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A very recent break from a long, cool trend

Researchers secure a floating platform used to take sediment cores from Sunday Lake, SW Alaska.
[Image courtesy of Darrell Kaufman, Northern Arizona University]

About 2,000 years ago, researchers say that the Arctic began cooling off and that cooling trend lasted all the way up to the 20th century. But, recently, the pattern of cooling in the Arctic has reversed, they say.

The Arctic is the region around Earth's North Pole, and it includes parts of Canada, Greenland, Russia, the United States, Iceland, Norway, Sweden, and Finland.

Darrell Kaufman and a team of researchers studied Arctic lakes, sampled ice from the region, and examined tree ring patterns in order to make a temperature record of the past 2,000 years in the Arctic. With this temperature record, they saw that the past ten years in the Arctic have been the warmest there in the past 2,000 years and that temperatures in the Arctic are about 1.4 degrees Celsius higher than they would be if the 2,000-year cooling trend had continued.

A small cirque glacier feeds meltwater into Upper Greyling Lake in south-central Alaska.
[Image courtesy of Darrell Kaufman, Northern Arizona University]

The long-term cooling event that began 2,000 years ago happened at the same time that changes in the Earth's orbit were changing the Arctic region of the planet, allowing more heat from the sun to escape into space. However, the rapid warming of the Arctic during the past century appears to be mostly related to human activity.

The researchers' findings that four of the five warmest decades in the past 2,000 years were between 1950 and 2000 should help to create more accurate climate models in the future.


This research appears in the 04 September 2009 issue of Science.