Climate Change: Scientific Consensus

There are many national and international scientific societies and associations that have come to a consensus, based on evidence, that human actions have contributed to increasing emissions of carbon dioxide and other greenhouse gases, and that they are already causing impacts. A selection of links to statements are included here, along with brief highlights.

American Academy of Pediatrics (2007) – There is broad scientific consensus that Earth's climate is warming rapidly and at an accelerating rate. Human activities, primarily the burning of fossil fuels, are very likely (>90% probability) to be the main cause of this warming. Climate-sensitive changes in ecosystems are already being observed, and fundamental, potentially irreversible, ecological changes may occur in the coming decades. Conservative environmental estimates of the impact of climate changes that are already in process indicate that they will result in numerous health effects to children. Anticipated direct health consequences of climate change include injury and death from extreme weather events and natural disasters, increases in climate-sensitive infectious diseases, increases in air pollution–related illness, and more heat-related, potentially fatal, illness. Within all of these categories, children have increased vulnerability compared with other groups.

American Association for the Advancement of Science (2006) – The scientific evidence is clear: global climate change caused by human activities is occurring no, and it is a growing threat to society. … The growing torrent of information presents a clear message: we are already experiencing global climate change.

American Association of Petroleum Geologists – Though cautious, members support expanding scientific climate research into the basic controls on climate specifically including the geological, solar and astronomic aspects of climate change, and support reducing emissions from fossil fuel use.

American Chemical Society (2007) – Careful and comprehensive scientific assessments have clearly demonstrated that the Earth’s climate system is changing rapidly in response to growing atmospheric burdens of greenhouse gases and absorbing aerosol particles (IPCC, 2007). There is very little room for doubt that observed climate trends are due to human activities. The threats are serious and action is urgently needed to mitigate the risks of climate change.

American Geophysical Union (2003, 2007) - 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. Global average surface temperatures increased on average by about 0.6°C over the period 1956–2006…. Recent changes in many physical and biological systems are linked with this regional climate change…. In the next 50 years, even the lower limit of impending climate change - an additional global mean warming of 1°C above the last decade - is far beyond the range of climate variability experienced during the past thousand years and poses global problems in planning for and adapting to it. Warming greater than 2°C above 19th century levels is projected to be disruptive, reducing global agricultural productivity, causing widespread loss of biodiversity, and - if sustained over centuries - melting much of the Greenland ice sheet with ensuing rise in sea level of several meters.

American Institute on Physics (2004) - 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.

American Medical Association (2008) – Ongoing global climate change is now widely accepted by the majority of scientists, climatologists, and meteorologists, and human activity is accelerating this process…. The potential exists for devastating events with serious health implications, including extreme heat and cold events, flooding and droughts, increases in vectors carrying infectious diseases, and increases in air pollution. The health effects from these events should be of concern to the medical community and require action.

American Meteorological Society (2003) - 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.

Geological Society of America (2006) – 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.

Intergovernmental Panel on Climate Change (2007) – An increasing body of observations gives a collective picture of a warming world and other changes in the climate system. There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities. Human actions are very likely the cause of global warming (probability ? 90%)

Joint Academies of Science (2001- 2009) - Explicitly acknowledged the IPCC position as representing the scientific consensus on climate change science. The national academies of the G8+5 nations issued a joint statement that “Climate change and sustainable energy supply are crucial challenges for the future of humanity. It is essential that world leaders agree on the emission reductions needed to combat negative consequences of anthropogenic climate change.”

National Academy of Sciences (2005) - We urge all nations, in the line with the UNFCCC principles, to take prompt action to reduce the causes of climate change, adapt to its impacts and ensure that the issue is included in all relevant national and international strategies. As national science academies, we commit to working with governments to help develop and implement the national and international response to the challenge of climate change.

National Research Council (2001) – 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. 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.

US Global Change Research Program (2009) - Observations show that warming of the climate is unequivocal. The global warming observed over the past 50 years is due primarily to human-induced emissions of heat-trapping gases. Climate-related changes have already been observed globally and in the United States. These include increases in air and water temperatures, reduced frost days, increased frequency and intensity of heavy downpours, a rise in sea level, and reduced snow cover, glaciers, permafrost, and sea ice.