Weird weather tied to polar winds
REUTERS
December 17, 1999
SAN FRANCISCO, Dec. 17 — Shifting wind patterns around the North Pole are partly to blame for a raft of weather changes in recent decades ranging from warmer temperatures in the Northern Hemisphere to declining sea-level pressure over the Arctic, researchers reported at a scientific meeting here. What’s not clear is whether the shift is natural, manmade or a combination.
“THE RECENT trend (of change) seems unprecedented in the historical model,” David Thompson of the University of Washington told reporters Thursday at a meeting of the American Geophysical Union.
Changes in the “polar vortex,” the pattern of winds which encircles the pole, may well be a sign of more severe weather shifts to come, he added.
He and other scientists presented reports showing that, on balance, the polar vortex has tightened since 1970 — meaning that the upper-atmosphere winds are blowing in a smaller, stronger circle around the polar region itself.
As a result, frigid polar weather has not moved as far south during the Northern Hemisphere winter, leading to climate changes ranging from higher temperatures across Europe and Asia to a sharp decrease in Spanish rainfall.
Scientists also theorize the shifting polar vortex could be responsible for fiercer winter storms across western North American and western Europe as higher temperatures in the lower, more-populous latitudes clash with the very cold temperatures above the North Pole, generating high-altitude winds that later pull heat and moisture from the Atlantic and Pacific oceans.
CAUSE UNCLEAR
While the effects of the change are becoming clear, scientists say they are still unsure if the shift is a natural phenomenon or part of a broader pattern of change blamed on accumulating greenhouse gasses.
“We can’t be sure that what we’re seeing is not natural,” said John Wallace, also of the University of Washington.
Those who believe man may be to blame theorize that as greenhouse gases warm the lower atmosphere they are cooling the upper atmosphere, setting up a climate change that is slowly drawing the vortex winds closer to the pole.
TIME WILL TELL?
Many weather observers hope the trend will become clearer over the next several years.
While the past couple of winters have seen a return to higher pressures over the Arctic and more wintry weather over parts of the Northern Hemisphere, they will be watching to see if this trend holds — if it does, it could mean that the earlier change in polar winds was part of a natural cycle that is now returning to normal.
But if the coming winters shift back toward warmer weather, Wallace and Thompson said in a press statement, “it would be enough to convince most scientists that the changes are human induced, that they’re not going to go away, and that they may be an indicator of even bigger changes to come.”