(Global mean land-ocean temperature change since 1880, relative to the 1951–1980 mean. The black line is the annual mean and the red line is the 5-year running mean. The green bars show uncertainty estimates. Source: NASA GISS)
The positioning of the scientific community towards climate change is reflected in the summary reports, statements of scientific organizations of national and international level, as well as opinion polls among climatologists. Currently, the scientific community as a whole endorses the position of the Intergovernmental Panel on Climate Change (IPCC) in January 2001, ruling that a growing number of observations demonstrate the reality of global warming, and that warming observed over the last 50 years is largely due to human activity. Since 2007, no scientific body of national or international level has disputed this claim, though some organizations have not taken position.
The summary reports evaluate the scientific literature, which in turn compiles the results of individual studies, in order to improve overall understanding of a phenomenon or to have an overview of current knowledge.
Intergovernmental Panel on Climate Change (IPCC) 2014
The 2014 IPCC report concluded that
”Continued emission of greenhouse gases will cause further warming and long-lasting changes in all components of the climate system, increasing the likelihood of severe, pervasive and irreversible impacts for people and ecosystems. Limiting climate change would require substantial and sustained reductions in greenhouse gas emissions which, together with adaptation, can limit climate change risks.”e gas emissions which, together with adaptation, can limit climate change risks.“
Intergovernmental Panel on Climate Change (IPCC) 2007
The 2007 IPCC report concluded that
“Human actions are ‘very likely‘ the cause of global warming, meaning a 90% or greater probability. Global warming in this case was indicated by an increase of 0.75 degrees in average global temperatures over the last 100 years.“
Academies and scientific societies
Since 2001, several national academies made statements (sometimes joint) affirming the reality of human-induced global warming and urging nations to reduce their emissions of greenhouse gases. Among the signatories of these statements include the national science academies.
Systematic reviews and opinion polls among scientists
John Cook et al. (2013)
An article published in May 15, 2013, by John Cook and other authors in Environmental Research Letters, has analyzed 11,944 summaries of research by 29,083 authors between 1991 and 2011. The authors concluded that 97.1% of 3,896 articles that take positions on the causes of global warming supports the scientific consensus that global warming is due to human activity. Furthermore this consensus is slightly increasing with time.
In August 2013, an article published in Science & Education criticized the statistical method used by Cook et al. Other criticisms were also made.
Anderegg, Prall, Harold, and Schneider (2010)
A 2010 article published in Proceedings of the National Academy of Sciences of the United States analyzed data publication and citation of 1,372 researchers in climate science and made the following two conclusions:
- 97-98% of researchers whose main publication is about climate science support the thesis of anthropogenic warming as described by the IPCC, and
- the climate expertise and scientific reputation of researchers that dispute this thesis is significantly lower than that of researchers that support it.
Peter Doran and Maggie Zimmerman (2009)
A study published in 2009 by Peter Doran and Maggie Zimmerman, from the Science Department of Earth and Environment at the University of Illinois at Chicago, and to which 3,146 scientists responded, reveals that 90% of scientists interviewed on the subject consider that global temperatures have “overall increase” since the nineteenth century, and 82% agree with the statement that human activities “contribute significantly to the change in global average temperatures.” These rates rise respectively to 96.2% and 97.4% among 79 specialists in climatology (those with “climate science” as a field of expertise and that have published more than 50% of their recent articles on the subject). Conversely, only 47% of 103 surveyed geologists believe that human activity is a significant factor of climate change. In conclusion the survey says:
“It seems that the debate on the authenticity of global warming and the role played by human activity is largely nonexistent among those who understand the nuances and scientific basis of long-term climate processes.“
Bray and von Storch (2008)
In 2008, Dennis Bray and Hans von Storch surveyed 2,058 climatologists in 34 countries. In total, 373 scientists (18.2%) responded to 76 questions of the survey. Many of these questions were using a scale from 1 to 7 (“not at all” to “strongly”) for answers. In question 20, “How are you convinced that climate change is occurring now, whether natural or man-made?” 67.1% responded sharply (7) 26.7% to a large extent (5-6), 6.2% to a small extent (4-2) and 0% not at all. To the question “Do you believe that climate change (recent or in the near future) are anthropogenic?“, 34.6% responded sharply (7) 48.9% to a large extent (5-6) 15.1% to a small extent (2-4) and 1.35% (1) “not at all”.
Naomi Oreskes (2004)
Proponents of the existence of a consensus about human responsibility for global warming are based on the position of several scientific institutions and the number of climate scientists involved in the IPCC analyzes. This consensus has sometimes been questioned by politicians, particularly in the United States. But according to a study published in the journal Science by science historian Naomi Oreskes, analysis of 928 abstracts of scientific articles selected from a database using the keywords “climate change” and published between 1993 and 2003 shows that none of them challenged the consensus defined by the IPCC.