"Recent warming in the Arctic has interrupted and reversed a long-term cooling cycle triggered by wobbles in Earth's orbit, according to new research.

The Arctic should still be cooling, an international team reports, but instead is warmer than it's been in at least 2,000 years, likely because of human interference.

"Something perturbed the system in the 20th century, and by far the most likely culprit is greenhouse gases," says climate scientist Scott Lamoureux, at Queen's University in Kingston, Ont., who collaborated on the study that will appear today in the journal Science.

Earth is in the midst of a periodic and natural change in its orientation to the sun. The wobble has shifted the planet's closest pass by the sun from September to January, reducing the intensity of sunlight reaching the Arctic in summer. The new study shows summer temperatures in the Arctic cooled in step with the reduced solar energy for almost 2,000 years. Then, they report, the cooling trend was abruptly interrupted in the 20th century even though the Earth continued to move away from the sun. It's now about one million kilometres further during the Northern Hemisphere's summer solstice than it was 2,000 years ago

The researchers combed through lake sediments, tree rings and ice cores to reconstruct temperatures for the Arctic going back 2,000 years, the most comprehensive long-term record yet.

Lamoureux and his colleagues from the U.S. and Europe, working independently at a network of 23 sites across the Arctic, have turned up evidence of "pervasive cooling" for 2,000 years. It came to an end when burning of fossil fuels began to send large amounts of carbon dioxide wafting into the atmosphere.

The reconstruction shows the last half of the 20th century was the warmest of the last 2,000 years - with four of the five warmest decades occurring between 1950 and 2000."

From the link above, for which thanks.


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