Global warming is the increase in the average temperature of the Earth's near-surface air and oceans since the mid-twentieth century, and its projected continuation. The average global air temperature near the Earth's surface increased 0.74 ± 0.18 ° C (1.33 ± 0.32 ° F ) during the hundred years ending in 2005.  The Intergovernmental Panel on Climate Change (IPCC) concludes "most of the observed increase in globally averaged temperatures since the mid-twentieth century is very likely due to the observed increase in anthropogenic (man-made) greenhouse gas concentrations"  via the greenhouse effect . Natural phenomena such as solar variation combined with volcanoes probably had a small warming effect from pre-industrial times to 1950 and a small cooling effect from 1950 onward.   These basic conclusions have been endorsed by at least thirty scientific societies and academies of science ,  including all of the national academies of science of the major industrialized countries
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This note was uploaded on 05/14/2008 for the course SCI 101 taught by Professor Webb during the Spring '08 term at Pitt CC.