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Cold Winters Caused By Natural Variability, Study Finds

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Met Office Wrong Again? Cold Winters Caused By Natural Variability, Study Finds

http://www.thegwpf.org/met-office-wrong-again-cold-winters-caused-by-natural-variability-study-finds/

Resurgence of cold winters in Europe and the US is mainly due to natural climate variability, new study finds.
Melting Arctic sea ice has been a prime suspect for causing the extreme winter cold experienced by North America and Europe in recent years. Now, researchers from the US, reckon that the natural temperature variation in the North Atlantic Ocean – or Atlantic Multidecadal Oscillation (AMO) – could also play a role.

AMO and cold spells
Sea surface temperatures in the North Atlantic tend to move through warm periods followed by cold periods, in a 60–70 year cycle known as the AMO. The ocean entered a warm – or positive – phase in the late 1990s.
Yannick Peings and Gudrun Magnusdottir of the University of California Irvine, US, believe that these warmer ocean temperatures can nudge the atmospheric circulation pattern known as the North Atlantic Oscillation into its negative phase. This is likely to cause colder-than-normal temperatures in the northern hemisphere in winter as it moves the North Atlantic jet stream and storm track south.
“Our study contributes to the growing debate about the link between Arctic sea ice loss and mid-latitude weather extremes,” Yannick Peings of the University of California Irvine, US, told environmentalresearchweb. “We find that the occurrence of the extreme events that has been attributed to Arctic warming only is actually promoted by the positive polarity of the AMO, especially over Europe and the eastern US. This suggests that the resurgence of cold winters over these regions is consistent with natural climate variability and is not simply a result of global change.”
The team reckons that the warmer sea surface temperatures associated with a positive phase of the AMO affect the NAO by shifting the atmospheric baroclinic zone over the North Atlantic basin. (The AMO may also alter atmospheric circulation indirectly by causing sea ice loss.) The warmer ocean takes 10–15 years to boot the North Atlantic Oscillation into its negative phase; it’s not yet clear why.
The findings have important implications for the decadal prediction of climate, according to Peing. “The AMO is an important source of predictability for winter climate of the North Atlantic sector,” he said. “For example, provided that the AMO remains in its positive polarity for one to two additional decades, cold and snowy weather conditions in winter should be favoured over Europe and the eastern US. Of course, many other parameters of the climate system may modulate the impact of the AMO on North Atlantic variability, but the AMO remains a non-negligible source of variability that one must consider.”

Full story
See also
Met Office: Arctic sea-ice loss linked to colder, drier UK winters
Decreasing amounts of ice in the far north is contributing to colder winters and drought, chief scientist Julia Slingo tells MPs – Full story

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