Global warming: Arctic temps out of synch with natural cycles

http://summitcountyvoice.com/2012/10/01/global-warming-arctic-temps-out-of-synch-with-natural-cycles/

Global warming: Arctic temps out of synch with natural cycles
Posted on October 1, 2012 by Bob Berwyn
By Summit Voice

SUMMIT COUNTY — Without ever-increasing concentrations of heat-trapping greenhouse gases in the atmosphere, the Arctic would gradually be cooling instead of experiencing the rapid warming that’s been documented in the past few decades.

The long-term cooling trend, documented back to at least 2,000 years ago, is related to wobbles in the Earth’s orbit that have reduced the intensity of sunlight reaching the Arctic in summertime, when Earth is farther from the Sun, according to a recent study led by scientists from Northern Arizona University and the National Center for Atmospheric Research.

But in the middle of the 20th century, the gradual cooling ended abruptly, replaced by a sharp increase in Arctic temperatures — even though orbital cycles would suggest a continued cooling trend. The research, based on geologic records and computer models, strongly suggests that the heat-trapping effects of greenhouse gases are overpowering natural climate cycles.

“This result is particularly important because the Arctic, perhaps more than any other region on Earth, is facing dramatic impacts from climate change,” said NCAR scientist David Schneider. “This study provides us with a long-term record that reveals how greenhouse gases from human activities are overwhelming the Arctic’s natural climate system.”

In the 1990s, Arctic temperatures reached their warmest level of any decade in at least 2,000 years. The results indicate that recent warming is more anomalous than previously documented, said Northern Arizona University’s Darrell Kaufman, lead author and head of the synthesis project.

The scientists reconstructed summer temperatures across the Arctic over the last 2,000 years by decade, extending a view of climate far beyond the 400 years of Arctic-wide records previously available at that level of detail.

“Scientists have known for a while that the current period of warming was preceded by a long-term cooling trend,” Kaufman said. “But our reconstruction quantifies the cooling with greater certainty than before.”

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