FILE - In this Aug. 29, 1938 file photo, smoke rises from smokestacks at Skoda’s main foundry in Pilsen, Czechoslovakia. A new study looking at 11,000 years of climate temperatures shows the world in the middle of a dramatic U-turn, lurching from near-record cooling to a heat spike. It shows how the globe for several thousands of years was cooling until an unprecedented reversal in the 20th century, which scientists say is further evidence that global warming isn’t natural but man-made since the start of the Industrial Revolution. The research was released Thursday, March 7, 2013 in the journal Science. (AP Photo)

Associated Press
FILE - In this Aug. 29, 1938 file photo, smoke rises from smokestacks at Skoda’s main foundry in Pilsen, Czechoslovakia. A new study looking at 11,000 years of climate temperatures shows the world in the middle of a dramatic U-turn, lurching from near-record cooling to a heat spike. It shows how the globe for several thousands of years was cooling until an unprecedented reversal in the 20th century, which scientists say is further evidence that global warming isn’t natural but man-made since the start of the Industrial Revolution. The research was released Thursday, March 7, 2013 in the journal Science. (AP Photo)
FILE - In this Aug. 29, 1938 file photo, smoke rises from smokestacks at Skoda’s main foundry in Pilsen, Czechoslovakia. A new study looking at 11,000 years of climate temperatures shows the world in the middle of a dramatic U-turn, lurching from near-record cooling to a heat spike. It shows how the globe for several thousands of years was cooling until an unprecedented reversal in the 20th century, which scientists say is further evidence that global warming isn’t natural but man-made since the start of the Industrial Revolution. The research was released Thursday, March 7, 2013 in the journal Science. (AP Photo)
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