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National and international science academies and professional societies have assessed the current scientific opinion on climate change, in particular recent global warming. These assessments have largely followed or endorsed the IPCC postition that "An increasing body of observations gives a collective picture of a warming world and other changes in the climate system... There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities".

This page documents scientific opinion as given by synthesis reports, bodies of national or international standing, and surveys of opinion among climate scientists. It does not document the views of individual scientists.

Statements by organizations

Intergovernmental Panel on Climate Change (IPCC)

In February 2007, the IPCC released a summary of a Fourth Assessment Report, which is not yet available. According to this summary, the Fourth Assessnent Report finds that human actions are "very likely" the cause of global warming, meaning a 90% or greater probability.

"The world's leading climate scientists said global warming has begun, is very likely caused by man, and will be unstoppable for centuries, ... . The phrase very likely translates to a more than 90 percent certainty that global warming is caused by man's burning of fossil fuels. That was the strongest conclusion to date, making it nearly impossible to say natural forces are to blame."

"The report said that an increase in hurricane and tropical cyclone strength since 1970 more likely than not can be attributed to man-made global warming. The scientists said global warming's connection varies with storms in different parts of the world, but that the storms that strike the Americas are global warming-influenced."

"On sea levels, the report projects rises of 7-23 inches by the end of the century. That could be augmented by an additional 4-8 inches if recent surprising polar ice sheet melt continues."

Joint science academies’ statement

In 2005 the national science academies of the G8 nations, plus Brazil, China and India, three of the largest emitters of greenhouse gases in the developing world, signed a statement on the global response to climate change. The statement stresses that the scientific understanding of climate change is now sufficiently clear to justify nations taking prompt action , and explicitly endorsed the IPCC consensus.

U.S. National Research Council, 2001

In 2001 the Committee on the Science of Climate Change of the National Research Council published Climate Change Science: An Analysis of Some Key Questions . This report explicitly endorses the IPCC view of attribution of recent climate change as representing the view of the scientific community:

The changes observed over the last several decades are likely mostly due to human activities, but we cannot rule out that some significant part of these changes is also a reflection of natural variability. Human-induced warming and associated sea level rises are expected to continue through the 21st century... The IPCC's conclusion that most of the observed warming of the last 50 years is likely to have been due to the increase in greenhouse gas concentrations accurately reflects the current thinking of the scientific community on this issue.

American Meteorological Society

The American Meteorological Society (AMS) statement adopted by their council in 2003 said:

There is now clear evidence that the mean annual temperature at the Earth's surface, averaged over the entire globe, has been increasing in the past 200 years. There is also clear evidence that the abundance of greenhouse gases in the atmosphere has increased over the same period. In the past decade, significant progress has been made toward a better understanding of the climate system and toward improved projections of long-term climate change... Human activities have become a major source of environmental change. Of great urgency are the climate consequences of the increasing atmospheric abundance of greenhouse gases... Because greenhouse gases continue to increase, we are, in effect, conducting a global climate experiment, neither planned nor controlled, the results of which may present unprecedented challenges to our wisdom and foresight as well as have significant impacts on our natural and societal systems.

Federal Climate Change Science Program, 2006

On May 2, 2006, the Federal Climate Change Science Program commissioned by the Bush administration in 2002 released the first of 21 assessments that concluded that there is clear evidence of human influences on the climate system (due to changes in greenhouse gases, aerosols, and stratospheric ozone) . The study said that observed patterns of change over the past 50 years cannot be explained by natural processes alone, though it did not state what percentage of climate change might be anthropogenic in nature.

Other organizations

Other scientific organizations have made position statements on climate change.

• American Geophysical Union position statement on greenhouse gases and climate change (also endorsed by the American Institute of Physics)
• Climate Change Science: An Analysis of Some Key Questions, National Academy of Sciences, Commission on Geosciences, Environment and Resources, (Washington, DC: National Academy Press, 2001).
• Joint statement on the Science of Climate Change, issued by the Australian Academy of Sciences, Royal Flemish Academy of Belgium for Sciences and the Arts, Brazilian Academy of Sciences, Royal Society of Canada, Caribbean Academy of Sciences, Chinese Academy of Sciences, French Academy of Sciences, German Academy of Natural Scientists Leopoldina, Indian National Science Academy, Indonesian Academy of Sciences, Royal Irish Academy, Accademia Nazionale dei Lincei (Italy), Academy of Sciences Malaysia, Academy Council of the Royal Society of New Zealand, Royal Swedish Academy of Sciences, and Royal Society (UK).
• A position paper of the Stratigraphy Commission of the Geological Society of London.
• Position Statement on Global Climate Change adopted by the Geological Society of America
• Policy Statement on Climate Variability and Change by the American Association of State Climatologists (AASC)
• Australian Medical Association statement on climate change
• American Chemical Society statement on Global Climate Change

The only major scientific organization that rejects the finding of human influence on recent climate is the American Association of Petroleum Geologists.

Recent surveys of scientists and scientific literature

Various surveys have been conducted to determine a scientific consensus on global warming. Few have been conducted within the last ten years.

Oreskes, 2004

A 2004 article by geologist and historian of science Naomi Oreskes summarized a study of the scientific literature on climate change. The essay concluded that there is a scientific consensus on the reality of anthropogenic climate change. The author analyzed 928 abstracts of papers from refereed scientific journals between 1993 and 2003, listed with the keywords "global climate change". Oreskes divided the abstracts into six categories: explicit endorsement of the consensus position, evaluation of impacts, mitigation proposals, methods, paleoclimate analysis, and rejection of the consensus position. 75% of the abstracts were placed in the first three categories, thus either explicitly or implicitly accepting the consensus view; 25% dealt with methods or paleoclimate, thus taking no position on current anthropogenic climate change; none of the abstracts disagreed with the consensus position, which the author found to be "remarkable". It was also pointed out, "authors evaluating impacts, developing methods, or studying paleoclimatic change might believe that current climate change is natural. However, none of these papers argued that point."

Bray and von Storch, 2003

A survey was conducted in 2003 by Dr. Dennis Bray and German climatologist Hans von Storch. Bray's submission to Science on December 22, 2004 was rejected but the survey's results were reported through non-scientific venues . The survey has been criticized on the grounds that it was performed on the web with no means to verify that the respondents were climate scientists or to prevent multiple submissions by the same individual. The survey required entry of a username and password, but this information was circulated to a climate skeptics mailing list and elsewhere on the internet. The survey received 530 responses from 27 different countries. One of the questions asked was "To what extent do you agree or disagree that climate change is mostly the result of anthropogenic causes?", with a value of 1 indicating strongly agree and a value of 7 indicating strongly disagree. The results showed a mean of 3.62, with 50 responses (9.4%) indicating "strongly agree" and 54 responses (9.7%) indicating "strongly disagree". The same survey indicates a 72% to 20% endorsement of the IPCC reports as accurate, and a 15% to 80% rejection of the thesis that "there is enough uncertainty about the phenomenon of global warming that there is no need for immediate policy decisions".

Older surveys

Survey of U.S. state climatologists 1997

In 1997, the conservative advocacy group Citizens for a Sound Economy surveyed America's 48 official state climatologists on questions related to climate change . Of the 36 respondents, 44% considered global warming to be a largely natural phenomenon, compared to 17% who considered warming to be largely manmade. The survey further found that 58% disagreed or somewhat disagreed with then-President Clinton's assertion that "the overwhelming balance of evidence and scientific opinion is that it is no longer a theory, but now fact, that global warming is for real". Eighty-nine percent agreed that "current science is unable to isolate and measure variations in global temperatures caused ONLY by man-made factors," and 61% said that historical data do not indicate "that fluctuations in global temperatures are attributable to human influences such as burning fossil fuels."

60% of the respondents said that reducing man-made CO2 emissions by 15% below 1990 levels would not prevent global temperatures from rising, and 86% said that reducing emissions to 1990 levels would not prevent rising temperatures. 39% agreed and 33% disagreed that "evidence exists to suggest that the earth is headed for another glacial period," though the time scale for the next glacial period was not specified.

Bray and von Storch, 1996

In 1996, Dennis Bray and Hans von Storch undertook a survery of climate scientists on attitudes towards global warming and related matters. The results were subsequently published in Bulletin of the American Meteorological Society. The paper addressed the views of climate scientists, with a response rate of 40% from a mail survey questionnaire to 1000 scientists in Germany, the USA and Canada. Most of the scientists believed that global warming was occurring and appropriate policy action should be taken, but there was wide disagreement about the likely effects on society and almost all agreed that the predictive ability of currently existing models was limited.

The abstract says:

The international consensus was, however, apparent regarding the utility of the knowledge to date: climate science has provided enough knowledge so that the initiation of abatement measures is warranted. However, consensus also existed regarding the current inability to explicitly specify detrimental effects that might result from climate change. This incompatibility between the state of knowledge and the calls for action suggests that, to some degree at least, scientific advice is a product of both scientific knowledge and normative judgment, suggesting a socioscientific construction of the climate change issue.

The survey was extensive, and asked numerous questions on many aspects of climate science, model formulation, and utility, and science/public/policy interactions. To pick out some of the more vital topics, from the body of the paper:

The resulting questionnaire, consisting of 74 questions, was pre-tested in a German institution and after revisions, distributed to a total of 1,000 scientists in North America and Germany... The number of completed returns was as follows: USA 149, Canada 35, and Germany 228, a response rate of approximately 40%...

...With a value of 1 indicating the highest level of belief that predictions are possible and a value of 7 expressing the least faith in the predictive capabilities of the current state of climate science knowledge, the mean of the entire sample of 4.6 for the ability to make reasonable predictions of inter-annual variability tends to indicate that scientists feel that reasonable prediction is not yet a possibility... mean of 4.8 for reasonable predictions of 10 years... mean of 5.2 for periods of 100 years...

...a response of a value of 1 indicates a strong level of agreement with the statement of certainty that global warming is already underway or will occur without modification to human behavior... the mean response for the entire sample was 3.3 indicating a slight tendency towards the position that global warming has indeed been detected and is underway.... Regarding global warming as being a possible future event, there is a higher expression of confidence as indicated by the mean of 2.6.

Other older surveys of scientists

It should be noted that these surveys are over 15 years old and the state of climate science has changed radically since their time; current beliefs of the scientific community are different as shown in the reviews cited above.

• Global Environmental Change Report, 1990: GECR climate survey shows strong agreement on action, less so on warming. Global Environmental Change Report 2, No. 9, pp. 1-3
• Stewart, T.R., Mumpower, J.L., and Reagan-Cirincione, P. (1992). Scientists' opinions about global climate change: Summary of the results of a survey. NAEP (National Association of Environmental Professionals) Newsletter, 17(2), 6-7.
• A 1991 Gallup poll of 400 members of the American Geophysical Union and the American Meteorological Society
  • Fairness and Accuracy in Reporting states that the report said that 66 % of the scientists said that human-induced global warming was occurring, with 10 % disagreeing and the rest undecided. In a correction Gallup stated: "Most scientists involved in research in this area believe that human-induced global warming is occurring now."
  • George Will reported "53 percent do not believe warming has occurred, and another 30 percent are uncertain." (Washington Post, September 3, 1992)
  • A 1993 publication by the politically conservative Heartland Institute states: "A Gallup poll conducted on February 13, 1992 of members of the American Geophysical Union and the American Meteorological Society - the two professional societies whose members are most likely to be involved in climate research - found that 18 percent thought some global warming had occurred, 33 percent said insufficient information existed to tell, and 49 percent believed no warming had taken place."

See also

• Attribution of recent climate change
• Avoiding Dangerous Climate Change
• Global warming controversy
• Scientists opposing the mainstream scientific assessment of global warming

References

1. Working Group 1, IPCC.
2. "Warming 'very likely' human-made". BBC News. BBC. 2007-02-01. Retrieved 2007-02-01. {{cite news}}: Check date values in: |date= (help)
3. Naomi Oreskes (December 3, 2004). "Beyond the Ivory Tower: The Scientific Consensus on Climate Change". Science. 306 (5702): 1686. doi:10.1126/science.1103618. (see also for an exchange of letters to Science)
9. Useless on-line survey of climate scientists
10. DIALOG and DISCCRS News

External links

• US EPA climate change and global warming website
• Univ. of Victoria Radio Interview October 18, 2006, Timothy Ball, former Professor of Climatology, Univ. of Winnipeg (mp3)
• Sherwood Rowland (Nobel Laureate for work on ozone depletion) gives his opinion on climate change 2006 Freeview video provided by the Vega Science Trust.
• Climate Change Science: An Analysis of Some Key Questions, National Academy of Sciences
• Joint Science Academies' Statement: Global Response to Climate Change, National Academy of Sciences
• Climate change special: State of denial New Scientist 4 November 2006
• The Denial Machine CBC Television 15 November 2006

• Climate change assessment and attribution
• Ecology