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|The Discovery of Global Warming February 2016|
A century of average surface temperatures of the Northern Hemisphere, looking back from 1980. (Shown as differences in °C from the 1946-60 mean.) Decades later, scientists concluded that the drop after 1940 was largely due to a rise in industrial pollution, which blocked some sunlight, augmented by a long-term cycle in the Pacific Ocean. Later data also showed that the decline was not seen in the Southern Hemisphere. For a graph of temperatures into the 21st century click here.
From P. D. Jones et al., Monthly Weather Review 110
(1982), p. 67,