Additional info from the Union of Concerned Scientists
Scientific societies and scientists have released statements and studies showing the growing consensus on climate change science. A common objection to taking action to reduce our heat-trapping emissions has been uncertainty within the scientific community on whether or not global warming is happening and if it is caused by humans. However, there is now an overwhelming scientific consensus that global warming is indeed happening and humans are contributing to it. Below are links to documents and statements attesting to this consensus.
Statement on climate change from 18 scientific associations (PDF)
"Observations throughout the world make it clear that climate change is occurring, and rigorous scientific research demonstrates that the greenhouse gases emitted by human activities are the primary driver." (October 2009)
American Meteorological Society: Climate Change: An Information Statement of the American Meteorological Society (PDF)
"Indeed, strong observational evidence and results from modeling studies indicate that, at least over the last 50 years, human activities are a major contributor to climate change." (February 2007)
American Physical Society: Statement on Climate Change (PDF)
"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." (November 2007)
American Geophysical Union: Human Impacts on Climate (PDF)
"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." (Adopted December 2003, Revised and Reaffirmed December 2007)
American Association for the Advancement of Science: AAAS Board Statement on Climate Change (PDF)
"The scientific evidence is clear: global climate change caused by human activities is occurring now, and it is a growing threat to society." (December 2006)
Geological Society of America: Global Climate Change
"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." (October 2006)
American Chemical Society: Statement on Global Climate Change
"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." (July 2004)
U.S. National Academy of Sciences: America’s Climate Choices
“Climate change is occurring, is caused largely by human activities, and poses significant risks for — and in many cases is already affecting—a broad range of human and natural systems.” (May 2010)
Joint Science Academies’ Statement: Global Response to Climate Change (PDF)
"Climate change is real. There will always be uncertainty in understanding a system as complex as the world’s climate. However there is now strong evidence that significant global warming is occurring." (June 2005, 11 national academies of science)
U.S. Climate Change Research Program, Global Climate Change Impacts in the United States
"Global warming is unequivocal and primarily human-induced. Global temperature has increased over the past 50 years. This observed increase is due primarily to human-induced emissions of heat-trapping gases." (2009)
Peter T. Doran and Maggie Kendall Zimmerman: Examining the Scientific Consensus on Climate Change (PDF)
"It seems that the debate on the authenticity of global warming and the role played by human activity is largely nonexistent among those who understand the nuances and scientific basis of long-term climate processes."
Doran surveyed 10,257 Earth scientists. Thirty percent responded to the survey which asked: 1. When compared with pre-1800s levels, do you think that mean global temperatures have generally risen, fallen, or remained relatively constant? and 2. Do you think human activity is a significant contributing factor in changing mean global temperatures?
Naomi Oreskes: Beyond the Ivory Tower: The Scientific Consensus on Climate Change
"Oreskes analyzed 928 abstracts published in refereed scientific journals between 1993 and 2003 and listed in the ISI database with the keywords 'climate change.'... Of all the papers, 75 percent either explicitly or implicitly accepted the consensus view that global warming is happening and humans are contributing to it; 25 percent dealt with methods or ancient climates, taking no position on current anthropogenic [human-caused] climate change. Remarkably, none of the papers disagreed with the consensus position."