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Europe’s Alpine region is going through its warmest period in 1,300 years, the head of an extensive climate study said Tuesday. “We are currently experiencing the warmest period in the Alpine region in 1,300 years,” Reinhard Boehm, a climatologist at Austria's Central Institute for Meteorology and Geodynamics said.

Boehm said the current warm period in the Alpine region began in the 1980s, noting that a similar warming occurred in the 10th and 12th centuries. However, the temperatures during those phases were “slightly under the temperatures we’ve experienced over the past 20 years.”

...leads to one question, what caused the global warming 1,300 years ago?