Scientific consensus on climate change

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 position 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, scientific bodies of national or international standing, and surveys of opinion among climate scientists. It does not document the views of individual scientists or self-selected lists of individuals such as petitions.

Statements by concurring organizations

Intergovernmental Panel on Climate Change (IPCC) 2007

Main article: Intergovernmental Panel on Climate Change

In February 2007, the IPCC released a summary of the forthcoming Fourth Assessment Report. According to this summary, the Fourth Assessment Report finds that human actions are "very likely" the cause of global warming, meaning a 90% or greater probability. Global warming in this case is indicated by an increase of 0.75 degrees in average global temperatures over the last 100 years.

The New York Times reports on the report:

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.

The Associated Press summarizes the position on sea level rise:

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 2007

In preparation for the 2007 G8 summit, the national science academies of the G8+5 nations issued a declaration referencing the position of the 2005 joint science academies' statement, and acknowledging the confirmation of their previous conclusion by recent research. Following the IPCC Fourth Assessment Report, the declaration states:

It is unequivocal that the climate is changing, and it is very likely that this is predominantly caused by the increasing human interference with the atmosphere. These changes will transform the environmental conditions on Earth unless counter-measures are taken.

Joint science academies’ statement 2005

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. The eleven signatories were the science academies of Brazil, Canada, China, France, Germany, India, Italy, Japan, Russia, the United Kingdom, and the United States.

Joint science academies’ statement 2001

In 2001, following the publication of the IPCC Third Assessment Report, sixteen national science academies issued a joint statement explicitly acknowledging the IPCC position as representing the scientific consensus on climate change science. The sixteen science academies that issued the statement were those of Australia, Belgium, Brazil, Canada, the Caribbean, China, France, Germany, India, Indonesia, Ireland, Italy, Malaysia, New Zealand, Sweden, and the United Kingdom.

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.

American Geophysical Union

The American Geophysical Union (AGU) statement adopted by the society in 2003 and revised in 2007 affirms that rising levels of greenhouse gases have caused and will continue to cause the global surface temperature to be warmer:

The Earth's climate is now clearly out of balance and is warming. Many components of the climate system—including the temperatures of the atmosphere, land and ocean, the extent of sea ice and mountain glaciers, the sea level, the distribution of precipitation, and the length of seasons—are now changing at rates and in patterns that are not natural and are best explained by the increased atmospheric abundances of greenhouse gases and aerosols generated by human activity during the 20th century. Global average surface temperatures increased on average by about 0.6°C over the period 1956–2006. As of 2006, eleven of the previous twelve years were warmer than any others since 1850. The observed rapid retreat of Arctic sea ice is expected to continue and lead to the disappearance of summertime ice within this century. Evidence from most oceans and all continents except Antarctica shows warming attributable to human activities. Recent changes in many physical and biological systems are linked with this regional climate change. A sustained research effort, involving many AGU members and summarized in the 2007 assessments of the Intergovernmental Panel on Climate Change, continues to improve our scientific understanding of the climate.

American Institute of Physics

The Governing Board of the American Institute of Physics endorsed the AGU statement on human-induced climate change:

The Governing Board of the American Institute of Physics has endorsed a position statement on climate change adopted by the American Geophysical Union (AGU) Council in December 2003.

American Astronomical Society

The American Astronomical Society has endorsed the AGU statement:

In endorsing the "Human Impacts on Climate" statement [issued by the American Geophysical Union], the AAS recognizes the collective expertise of the AGU in scientific subfields central to assessing and understanding global change, and acknowledges the strength of agreement among our AGU colleagues that the global climate is changing and human activities are contributing to that change.

American Physical Society

"Emissions of greenhouse gases from human activities are changing the atmosphere in ways that affect the Earth's climate. Greenhouse gases include carbon dioxide as well as methane, nitrous oxide and other gases. They are emitted from fossil fuel combustion and a range of industrial and agricultural processes.

"The evidence is incontrovertible: Global warming is occurring. If no mitigating actions are taken, significant disruptions in the Earth’s physical and ecological systems, social systems, security and human health are likely to occur. We must reduce emissions of greenhouse gases beginning now."

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. Though it did not state what percentage of climate change might be anthropogenic, the assessment concluded:

Studies ... show clear evidence of human influences on the climate system (due to changes in greenhouse gases, aerosols, and stratospheric ozone). ... The observed patterns of change over the past 50 years cannot be explained by natural processes alone, nor by the effects of short-lived atmospheric constituents (such as aerosols and tropospheric ozone) alone.

American Association for the Advancement of Science

The American Association for the Advancement of Science stated, "The scientific evidence is clear: global climate change caused by human activities is occurring now, and it is a growing threat to society."

Stratigraphy Commission of the Geological Society of London

The Stratigraphy Commission of the Geological Society of London stated, "We find that the evidence for human-induced climate change is now persuasive, and the need for direct action compelling."

Geological Society of America

"The Geological Society of America (GSA) supports the scientific conclusions that Earth’s climate is changing; the climate changes are due in part to human activities; and the probable consequences of the climate changes will be significant and blind to geopolitical boundaries. Furthermore, the potential implications of global climate change and the time scale over which such changes will likely occur require active, effective, long-term planning."

American Chemical Society

The American Chemical Society stated:

Careful and comprehensive scientific assessments have clearly demonstrated that the Earth’s climate system is changing rapidly in response to growing atmospheric burdens of greenhouse gases and absorbing aerosol particles (IPCC, 2007). There is very little room for doubt that observed climate trends are due to human activities. The threats are serious and action is urgently needed to mitigate the risks of climate change.

The reality of global warming, its current serious and potentially disastrous impacts on Earth system properties, and the key role emissions from human activities play in driving these phenomena have been recognized by earlier versions of this ACS policy statement (ACS, 2004), by other major scientific societies, including the American Geophysical Union (AGU, 2003), the American Meteorological Society (AMS, 2007) and the American Association for the Advancement of Science (AAAS, 2007), and by the U. S. National Academies and ten other leading national academies of science (NA, 2005). This statement reviews key global climate change impacts and recommends actions required to mitigate or adapt to currently anticipated consequences.

Engineers Australia (The Institution of Engineers Australia)

"Engineers Australia believes that Australia must act swiftly and proactively in line with global expectations to address climate change as an economic, social and environmental risk... We believe that addressing the costs of atmospheric emissions will lead to increasing our competitive advantage by minimising risks and creating new economic opportunities. Engineers Australia believes the Australian Government should ratify the Kyoto Protocol."

The Canadian Meteorological and Oceanographic Society

"CMOS endorses the process of periodic climate science assessment carried out by the Intergovernmental Panel on Climate Change and supports the conclusion, in its Third Assessment Report, which states that the balance of evidence suggests a discernible human influence on global climate."

Noncommittal statements

American Association of State Climatologists

The 2001 statement from the American Association of State Climatologists noted the difficulties with predicting impacts due to climate change, while acknowledging that human activities are having an effect on climate:

Climate prediction is difficult because it involves complex, nonlinear interactions among all components of the earth’s environmental system. (...) The AASC recognizes that human activities have an influence on the climate system. Such activities, however, are not limited to greenhouse gas forcing and include changing land use and sulfate emissions, which further complicates the issue of climate prediction. Furthermore, climate predictions have not demonstrated skill in projecting future variability and changes in such important climate conditions as growing season, drought, flood-producing rainfall, heat waves, tropical cyclones and winter storms. These are the type of events that have a more significant impact on society than annual average global temperature trends. Policy responses to climate variability and change should be flexible and sensible – The difficulty of prediction and the impossibility of verification of predictions decades into the future are important factors that allow for competing views of the long-term climate future. Therefore, the AASC recommends that policies related to long-term climate not be based on particular predictions, but instead should focus on policy alternatives that make sense for a wide range of plausible climatic conditions regardless of future climate.

American Association of Petroleum Geologists (AAPG)

The American Association of Petroleum Geologists (AAPG) Position Statement on climate change states that "the AAPG membership is divided on the degree of influence that anthropogenic CO2 has on recent and potential global temperature increases ... Certain climate simulation models predict that the warming trend will continue, as reported through NAS, AGU, AAAS and AMS. AAPG respects these scientific opinions but wants to add that the current climate warming projections could fall within well-documented natural variations in past climate and observed temperature data. These data do not necessarily support the maximum case scenarios forecast in some models."

Prior to the adoption of this statement, the AAPG was the only major scientific organization that rejected the finding of significant human influence on recent climate, according to a statement by the Council of the American Quaternary Association. The AAPG updated its statement in part because the previous statement was "not supported by a significant number of our members and prospective members".

Statements by dissenting organizations

With the July 2007 release of the revised statement by the American Association of Petroleum Geologists, no remaining scientific body of national or international standing is known to reject the basic findings of human influence on recent climate.

Scientific consensus

A question which frequently arises in conveying the scientific opinion to a broader audience is to what extent that opinion rises to the level of a consensus. Several scientific organizations have explicitly used the term "consensus" in their statements:

• American Association for the Advancement of Science: "The conclusions in this statement reflect the scientific consensus represented by, for example, the Intergovernmental Panel on Climate Change, and the Joint National Academies' statement."
• US National Academy of Science: "In the judgment of most climate scientists, Earth’s warming in recent decades has been caused primarily by human activities that have increased the amount of greenhouse gases in the atmosphere. ... On climate change, [the National Academies’ reports] have assessed consensus findings on the science..."
• Joint Science Academies' statement, 2005: "We recognise the international scientific consensus of the Intergovernmental Panel on Climate Change (IPCC)."
• Joint Science Academies' statement, 2001: "The work of the Intergovernmental Panel on Climate Change (IPCC) represents the consensus of the international scientific community on climate change science. We recognise IPCC as the world’s most reliable source of information on climate change and its causes, and we endorse its method of achieving this consensus."
• American Meteorological Society: "The nature of science is such that there is rarely total agreement among scientists. Individual scientific statements and papers—the validity of some of which has yet to be assessed adequately—can be exploited in the policy debate and can leave the impression that the scientific community is sharply divided on issues where there is, in reality, a strong scientific consensus. ...IPCC assessment reports are prepared at approximately five-year intervals by a large international group of experts who represent the broad range of expertise and perspectives relevant to the issues. The reports strive to reflect a consensus evaluation of the results of the full body of peer-reviewed research. ... They provide an analysis of what is known and not known, the degree of consensus, and some indication of the degree of confidence that can be placed on the various statements and conclusions."

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". According to the report, "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 Dennis Bray and 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 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."

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. 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.. Bray and von Storch have recently defended their results and accused climate change skeptics of interpreting the results with bias.

Survey of U.S. state climatologists 1997

In 1997, the conservative think tank Citizens for a Sound Economy surveyed America's 48 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 man-made. 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."

Sixty percent 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. Thirty nine percent 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 survey of climate scientists on attitudes towards global warming and related matters. The results were subsequently published in the 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

Note that the following surveys are over 15 years old. The state of climate science and the beliefs of climate scientists have changed radically since their time, as demonstrated by 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 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

• Scientific consensus
• Australian Medical Association position statement on climate change, Sept. 21, 2005
• Global warming controversy
• National Registry of Environmental Professionals survey on climate change
• List of scientists opposing the mainstream scientific assessment of global warming

External links

• US EPA climate change and global warming website
• 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
• Sun Science largely ignored in climate change debate