Average temperatures on earth have increased at a rate far faster than can be explained by natural climate changes. A 2008 study compared data from tree rings, ice cores, and corals over the past millennium with recent temperature records. The study created the famous “hockey stick” graph, showing that the rise in earth’s temperature over the preceding decade had occurred at a rate faster than any warming period over the last 1,700 years. 23 In 2012 the Berkeley scientists found that the average temperature of the earth’s land increased 2.5°F over 250 years (1750-2000), with 1.5°F of that increase in the last 50 years. 21 Lead researcher Richard A. Muller, PhD, said “it appears likely that essentially all of this increase in temperature results from the human emission of greenhouse gases.” 22 In 2013, a surface temperature study published in Science found that global warming over the past 100 years has proceeded at a rate faster than at any time in the past 11,300 years. 3 According to the IPCC’s 2014 Synthesis Report, human actions are “extremely likely” (95-100% confidence) to have been the main cause of 20th century global warming, and the surface temperature warming since the 1950s is “unprecedented over decades to millennia.” 24


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