National Academy of Sciences National Academy of Sciences

The eruption of Mount Pinatubo in the Philippines in 1991 spewed almost 20 million tons of sulfur dioxide into the atmosphere, causing worldwide temperatures to drop half a degree on average. Arlan Naeg/AFP/Getty Images hide caption

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Arlan Naeg/AFP/Getty Images

Scientific Pros Weigh The Cons Of Messing With Earth's Thermostat

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A member of the Ya̧nomamö people at Irotatheri community in Venezuela's Amazonas state, near the Brazilian border, in September 2012. Leo Ramirez/AFP/Getty Images hide caption

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Leo Ramirez/AFP/Getty Images

July 2010: Two pelicans sit on booms protecting Queen Bess Island, La., from oil that spilled after the Deepwater Horizon rig exploded in April. Chris Graythen/Getty Images hide caption

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Chris Graythen/Getty Images

Navy specialists repair a weather buoy collecting data for the National Oceanic and Atmospheric Administration (NOAA) off the Atlantic coast of Africa. President Richard Nixon, a Republican, created NOAA, one of our principal resources for understanding the Earth's climate. Elizabeth Merriam/U.S. Navy hide caption

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Elizabeth Merriam/U.S. Navy