Natural Causes of Rapid Temperature Change
(p. C4) Some three decades after Laki, 1816 was known as the "year without a summer" thanks to a big eruption in Indonesia. Even Mount Pinatubo in the Philippines in 1991 caused a brief, though small, drop in world temperatures.
Other abrupt coolings have been bigger but less explicable. Earlier this year, two scientists from Brown University used lake sediments to conclude that the sharp cooling in Greenland during the late Middle Ages, which extinguished the Norse colonies, saw temperatures drop by seven degrees Fahrenheit in 80 years, much faster than recent warming there. Conversely, Greenland's temperature shot up by around 13 degrees in 50 years as the world came out of the last ice age 12,000 years ago and the ice sheets of North America and northern Europe retreated--again, unlike today's slow increase.
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