Oscillations of a Chilly Variety




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I returned from a trip to Boston this weekend to find much warmer temperatures in the nation’s capital. Although I did not venture outside the office midday, Weather.com tells me today’s high was in the mid-50s. Many around me are welcoming the shift to milder weather; I must admit I enjoyed the cold snap, and particularly the great Mid-Atlantic blizzard that blanketed the city in over a foot of snow just before the holiday “recess.” Of course, I’m not a farmer dependent on seasonable conditions to sustain crop yields–and even I missed the fresh produce that succumbed to the frost when I visited the local market last month.

Why did the entire Eastern U.S. and much of Eurasia experience such a chilly several weeks? You may or may not have heard buzz about the Arctic Oscillation, a climatic phenomenon not unlike El Niño/La Niña. The main difference: The Arctic Oscillation (AO) is a north-south shift in pressure and temperature in the atmosphere and ocean, while El Niño/La Niña is an east-west shift in pressure and temperature. Well, at a basic level.

Check out this thematic map, which compares December 2009 surface temperatures with December 2000-2008 averages around the globe.

You can see clearly by the blue gradation that North America,
Northwestern Europe, and much of Asia were colder this December than in
years past. However, look at Greenland and Alaska. A key characteristic
of oscillations is that colder-than-average temperatures impact some
regions at the same time that warmer-than-average temperatures affect
other regions. Again, it’s all about shifts in global pressure systems.

At the bottom righthand corner of the page, you’ll see the January 8th
“image of the day,” a satellite image showing snow across Great
. If you guessed that this uncharacteristic weather was a result
of the AO, you’re right!

A few reasons why geographers care about the AO:

1) Polar warming. Global warming has meant warmer average annual
temperatures in polar regions such as Greenland and Alaska. This has
resulted in the melting of glaciers, which impacts sea levels and
animals like polar bears that rely on ice cover for hunting and
shelter. A warmer-than-average winter could exacerbate an already
troublesome situation.

2) Food distribution: Freezing temperatures threatened crops in the
Southeastern U.S
. such as strawberry, tomato, and citrus, which are
primary food sources for other regions of the country.

3) The great climate “debate.” The Arctic Oscillation is a natural,
cyclical climate phenomenon that is NOT related to global warming.
However, scientists fear that people’s immediate experience of colder
weather could increase public skepticism about global warming.

Image courtesy NASA Earth Observatory.

Sarah Jane for My Wonderful World

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