How strong is the scientific evidence that Earth is warming and that humans are the main cause?

January 23, 2014

There is overwhelming scientific evidence that Earth is warming and a preponderance of scientific evidence that human activities are the main cause. Thousands of weather stations worldwide—over land and ocean—have been recording daily high and low temperatures for many decades and, in some locations, for more than a century. When different scientific and technical teams in different U.S. agencies (e.g., NOAA and NASA) and in other countries (e.g., the U.K.'s Hadley Centre) average these data together, essentially the same results are found: Earth's average surface temperature has risen by about 1.5°F (0.85°C) since 1880.

The primary cause is that, over the last 200 years, human activities have added about 500 billion metric tons of carbon dioxide to the atmosphere, increasing the abundance of this heat-trapping gas by about 40 percent. Today, humans add about 70 million metric tons of carbon dioxide to the atmosphere every day. The amount of carbon dioxide in the atmosphere has increased from about 278 parts per million (ppm) in 1800 to over 400 ppm today. Today's carbon dioxide levels are unusually high; much higher than at any other time in the last 800,000 years. The warming influence of heat-trapping gases was recognized in the mid-1800s.

Coalbrookdale by Night

Philip James de Loutherbourg's 1801 painting, Coalbrookdale by Night, came to symbolize the start of the Industrial Revolution, when humans began to harness the power of fossil fuels—and to contribute significantly to Earth's atmospheric greenhouse gas composition. Image from Wikipedia.

Additionally, many other lines of evidence confirm that our world has warmed over multiple decades:


Blunden, J., and D. S. Arndt, eds (2013): State of the Climate in 2012. Bull. Amer. Meteor. Soc., 94 (8), S1–S238.

National Fish, Wildlife, and Plants Climate Adaptation Partnership (2012): National Fish, Wildlife, and Plants Climate Adaptation Strategy. Association of Fish and Wildlife Agencies, Council on Environmental Quality, Great Lakes Indian Fish and Wildlife Commission, National Oceanic and Atmospheric Administration, and U.S. Fish and Wildlife Service. Washington, D.C. DOI: 10.3996/082012-FWSReport-1

Perovich, D., W. Meier, M. Tschudi, S. Gerland, and J. Richter-Menge (2012): "Sea Ice." Arctic Report Card: Update for 2012. A website published by the Study of Environmental Arctic Change, the Conservation of Arctic Flora and Fauna, the Arctic Monitoring and Assessment Programme, and the National Oceanic and Atmospheric Administration ( (Accessed July 2013.)

IPCC (2007): Climate Change 2007: The Physical Science Basis. Contribution of Working Group 1 to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor, and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 996 pp.

NASA JPL: "Consensus: 97% of climate scientists agree." Global Climate Change. A website at NASA's Jet Propulsion Laboratory ( (Accessed July 2013.)