0000-0001-7025-7256 1 &
• Lutz Bornmann   ORCID: orcid.org/0000-0003-0810-7091 1 , 2  

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Research on heat waves (periods of excessively hot weather, which may be accompanied by high humidity) is a newly emerging research topic within the field of climate change research with high relevance for the whole of society. In this study, we analyzed the rapidly growing scientific literature dealing with heat waves. No summarizing overview has been published on this literature hitherto. We developed a suitable search query to retrieve the relevant literature covered by the Web of Science (WoS) as complete as possible and to exclude irrelevant literature ( n  = 8,011 papers). The time evolution of the publications shows that research dealing with heat waves is a highly dynamic research topic, doubling within about 5 years. An analysis of the thematic content reveals the most severe heat wave events within the recent decades (1995 and 2003), the cities and countries/regions affected (USA, Europe, and Australia), and the ecological and medical impacts (drought, urban heat islands, excess hospital admissions, and mortality). An alarming finding is that the limit for survivability may be reached at the end of the twenty-first century in many regions of the world due to the fatal combination of rising temperatures and humidity levels measured as “wet-bulb temperature” (WBT). Risk estimation and future strategies for adaptation to hot weather are major political issues. We identified 104 citation classics, which include fundamental early works of research on heat waves and more recent works (which are characterized by a relatively strong connection to climate change).

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1 Introduction

As a consequence of the well-documented phenomenon of global warming, climate change has become a major research field in the natural and medical sciences, and more recently also in the social and political sciences. The scientific community has contributed extensively to a comprehensive understanding of the earth’s climate system, providing various data and projections on the future climate as well as on the effects and risks of anticipated global warming (IPCC 2014; CSSR 2017; NCA4 2018; and the multitude of references cited therein). During recent decades, climate change has also become a major political, economic, and environmental issue and a central theme in political and public debates.

One consequence of global warming is the increase of extreme weather events such as heat waves, droughts, floods, cyclones, and wildfires. Some severe heat waves occurring within the last few decades made heat waves a hot topic in climate change research, with “hot” having a dual meaning: high temperature and high scientific activity. “More intense, more frequent, and longer lasting heat waves in the twenty-first century” is the title of a highly cited paper published 2004 in Science (Meehl and Tebaldi 2004 ). This title summarizes in short what most climate researchers anticipate for the future. But what are heat waves (formerly also referred to as “heatwaves”)? In general, a heat wave is a period of excessively hot weather, which may be accompanied by high humidity. Since heat waves vary according to region, there is no universal definition, but only definitions relative to the usual weather in the area and relative to normal temperatures for the season. The World Meteorological Organization (WMO) defines a heat wave as 5 or more consecutive days of prolonged heat in which the daily maximum temperature is higher than the average maximum temperature by 5 °C (9 °F) or more ( https://www.britannica.com/science/heat-wave-meteorology ).

Europe, for example, has suffered from a series of intense heat waves since the beginning of the twenty-first century. According to the World Health Organization (WHO) and various national reports, the extreme 2003 heat wave caused about 70,000 excess deaths, primarily in France and Italy. The 2010 heat wave in Russia caused extensive crop loss, numerous wildfires, and about 55,000 excess deaths (many in the city of Moscow). Heat waves typically occur when high pressure systems become stationary and the winds on their rear side continuously pump hot and humid air northeastward, resulting in extreme weather conditions. The more intense and more frequently occurring heat waves cannot be explained solely by natural climate variations and without human-made climate change (IPCC 2014; CSSR 2017; NCA4 2018). Scientists discuss a weakening of the polar jet stream caused by global warming as a possible reason for an increasing probability for the occurrence of stationary weather, resulting in heavy rain falls or heat waves (Broennimann et al. 2009 ; Coumou et al. 2015 ; Mann 2019 ). This jet stream is one of the most important factors for the weather in the middle latitude regions of North America, Europe, and Asia.

Until the end of the twentieth century, heat waves were predominantly seen as a recurrent meteorological fact with major attention to drought, being almost independent from human activities and unpredictable like earthquakes. However, since about 1950, distinct changes in extreme climate and weather events have been increasingly observed. Meanwhile, climate change research has revealed that these changes are clearly linked to the human influence on the content of greenhouse gases in the earth’s atmosphere. Climate-related extremes, such as heat waves, droughts, floods, cyclones, and wildfires, reveal significant vulnerability to climate change as a result of global warming.

In recent years, research on heat waves has been established as an emerging research topic within the large field of current climate change research. Bibliometric analyses are very suitable in order to have a systematic and quantitative overview of the literature that can be assigned to an emerging topic such as research dealing with heat waves (e.g., Haunschild et al. 2016 ). No summarizing overview on the entire body of heat wave literature has been published until now. However, a bibliometric analysis of research on urban heat islands as a more specific topic in connection with heat waves has been performed (Huang and Lu 2018 ).

In this study, we analyzed the publications dealing with heat waves using appropriate bibliometric methods and tools. First, we determined the amount and time evolution of the scientific literature dealing with heat waves. The countries contributing the most papers are presented. Second, we analyzed the thematic content of the publications via keywords assigned by the WoS. Third, we identified the most important (influential) publications (and also the historical roots). We identified 104 citation classics, which include fundamental early works and more recent works with a stronger connection to climate change.

2 Heat waves as a research topic

The status of the current knowledge on climate change is summarized in the Synthesis Report of the Fifth Assessment Report (AR5) of the Intergovernmental Panel on Climate Change (IPCC) (IPCC 2014, https://www.ipcc.ch/report/ar5/syr/ ). This panel is the United Nations body for assessing the science related to climate change. The Synthesis Report is based on the reports of the three IPCC Working Groups , including relevant Special Reports . In its Summary for Policymakers , it provides an integrated view of climate change as the final part of the Fifth Assessment Report (IPCC 2014, https://www.ipcc.ch/site/assets/uploads/2018/02/AR5_SYR_FINAL_SPM.pdf ).

In the chapter Extreme Events , it is stated that “changes in many extreme weather and climate events have been observed since about 1950. Some of these changes have been linked to human influences, including a decrease in cold temperature extremes, an increase in warm temperature extremes, an increase in extreme high sea levels and an increase in the number of heavy precipitation events in a number of regions … It is very likely that the number of cold days and nights has decreased and the number of warm days and nights has increased on the global scale. It is likely that the frequency of heat waves has increased in large parts of Europe, Asia and Australia. It is very likely that human influence has contributed to the observed global scale changes in the frequency and intensity of daily temperature extremes since the mid-twentieth century. It is likely that human influence has more than doubled the probability of occurrence of heat waves in some locations” (p. 7–8). Under Projected Changes , the document summarizes as follows: “Surface temperature is projected to rise over the twenty-first century under all assessed emission scenarios. It is very likely that heat waves will occur more often and last longer, and that extreme precipitation events will become more intense and frequent in many regions” (p. 10).

With regard to the USA, the Climate Science Special Report of the U.S. Global Change Research Program (CSSR 2017, https://science2017.globalchange.gov/ ) mentions quite similar observations and states unambiguously in its Fourth National Climate Assessment (Volume I) report ( https://science2017.globalchange.gov/downloads/CSSR2017_FullReport.pdf ) under Observed Changes in Extremes that “the frequency of cold waves has decreased since the early 1900s, and the frequency of heat waves has increased since the mid-1960s (very high confidence). The frequency and intensity of extreme heat and heavy precipitation events are increasing in most continental regions of the world (very high confidence). These trends are consistent with expected physical responses to a warming climate [p. 19]. Heavy precipitation events in most parts of the United States have increased in both intensity and frequency since 1901 (high confidence) [p. 20]. There are important regional differences in trends, with the largest increases occurring in the northeastern United States (high confidence). Recent droughts and associated heat waves have reached record intensity in some regions of the United States … (very high confidence) [p. 21]. Confidence in attribution findings of anthropogenic influence is greatest for extreme events that are related to an aspect of temperature” (p. 123).

Among the key findings in the chapter on temperature changes in the USA, the report states that “there have been marked changes in temperature extremes across the contiguous United States. The frequency of cold waves has decreased since the early 1900s, and the frequency of heat waves has increased since the mid-1960s (very high confidence). Extreme temperatures in the contiguous United States are projected to increase even more than average temperatures. The temperatures of extremely cold days and extremely warm days are both expected to increase. Cold waves are projected to become less intense while heat waves will become more intense (very high confidence) [p. 185]. Most of this methodology as applied to extreme weather and climate event attribution, has evolved since the European heat wave study of Stott et al.” (p. 128).

Heat waves are also discussed in the Fourth National Climate Assessment (Volume II) report (NCA4 2018, https://nca2018.globalchange.gov/ ). The Report-in-Brief ( https://nca2018.globalchange.gov/downloads/NCA4_Report-in-Brief.pdf ) for example states: “More frequent and severe heat waves and other extreme events in many parts of the United States are expected [p. 38]. Heat waves and heavy rainfalls are expected to increase in frequency and intensity [p. 93]. The season length of heat waves in many U.S. cities has increased by over 40 days since the 1960s [p. 30]. Cities across the Southeast are experiencing more and longer summer heat waves [p. 123]. Exposure to hotter temperatures and heat waves already leads to heat-associated deaths in Arizona and California. Mortality risk during a heat wave is amplified on days with high levels of ground-level ozone or particulate air pollution” (p. 150).

In summary, climate change research expects more frequent and more severe heat wave events as a consequence of global warming. It is likely that the more frequent and longer lasting heat waves will significantly increase excess mortality, particularly in urban regions with high air pollution. Therefore, research around heat waves will become increasingly important and is much more than a temporary research fashion.

3 Methodology

3.1 dataset used.

This analysis is based on the relevant literature retrieved from the following databases accessible under the Web of Science (WoS) of Clarivate Analytics: Web of Science Core Collection: Citation Indexes, Science Citation Index Expanded (SCI-EXPANDED), Social Sciences Citation Index (SSCI), Arts & Humanities Citation Index (A&HCI), Conference Proceedings Citation Index—Science (CPCI-S), Conference Proceedings Citation Index—Social Science & Humanities (CPCI-SSH), Book Citation Index—Science (BKCI-S), Book Citation Index—Social Sciences & Humanities (BKCI-SSH), Emerging Sources Citation Index (ESCI).

We applied the search query given in Appendix 1 to cover the relevant literature as completely as possible and to exclude irrelevant literature. We practiced an iterative query optimization by identifying and excluding the WoS subject categories with most of the non-relevant papers. For example, heat waves are also mentioned in the field of materials science but have nothing to do with climate and weather phenomena. Unfortunately, WoS obviously assigned some heat wave papers related to climate to materials science-related subject categories. Therefore, these subject categories were not excluded. By excluding the other non-relevant subject categories, 597 out of 8,568 papers have been removed, resulting in a preliminary publication set of 7,971 papers (#2 of the search query). But this is no safe method, since the excluded categories may well include some relevant papers. Therefore, we have combined these 597 papers with search terms related to climate or weather and retrieved 62 relevant papers in addition, which we added to our preliminary paper subset, eventually receiving 8,033 publications (#3 to #5 of the search query).

Commonly, publication sets for bibliometric analyses are limited to articles, reviews, and conference proceedings as the most relevant document types and are restricted to complete publication years. In this study, however, we have included all relevant WoS document types for a better literature coverage of the research topic analyzed. For example, conference meetings and early access papers may well be interesting for the content analysis of the literature under study. Such literature often anticipates important results, which are published later as regular articles. Furthermore, we have included the literature until the date of search for considering the recent rapid growth of the field. Our search retrieved a final publication set of 8,011 papers indexed in WoS until the date of search (July 1, 2021) and dealing with heat waves (#6 of the search query). We have combined this publication set with climate change-related search terms from a well-proven search query (Haunschild et al. 2016 ) resulting in 4,588 papers dealing with heat waves in connection with climate change or global warming (# 11 of the search query). Also, we have selected a subset of 2,373 papers dealing with heat waves and mortality (#13 of the search query). The complete WoS search query is given in Appendix 1.

The final publication set of 8,011 papers dealing with heat waves still contains some non-relevant papers primarily published during the first half of the twentieth century, such as some Nature papers within the WoS category Multidisciplinary Sciences . Since these papers are assigned only to this broad subject category and have no abstracts and no keywords included, they cannot be excluded using the WoS search and refinement functions. We do not expect any bias through these papers, because their keywords do not appear in our maps. Also, they normally contain very few (if any) cited references, which could bias/impact our reference analysis.

3.2 Networks

We used the VOSviewer software (Van Eck and Waltman 2010 ) to map co-authorship with regard to the countries of authors (88 countries considered) of the papers dealing with heat waves ( www.vosviewer.com ). The map of the cooperating countries presented is based on the number of joint publications. The distance between two nodes is proportionate to the number of co-authored papers. Hence, largely cooperating countries are positioned closer to each other. The size of the nodes is proportionate to the number of papers published by authors of the specific countries.

The method that we used for revealing the thematic content of the publication set retrieved from the WoS is based on the analysis of keywords. For better standardization, we chose the keywords allocated by the database producer (keywords plus) rather than the author keywords. We also used the VOSviewer for mapping the thematic content of the 104 key papers selected by reference analysis. This map is also based on keywords plus.

The term maps (keywords plus) are based on co-occurrence for positioning the nodes on the maps. The distance between two nodes is proportionate to the co-occurrence of the terms. The size of the nodes is proportionate to the number of papers with a specific keyword. The nodes on the map are assigned by VOSviewer to clusters based on a specific cluster algorithm (the clusters are highlighted in different colors). These clusters identify closely related (frequently co-occurring) nodes, where each node is assigned to only one cluster.

3.3 Reference Publication Year Spectroscopy

A bibliometric method called “Reference Publication Year Spectroscopy” (RPYS, Marx et al. 2014 ) in combination with the tool CRExplorer ( http://www.crexplorer.net , Thor et al. 2016a , b ) has proven useful for exploring the cited references within a specific publication set, in order to detect the most important publications of the relevant research field (and also the historical roots). In recent years, several studies have been published, in which the RPYS method was basically described and applied (Marx et al. 2014 ; Marx and Bornmann 2016 ; Comins and Hussey 2015 ). In previous studies, Marx et al. have analyzed the roots of research on global warming (Marx et al. 2017a ), the emergence of climate change research in combination with viticulture (Marx et al. 2017b ), and tea production (Marx et al. 2017c ) from a quantitative (bibliometric) perspective. In this study, we determined which references have been most frequently cited by the papers dealing with heat waves.

RPYS is based on the assumption that peers produce a useful database by their publications, in particular by the references cited therein. This database can be analyzed statistically with regard to the works most important for their specific research field. Whereas individual scientists judge their research field more or less subjectively, the overall community can deliver a more objective picture (based on the principle of “the wisdom of the crowds”). The peers effectively “vote” via their cited references on which works turned out to be most important for their research field (Bornmann and Marx 2013 ). RPYS implies a normalization of citation counts (here: reference counts) with regard to the research area and the time of publication, which both impact the probability to be cited frequently. Basically, the citing and cited papers analyzed were published in the same research field and the reference counts are compared with each other only within the same publication year.

RPYS relies on the following observation: the analysis of the publication years of the references cited by all the papers in a specific research topic shows that publication years are not equally represented. Some years occur particularly frequently among the cited references. Such years appear as distinct peaks in the distribution of the reference publication years (i.e., the RPYS spectrogram). The pronounced peaks are frequently based on a few references that are more frequently cited than other references published in the same year. The frequently cited references are—as a rule—of specific significance to the research topic in question (here: heat waves) and the earlier references among them represent its origins and intellectual roots (Marx et al. 2014 ).

The RPYS changes the perspective of citation analysis from a times cited to a cited reference analysis (Marx and Bornmann 2016 ). RPYS does not identify the most highly cited papers of the publication set being studied (as is usually done by bibliometric analyses in research evaluation). RPYS aims to mirror the knowledge base of research (here: on heat waves).

With time, the body of scientific literature of many research fields is growing rapidly, particularly in climate change research (Haunschild et al. 2016 ). The growth rate of highly dynamic research topics such as research related to heat waves is even larger. As a consequence, the number of potentially citable papers is growing substantially. Toward the present, the peaks of individual publications lie over a broad continuum of newer publications and are less numerous and less pronounced. Due to the many publications cited in the more recent years, the proportion of individual highly cited publications in specific reference publication years falls steadily. Therefore, the distinct peaks in an RPYS spectrogram reveal only the most highly cited papers, in particular the earlier references comprising the historical roots. Further inspection and establishing a more entire and representative list of highly cited works requires consulting the reference table provided by the CRExplorer. The most important references within a specific reference publication year can be identified by sorting the cited references according to the reference publication year (RPY) and subsequently according to the number of cited references (N_CR) in a particular publication year.

The selection of important references in RPYS requires the consideration of two opposing trends: (1) the strongly growing number of references per reference publication year and (2) the fall off near present due to the fact that the newest papers had not sufficient time to accumulate higher citation counts. Therefore, we decided to set different limits for the minimum number of cited references for different periods of reference publication years (1950–1999: N_CR ≥ 50, 2000–2014: N_CR ≥ 150, 2015–2020: N_CR ≥ 100). This is somewhat arbitrary, but is helpful in order to adapt and limit the number of cited references to be presented and discussed.

In order to apply RPYS, all cited references ( n  = 408,247) of 216,932 unique reference variants have been imported from the papers of our publication set on heat waves ( n  = 8,011). The cited reference publication years range from 1473 to 2021. We removed all references (297 different cited reference variants) with reference publication years prior to 1900. Due to the very low output of heat wave-related papers published before 1990, no relevant literature published already in the nineteenth century can be expected. Also, global warming was no issue before 1900 since the Little Ice Age (a medieval cold period) lasted until the nineteenth century. The references were sorted according to RPY and N_CR for further inspection.

The CRExplorer offers the possibility to cluster and merge variants of the same cited reference (Thor et al. 2016a , b ). We clustered and merged the associated reference variants in our dataset (which are mainly caused by misspelled references) using the corresponding CRExplorer module, clustering the reference variants via volume and page numbers and subsequently merging aggregated 374 cited references (for more information on using the CRExplorer see “guide and datasets” at www.crexplorer.net ).

After clustering and merging, we applied a further cutback: to focus the RPYS on the most pronounced peaks, we removed all references ( n  = 212,324) with reference counts below 10 (resulting in a final number of 3,937 cited references) for the detection of the most frequently cited works. A minimum reference count of 10 has proved to be reasonable, in particular for early references (Marx et al. 2014 ). The cited reference publication years now range from 1932 to 2020.

In this study, we have considered all relevant WoS document types for a preferably comprehensive coverage of the literature of the research topic analyzed. The vast majority of the papers of our publication set, however, have been assigned to the document types “article” ( n  = 6.738, 84.1%), “proceedings paper” ( n  = 485, 6.1%), and “review” ( n  = 395 papers, 4.9%). Note that some papers belong to more than one document type.

4.1 Time evolution of literature

In Fig.  1 , the time evolution between 1990 and 2020 of the publications dealing with heat waves is shown (there are only 109 pre-1990 publications dealing with heat waves and covered by the WoS).

Time evolution of the overall number of heat wave publications, of heat wave publications in connection with climate change, and of heat wave publications in connection with mortality, each between 1990 and 2020. For comparison, the overall number of publications (scaled down) in the field of climate change research and the total number of publications covered by the WoS database (scaled down, too) are included

According to Fig.  1 , research dealing with heat waves is a highly dynamic research topic, currently doubling within about 5 years. The number of papers published per year shows a strong increase: since around 2000, the publication output increased by a factor of more than thirty, whereas in the same period, the overall number of papers covered by the WoS increased only by a factor of around three. Also, the portion of heat wave papers dealing with climate change increased substantially: from 16.1 in the period 1990–1999 to 25.7% in 2000, reaching 66.9% in 2020. The distinct decrease of the overall number of papers covered by the WoS between 2019 and 2020 might be a result of the Covid-19 pandemic.

With regard to the various impacts of heat waves, excess mortality is one of the most frequently analyzed and discussed issues in the scientific literature (see below). Whereas the subject specific literature on heat waves increased from 2000 to 2020 by a factor of 33.6, literature on heat waves dealing with mortality increased from 2000 to 2020 by a factor of 51.5. The dynamics of the research topic dealing with heat waves is mirrored by the WoS Citation Report , which shows the time evolution of the overall citation impact of the papers of the publication set (not presented). The citation report curve shows no notable citation impact before 2005, corresponding to the increase of the publication rate since about 2003 as shown in Fig.  1 .

4.2 Countries of authors

In Table 1 , the number of papers assigned to the countries of authors with more than 100 publications dealing with heat waves is presented, showing the national part of research activities on this research topic. For comparative purposes, the percentage of overall papers in WoS of each country is shown. As a comparison with the overall WoS, we only considered WoS papers published between 2000 and 2020, because the heat wave literature started to grow substantially around 2000.

The country-specific percentages from Table 1 are visualized in Fig.  2 . Selected countries are labeled. Countries with a higher relative percentage of more than two percentage points in heat wave research than in WoS overall output are marked blue (blue circle). Countries with a relative percentage at least twice as high in heat wave research than in overall WoS output are marked green (green cross), whereas countries with a relative percentage at most half as much in heat wave research than in overall WoS output are marked with a yellow cross. Only Japan has a much lower output in heat wave research than in WoS overall output, as indicated by the red circle and yellow cross. Most countries are clustered around the bisecting line and are marked gray (gray circle). China and the USA are outside of the plot region. Both countries are rather close to the bisecting line. Some European countries show a much larger activity in heat wave research than in overall WoS output. Australia shows the largest difference and ratio in output percentages as shown by the blue circle and green cross.

Publication percentages of countries in Table 1 . Countries with large deviations between heat wave output and overall WoS output are labeled. Countries with an absolute percentage of more than two percentage points higher (lower) in heat wave research than in overall WoS output are marked blue (red). Countries with a relative percentage at least twice as high (at most half as much) in heat wave research than in overall WoS output are marked green (yellow)

The results mainly follow the expectations of such bibliometric analyses, with one distinct exception: Australia increasingly suffers from extreme heat waves and is comparatively active in heat wave research—compared with its proportion of scientific papers in general. The growth factor of the Australian publication output since 2010 is 8.5, compared to 5.3 for the USA and 3.3 for Germany.

Figure  3 shows the co-authorship network with regard to the countries of authors of the papers dealing with heat waves using the VOSviewer software.

Co-authorship overlay map with regard to the countries of authors and their average publication years from the 8,011 papers dealing with heat waves. The minimum number of co-authored publications of a country is 5; papers with more than 25 contributing countries are neglected; of the 135 countries, 89 meet the threshold, and 88 out of 89 countries are connected and are considered (one country, Armenia, that is disconnected from the network has been removed). The co-authorship network of a single country can be depicted by clicking on the corresponding node in the interactive map. Readers interested in an in-depth analysis can use VOSviewer interactively and zoom into the map via the following URL: https://tinyurl.com/3ywkwv8t

According to Fig.  3 and in accordance with Table 1 , the USA is most productive in heat wave research. This is not unexpected, because the US publication output is at the top for most research fields. However, this aside, the USA has been heavily affected by heat wave events and is leading with regard to the emergence of the topic. Australia appears as another major player and is strongly connected with the US publications within the co-authorship network and thus appears as a large node near the US node in the map. Next, the leading European countries England, France, Germany, Italy, and Spain appear.

The overlay version of the map includes the time evolution of the research activity in the form of coloring of the nodes. The map shows the mean publication year of the publications for each specific author country. As a consequence, the time span of the mean publication years ranges only from 2014 to 2018. Nevertheless, the early activity in France and the USA and the comparatively recent activity in Australia and China, with the European countries in between, become clearly visible.

4.3 Topics of the heat wave literature

Figure  4 shows the keywords (keywords plus) map for revealing the thematic content of our publication set using the VOSviewer software. This analysis is based on the complete publication set ( n  = 8,011). The minimum number of occurrences of keywords is 10; of the 10,964 keywords, 718 keywords met the threshold. For each of the 718 keywords, the total strength of the co-occurrence links with other keywords was calculated. The keywords with the greatest total link strength were selected for presentation in the map.

Co-occurrence network map of the keywords plus from the 8,011 papers dealing with heat waves for a rough analysis of the thematic content. The minimum number of occurrences of keywords is 10; of the 10,964 keywords, 718 meet the threshold. Readers interested in an in-depth analysis can use VOSviewer interactively and zoom into the map via the following URL: https://tinyurl.com/enrdbw

According to Fig.  4 , the major keywords are the following: climate change, temperature, mortality, impact, heat waves (searched), and variability. The colored clusters identify closely related (frequently co-occurring) nodes. The keywords marked red roughly originate from fundamental climate change research focused on the hydrological cycle (particularly on drought), the keywords of the green cluster are around heat waves and moisture or precipitation, the keywords marked blue result from research concerning impacts of heat waves on health, the keywords marked yellow are focused on the various other impacts of heat waves, and the keywords of the magenta cluster are around adaptation and vulnerability in connection with heat waves.

The clustering by the VOSviewer algorithm provides basic categorizations, but many related keywords also appear in different clusters. For example, severe heat wave events are marked in different colors. For a better overview of the thematic content of the publications dealing with heat waves, we have assigned the keywords of Fig.  4 (with a minimum number of occurrences of 50) to ten subject categories (each arranged in the order of occurrence):

Countries/regions: United-States, Europe, France, China, Pacific, Australia, London, England

Cities: cities, city, US cities, Chicago, communities

Events: 2003 heat-wave, 1995 heat-wave

Impacts: impact, impacts, air-pollution, drought, soil-moisture, exposure, heat-island, urban, islands, photosynthesis, pollution, heat-island, air-quality, environment, precipitation extremes, biodiversity, emissions

Politics: risk, responses, vulnerability, adaptation, management, mitigation, risk-factors, scenarios

Biology: vegetation, forest, diversity, stomatal conductance

Medicine: mortality, health, stress, deaths, morbidity, hospital admissions, public-health, thermal comfort, population, heat, sensitivity, human health, disease, excess mortality, heat-stress, heat-related mortality, comfort, behavior, death, stroke

Climate research: climate change, temperature, climate, model, simulation, energy, projections, simulations, cmip5, ozone, el-nino, parametrization, elevated CO 2 , models, climate variability, carbon, carbon-dioxide

Meteorology: heat waves, variability, precipitation, summer, heat-wave, weather, ambient-temperature, waves, extremes, wave, cold, water, rainfall, circulation, heat, air-temperature, extreme heat, climate extremes, heatwaves, temperature extremes, temperatures, temperature variability, high-temperature, ocean, extreme temperatures, atmospheric circulation, interannual variability, sea-surface temperature, oscillation, surface temperature, surface

Broader terms (multi-meaning): trends, events, patterns, growth, performance, time-series, indexes, system, dynamics, association, index, tolerance, productivity, ensemble, resilience, increase, quality, prediction, frequency, particulate matter, future, framework, 20 th -century, time, reanalysis, systems

Although allocated by the database provider, the keywords are not coherent. For example, the same keyword may appear as singular or plural, and complex keywords are written with and without hyphens.

In order to compare the thematic content of the complete publication set with the earlier literature on heat waves, we have analyzed the pre-2000 publications ( n  = 297) separately. Figure  5 shows the keywords (keywords plus) map for revealing the thematic content of the pre-2000 papers.

Co-occurrence network map of the keywords plus from the 297 pre-2000 papers dealing with heat waves for a rough analysis of the thematic content. The minimum number of occurrences of keywords is 1; of the 389 keywords, 277 keywords are connected, and all items are shown. Readers interested in an in-depth analysis can use VOSviewer interactively and zoom into the map via the following URL: https://tinyurl.com/u2zzr399

The major nodes in Fig.  5 are heat waves (searched), temperature, United States, and mortality, with climate change appearing only as a smaller node here. Obviously, the connection between heat waves and climate change was not yet pronounced, which can also be seen from Fig.  1 . Compared with Fig.  4 , the thematic content of the clusters is less clear and the clusters presented in Fig.  5 can hardly be assigned to specific research areas. For a better overview of the thematic content of the early publications dealing with heat waves, we have assigned the connected keywords of Fig.  5 to seven subject categories:

Countries/regions: United-States, Great-Plains

Cities: St-Louis, Athens, Chicago

Events: 1980 heat-wave, 1995 heat-wave

Impacts: impacts, responses, drought, precipitation, comfort, sultriness

Climate research: climate, climate change, model, temperature, variability

Medicine: cardiovascular deaths, mortality, air pollution

Meteorology: atmospheric flow, weather, heat, humidity index

4.4 Important publications

Figures  6 – 8 show the results of the RPYS analysis performed with the CRExplorer and present the distribution of the number of cited references across the reference publication years. Figure  6 shows the RPYS spectrogram of the full range of reference publication years since 1925. Figure  7 presents the spectrogram for the reference publication year period 1950–2000 for better resolving the historical roots. Figure  8 shows the spectrogram for the period 2000–2020, comprising the cited references from the bulk of the publication set analyzed.

Annual distribution of cited references throughout the time period 1925–2020, which have been cited in heat wave-related papers (published between 1964 and 2020). Only references with a minimum reference count of 10 are considered

Annual distribution of cited references throughout the time period 1950–2000, which have been cited in heat wave-related papers (published between 1972 and 2020). Only references with a minimum reference count of 10 are considered

Annual distribution of cited references throughout the time period 2000–2020, which have been cited in heat wave-related papers (published between 2000 and 2020). Only references with a minimum reference count of 10 are considered

The gray bars (Fig.  6 ) and red lines (Figs. 7 – 8 ) in the graphs visualize the number of cited references per reference publication year. In order to identify those publication years with significantly more cited references than other years, the (absolute) deviation of the number of cited references in each year from the median of the number of cited references in the two previous, the current, and the two following years (t − 2; t − 1; t; t + 1; t + 2) is also visualized (blue lines). This deviation from the 5-year median provides a curve smoother than the one in terms of absolute numbers. We inspected both curves for the identification of the peak papers.

Which papers are most important for the scientific community performing research on heat waves? We use the number of cited references (N_CR) as a measure of the citation impact within the topic-specific literature of our publication set. N_CR should not be confused with the overall number of citations of the papers as given by the WoS citation counts (times cited). These citation counts are based on all citing papers covered by the complete database (rather than a topic-specific publication set) and are usually much higher.

Applying the selection criteria mentioned above (minimum number of cited references between 50 and 150 in three different periods), 104 references have been selected as key papers (important papers most frequently referenced within the research topic analyzed) and are presented in Table 2 in Appendix 2. The peak papers corresponding to reference publication years below about 2000 can be seen as the historical roots of the research topic analyzed. Since around 2000, the number of references with the same publication year becomes increasingly numerous, usually with more than one highly referenced (cited) paper at the top. Although there are comparatively fewer distinct peaks visible in the RPYS spectrogram of Fig.  8 , the most frequently referenced papers can easily be identified via the CRE reference listing. Depending on the specific skills and needs (i.e., the expert knowledge and the intended depth of the analysis), the number of top-referenced papers considered key papers can be defined individually.

Table 2 lists the first authors and titles of the 104 key papers selected, their number of cited references (N_CR), and the DOIs for easy access. Some N_CR values are marked by an asterisk, indicating a high value of the N_TOP10 indicator implemented in the CRExplorer. The N_TOP10 indicator value is the number of reference publication years in which a focal cited reference belongs to the 10% most referenced publications. In the case of about half of the cited references in Table 2 ( n  = 58), the N_TOP10 value exceeded a value of 9. The three highest values in our dataset are 24, 21, and 20.

Out of the 104 key papers from Table 2 , 101 have a DOI of which we found 101 papers in the WoS. Three papers have no DOI but could be retrieved from WoS. The altogether 104 papers were exported and their keywords (keywords plus) were displayed in Fig.  9 for revealing the thematic content of the key papers from the RPYS analysis at a glance.

Co-occurrence network map of the keywords plus of the 104 key papers dealing with heat waves selected applying RPYS via CRE software and listed in Table 2 . The minimum number of occurrences of keywords is 2; of the 310 keywords, 91 meet the threshold. Readers interested in an in-depth analysis can use VOSviewer interactively and zoom into the map via the following URL: https://tinyurl.com/4vwpc4t2

Overall, the keywords mapped in Fig.  9 are rather similar to the keywords presented in Fig.  4 . Besides climate change, temperature, weather, and air-pollution, the keywords deaths, health, mortality, and United-States appear as the most pronounced terms.

The key papers presented in Table 2 can be categorized as follows: (1) papers dealing with specific heat wave events, (2) the impact of heat waves on human health, (3) heat wave-related excess mortality and implications for prevention, (4) the interaction between air pollution and high temperature, (5) circulation pattern and the meteorological basis, (6) future perspectives and risks, and (7) climate models, indicators, and statistics.

5 Discussion

Today, the hypothesis of a human-induced climate change is no longer abstract but has become a clear fact, at least for the vast majority of the scientific community (IPCC 2014; CSSR 2017; NCA4 2018; and the multitude of references cited therein). The consequences of a warmer climate are already obvious. The rapidly growing knowledge regarding the earth’s climate system has revealed the connection between global warming and extreme weather events. Heat waves impact people directly and tangibly and many people are pushing for political actions. Research on heat waves came up with the occurrence of some severe events in the second half of the twentieth century and was much stimulated by the more numerous, more intense, and longer lasting heat waves that have occurred since the beginning of the twenty-first century.

As already mentioned in Sect.  1 , the more intense and more frequently occurring heat waves cannot be explained solely by natural climate variations but only with human-made climate change. As a consequence, research on heat waves has become embedded into meteorology and climate change research and has aimed to understand the specific connection with global warming. Scientists discuss a weakening of the polar jet stream as a possible reason for an increasing probability for the occurrence of heat waves (e.g., Broennimann et al. 2009 ; Coumou et al. 2015 ; Mann 2019 ). Climate models are used for projections of temperature and rainfall variability in the future, based on various scenarios of greenhouse gas emissions. As a result, the corresponding keywords appear in the maps of Figs. 4 and 9 . Also, the application of statistics plays a major role in the papers of our publication set; some of the most highly referenced (early) papers in Table 2 primarily deal with statistical methods. These methods provide the basis for research on heat waves.

Our analysis shows that research on heat waves has become extremely important in the medical area, since severe heat waves have caused significant excess mortality (e.g., Kalkstein and Davis 1989 ; Fouillet et al. 2006 ; Anderson and Bell 2009 , 2011 ). The most alarming is that the limit for survivability may be reached at the end of the twenty-first century in many regions of the world due to the fatal combination of rising temperatures and humidity levels (e.g., Pal and Eltahir 2016 ; Im et al. 2017 ; Kang and Eltahir 2018 ). The combination of heat and humidity is measured as the “wet-bulb temperature” (WBT), which is the lowest temperature that can be reached under current ambient conditions by the evaporation of water. At 100% relative humidity, the wet-bulb temperature is equal to the air temperature and is different at lower humidity levels. For example, an ambient temperature of 46 °C and a relative humidity of 50% correspond to 35 °C WBT, which is the upper limit that can kill even healthy people within hours. By now, the limit of survivability has almost been reached in some places. However, if global warming is not seriously tackled, deadly heat waves are anticipated for many regions that have contributed little to climate change.

According to high-resolution climate change simulations, North China and South Asia are particularly at risk, because the annual monsoon brings hot and humid air to these regions (Im et al. 2017 ; Kang and Eltahir 2018 ). The fertile plain of North China has experienced vast expansion of irrigated agriculture, which enhances the intensity of heat waves. South Asia, a region inhabited by about one-fifth of the global human population, is likely to approach the critical threshold by the late twenty-first century, if greenhouse gas emissions are not lowered significantly. In particular, the densely populated agricultural regions of the Ganges and Indus river basins are likely to be affected by extreme future heat waves. Also, the Arabic-speaking desert countries of the Gulf Region in the Middle East and the French-speaking parts of Africa are expected to suffer from heat waves beyond the limit of human survival. But to date, only 12 papers have been published on heat waves in connection with wet-bulb temperature (#15 of the search query); no paper was published before 2016. Some papers report excess hospital admissions during heat wave events (e.g., Semenza et al. 1999 ; Knowlton et al. 2009 ), with the danger of a temporary capacity overload of local medical systems in the future. Presumably, this will be an increasingly important issue in the future, when more and larger urban areas are affected by heat waves beyond the limit of human survival indicated by wet-bulb temperatures above 35° C.

The importance of heat waves for the medical area is underlined by the large portion of papers discussing excess hospital admissions and excess mortality during intense heat wave events, particularly in urban areas with a high population density. As was the case during the boom phase of the Covid-19 pandemic, local medical health care systems may become overstressed by long-lasting heat wave events and thus adaptation strategies are presented and discussed. Finally, the analysis of the keywords in this study reveals the connection of heat wave events with air pollution in urban regions. There seems to be evidence of an interaction between air pollution and high temperatures in the causation of excess mortality (e.g., Katsouyanni et al. 1993 ). Two more recent papers discuss the global risk of deadly heat (Mora et al. 2017 ) and the dramatically increasing chance of extremely hot summers since the 2003 European heat wave (Christidis et al. 2015 ).

Another important topic of the heat wave papers is related to the consequences for agriculture and forestry. Reduced precipitation and soil moisture result in crop failure and put food supplies at risk. Unfortunately, large regions of the world that contribute least to the emission of greenhouse gases are affected most by drought, poor harvests, and hunger. Some more recent papers discuss the increasing probability of marine heat waves (Oliver et al. 2018 ) and the consequences for the marine ecosystem (Smale et al. 2019 ).

The results of this study should be interpreted in terms of its limitations:

We tried to include in our bibliometric analyses all relevant heat wave papers covered by the database. Our long-standing experience in professional information retrieval has shown, however, that it is sheer impossible to get complete and clean results by search queries against the backdrop of the search functions provided by literature databases like WoS or others. Also, the transition from relevant to non-relevant literature is blurred and is a question of the specific needs. In this study, we used bibliometric methods that are relatively robust with regard to the completeness and precision of the publication sets analyzed. For example, it is an advantage of RPYS that a comparatively small portion of relevant publications (i.e., an incomplete publication set) contains a large amount of the relevant literature as cited references. The number of cited references is indeed lowered as a consequence of an incomplete publication set. However, this does not significantly affect the results, since the reference counts are only used as a relative measure within specific publication years.

As most literature databases, the WoS does not cover each and every scientific journal but only a carefully selected set of core journals most important for scientific disciplines. The coverage or comprehensiveness of the database can be estimated by comparing the number of all cited references with the number of the linked cited references (i.e., the references, which correspond to papers appearing in publications covered by the database as publication records). Based on the publication years 1990, 1995, 2000, 2005, and 2010, about 70% of all references in the natural sciences are linked references (Marx and Bornmann 2015 ). Thus, about 30% of the cited literature of these disciplines is not covered by the database in the form of paper records, presumably many non-English publications. It may be true that the publication set analyzed is biased toward mid-latitude developed countries, disadvantaging countries with most people suffering from humid heat waves. Parts of the most extreme heat waves occur in the French-speaking parts of Africa and the Arabic-speaking desert countries. Presumably, relevant literature like national reports discussing for example the local impact of extreme heat waves is not included in this analysis. However, if such documents were highly relevant, they should be cited in the literature covered by the WoS. In this case, our RPYS analysis would have discovered them. Therefore, we are confident that at least the highly relevant documents of the heat wave literature are considered in our analysis.

Two other limitations of this study refer to the RPYS of the heat wave paper set:

There are numerous rather highly cited references retrieved by RPYS via CRExplorer but not considered in the listing of Table 2 due to the selection criteria applied. Many of these non-selected papers have N_CR values just below the limits that we have set. Therefore, papers not included in our listing are not per se qualified as much less important or even unimportant.

In the interpretation of cited references counts, one should have in mind that they rely on the “popularity” of a publication being cited in subsequent research. The counts measure impact but not scientific importance or accuracy (Tahamtan and Bornmann 2019 ). Note that there are many reasons why authors cite publications (Tahamtan and Bornmann 2018 ), thus introducing a lot of “noise” in the data (this is why RPYS focuses on the cited reference peaks).

Our suggestions for future empirical analysis refer to the impact of the scientific heat wave discourse on social networks and funding of basic research on heat waves around topics driven by political pressure. Whereas this paper focuses on the scientific discourse around heat waves, it would be interesting if future studies were to address the policy relevance of the heat waves research.

Data availability

Not applicable.

Code availability

Change history, 23 february 2022.

The original version of this paper was updated to add the missing compact agreement Open Access funding note.

Anderson BG, Bell ML (2009) Weather-related mortality how heat, cold, and heat waves affect mortality in the United States. Epidemiology 20(2):205–213. https://doi.org/10.1097/EDE.0b013e318190ee08

Anderson GB, Bell ML (2011) Heat waves in the United States: mortality risk during heat waves and effect modification by heat wave characteristics in 43 U.S. communities. Enviro Health Perspect 119(2):210–218. https://doi.org/10.1289/ehp.1002313

Article   Google Scholar  

Bornmann L, Marx W (2013) The wisdom of citing scientists. J Am Soc Inf Sci 65(6):1288–1292. https://doi.org/10.1002/asi.23100

Broennimann S, Stickler A, Griesser T, Ewen T, Grant AN, Fischer AM, Schraner M, Peter T, Rozanov E, Ross T (2009) Exceptional atmospheric circulation during the "Dust Bowl". Geophysical Research Letters 36: article number L08802. https://doi.org/10.1029/2009GL037612

Christidis N, Jones G, Stott P (2015) Dramatically increasing chance of extremely hot summers since the 2003 European heatwave. Nat Clim Chang 5:46–50. https://doi.org/10.1038/nclimate2468

Comins JA, Hussey TW (2015) Detecting seminal research contributions to the development and use of the global positioning system by Reference Publication Year Spectroscopy. Scientometrics 104:575–580. https://doi.org/10.1007/s11192-015-1598-2

Coumou D, Lehmann J, Beckmann J (2015) The weakening summer circulation in the Northern Hemisphere mid-latitudes. Science 348:324–327. https://doi.org/10.1126/science.1261768

CSSR 2017: Climate Science Special Report: Fourth National Climate Assessment, Volume I [Wuebbles, D.J., D.W. Fahey, K.A. Hibbard, D.J. Dokken, B.C. Stewart, and T.K. Maycock (eds.)]. U.S. Global Change Research Program, Washington, DC, USA, 470, https://doi.org/10.7930/J0J964J6 , https://science2017.globalchange.gov/downloads/CSSR2017_FullReport.pdf

Fouillet A, Rey G, Laurent F, Pavillon G, Bellec S, Guihenneuc-Jouyaux C, Clavel J, Jougla E, Hemon D (2006) Excess mortality related to the August 2003 heat wave in France. Int Arch Occup Environ Health 80(1):16–24. https://doi.org/10.1007/s00420-006-0089-4

Haunschild R, Bornmann L, Marx W (2016) Climate change research in view of bibliometrics. PLoS ONE 11:e0160393. https://doi.org/10.1371/journal.pone.0160393

Huang QF, Lu YQ (2018) Urban heat island research from 1991 to 2015: a bibliometric analysis. Theoret Appl Climatol 131(3–4):1055–1067. https://doi.org/10.1007/s00704-016-2025-1

Im ES, Pal JS, Eltahir EAB (2017) Deadly heat waves projected in the densely populated agricultural regions of South Asia. Science Advances 3(8): article number e1603322. https://doi.org/10.1126/sciadv.1603322

IPCC 2014: Climate change, Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, R.K. Pachauri and L.A. Meyer (eds.)]. IPCC, Geneva, Switzerland, 151 https://www.ipcc.ch/report/ar5/syr/

IPCC 2014: Climate Change, Summary for Policymakers. In: IPCC, 2014: Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, R.K. Pachauri and L.A. Meyer (eds.)]. IPCC, Geneva, Switzerland, 151 https://www.ipcc.ch/site/assets/uploads/2018/02/AR5_SYR_FINAL_SPM.pdf

Kalkstein LS, Davis RE (1989) Weather and human mortality – an evaluation of demographic and interregional responses in the United-States. Ann Assoc Am Geogr 79(1):44–64. https://doi.org/10.1111/j.1467-8306.1989.tb00249.x

Kang S, Eltahir EAB (2018) North China Plain threatened by deadly heatwaves due to climate change and irrigation. Nature Communications 9: article number 2894. https://doi.org/10.1038/s41467-018-05252-y

Katsouyanni K, Pantazopoulou A, Touloumi G, Tselepidaki I, Moustris K, Asimakopoulos D, Poulopoulou G, Trichopoulos D (1993) Evidence for interaction between air-pollution and high-temperature in the causation of excess mortality. Arch Environ Health 48(4):235–242. https://doi.org/10.1080/00039896.1993.9940365

Knowlton K, Rotkin-Ellman M, King G, Margolis HG, Smith D, Solomon G, Trent R, English P (2009) The 2006 California heat wave: impacts on hospitalizations and emergency department visits. Environ Health Perspect 117(1):61–67. https://doi.org/10.1289/ehp.11594

Mann ME (2019) The weather amplifier: strange waves in the jet stream foretell a future full of heat waves and floods. Sci Am 320(3):43–49

Google Scholar  

Marx W, Bornmann L, Barth A, Leydesdorff L (2014) Detecting the historical roots of research fields by Reference Publication Year Spectroscopy (RPYS). J Am Soc Inf Sci 65:751–764. https://doi.org/10.1002/asi.23089

Marx W, Bornmann L (2015) On the causes of subject-specific citation rates in Web of Science. Scientometrics 102(2):1823–1827. https://doi.org/10.1007/s11192-014-1499-9

Marx W, Bornmann L (2016) Change of perspective: Bibliometrics from the point of view of cited references. A literature overview on approaches to the evaluation of cited references in bibliometrics. Scientometrics 109(2):1397–1415. https://doi.org/10.1007/s11192-016-2111-2

Marx W, Haunschild R, Thor A, Bornmann L (2017a) Which early works are cited most frequently in climate change research literature? A bibliometric approach based on reference publication year spectroscopy. Scientometrics 110(1):335–353. https://doi.org/10.1007/s11192-016-2177-x

Marx W, Haunschild R, Bornmann L (2017b) Climate change and viticulture—a quantitative analysis of a highly dynamic research field. Vitis 56:35–43. https://doi.org/10.5073/vitis.2017.56.35-43

Marx W, Haunschild R, Bornmann L (2017c) Global warming and tea production – the bibliometric view on a newly emerging research topic. Climate 5(3): article number 46. https://doi.org/10.3390/cli5030046

Meehl GA, Tebaldi C (2004) More intense, more frequent, and longer lasting heat waves in the 21 st century. Science 305:994–997. https://doi.org/10.1126/science.1098704

Mora C, Dousset B, Caldwell I et al (2017) Global risk of deadly heat. Nat Clim Chang 7:501–506. https://doi.org/10.1038/nclimate3322

NCA4 2018: Fourth National Climate Assessment, Volume II: impacts, risks, and adaptation in the United States. https://nca2018.globalchange.gov/ NCA 2018 Report-in-Brief: https://nca2018.globalchange.gov/downloads/NCA4_Report-in-Brief.pdf

Oliver ECJ, Donat MG, Burrows MT et al (2018) Longer and more frequent marine heatwaves over the past century. Nat Commun 9:1324. https://doi.org/10.1038/s41467-018-03732-9

Pal JS, Eltahir EAB (2016) Future temperature in southwest Asia projected to exceed a threshold for human adaptability. Nat Clim Chang 6(2):197–200. https://doi.org/10.1038/NCLIMATE2833

Semenza JC, McCullough JE, Flanders WD, McGeehin MA, Lumpkin JR (1999) Excess hospital admissions during the July 1995 heat wave in Chicago. Am J Prev Med 16(4):269–277. https://doi.org/10.1016/S0749-3797(99)00025-2

Smale DA, Wernberg T, Oliver ECJ et al (2019) Marine heatwaves threaten global biodiversity and the provision of ecosystem services. Nat Clim Chang 9:306–312. https://doi.org/10.1038/s41558-019-0412-1

Tahamtan I, Bornmann L (2018) Core elements in the process of citing publications: Conceptual overview of the literature. J Informet 12:203–216. https://doi.org/10.1016/j.joi.2018.01.002

Tahamtan I, Bornmann L (2019) What do citation counts measure? An updated review of studies on citations in scientific documents published between 2006 and 2018. Scientometrics 121:1635–1684. https://doi.org/10.1007/s11192-019-03243-4

Thor A, Marx W, Leydesdorff L, Bornmann L (2016a) Introducing CitedReferencesExplorer (CRExplorer): a program for Reference Publication Year Spectroscopy with cited references disambiguation. J Informet 10:503–515. https://doi.org/10.1016/j.joi.2016.02.005

Thor A, Marx W, Leydesdorff L, Bornmann L (2016b) New features of CitedReferencesExplorer (CRExplorer). Scientometrics 109:2049–2051. https://doi.org/10.1007/s11192-016-2082-3

Thor A, Bornmann L, Marx W, Mutz R (2018) Identifying single influential publications in a research field: new analysis opportunities of the CRExplorer. Scientometrics 116(1):591–608. https://doi.org/10.1007/s11192-018-2733-7

Van Eck NJ, Waltman L (2010) Software survey: VOSviewer, a computer program for bibliometric mapping. Scientometrics 84(2):523–538. https://doi.org/10.1007/s11192-009-0146-3

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Consensus on consensus: a synthesis of consensus estimates on human-caused global warming

John Cook 16,1,2,3 , Naomi Oreskes 4 , Peter T Doran 5 , William R L Anderegg 6,7 , Bart Verheggen 8 , Ed W Maibach 9 , J Stuart Carlton 10 , Stephan Lewandowsky 11,2 , Andrew G Skuce 12,3 , Sarah A Green 13 , Dana Nuccitelli 3 , Peter Jacobs 9 , Mark Richardson 14 , Bärbel Winkler 3 , Rob Painting 3 and Ken Rice 15

Published 13 April 2016 • © 2016 IOP Publishing Ltd Environmental Research Letters , Volume 11 , Number 4 Citation John Cook et al 2016 Environ. Res. Lett. 11 048002 DOI 10.1088/1748-9326/11/4/048002

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1 Global Change Institute, University of Queensland, Australia

2 School of Psychology, University of Western Australia, Australia

3 Skeptical Science, Brisbane, Queensland, Australia

4 Department of the History of Science, Harvard University, USA

5 Geology and Geophysics, Louisiana State University, USA

6 Department of Biology, University of Utah, USA

7 Princeton Environmental Institute, Princeton University, USA

8 Amsterdam University College, The Netherlands

9 Department of Environmental Science and Policy, George Mason University, USA

10 Texas Sea Grant College Program, Texas A&M University, College Station, TX USA

11 University of Bristol, UK

12 Salt Spring Consulting Ltd, Salt Spring Island, BC, Canada

13 Department of Chemistry, Michigan Technological University, USA

14 University of Reading, Reading, UK, now at Jet Propulsion Lab, California Institute of Technology, Pasadena, USA

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16 Author to whom any correspondence should be addressed.

J Stuart Carlton https://orcid.org/0000-0003-2530-8688

Stephan Lewandowsky https://orcid.org/0000-0003-1655-2013

• Received 28 April 2015
• Revised 27 November 2015
• Accepted 1 March 2016
• Published 13 April 2016

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The consensus that humans are causing recent global warming is shared by 90%–100% of publishing climate scientists according to six independent studies by co-authors of this paper. Those results are consistent with the 97% consensus reported by Cook et al ( Environ. Res. Lett . 8 024024 ) based on 11 944 abstracts of research papers, of which 4014 took a position on the cause of recent global warming. A survey of authors of those papers ( N  = 2412 papers) also supported a 97% consensus. Tol (2016 Environ. Res. Lett. 11 048001 ) comes to a different conclusion using results from surveys of non-experts such as economic geologists and a self-selected group of those who reject the consensus. We demonstrate that this outcome is not unexpected because the level of consensus correlates with expertise in climate science. At one point, Tol also reduces the apparent consensus by assuming that abstracts that do not explicitly state the cause of global warming ('no position') represent non-endorsement, an approach that if applied elsewhere would reject consensus on well-established theories such as plate tectonics. We examine the available studies and conclude that the finding of 97% consensus in published climate research is robust and consistent with other surveys of climate scientists and peer-reviewed studies.

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1. Introduction

Climate scientists overwhelmingly agree that humans are causing recent global warming. The consensus position is articulated by the Intergovernmental Panel on Climate Change (IPCC) statement that 'human influence has been the dominant cause of the observed warming since the mid-20th century' (Qin et al 2014 , p 17). The National Academies of Science from 80 countries have issued statements endorsing the consensus position (table S2). Nevertheless, the existence of the consensus continues to be questioned. Here we summarize studies that quantify expert views and examine common flaws in criticisms of consensus estimates. In particular, we are responding to a comment by Tol ( 2016 ) on Cook et al ( 2013 , referred to as C13). We show that contrary to Tol's claim that the results of C13 differ from earlier studies, the consensus of experts is robust across all the studies conducted by coauthors of this correspondence.

Tol's erroneous conclusions stem from conflating the opinions of non-experts with experts and assuming that lack of affirmation equals dissent. A detailed technical response to Tol is provided in (S1) where we specifically address quibbles about abstract ID numbers, timing of ratings, inter-rater communication and agreement, and access to ratings. None of those points raised by Tol affect the calculated consensus. Most importantly, the 97% consensus derived from abstract ratings is validated by the authors of the papers studied who responded to our survey ( N  = 2142 papers) and also reported a 97% consensus in papers taking a position. The remainder of this paper shows that a high level of scientific consensus, in agreement with our results, is a robust finding in the scientific literature. This is used to illustrate and address the issues raised by Tol that are relevant to our main conclusion.

2. Assessing expert consensus

Efforts to measure scientific consensus need to identify a relevant and representative population of experts, assess their professional opinion in an appropriate manner, and avoid distortions from ambiguous elements in the sample. Approaches that have been employed to assess expert views on anthropogenic global warming (AGW) include analysing peer-reviewed climate papers (Oreskes 2004 ; C13), surveying members of the relevant scientific community (Bray and von Storch 2007 , Doran and Zimmerman 2009 , Bray 2010 , Rosenberg et al 2010 , Farnsworth and Lichter 2012 , Verheggen et al 2014 , Stenhouse et al 2014 , Carlton et al 2015 ), compiling public statements by scientists (Anderegg et al 2010 ), and mathematical analyses of citation patterns (Shwed and Bearman 2010 ). We define domain experts as scientists who have published peer-reviewed research in that domain, in this case, climate science. Consensus estimates for these experts are listed in table 1 , with the range of estimates resulting primarily from differences in selection of the expert pool, the definition of what entails the consensus position, and differences in treatment of no position responses/papers.

Table 1.   Estimates of consensus on human-caused global warming among climate experts.

The studies in table 1 have taken various approaches to selecting and querying pools of experts. Oreskes ( 2004 ) identified expressions of views on AGW in the form of peer-reviewed papers on 'global climate change'. This analysis found no papers rejecting AGW in a sample of 928 papers published from 1993 to 2003, that is, 100% consensus among papers stating a position on AGW.

Following a similar methodology, C13 analysed the abstracts of 11 944 peer-reviewed papers published between 1991 and 2011 that matched the search terms 'global climate change' or 'global warming' in the ISI Web of Science search engine. Among the 4014 abstracts stating a position on human-caused global warming, 97.1% were judged as having implicitly or explicitly endorsed the consensus. In addition, the study authors were invited to rate their own papers, based on the contents of the full paper, not just the abstract. Amongst 1381 papers self-rated by their authors as stating a position on human-caused global warming, 97.2% endorsed the consensus.

Shwed and Bearman ( 2010 ) employed citation analysis of 9432 papers on global warming and climate published from 1975 to 2008. Unlike surveys or classifications of abstracts, this method was entirely mathematical and blind to the content of the literature being examined. By determining the modularity of citation networks, they concluded, 'Our results reject the claim of inconclusive science on climate change and identify the emergence of consensus earlier than previously thought' (p. 831). Although this method does not produce a numerical consensus value, it independently demonstrates the same level of scientific consensus on AGW as exists for the fact that smoking causes cancer.

Anderegg et al ( 2010 ) identified climate experts as those who had authored at least 20 climate-related publications and chose their sample from those who had signed public statements regarding climate change. By combining published scientific papers and public statements, Anderegg et al determined that 97%–98% of the 200 most-published climate scientists endorsed the IPCC conclusions on AGW.

Other studies have directly queried scientists, typically choosing a sample of scientists and identifying subsamples of those who self-identify as climate scientists or actively publish in the field. Doran and Zimmerman ( 2009 ) surveyed 3146 Earth scientists, asking whether 'human activity is a significant contributing factor in changing mean global temperatures,' and subsampled those who were actively publishing climate scientists. Overall, they found that 82% of Earth scientists indicated agreement, while among the subset with greatest expertise in climate science, the agreement was 97.4%.

Bray and von Storch ( 2007 ) and Bray ( 2010 ) repeatedly surveyed different populations of climate scientists in 1996, 2003 and 2008. The questions did not specify a time period for climate change (indeed, in 2008, 36% of the participants defined the term 'climate change' to refer to 'changes in climate at any time for whatever reason'). Therefore, the reported consensus estimates of 40% (1996) and 53% (2003) (which included participants not stating a view on AGW) suffered from both poor control of expert selection and ambiguous questions. Their 2008 study, finding 83% agreement, had a more robust sample selection and a more specific definition of the consensus position on attribution.

Verheggen et al ( 2014 ) surveyed 1868 scientists, drawn in part from a public repository of climate scientists (the same source as was used by Anderegg et al ), and from scientists listed in C13, supplemented by authors of recent climate-related articles and with particular effort expended to include signatories of public statements critical of mainstream climate science. 85% of all respondents (which included a likely overrepresentation of contrarian non-scientists) who stated a position agreed that anthropogenic greenhouse gases (GHGs) are the dominant driver of recent global warming. Among respondents who reported having authored more than 10 peer-reviewed climate-related publications, approximately 90% agreed that greenhouse gas emissions are the primary cause of global warming.

Stenhouse et al ( 2014 ) collected responses from 1854 members of the American Meteorological Society (AMS). Among members whose area of expertise was climate science, with a publication focus on climate, 78% agreed that the cause of global warming over the past 150 years was mostly human, with an additional 10% (for a total of 88%) indicating the warming was caused equally by human activities and natural causes. An additional 6% answered 'I do not believe we know enough to determine the degree of human causation.' To make a more precise comparison with the Doran and Zimmerman findings, these respondents were emailed one additional survey question to ascertain if they thought human activity had contributed to the global warming that has occurred over the past 150 years; among the 6% who received this question, 5% indicated there had been some human contribution to the warming. Thus, Stenhouse et al ( 2014 ) concluded that '93% of actively publishing climate scientists indicated they are convinced that humans have contributed to global warming.'

Carlton et al ( 2015 ) adapted questions from Doran and Zimmerman ( 2009 ) to survey 698 biophysical scientists across various disciplines, finding that 91.9% of them agreed that (1) mean global temperatures have generally risen compared with pre-1800s levels and that (2) human activity is a significant contributing factor in changing mean global temperatures. Among the 306 who indicated that 'the majority of my research concerns climate change or the impacts of climate change', there was 96.7% consensus on the existence of AGW.

The Pew Research Center ( 2015 ) conducted a detailed survey of 3748 members of the American Association for the Advancement of Science (AAAS) to assess views on several key science topics. Across this group, 87% agreed that 'Earth is warming due mostly to human activity.' Among a subset of working PhD Earth scientists, 93% agreed with this statement.

Despite the diversity of sampling techniques and approaches, a consistent picture of an overwhelming consensus among experts on anthropogenic climate change has emerged from these studies. Another recurring finding is that higher scientific agreement is associated with higher levels of expertise in climate science (Oreskes 2004 , Doran and Zimmerman 2009 , Anderegg 2010 , Verheggen et al 2014 ).

3. Interpreting consensus data

How can vastly different interpretations of consensus arise? A significant contributor to variation in consensus estimates is the conflation of general scientific opinion with expert scientific opinion. Figure 1 demonstrates that consensus estimates are highly sensitive to the expertise of the sampled group. An accurate estimate of scientific consensus reflects the level of agreement among experts in climate science; that is, scientists publishing peer-reviewed research on climate change. As shown in table 1 , low estimates of consensus arise from samples that include non-experts such as scientists (or non-scientists) who are not actively publishing climate research, while samples of experts are consistent in showing overwhelming consensus.

Figure 1.  Level of consensus on AGW versus expertise across different studies. Right colour bar indicates posterior density of Bayesian 99% credible intervals. Only consensus estimates obtained over the last 10 years are included (see S2 for further details and tabulation of acronyms).

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Tol ( 2016 ) reports consensus estimates ranging from 7% to 100% from the same studies described above. His broad range is due to sub-groupings of scientists with different levels of expertise. For example, the sub-sample with 7% agreement was selected from those expressing an 'unconvinced' position on AGW (Verheggen et al 2014 ). This selection criterion does not provide a valid estimate of consensus for two reasons: first, this subsample was selected based on opinion on climate change, predetermining the level of estimated consensus. Second, this does not constitute a sample of experts, as non-experts were included. Anderegg ( 2010 ) found that nearly one-third of the unconvinced group lacked a PhD, and only a tiny fraction had a PhD in a climate-relevant discipline. Eliminating less published scientists from both these samples resulted in consensus values of 90% and 97%–98% for Verheggen et al ( 2014 ) and Anderegg et al ( 2010 ), respectively. Tol's ( 2016 ) conflation of unrepresentative non-expert sub-samples and samples of climate experts is a misrepresentation of the results of previous studies, including those published by a number of coauthors of this paper.

In addition to varying with expertise, consensus estimates may differ based on their approach to studies or survey responses that do not state an explicit position on AGW. Taking a conservative approach, C13 omitted abstracts that did not state a position on AGW to derive its consensus estimate of 97%; a value shown to be robust when compared with the estimate derived from author responses. In contrast, in one analysis, Tol ( 2016 ) effectively treats no-position abstracts as rejecting AGW, thereby deriving consensus values less than 35%. Equating no-position papers with rejection or an uncertain position on AGW is inconsistent with the expectation of decreasing reference to a consensual position as that consensus strengthens (Oreskes 2007 , Shwed and Bearman 2010 ). Powell ( 2015 ) shows that applying Tol's method to the established paradigm of plate tectonics would lead Tol to reject the scientific consensus in that field because nearly all current papers would be classified as taking 'no position'.

4. Conclusion

We have shown that the scientific consensus on AGW is robust, with a range of 90%–100% depending on the exact question, timing and sampling methodology. This is supported by multiple independent studies despite variations in the study timing, definition of consensus, or differences in methodology including surveys of scientists, analyses of literature or of citation networks. Tol ( 2016 ) obtains lower consensus estimates through a flawed methodology, for example by conflating non-expert and expert views, and/or making unsupported assumptions about sources that do not specifically state a position about the consensus view.

An accurate understanding of scientific consensus, and the ability to recognize attempts to undermine it, are important for public climate literacy. Public perception of the scientific consensus has been found to be a gateway belief, affecting other climate beliefs and attitudes including policy support (Ding et al 2011 , McCright et al 2013 , van der Linden et al 2015 ). However, many in the public, particularly in the US, still believe scientists disagree to a large extent about AGW (Leiserowitz et al 2015 ), and many political leaders, again particularly in the US, insist that this is so. Leiserowitz et al ( 2015 ) found that only 12% of the US public accurately estimate the consensus at 91%–100%. Further, Plutzer et al 2016 found that only 30% of middle-school and 45% of high-school science teachers were aware that the scientific consensus is above 80%, with 31% of teachers who teach climate change presenting contradictory messages that emphasize both the consensus and the minority position.

Misinformation about climate change has been observed to reduce climate literacy levels (McCright et al 2016 , Ranney and Clark 2016 ), and manufacturing doubt about the scientific consensus on climate change is one of the most effective means of reducing acceptance of climate change and support for mitigation policies (Oreskes 2010 , van der Linden et al 2016 ). Therefore, it should come as no surprise that the most common argument used in contrarian op-eds about climate change from 2007 to 2010 was that there is no scientific consensus on human-caused global warming (Elsasser and Dunlap 2012 , Oreskes and Conway 2011 ). The generation of climate misinformation persists, with arguments against climate science increasing relative to policy arguments in publications by conservative organisations (Boussalis and Coan 2016 ).

Consequently, it is important that scientists communicate the overwhelming expert consensus on AGW to the public (Maibach et al 2014 , Cook and Jacobs 2014 ). Explaining the 97% consensus has been observed to increase acceptance of climate change (Lewandowsky et al 2013 , Cook and Lewandowsky 2016 ) with the greatest change among conservatives (Kotcher et al 2014 ).

From a broader perspective, it doesn't matter if the consensus number is 90% or 100%. The level of scientific agreement on AGW is overwhelmingly high because the supporting evidence is overwhelmingly strong.

Acknowledgments

We thank Richard Tol for his comment on C13. Thanks to Neal J King and Robert Way for helpful comments on this note, and to Collin Maessen for his initial efforts contacting authors of previous consensus studies.

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Climate change is the long-term alteration in the Earth’s average weather conditions believed to be driven by greenhouse gases (GHG): carbon dioxide (CO 2 ), methane (CH 4 ) and nitrous oxide (N 2 O). These alterations are expected to cause more extreme weather events, gradually warmer global temperatures and greater amounts of precipitation. Roughly 20% of the Earth’s CO 2 , one-third of CH 4 and two-thirds of N 2 O emissions, originate from soils, and earthworms are known to accelerate GHG. As climate change proceeds, there is expected to be an increase in global temperature of 2-6ºC. Temperature is a key factor in determining the rate of soil biological processes that produce and consume GHG. To test how temperature could impact the effects of earthworms on GHG production in soils, we placed earthworms in microcosms with agricultural or forest soil with plant detritus, and incubated the microcosms at 15ºC and 20ºC for six weeks. We found that CH 4 soil consumption decreased at higher temperature and in the presence of earthworms, while CH 4 consumption fluctuated negatively and positively in soils without earthworms at both lower and higher temperature. Production of CO 2 decreased at higher temperature in the absence of earthworms, but production increased in the presence of earthworms at higher temperature. N 2 O production increased, lowering the soils ability to absorb N 2 O, with higher temperature and the presence of earthworms. CH 4 production was increased in agriculture soil with some minor decrease in absorption in forest soil. CO 2 production fluctuated greatly in agriculture soil. Forest soil CO 2 production was mostly stable with little variability. Both soils experienced the same trend in N 2 O flux where there was a sudden production of gas followed by a slowed leveling out with minor fluctuation between production and consumption. Our results show strong evidence that changes in temperature, due to climate change, can impact the effect of earthworms on GHG production and consumption.

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Focus: Spring 2024

Climate change is the most serious public health challenge of our time. This handbook seeks to inform with rigorous, world-class science from YSPH experts. Plus, actions you can take for a healthy planet.

• Features The Tremendous Public Health Opportunity of Climate Action The Unwavering Voice of Youth Climate Change and Mental Health: Thinking Beyond Disasters Improving Climate Change Communication in the Global South Gas Stoves and Public Health States Address Climate Change Beyond Heatwaves: How Rising Temperatures Affect Our Health Air Pollution, Global Warming and Cognition Connecticut Builds Climate and Health Resiliency Learn About the Yale Center on Climate Change and Health, and Create Your Action Plan
• Dean’s Message Dean's Message from Megan L. Ranney - Spring 2024
• Voices Yale Climate Experts Speak Out About Climate Change

The Tremendous Public Health Opportunity of Climate Action

The unwavering voice of youth, climate change and mental health: thinking beyond disasters, improving climate change communication in the global south, gas stoves and public health, states address climate change, beyond heatwaves: how rising temperatures affect our health, air pollution, global warming and cognition, connecticut builds climate and health resiliency, learn about the yale center on climate change and health, and create your action plan, dean’s message, dean's message from megan l. ranney - spring 2024, yale climate experts speak out about climate change.

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• v.8(1); 2017 Jan

Global Warming and Its Health Impact

Since the mid-19 th century, human activities have increased greenhouse gases such as carbon dioxide, methane, and nitrous oxide in the Earth's atmosphere that resulted in increased average temperature. The effects of rising temperature include soil degradation, loss of productivity of agricultural land, desertification, loss of biodiversity, degradation of ecosystems, reduced fresh-water resources, acidification of the oceans, and the disruption and depletion of stratospheric ozone. All these have an impact on human health, causing non-communicable diseases such as injuries during natural disasters, malnutrition during famine, and increased mortality during heat waves due to complications in chronically ill patients. Direct exposure to natural disasters has also an impact on mental health and, although too complex to be quantified, a link has even been established between climate and civil violence.

Over time, climate change can reduce agricultural resources through reduced availability of water, alterations and shrinking arable land, increased pollution, accumulation of toxic substances in the food chain, and creation of habitats suitable to the transmission of human and animal pathogens. People living in low-income countries are particularly vulnerable.

Climate change scenarios include a change in distribution of infectious diseases with warming and changes in outbreaks associated with weather extreme events. After floods, increased cases of leptospirosis, campylobacter infections and cryptosporidiosis are reported. Global warming affects water heating, rising the transmission of water-borne pathogens. Pathogens transmitted by vectors are particularly sensitive to climate change because they spend a good part of their life cycle in a cold-blooded host invertebrate whose temperature is similar to the environment. A warmer climate presents more favorable conditions for the survival and the completion of the life cycle of the vector, going as far as to speed it up as in the case of mosquitoes. Diseases transmitted by mosquitoes include some of the most widespread worldwide illnesses such as malaria and viral diseases. Tick-borne diseases have increased in the past years in cold regions, because rising temperatures accelerate the cycle of development, the production of eggs, and the density and distribution of the tick population. The areas of presence of ticks and diseases that they can transmit have increased, both in terms of geographical extension than in altitude. In the next years the engagement of the health sector would be working to develop prevention and adaptation programs in order to reduce the costs and burden of climate change.

Introduction

In the last decade, the interest in the effect of climate change on human health has increased. The impact of Homo sapiens and his activities on the Earth's complex ecosystem have started since the beginning of farming, but it is only with the industrial revolution in the 18 th century that the changes produced by human activities on planet Earth have been accelerating exponentially. Precisely, because of the role played by Homo sapiens in changing the ecosystem in order to ensure his survival and his development, the actual geological era, which follows the Holocene, is called the Anthropocene. 1

The Fifth Assessment Report of IPCC (Intergovernmental Panel n Climate Change), finalized in November 2014 confirms that human activities have produced since the mid-19 th century, an increase in greenhouse gases such as carbon dioxide, methane, and nitrous oxide in the Earth's atmosphere and an increase in average temperature without comparison in human history. The Earth's temperature has been relatively constant over many centuries ago, meanwhile in the last two centuries the changes registered are unprecedented on time scales ranging from decades to millennia. The rate of change in climate is faster now than in any other period in the past thousand years.

Weather and Climate

Two key concepts in climate science are “weather” and “climate.” Weather refers to the conditions of the atmosphere at a certain place and time with reference to temperature, pressure, humidity, wind, and other key parameters (meteorological elements), the presence of clouds, precipitation and the presence of special phenomena, such as thunderstorms, dust storms, tornados and others. Climate is defined as the average weather, or as the statistical description in terms of the mean and variability of relevant quantities over a period of time ranging from months to thousands or millions of years. 2

Temperature

The global average surface temperature has increased by 0.6 °C since the late 1950's and snow cover and ice extent have diminished. An average rise of 10–20 cm in the sea level has been reported and the temperature of the oceans has increased. 3

The fourth Assessment Report (AR4) projected changes in climate until 2100 foresee including higher maximum temperature and more hot days, and higher minimum temperature and fewer cold days, as virtually certain; increase in the length and intensity in warm spells, hot waves, and precipitation, as very likely; and droughts or dryness, changes in intensity, frequency, and duration of tropical cyclone activity, and increase in extreme sea level, as likely, excluding tsunami. 2 , 4

Effects of Global Warming

The effects of rising temperature include soil degradation, loss of productivity of agricultural land and desertification, loss of biodiversity, degradation of ecosystems, reduced fresh-water resources, acidification of oceans, and the disruption and depletion of stratospheric ozone. 5

A great attention has been given to the relationship between climate change and rising risk of infectious diseases, mostly to the vector-borne infections. However, non-communicable diseases can also heavily affect human health.

The increase in average temperature has consequences that occur acutely—such as during natural disasters and extreme events like floods, hurricanes, droughts, heat waves—or it can occur over time through reduced availability of water, drying up the soil, alterations and shrinking arable land, increased pollution, and creation of habitats favorable to the transmission of human and animal pathogens, either directly or via insect vectors.

Populations living in delta regions, low lying small island states, and many arid regions where drought and availability of water are already problematic, are at risk of suffering the effects of global warming. 6 People living in low-income countries, disposing of less technological resources either to protect themselves against extreme events are particularly vulnerable.

Climate change and increase in greenhouse gases can be considered universal, while land use changes have only local impacts. However, despite they occur locally, they have also a feed-back to the global climate and bio-geochemistry. 7

Agriculture and Water Resources

The effect of temperature on agriculture is linked to the availability of water and food production, which can be threatened by prolonged periods of drought or by the excessive rainfall. The agricultural sector employs 70% of water resources, representing the largest user of fresh water. During the last century, irrigated areas have risen fivefold. For 2025 forecast shows that 64% of the world's population will live in water-stressed basins. 8

According to AR4, the variation in the amount and intensity of rainfall will have an overall negative impact on agriculture. Indeed, in areas where precipitation decreases, the availability of total water resources will be reduced, while in areas where an increase in precipitation is expected, the variability and intensity of rainfall could have a negative impact on the seasonal distribution of rainfall and raise the risk of flood and water pollution.

Rising temperature is not the only cause of soil aridity; exploitation of the environment, deforestation, and loss of biodiversity are also important contributing factors. It is estimated that a 2.5 °C increase in global temperature above the pre-industrial level may produce major biodiversity losses in both endemic plants and animals; 41%–51% of endemic plants in southern Africa would be lost, and so do between 13% and 80% of various fauna in the same region. Globally, 20%–30% of all plant and animal species assessed so far would be at high risk of extinction with such a temperature rise. 4

Higher temperatures may also facilitate the introduction of new pathogens, vectors, or hosts that result in increasing need of pesticides and fertilizers in agriculture. These toxic substances accumulate in the food chain, pollute ground water resources, and could be easily spread through the air. Risks from many pathogens, particulate and particle-associated contaminants could thus significantly increase human exposures to pathogens and chemicals in agricultural and even in temperate regions ( Table 1 ). 9

Effect of Extreme Events

An extreme weather event is one that is rare at a particular place and/or time of year. A single extreme event cannot generally be directly attributed to anthropogenic influence, although the change in likelihood for the event to occur has been determined for some events by accounting for observed changes in climate. 2

Unlike geophysical disasters whose causes have not been influenced by human action, hydro-meteorological and climate-related events are the result of the burning of fossil fuels and deforestation. Since 1950, the frequency, intensity, spatial extent, and duration of these events have changed and projections show that they continue to increase with climate change. 10

Even in temperate regions, the climate forecasting models indicate that the total rainfall will decrease but will tend to increase their intensity. 11 When the climate system acquires more energy from higher average air temperatures and the latent heat of increased water vapor, the frequency of extreme weather events (storms, hurricanes, rain-related floods, droughts, etc ) is expected to increase. 2

In 2012, about 32 million people fled their homes because of catastrophes. The higher burden of natural disasters is endured by people living in low-income countries because they are directly affected by environmental degradation and they have less chance to defend themselves against the threat of their immediate environment and health. 12

Direct Exposure of Extreme Weather Events

The potential health impacts of extreme weather events include both direct effects, such as traumatic deaths, and indirect effects, such as illnesses associated with ecologic or social disruption. 13

The consequences in the immediate term are an increased mortality due to injuries, while afterwards there could be an effect on water quality, which could be contaminated by pathogens or chemicals. Floods have already been demonstrated to enhance the contamination of water bodies by pesticides and are followed by outbreaks of infectious diseases. 14

The effect of drought is manifested in an immediate way on the populations of the poorest countries. The loss of crops or livestock has an immediate consequence on the nutritional status of the population, causing malnutrition, under-nutrition, and compromised childhood development due to declines in local agriculture. Recurrent famine due to drought led to widespread loss of livestock, population displacement, and malnutrition in the Horn of Africa. In 2000, after three years of drought, famine has placed an estimated 10 million persons at risk of starvation. Malnutrition and measles were reported to be important causes of mortality among people aged <14 years. 15

Impact on Mental Health and Conflicts

There is an increased burden of psychological diseases and injuries related to natural disasters potentially wide but under-examined, underestimated and not adequately monitored. The mental health situation may be directly connected to the event, as in post-traumatic stress disorder (PTSD) or become chronic. 12 Rubonis and Bickmann reported an increase of approximately 17% in the global rate of psychopathology during disasters. They affirmed that psychological morbidity tends to affect 30%–40% of the disaster population within the first year, with a persistent burden of disease expected to remain chronic. 16 PTSD does not only affect victims of disasters but also has a prevalence of 10%–20% among rescue workers. 17

Another aspect related to the impact the climate change can have on communities is linked to the onset of conflicts. Without interventions designed to protect the most fragile ecosystems, desertification threatens the economies based on subsistence agriculture. This can generate conflicts regarding the access to water resources, and can increase tension between populations of farmers and nomadic herders. Statistical studies have linked climate and civil violence. Regression models have been applied to identify relationships between measures of civil conflict and climate variables, such as rainfall and temperature. Burke, examining the period 1981–2002 in sub-Saharan Africa, found a relationship between the annual incidence of civil conflict resulting in at least 1000 deaths and warmer temperatures in the same and preceding years. However, although climate change could be seen as a risk of civil violence, a quantitative model could also consider other drives to explain the origin of conflicts. 18

The damage to agriculture could indirectly affect distant countries from the concerned regions. The loss of about one-third of the grain produced due to the extreme heat and fires during the summer 2010 in western Russia, has increased the price of the wheat worldwide. In fact, in the Russian Federation the flour prices were increased by 20%, and finally urban populations in low-income countries like Pakistan and Egypt, were challenged. 19

Effects of Heat Waves

Heat waves lead to an excess mortality, even in developed countries, because mortality generally increases at temperatures both above and below an optimum value. In cold areas the increase in mortality is more closely related to cold season 20 because of the epidemic spread of air-borne viral infections ( Table 2 ) 21 - 26 and secondary bacterial infections and cardiovascular complications. Low temperatures cause cardiovascular and respiratory alterations including bronchoconstriction, and reduction in mucociliary defense and other immunological reactions. These conditions make people more receptive to air-borne pathogens. Transmission of infections is also favored by staying in closed crowded spaces, which is not uncommon during cold seasons.

Populations residing in colder climates are more sensitive to heat and heat waves. It was estimated that the heat wave that occurred in Europe, especially France, during August 2003 caused an excess mortality of 14800 deaths. 27 Patients with chronic diseases such as hypertension, heart disease, diabetes, and obesity are more vulnerable to excessive temperatures and at risk of complications. 28 - 30 Beginning with each heat wave period and slightly during its course, a 14% increase in the risk of out-of-hospital cardiac arrest has been reported. 31 Patients suffering from asthma are more hospitalized during extreme heat and precipitation events. It has been hypothesized that thunderstorm events or periods of heavy rainfall and intense wind can trigger the release of fungal spores that are carried by wind, resulting in increased exposure to these allergens. 32 - 35 Another event reported during hot season is the rise in the incidence of urolithiasis. This is believed to be attributed the physiological link between high heat exposure, sweat function, dehydration, and kidney function, with a consequent apparent increase in kidney stone incidence in hotter climate. 29 , 36

Near the polar ice cap at 81° North of Svalbard (Andrew Shiva, CC BY-SA 4.0)

Parched earth, typical of a drought (Atmospheric Research, CSIRO, CC BY 3.0)

Satellite image of Hurricane Isabel about 650 km North of Puerto Rico on September 14, 2003 (Jacques Descloitres, MODIS Rapid Response Team, NASA/GSFC)

El Niño

El Niño Southern Oscillation is a climate event that originates in the Pacific Ocean but has wide-ranging consequences for weather around the world. Globally, it is linked to an increased impact of natural disasters and is especially associated with droughts and floods and with transmission of infectious disease, water-borne and vector-borne diseases, 37 particularly malaria. 38 , 39 Although cholera outbreaks occur in Burundi, Rwanda, Democratic Republic of Congo, Tanzania, Uganda, and Kenya almost every year since 1977, in African Great Lakes Region (AGLR) the incidence of cholera greatly increases during years of El Niño warm events and decreases or remains stable between these periods. 40

El Niño events can produce significant abnormalities in atmospheric general circulations and weather conditions. El Niño events cause changes in sea surface temperature (SST) in the Pacific Ocean, impact the Walker Circulation, and displace the convective area. These changes in atmospheric circulation cause abnormalities in the monsoon system and moisture fields in eastern Asia.

As El Niño has an influence on rainfall and wind speed, it can affect the persistence or moving polluting dust. The 2015 El Niño has had significant effects on air pollution in eastern China, especially in the region including the capital city of Beijing where aerosol pollution was significantly enhanced. 41 The relationship between air pollution and asthma has been well-established. Air pollution is made up of gases and particulate matters that can be transported into the alveoli depending on their size. Particulate matters can produce damage to the whole respiratory apparatus. Exposure to these agents can cause acute pulmonary diseases such as chronic obstructive pulmonary disease (COPD), asthma, and if continues for a long time, it can activate cellular mediators leading to pulmonary fibrosis. 42

Finally, in rural setting, a neglected effect of warm temperature is the increased exposure to snakebites. Snakes are ectothermic organisms whose distribution, movement, and behaviors change as a function of weather fluctuations. In Costa Rica, high numbers of snakebites occur during the cold and hot phases of El Niño. Like other tropical diseases, snakebites occur more frequently in poor settings, thus reflecting the general vulnerability of impoverished human populations to the adverse effects of climate change. 43

Climate Change and Infectious Diseases

Climate mainly affects the range of infectious diseases, whereas weather affects the timing and intensity of outbreaks. Climate change scenarios include a change in the distribution of infectious diseases with warming and changes in outbreaks associated with weather extremes. 44 Statistical models are used to estimate the global burden of some infectious diseases as a result of climate change. According to the models, by 2030, 10% more diarrheal diseases are expected, affecting primarily the young children.

If global temperature increases by 2–3 °C, as it is expected to, the population at risk for malaria could increase by 3%–5%. 45

Infectious Diseases during Extreme Events

Floods not only have direct effects but also increase the risk of microbiological water pollution. Excess cases of leptospirosis and campylobacter enteritis have been reported after flooding in the Czech Republic 46 and in coastal areas of Maryland during extreme precipitation events 47 . Similarly, an outbreak of cryptosporidiosis began six weeks after the peak of an extensive river flooding in Germany. 48

Global warming also affects the water heating and transmission of water-borne pathogens, through the establishment of a more suitable environment for bacterial growth. The higher sea surface temperature and sea level has resulted in rising water-borne infectious and toxin-related illnesses such as cholera and shellfish poisoning. 44

Proliferation of micro-organisms such as Vibrio vulnificus and V. cholerae non-O1/O139, 49 and infection of wounds and sepsis affecting bathers have been reported as consequence of water temperatures above the average in the Baltic Sea and the North Sea during the hot summer of 2006. 50

Vector-borne Diseases and Mosquitoes

The transmission of infectious diseases through vectors is more complex, particularly when humans or livestock, in the case of diseases of veterinary interest, are not the only reservoir. The key elements in the epidemiology of vector-borne diseases include the ecology and behavior of the host, the ecology and behavior of the carrier, and the level of immunity of population.

Pathogens transmitted by vectors are particularly sensitive to climate change because they spend a good part of their life cycle in an ectothermic invertebrate host whose temperature is similar to the environment. 51 A warmer climate presents a more favorable condition for the survival and completion of the life cycle of the vector, going as far as to speed it up as in the case of mosquitoes.

Comparing the maturation of mosquitoes in huts in forest areas and in deforested areas, in which there was a difference of a few degrees, has allowed to estimate the percentage of insects that are passed by the larval form to the adult form (from 65% to 82%) and the reduction of the period required for the development, which passed from 9 to 8 days, in warmer areas. 52

Mosquitoes are found worldwide, except in regions permanently covered by ice. There are about 3500 species of mosquitoes, almost three-quarters of which are present in tropical and subtropical wetlands. Mosquitoes typical of temperate regions have had to develop strategies to survive the winter, as well as pathogens that can be transmitted. In tropical regions, similarly, adaptations were needed to survive the unfavorable times of prolonged drought. In both cases, these adaptive mechanisms have affected the seasonality of transmission. 53

Rising temperature has allowed the extension of the area of distribution of certain diseases. Diseases transmitted by mosquitoes include some of the most widespread illness worldwide. Some of them are caused by parasites, such as Plasmodium spp , the agent of malaria, the main parasitic disease, causing 214 million of new cases in 2015. 54

Temperature affects each stage of mosquitoes' lifecycle. 55 , 56 There is a minimum and maximum temperature threshold above and below which the development and survival of the vector and the parasite are not possible. Above a certain temperature anopheles mosquito vectors of malaria, cannot survive; 57 their life cycle is so fast that does not allow the development of Plasmodium within their salivary glands. The temperature is a variable that affects development of both the vector population and the parasite within the vector; meanwhile the availability of water and moisture affects the vector only. 58 In recent decades, outbreaks of malaria have been reported from many mountainous regions of Kenya, Uganda, and Rwanda, 58 but a high degree of temporal and spatial variation in the climate of East Africa suggests further that claimed associations between local malaria resurgence and regional changes in climate are overly simplistic. Increases in malaria have been attributed to migration, breakdown in both health service provision and vector control operations, and deforestation. Economic, social, and political factors can therefore, explain recent resurgence in malaria rather than climate change. 59 Models have been elaborated to predict in the next years the distribution of malaria. They forecast an extension of areas of endemic malaria and a shift in the affected areas.

Patterns considering Anopheles gambiae vector complex species estimate that climate change effects on African malaria vectors are shifting their distributional potential from West to East and South. Although it is likely a reduction of the malaria burden, these epidemiological changes will pose novel public health problems in areas where it has not previously been common. 60

The reintroduction of malaria in previously endemic areas of Europe and in temperate regions is theoretically possible. In case of the reappearance of the vector, the human carriers of gametocytes, the forms of the parasite transmissible to the mosquito, would also be present in adequate numbers and for a sufficient period to support the transmission. 61 , 62 That is why in southern Europe even though the vector circulates, a limited number of subjects were involved during outbreaks. 63 - 65

Mosquitoes can also transmit viral infections to humans and other vertebrates. Regarded as a typical of tropical or subtropical regions, these diseases and their vectors have begun to be reported in temperate regions. In recent decades, epidemics with autochthonous transmission of dengue fever and chikungunya, both carried by the mosquito Aedes albopictus , have been described in Europe and the USA. 66 These outbreaks were introduced by travelers from endemic areas, but the presence of a vector has allowed the transmission to local population. 67 , 68 Although generally considered a secondary vector of dengue fever, A. albopictus is also able to transmit other viruses including yellow fever. It was introduced in Europe in the 1970's and now it is present in at least 12 states and could go until reach even Scandinavia. 69

Recently, Zika virus has emerged as a “public health emergency of international concern,” according to World Health Organization. Whether the risk of outbreaks or autochthonous cases of Zika virus infections during the summer season in Europe is possible due to the presence of Aedes , is not yet established. 70

For these viruses, which are limited to humans, vector control measures have allowed to contain the spread of the disease. Conversely, a virus such as the West Nile virus, which has a large reservoir constituted by wild birds, could easily become endemic. 71 After the first outbreak reported in Europe in the South of France, and in the USA in the city of New York, West Nile virus is now firmly established in these areas. 72 Their diffusion is supported by mild winters, springs and dry summers, heat waves early in the season and wet fall. 73

Vector-borne Diseases and Ticks

Ticks are responsible for the transmission of both viruses and bacteria. Rising temperature accelerates the cycle of development, the production of eggs, and the density and distribution of their population. 74 , 75

The areas of presence of ticks and diseases that can be transmitted have increased in terms of geographical extension and in altitude. It is possible that the rising temperature could already lead to change in the distribution of the population of Ixodes ricinus , vector of viral infections such as tick-borne encephalitis and Lyme disease in Europe.

The increased incidence of tick-borne encephalitis has also been linked to milder and shorter winters and the consequent extension of the period of tick activity. 76 - 79

In addition to climate change, among the leading causes of increased transmission of tick-borne diseases the abandoning of agricultural lands would also be considered, which has allowed the proliferation of rodents reservoir, and the establishment of ecological niches suitable to ticks in urban parks ( Table 3 ). 80

The global changes that we are currently experiencing have never happened before. They include climate change and variability, change of composition of the atmosphere, use of the earth's surface for expansion of agricultural lands and deforestation. Other changes include an extension of the inhabited rural areas, urbanization, globalization of trade and transports, displacement of populations, diffusion of new plant species, spread of human and animal diseases, and improvements in conditions of life and diffusion of advanced technologies worldwide. 81

Climate change represents one of the main environmental and health equity challenges of our time because the burden of climate-sensitive diseases is the greatest for the poorest populations. 82 Many of the health impacts of climate are a particular threat to poor people in low- and middle-income countries. For example, the mortality rate derived from vector-borne diseases is almost 300 times greater in developing nations than in developed countries, posing as a significant cause of death, disease burden and health inequity, as brake on socioeconomic development, and as a strain on health services. 83

In urban setting, the local climate conditions, where people live and work, create most of the direct human health hazards, such as those due to the urban-heat-island effect. Therefore, a more indirect health effects is often associated with global or large-scale regional climate change. Like other effects of rising temperature, the consequences of global warming are also worse in low-income countries where urbanization have occurred rapidly and without planning. 84

In the next years, in order to contain the global warming, technologies that reduce greenhouse emissions and the consumption of water resources would be needed. A constant need to ensure access to food and availability of protein to the growing world population through agricultural techniques that increase the productivity without depleting the soil would be experienced. Finally, it is important not to forget the most directly and indirectly exposures to damages and results of climate change.

The engagement of the health sector would deal with the increasing pollution-related diseases, to extreme weather events, and would develop knowledge and skills in local prevention/adaptation programs, in order to reduce the costs and burden of the consequences of climate change. 85 Health system needs to strengthen primary health care, develop preventive programs, put special attention towards the vulnerable communities and regions, encourage community participation in grass root planning, emergency preparedness, and make capacity to forecast future health risks. 86

To prevent the spread of infectious and vector-borne diseases, it would be necessary to establish an integrated notification network of veterinary, entomological and human survey, with particular attention to avoid the introduction of new human and animal pathogens. 87

Health professionals everywhere have a responsibility to put health at the heart of climate change negotiations. Firstly, because climate change already has a major adverse impact on the health of human populations. Secondly, because reducing greenhouse gas emissions has unrivalled opportunities for improving public health. 88

Conflict of Interest:

None declared.

Cite this article as: Rossati A. Global warming and its health impact. Int J Occup Environ Med 2017;8:7-20. doi: 10.15171/ijoem.2017.963

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