SCIENTIFIC SUPPORT FOR HUMAN-CAUSED CLIMATE CHANGE

Environmental groups have warned of the contribution to climate change from human activities for decades. It has taken the scientific community many years to begin making definitive statements about the accuracy of these claims. It should be noted that while the overwhelming majority of scientists now accept that human activities are a major cause of global warming, there is still a small number of scientists who disagree with these conclusions.

evidence supporting global warming & human causes

The fact that carbon dioxide absorbs and emits IR radiation has been known for over a century. Gas bubbles trapped in ice cores give us a detailed record of atmospheric chemistry and temperature back more than four hundred thousand years, with the temperature record confirmed by other geologic evidence. This record tells us that carbon dioxide and temperature rise and fall tightly together. The recent rise in carbon dioxide and other greenhouse gases is greater than any in hundreds of thousands of years and this is human-caused.

The historical temperature record shows a rise of 0.4–0.8 °C over the last 100 years, and the current warmth is unusual in the past 1000 years. Climate change attribution studies using both models and observations find that the warming of the last 50 years is likely caused by human activity. Natural variability (including solar variation) alone cannot explain the recent change. Climate models can reproduce the observed trend only when greenhouse gas forcing is included.

There is a scientific consensus behind all of the above, reflected in official statements by professional associations related to climate science. Humankind is performing a great geophysical experiment and if it turns out badly — however that is defined — we cannot undo it. We cannot even abruptly turn it off. Too many of the things we are doing now have long-term ramifications for centuries into the future.

Climate models predict more warming, and other climate effects such as sea level rise, more frequent and severe storms, drought and heat waves in the future.

Statements by organizations 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.

Intergovernmental Panel on Climate Change

The IPCC (created in 1988 by the World Meteorological Organization and the UN’s Environmental Programme) said in its Second Assessment Report (SAR) in 1995, "the balance of evidence suggests that there is a discernible human influence on global climate." 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). This statement was strengthened in the Third Assessment Report (TAR) in 2001, in which the IPCC said:

"There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities."
"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, 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.

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.

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 on climate change

Other scientific organizations have made position statements on climate change.

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 of scientists on climate change

Various surveys have been conducted to determine a scientific consensus on the soundness of global warming theory.

Oreskes, 2004

In December 2004, Science published an article by UC San Diego geologist and historian of science Naomi Oreskes 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, "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." However, Dr. Benny Peiser of Liverpool John Moores University subsequently reviewed the journals in the same database and found that only 1% of the papers explicitly endorsed the "consensus" as defined in Oreskes' paper; that almost three times as many papers explicitly doubted or rejected the "consensus" as explicitly endorsed it; and that fewer than one-third either explicitly or implicitly endorsed it.

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 Bulletin of the American Meteorological Society Vol. 80, No. 3, March 1999 439-455. 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, the resulting questionnaire of 74 question, 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.

Survey of US state climatologists

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% of the climatologists 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 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% 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. By a 39% to 33% margin, more climatologists agreed 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.

Other Opinion Surveys of Scientists

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, "that 53 percent do not believe warming has occurred, and another 30 percent are uncertain."
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."
It should be noted that these surveys are over 10 years old and the state of climate science has changed radically since their time; therefore current beliefs of the scientific community are likely to be different.

Click here to go to the home page www.climatechange.110mb.com

This information is licensed under the GNU Free Documentation. It is derivative of articles on Climate Change, Global Warming and related environmental issues at http://en.wikipedia.org