Greenhouse gas emissions have helped reverse the Arctic’s 2,000-year (at least) cooling streak, suggests a new report in Science.

The authors reconstructed the past two millennia of Arctic temperatures based on records from lake sediments, ice cores and tree rings, and found that the Arctic had been cooling throughout the data set — until this century, when the trend halted and reversed. Four of the five warmest decades in the past 2,000 years between 1950 and 2000, with the most recent decade the hottest of them all. The Arctic had been cooling due to a wobble in its orbit, causing less summer sunshine to hit its surface.

According to first author Darrell Kaufman, “the 20th century stands out in strong contrast to the cooling that should have continued. The last half-century was the warmest of the 2,000-year temperature record, and the last 10 years have been especially dramatic.” (BBC)

The authors’ model shows that the Arctic temperatures should have kept cooling for another 4,000 years before the trend reversed — had greenhouse gas emissions in the latter half of the 20th century not overwhelmed the natural cycle (MongaBay).

Current Arctic temperatures are about 1.4 degrees Celsius higher than they would have been had the 2,000-year cooling trend continued, leading to the suggestion that “this era really is the Anthropocene — a geological period of our own making, either by accident or design” (NY Times Dot Earth blog). The blog also quotes climate scientist Thomas Crowley, who notes that this “strengthens the argument that humans are now capable of preventing the onset of a future ice age”. That quote prompted an update on the blog, where the author noted the concern that these implications “might be abused by folks fighting restrictions on greenhouse gases”.

Other coverage:

Arctic reverses trend, is warmest in two millennia – AP

Warmest Arctic temperatures for 2,000 years, says new study – CNN

Abrupt reversal detected in Arctic cooling trend – SF Chronicle

Arctic Warming Overtakes 2,000 Years of Natural Cooling – NCAR press release