Subj: Polar wind shift marks new
global weather worry
Date: 12/17/99 11:46:45 AM Pacific Standard Time
From: firstname.lastname@example.org (New Millennium)
12/16/1999 20:37:00 ET
Polar wind shift marks new global weather worry
SAN FRANCISCO (Reuters) - 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, scientists said on Thursday.
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, they
"The recent trend (of change) seems unprecedented in the historical
model," David Thompson of the University of Washington told reporters at
a meeting of the American Geophysical Union here.
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
Scientists also theorise 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.
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 of the University of Washington.
Those who believe man may be to blame theorise 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
Many weather observers hope the trend will become clearer over the next
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.
If the coming winters shift back toward warmer weather, however, "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," Wallace and Thompson said in