From time to time, a politician or scientist makes the news for disputing some of the facts about human-induced climate change (global warming). These remarks can often be exaggerated or taken out of context, as in the recent example of climate scientist John Christy (who apparently agrees that humans are causing global warming but takes exception to the “catastrophism” that often accompanies climate change discussions). I thought it would be useful to collect positions from various scientific organizations. This list focuses on United States institutions, since that is where I live and also because there seems to be more confusion here than in much of the world.
The clear authority, the Nobel Peace Prize–winning United Nations Intergovernmental Panel on Climate Change (IPCC). Established by the World Meterological Organization and the United Nations Environment Programme in 1988, the IPCC’s reports are considered authoritative by governments and scientists worldwide. I’d actually like to cover this report in more detail in a future post, but below is abstracted from the Summary for Policymakers of the Synthesis Report of the IPCC Fourth Assessment Report (PDF):
Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level. Observational evidence from all continents and most oceans shows that many natural systems are being affected by regional climate changes, particularly temperature increases…Most of the observed increase in globally averaged temperatures since the mid–20th century is very likely due to the observed increase in anthropogenic GHG [greenhouse gas] concentrations. It is likely there has been significant anthropogenic warming over the past 50 years averaged over each continent (except Antarctica)…Anthropogenic warming over the last three decades has likely had a discernible influence at the global scale on observed changes in many physical and biological systems…
The joint national science academies of the G8+5 nations (including the U.S. National Academy of Sciences) published a combined statement. Backed also by the Academia Brasileira de Ciéncias (Brazil), Académie des Sciences (France), Accademia Nazionale dei Lincei (Italy), Russian Academy of Sciences (Russia), Royal Society of Canada (Canada), Deutsche Akademie der Naturforscher Leopoldina (Germany), Science Council of Japan (Japan), Academy of Science of South Africa (South Africa), Chinese Academy of Sciences (China), Indian National Science Academy (India), Academia Mexicana de Ciencias (Mexico), and the Royal Society (United Kingdom), the statement (PDF) included the following:
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.
The American Association for the Advancement of Science, the organization that publishes the prestigious journal Science, takes the following position (PDF):
The scientific evidence is clear: global climate change caused by human activities is occurring now, and it is a growing threat to society. Accumulating data from across the globe reveal a wide array of effects: rapidly melting glaciers, destabilization of major ice sheets, increases in extreme weather, rising sea level, shifts in species ranges, and more. The pace of change and the evidence of harm have increased markedly over the last five years. The time to control greenhouse gas emissions is now.
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.
…Despite the uncertainties noted above, there is adequate evidence from observations and interpretations of climate simulations to conclude that the atmosphere, ocean, and land surface are warming; that humans have significantly contributed to this change; and that further climate change will continue to have important impacts on human societies, on economies, on ecosystems, and on wildlife through the 21st century and beyond. Focusing on the next 30 years, convergence among emission scenarios and model results suggest strongly that increasing air temperatures will reduce snowpack, shift snowmelt timing, reduce crop production and rangeland fertility, and cause continued melting of the ice caps and sea level rise. Important goals for future work include the need to understand the relation of climate at the state and regional level to the patterns of global climate and to reverse the decline in observational networks that are so critical to accurate climate monitoring and prediction.
According to NOAA and NASA data, the Earth’s average surface temperature has increased by about 1.2 to 1.4ºF in the last 100 years. Eleven of the last twelve years rank among the 12 warmest years on record (since 1850), with the warmest two years being 1998 and 2005. Most of the warming in recent decades is very likely the result of human activities. Other aspects of the climate are also changing such as rainfall patterns, snow and ice cover, and sea level. If greenhouse gases continue to increase, climate models predict that the average temperature at the Earth’s surface could increase from 3.2 to 7.2ºF above 1990 levels by the end of this century. Scientists are certain that human activities are changing the composition of the atmosphere, and that increasing the concentration of greenhouse gases will change the planet’s climate. But they are not sure by how much it will change, at what rate it will change, or what the exact effects will be.
Human activities are increasingly altering the Earth’s climate. These effects add to natural influences that have been present over Earth’s history. Scientific evidence strongly indicates that natural influences cannot explain the rapid increase in global near-surface temperatures observed during the second half of the 20th century.
Human impacts on the climate system include increasing concentrations of atmospheric greenhouse gases (e.g., carbon dioxide, chlorofluorocarbons and their substitutes, methane, nitrous oxide, etc.), air pollution, increasing concentrations of airborne particles, and land alteration. A particular concern is that atmospheric levels of carbon dioxide may be rising faster than at any time in Earth’s history, except possibly following rare events like impacts from large extraterrestrial objects.
Atmospheric carbon dioxide concentrations have increased since the mid-1700s through fossil fuel burning and changes in land use, with more than 80% of this increase occurring since 1900. Moreover, research indicates that increased levels of carbon dioxide will remain in the atmosphere for hundreds to thousands of years. It is virtually certain that increasing atmospheric concentrations of carbon dioxide and other greenhouse gases will cause global surface climate to be warmer.
The American Geophysical Union (AGU) notes that human impacts on the climate system include increasing concentrations of greenhouse gases in the atmosphere, which is significantly contributing to the warming of the global climate. The climate system is complex, however, making it difficult to predict detailed outcomes of human-induced change: there is as yet no definitive theory for translating greenhouse gas emissions into forecasts of regional weather, hydrology, or response of the biosphere. As the AGU points out, our ability to predict global climate change, and to forecast its regional impacts, depends directly on improved models and observations.
The American Astronomical Society (AAS) joins the AGU in calling for peer-reviewed climate research to inform climate-related policy decisions, and, as well, to provide a basis for mitigating the harmful effects of global change and to help communities adapt and become resilient to extreme climatic events.
In endorsing the “Human Impacts on Climate” statement, 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.
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.
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.
Accumulating evidence clearly shows that our environment and the global climate system are changing. Global average temperatures, atmospheric greenhouse gas concentrations, sea levels, and extreme weather events are on the rise. In order to place these changes in the context of environmental policy, it is necessary to recognize that the climate is a dynamic system. The geochemical record demonstrates that large, and sometimes rapid, climate changes have occurred in the past without the influences of modern development. There is now general agreement among scientific experts that the recent warming trend is real (and particularly strong within the past 20 years), that most of the observed warming is likely due to increased atmospheric greenhouse gas concentrations, and that climate change could have serious adverse effects by the end of this century.
Indications of changes in the earth’s future climate must be treated with the utmost seriousness, and with the precautionary principle uppermost in our minds. Extensive climate changes may alter and threaten the living conditions of much of mankind. They may induce large-scale migration and lead to greater competition for the earth’s resources. Such changes will place particularly heavy burdens on the world’s most vulnerable countries. There may be increased danger of violent conflicts and wars, within and between states.
Through the scientific reports it has issued over the past two decades, the IPCC has created an ever-broader informed consensus about the connection between human activities and global warming. Thousands of scientists and officials from over one hundred countries have collaborated to achieve greater certainty as to the scale of the warming. Whereas in the 1980s global warming seemed to be merely an interesting hypothesis, the 1990s produced firmer evidence in its support. In the last few years, the connections have become even clearer and the consequences still more apparent.
World leaders are taking an active role. U.N. Secretary General Ban Ki-moon has been an active proponent of action. See, for example, his recent briefing to the General Assembly:
…We look to Governments to agree on a road map for negotiations that will ensure a new climate change agreement by 2009. This date is important not only to ensure continuity after 2012, when the existing regime expires — but equally, to address the desperate urgency of the situation itself, as underscored by the IPCC…
And U.S. President George Bush has emphasized the importance of fighting climate change, though progress has been underwhelming.
Energy security and climate change are two of the great challenges of our time. The United States takes these challenges seriously. The world’s response will help shape the future of the global economy and the condition of our environment for future generations.
…Seven in 10 Americans (71%) say that human activity is “a significant cause of climate change.” By a margin of 59 percent to 33 percent, Americans say it is necessary to take “major steps starting very soon” rather than “modest steps over the coming years.” Only 6 percent say “it is not necessary to take any steps.”…
And a LiveScience article summarized several recent polls:
Nearly three-quarters of Americans are willing to pay more taxes to support local government efforts aimed at mitigating global warming…Americans were willing to pay more money in property taxes, home costs and utility fees to support initiatives that would encourage people to use less energy and get that energy from alternative sources…concern for the environment is growing among Americans and bolder action is desired…Americans are pessimistic about the current state of the environment and disapprove of how the government has been handling environmental issues…a majority of Americans believe that society must take action to reduce the effects of global warming, partly by enacting a new national treaty that would require much more drastic reductions in carbon dioxide than those required by the Kyoto Protocol (which the United States never ratified)…
“Nearly half of Americans now believe that global warming is either already having dangerous impacts on people around the world or will in the next 10 years—a 20 percentage-point increase since 2004. These results indicate a sea change in public opinion,” said Anthony Leiserowitz, director of Yale Project on Climate Change, in response to the findings of the earlier poll.
The science has been well-established. The urgency has been well-established. The time for serious action is long overdue.