*[Enwl] Commentary: Global Warming Leads to Cold Weather Changes Too

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Bundle Up, It's Global Warming

By JUDAH COHEN
Published: December 25, 2010

THE earth continues to get warmer, yet it's
feeling a lot colder outside. Over the past few
weeks, subzero temperatures in Poland claimed 66
lives; snow arrived in Seattle well before the
winter solstice, and fell heavily enough in
Minneapolis to make the roof of the Metrodome
collapse; and last week blizzards closed Europe's
busiest airports in London and Frankfurt for
days, stranding holiday travelers. The snow and
record cold have invaded the Eastern United
States, with more bad weather predicted.

All of this cold was met with perfect comic
timing by the release of a World Meteorological
Organization report showing that 2010 will
probably be among the three warmest years on
record, and 2001 through 2010 the warmest decade
on record.

How can we reconcile this? The not-so-obvious
short answer is that the overall warming of the
atmosphere is actually creating cold-weather
extremes. Last winter, too, was exceptionally
snowy and cold across the Eastern United States
and Eurasia, as were seven of the previous nine
winters.

For a more detailed explanation, we must turn our
attention to the snow in Siberia.

Annual cycles like El Niño/Southern Oscillation,
solar variability and global ocean currents
cannot account for recent winter cooling. And
though it is well documented that the earth's
frozen areas are in retreat, evidence of thinning
Arctic sea ice does not explain why the world's
major cities are having colder winters.

But one phenomenon that may be significant is the
way in which seasonal snow cover has continued to
increase even as other frozen areas are
shrinking. In the past two decades, snow cover
has expanded across the high latitudes of the
Northern Hemisphere, especially in Siberia, just
north of a series of exceptionally high mountain
ranges, including the Himalayas, the Tien Shan
and the Altai.

The high topography of Asia influences the
atmosphere in profound ways. The jet stream, a
river of fast-flowing air five to seven miles
above sea level, bends around Asia's mountains in
a wavelike pattern, much as water in a stream
flows around a rock or boulder. The energy from
these atmospheric waves, like the energy from a
sound wave, propagates both horizontally and
vertically.

As global temperatures have warmed and as Arctic
sea ice has melted over the past two and a half
decades, more moisture has become available to
fall as snow over the continents. So the snow
cover across Siberia in the fall has steadily
increased.

The sun's energy reflects off the bright white
snow and escapes back out to space. As a result,
the temperature cools. When snow cover is more
abundant in Siberia, it creates an unusually
large dome of cold air next to the mountains, and
this amplifies the standing waves in the
atmosphere, just as a bigger rock in a stream
increases the size of the waves of water flowing
by.

The increased wave energy in the air spreads both
horizontally, around the Northern Hemisphere, and
vertically, up into the stratosphere and down
toward the earth's surface. In response, the jet
stream, instead of flowing predominantly west to
east as usual, meanders more north and south. In
winter, this change in flow sends warm air north
from the subtropical oceans into Alaska and
Greenland, but it also pushes cold air south from
the Arctic on the east side of the Rockies.
Meanwhile, across Eurasia, cold air from Siberia
spills south into East Asia and even
southwestward into Europe.

That is why the Eastern United States, Northern
Europe and East Asia have experienced
extraordinarily snowy and cold winters since the
turn of this century. Most forecasts have failed
to predict these colder winters, however, because
the primary drivers in their models are the
oceans, which have been warming even as winters
have grown chillier. They have ignored the snow
in Siberia.

Last week, the British government asked its chief
science adviser for an explanation. My advice to
him is to look to the east.

It's all a snow job by nature. The reality is,
we're freezing not in spite of climate change but
because of it.

Judah Cohen is the director of seasonal
forecasting at an atmospheric and environmental
research firm.



http://www.nytimes.com/2010/12/26/opinion/26cohen.html


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Sent: Wednesday, December 29, 2010 5:53 PM
Subject: Commentary: Global Warming Leads to Cold Weather Changes Too




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