Scientific opinion on climate change
Various prominent bodies have commented on global warming, most notably the Intergovernmental Panel on Climate Change (IPCC). National and international scientific groups have issued statements both detailing and summarizing the current state of scientific knowledge on the earth's climate.
- Main article: Intergovernmental Panel on Climate Change
The IPCC said in its Second Assessment Report (SAR) in 1995 that the balance of evidence suggests that there is a discernible human influence on global climate" and strengthened this in its Third Assessment Report (TAR) in 2001 to "There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities". Note that "balance of evidence" is not intended to suggest unambiguous proof; it is a reference to the standards of proof required in English civil law (balance of evidence) as opposed to criminal law (beyond reasonable doubt).
In the 2001 TAR the IPCC said:
- In the light of new evidence and taking into account the remaining uncertainties, most of the observed warming over the last 50 years is likely to have been due to the increase in greenhouse gas concentrations .
Joint science academies’ statement
In 2005 the national science academies of the G8 nations and 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.
US 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 science community:
- 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. 
The summary begins with:
- Greenhouse gases are accumulating in Earth's atmosphere as a result of human activities, causing surface air temperatures and subsurface ocean temperatures to rise. Temperatures are, in fact, rising. 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. (ibid.)
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... The report by the IPCC stated that the global mean temperature is projected to increase by 1.4°C-5.8°C in the next 100 years... 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. It is a long-term problem that requires a long-term perspective. Important decisions confront current and future national and world leaders. 
Statements on global warming
Some scientific organisations who have made position statements on climate change.
- Intergovernmental panel on climate change
- American Meteorological Society Statement
- American Geophysical Union position statement on greenhouse gases and climate change
- 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 sixteen national academies of science from around the world.
- A position paper of the Stratigraphy Commission of the Geological Society of London.
- Policy Statement on Climate Variability and Change by the American Association of State Climatologists (AASC)
The Summary Report of the World Climate Change Conference, Moscow, 2003, included: "The Intergovernmental Panel on Climate Change (IPCC) has provided the basis for much of our present understanding of knowledge in this field in its Third Assessment Report (TAR) in 2001. An overwhelming majority of the scientific community has accepted its general conclusions that climate change is occurring, is primarily a result of human emissions of greenhouse gases and aerosols, and that this represents a threat to people and ecosystems." 
Surveys have shown scientists split on the issue of whether global warming theory has been adequately proven, but with a majority agreeing that global warming will occur in future if human behavior does not change.
In December 2004, Science published an opinion essay  that 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". The abstracts were divided 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 that "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."
Soon after, Benny Peiser, a social anthropologist claimed to replicate the Oreskes study (but actually used a different set of abstracts ) and to have falsified it, writing a letter to Science  that was rejected for publication. The letter stated that only one percent of the papers explicitly endorsed the "consensus position," and that less than a third -- not three-fourths -- accept it implicitly. He also identified 34 articles which "reject or doubt the view that human activities are the main drivers of "the observed warming over the last 50 years" - a claim which an examination of the relevant abstracts  does not support.
Bray and von Storch, 1996
In 1996 a survey of climate scientists on attitudes towards global warming and related matters was undertaken by Dennis Bray and Hans von Storch. The results were subsequently published in Bulletin of the American Meteorological Society Vol. 80, No. 3, March 1999 439-455.  The paper addressed the views of climate science, with a response rate of 40% from a mail survey questionnaire to 1000 scientists in Germany, the USA and Canada. Almost all scientists agreed that the skill of 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 were 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.
Survey of US state climatologists
In 1997, a survey was conducted by Citizens for a Sound Economy, an organization that lobbies against the adoption of policy measures to slow global warming. It claimed that 36 of America's 48 official state climatologists participated in the survey. Unfortunately neither the original survey questions nor the complete responses are available, only a press release describing it. The survey is reported to have found that by a margin of 44% to 17%, state climatologists believe that global warming is largely a natural phenomenon. The survey further found that 58% of the climatologists 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", while only 36% agreed with the assertion. Eighty-nine percent of the climatologists agreed that "current science is unable to isolate and measure variations in global temperatures caused only by man-made factors," and 61 percent said that the 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 percent below 1990 levels would not prevent global temperatures from rising, and 86 percent said that reducing emissions to 1990 levels would not prevent rising temperatures. It is not clear whether they mean by this that changing CO2 levels would have little effect on climate (which they expect to continue rising for some unspecified reason), or if even CO2 at 1990 levels could be expected to lead to more warming.
Finally, by a 39 to 33 percent margin, more climatologists say that, "evidence exists to suggest that the earth is headed for another glacial period." 
Other known surveys
- 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
- George Will reported "that 53 percent do not believe warming has occurred, and another 30 percent are uncertain."
- Fairness and Accuracy in Reporting states that the report said that 66 percent of the scientists said that human-induced global warming was occurring, with 10 percent 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."
- A 1993 Heartland Institute publication 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."