Last updated October 5, 2017

Global Warming

From 1880 to 2012, the Earth warmed by 1.5°F (0.85°C) reversing a long term cooling trend. The physics behind the Earth’s temperature imbalance is simple. Scientists first realized that gases in the atmosphere cause a greenhouse effect in the 19th century and have known since the late 1970s that humans are now driving this effect, trapping more of the Earth’s infrared energy close to the surface through fossil fuel emissions. The atmospheric concentration of greenhouse gases has increased from 280 parts per million in preindustrial times to what is now over 400 ppm.

Global trends

“Each of the last three decades has been successively warmer at the Earth’s surface than any preceding decade since 1850. The period from 1983 to 2012 was likely the warmest 30-year period of the last 1400 years in the Northern Hemisphere.”[1]

“The globally averaged combined land and ocean surface temperature data...show a warming of 1.5°F (0.85°C) over the period 1880 to 2012.”[1]

“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, sea level has risen, and the concentrations of greenhouse gases have increased.”[1]

US trends and projections

“U.S. average temperature has increased by 1.3°F to 1.9°F since 1895, and most of this increase has occurred since 1970.”[2]

The 2000 to 2010 decade was the nation’s and the world’s hottest on record,[2] and 2012 and 2015 were the first and second hottest years on record in the continental United States.

“Temperatures are projected to rise another 2°F to 4°F in most areas of the United States over the next few decades.”[2]

“Models unequivocally project large and historically unprecedented future warming in every region of the U.S. under all of the scenarios used in this assessment.”[2]