Multiple studies published in peer-reviewed scientific journals1 show that 97 percent or more of actively publishing climate scientists agree*: Climate-warming trends over the past century are extremely likely due to human activities. In addition, most of the leading scientific organizations worldwide have issued public statements endorsing this position. The following is a partial list of these organizations, along with links to their published statements and a selection of related resources.
AMERICAN SCIENTIFIC SOCIETIES
Statement on climate change from 18 scientific associations
"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." (2009)2
American Association for the Advancement of Science
"The scientific evidence is clear: global climate change caused by human activities is occurring now, and it is a growing threat to society." (2006)3
American Chemical Society
"Comprehensive scientific assessments of our current and potential future climates clearly indicate that climate change is real, largely attributable to emissions from human activities, and potentially a very serious problem." (2004)4
American Geophysical Union
"Human‐induced climate change requires urgent action. Humanity is the major influence on the global climate change observed over the past 50 years. Rapid societal responses can significantly lessen negative outcomes." (Adopted 2003, revised and reaffirmed 2007, 2012, 2013)5
American Medical Association
"Our AMA ... supports the findings of the Intergovernmental Panel on Climate Change’s fourth assessment report and concurs with the scientific consensus that the Earth is undergoing adverse global climate change and that anthropogenic contributions are significant." (2013)6
American Meteorological Society
"It is clear from extensive scientific evidence that the dominant cause of the rapid change in climate of the past half century is human-induced increases in the amount of atmospheric greenhouse gases, including carbon dioxide (CO2), chlorofluorocarbons, methane, and nitrous oxide." (2012)7
American Physical Society
"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." (2007)8
The Geological Society of America
"The Geological Society of America (GSA) concurs with assessments by the National Academies of Science (2005), the National Research Council (2006), and the Intergovernmental Panel on Climate Change (IPCC, 2007) that global climate has warmed and that human activities (mainly greenhouse‐gas emissions) account for most of the warming since the middle 1900s." (2006; revised 2010)9
International academies: Joint statement
"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. The evidence comes from direct measurements of rising surface air temperatures and subsurface ocean temperatures and from phenomena such as increases in average global sea levels, retreating glaciers, and changes to many physical and biological systems. It is likely that most of the warming in recent decades can be attributed to human activities (IPCC 2001)." (2005, 11 international science academies)10
U.S. National Academy of Sciences
"The scientific understanding of climate change is now sufficiently clear to justify taking steps to reduce the amount of greenhouse gases in the atmosphere." (2005)11
U.S. GOVERNMENT AGENCIES
U.S. Global Change Research Program
"The global warming of the past 50 years is due primarily to human-induced increases in heat-trapping gases. Human 'fingerprints' also have been identified in many other aspects of the climate system, including changes in ocean heat content, precipitation, atmospheric moisture, and Arctic sea ice." (2009, 13 U.S. government departments and agencies)12
Intergovernmental Panel on Climate Change
“Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia. The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, and sea level has risen.”13
“Human influence on the climate system is clear, and recent anthropogenic emissions of greenhouse gases are the highest in history. Recent climate changes have had widespread impacts on human and natural systems.”14
List of worldwide scientific organizations
The following page lists the nearly 200 worldwide scientific organizations that hold the position that climate change has been caused by human action.
The following page contains information on what federal agencies are doing to adapt to climate change.
*Technically, a “consensus” is a general agreement of opinion, but the scientific method steers us away from this to an objective framework. In science, facts or observations are explained by a hypothesis (a statement of a possible explanation for some natural phenomenon), which can then be tested and retested until it is refuted (or disproved).
As scientists gather more observations, they will build off one explanation and add details to complete the picture. Eventually, a group of hypotheses might be integrated and generalized into a scientific theory, a scientifically acceptable general principle or body of principles offered to explain phenomena.
Earth’s surface will almost certainly not warm up four or five degrees Celsius by 2100, according to a study which, if correct, voids worst-case UN climate change predictions.
A revised calculation of how greenhouse gases drive up the planet’s temperature reduces the range of possible end-of-century outcomes by more than half, researchers said in the report, published in the journal Nature.
“Our study all but rules out very low and very high climate sensitivities,” said lead author Peter Cox, a professor at the University of Exeter.
Japan breakthrough could improve weather warnings and save lives
How effectively the world slashes CO2 and methane emissions, improves energy efficiency and develops technologies to remove CO2 from the air will determine whether climate change remains manageable or unleashes a maelstrom of human misery.
But uncertainty about how hot things will get also stems from the inability of scientists to nail down a very simple question: By how much will Earth’s average surface temperature go up if the amount of CO2 in the atmosphere is doubled?
That “known unknown” is called equilibrium climate sensitivity, and for the last 25 years the UN’s Intergovernmental Panel on Climate Change – the ultimate authority on climate science – has settled on a range of 1.5C to 4.5C (2.7 to 8.1 degrees Fahrenheit).
Cox and colleagues, using a new methodology, have come up with a far narrower range: 2.2C to 3.4C, with a best estimate of 2.8C.
If accurate, it precludes the most destructive doomsday scenarios. “These scientists have produced a more accurate estimate of how the planet will respond to increasing CO2 levels,” said Piers Forster, director of the Priestley International Centre for Climate at the University of Leeds.
Ambitious 1.5C Paris climate target is still possible, new analysis shows
Gabi Hegerl, a climate scientist at the University of Edinburgh who, like Forster, did not take part in the research, added: “Having lower probability for very high sensitivity is reassuring. Very high sensitivity would have made it extremely hard to limit climate change according to the Paris targets.”
The landmark Paris climate agreement in 2015 called for capping global warming at “well under” 2C compared to a pre-industrial benchmark, and pursuing efforts for a 1.5C ceiling.
The findings should not be seen as taking pressure off the need to tackle climate change, the authors and other experts warned. “We will still see significant warming and impacts this century if we don’t increase our ambition to reduce CO2 emissions,” said Forster.
Even a 1.5C increase will have consequences. With a single degree Celsius of warming so far, the Earth is already coping with a crescendo of climate impacts including deadly droughts, erratic rainfall, and storm surges engorged by rising seas.
A 3.5 C world, scientists say, could pull at the fabric of civilisation.
Since industrialisation took off in the early 19th century, CO2 concentrations in the atmosphere have increased by nearly half, from 280 parts per million to 407 parts per million.
Climate change: ‘human fingerprint’ found on global extreme weather
Up to now global warming predictions have focused on the historical temperature record.
Cox and colleagues instead “considered the year-to-year fluctuations in global temperature,” said Richard Allan, a climate scientist at the University of Reading.
By analysing the responsiveness of short-term changes in temperature to “nudges and bumps” in the climate system, he explained, they were able to exclude the outcomes that would have resulted in devastating increases of 4C or more by 2100.
One wild card not taken into consideration by the new model is the possibility of rapid shifts in climate brought on by the planet itself. “There is indeed evidence that the climate system can undergo abrupt changes or ‘tipping points’,” Cox said.
The collapse of the gulf stream, the thawing of carbon-rich permafrost, or the melting of ice sheets on Greenland and Antarctica – any of these could quickly change the equation, and not in the Earth’s favour.