(Related: "Pollution From U.S., Europe, Others Speeding Arctic Warming, Study Says" [March 16, 2007].)
"This assumption is that if this [heat flow] has increased—which we see in the data that it has—then it has contributed to the warming in the Arctic, not only at the surface, but higher in the atmosphere," Graversen said.
Increased moisture in northward-moving air also plays a role, he said, because when the water vapor condenses into clouds and snow, it releases energy, warming the air.
Nobody knows how much of this change is the result of human emissions of planet-warming gases such as carbon dioxide, but it's likely that they play a role.
"Many models suggest an increase in energy transport when more greenhouse gases are introduced into them," he said.
"Changes in the circulation in the atmosphere might have had a much larger effect than previously thought, but these changes may also have been induced by greenhouse gases."
The new finding doesn't downplay the effects of declining snow and ice. In fact, the scientists wrote, solar heating of denuded landscapes might become increasingly important as ice continues to retreat.
"Much of the present warming, however, appears to be linked to other processes, such as atmospheric energy transports," the authors conclude.
That's an important message, said John Walsh, President's Professor of Global Climate Change at the International Arctic Research Center for the University of Alaska, Fairbanks, who was not involved in the study.
"Were it not for this increase in poleward heat transport, the Arctic might have warmed less and the middle latitudes might have warmed more than actually happened over the past several decades," he said via email.
In other words, he added, "warming might have been more apparent in the heavily populated areas of the world, i.e., the middle latitudes, if there had not been the increase of heat transport identified" by Graversen and his colleagues.
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