Almost every major scientific organization in the world agrees that the evidence is clear. Human activity is warming the climate and the danger is serious.
NASA’s climate website:
Ninety-seven percent of climate scientists agree that climate-warming trends over the past century are very likely due to human activities, and most of the leading scientific organizations worldwide have issued public statements endorsing this position.
American Association for the Advancement of Science, official statement (2006):
The scientific evidence is clear: global climate change caused by human activities is occurring now, and it is a growing threat to society.
American Geophysical Union, official statement (2007):
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.
American Physical Society, official statement (2007):
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.
National Research Council, official report (2010):
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.
American Chemical Society, official statement (2010):
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.
“Earth’s energy imbalance and implications,” James Hansen et al., Atmospheric Chemistry and Physics (2011):
The strong positive energy imbalance during the solar minimum, and the consistency of the planet’s energy imbalance with expectations based on estimated human-made climate forcing, together constitute a smoking gun, a fundamental verification that human-made climate forcing is the dominant forcing driving global climate change. Positive net forcing even during solar minimum assures that global warming will be continuing on decadal time scales.
American Meteorological Society, official statement (2012):
There is unequivocal evidence that Earth’s lower atmosphere, ocean, and land surface are warming; sea level is rising; and snow cover, mountain glaciers, and Arctic sea ice are shrinking. The dominant cause of the warming since the 1950s is human activities. This scientific finding is based on a large and persuasive body of research. The observed warming will be irreversible for many years into the future, and even larger temperature increases will occur as greenhouse gases continue to accumulate in the atmosphere. Avoiding this future warming will require a large and rapid reduction in global greenhouse gas emissions. The ongoing warming will increase risks and stresses to human societies, economies, ecosystems, and wildlife through the 21st century and beyond, making it imperative that society respond to a changing climate.
“A Decade of Weather Extremes,” Dim Coumou and Stefan Rahmstorf, Nature Climate Change (2012):
Many lines of evidence — statistical analysis of observed data, climate modelling and physical reasoning — strongly indicate that some types of extreme event, most notably heatwaves and precipitation extremes, will greatly increase in a warming climate and have already done so. […]
The evidence is strong that anthropogenic, unprecedented heat and rainfall extremes are here — and are causing intense human suffering.
American Geophysical Union, official statement (2013):
Human-induced climate change requires urgent action. […] Extensive, independent observations confirm the reality of global warming. These observations show large-scale increases in air and sea temperatures, sea level, and atmospheric water vapor; they document decreases in the extent of mountain glaciers, snow cover, permafrost, and Arctic sea ice. These changes are broadly consistent with long-understood physics and predictions of how the climate system is expected to respond to human-caused increases in greenhouse gases. The changes are inconsistent with explanations of climate change that rely on known natural influences.