The Arctic has been warming faster than any other region on Earth, a fact that is usually attributed to human releases of greenhouse gases.
But a new study reports that 50 percent of the warming the Arctic has experienced in the last 30 years could be coming from natural variations in large-scale climate cycles.
"Half the warming can be explained by anthropogenic forcing," said study author Qinghua Ding, a research scientist at the University of Washington.
The other half? That comes from circulation patterns that start in an area about as un-Arctic as it gets: the tropical Pacific Ocean, Ding said.
Cracks between sheets of sea ice are called leads, as as seen in this image of Arctic sea ice from the DMS instrument from a recent Operation IceBridge aerial survey. Credit: NASA/GSFC
In a study released yesterday in the journal Nature, Ding used models to find that a cooling trend in the eastern Pacific Ocean is causing atmospheric waves that ripple out and affect climate as far away as Greenland.
"These waves will propagate like the water wave from dropping a stone in the center of a pond," Ding said.
As long as the surface temperatures of the eastern tropical Pacific remain cold (scientists are not sure of the cause of these lower temperatures), those waves keep coming.
Arctic warming not uniform
"It will generate local circulation over Greenland, and the local circulation will favor warming in that region," Ding said.
The study authors, who include polar climate experts, noted that the way that the Arctic is warming is highly regional, with the most prominent warming in northeastern Canada and Greenland.
Those areas have seen warming of 1 degree Celsius per decade since 1979, or twice the average warming.
The regional nature of Arctic warming led them to think at least some of the warming might be caused by natural cycles. If the warming was all caused by human emissions, they would expect it to be occurring more uniformly over the entire Arctic.
They also saw that a lot of warming had occurred in the troposphere, a higher layer of the atmosphere, as well as at the surface -- another fingerprint of a natural climate cycle affecting the warmth, not just greenhouse gases.
The study authors had also shown in the past that waves generating from this part of the Pacific were affecting temperatures in West Antarctica and the Pine Island Glacier.
One area for future research, Ding said, is how sea ice may be affected by these processes. This study looked at land surface temperatures and the troposphere, but not at sea ice, which has also been dramatically declining in the Arctic.
Reprinted from ClimateWire with permission from Environment & Energy Publishing, LLC. 202-628-6500.
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