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Various national and international bodies and societies, and individual scientists have expressed opinions on climate change or global warming in the last few decades. This article addresses those opinions.1 Pronouncements
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 detailing and also summarizing the current state of scientific knowledge on the earth's climate see below. The original scientific literature is often inaccessible to the layperson (both literally, because they do not have access to appropriate libraries, and because the scientific writing style is unfamiliar), but the summaries and position statements are usually written to be intelligible to the informed layperson.
It is commonplace to see the assertion that the IPCC represents the consensus of opinion of climate scientists; it is also common to see this view disputed, e.g. SEPP. This page exists to provide evidence from published surveys (and possibly even petitions) of the general current of scientific thought rather than the opinions of individual scientists.
2 IPCC
The IPCC said in the second assessment report in 1995 that the balance of evidence suggests that there is a discernible human influence on global climate and strengthened this in the third report in 2001 with 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 1995 SAR the IPCC said:
- "our ability to quantify the human influence on global climate is currently limited because the expected signal is still emerging from the noise of natural variability, and because there are uncertainties in key factors. These include the magnitude and patterns of long term variability…." (emphasis added) [1]
In the intervening 6 years much research was done, and the 2001 TAR 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." (emphasis added) [2].
3 National Research Council
A National Research Council report concluded that
- "[g]reenhouse gases are accumulating in the Earth's atmosphere as a result of human activities, causing surface air temperatures and subsurface ocean temperatures to rise. . . . 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" (National Research Council 2001, quoted in [3])
4 American Meteorological Society
The 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." [4]
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