If this is global warming, why are so many people wading through more snow than ever before! Remember the snowfalls in New York and Washington DC. And the roofs caving in Ontario & Quebec...?? Frozen fountains in Rome!? People trying to escape winter are getting hit with unusual snowstorms!
If you've attended my lecture on Ocean Currents, Changing Climates & Extreme Storms you might remember that I prefer the term Climatic Instability to Global Warming. There's growing evidence of instability in the polar jet stream. The deterioration of the Polar Vortex could be leading to some of these extreme winter weather events.The NOAA has an excellent website to explain the Warm Arctic, Cold Continents pattern.
The graphic below shows the historic, relatively-stable polar vortex of 1968-96 compared to the destabilized vortex pattern we're experiencing lately in December (e.g., Dec 2009).
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| The low Arctic pressure field is shown by purple colors in the figure for December 1968–1996. Strong Polar Vortex winds circle this pressure field, trapping cold air in the Arctic regions. In December 2009, this pattern broke down, Polar Vortex winds weakened (green colors) and cold Arctic air (which parallels the color contours) flowed southward. Graphic credit NOAA |
"This change in wind directions is called the Warm Arctic-Cold Continents
climate pattern,” writes James Overland of the U.S. National Oceanic
and Atmospheric Administration (NOAA). “The jet-stream breakdown last winter
was the most extreme in 145 years of record. Loss of sea ice is
certainly not the whole story behind cold mid-latitude winters, but it’s
a constant push in that direction.”
“When the Polar Vortex — a ring of winds circling the Arctic — breaks down, this allows cold air to spill south, affecting the eastern United States and other regions,” says Dr. Overland. “This can result in a warmer-than-average Arctic region and colder temperatures that may include severe winter weather events on the North American and European continents.”
“When the Polar Vortex — a ring of winds circling the Arctic — breaks down, this allows cold air to spill south, affecting the eastern United States and other regions,” says Dr. Overland. “This can result in a warmer-than-average Arctic region and colder temperatures that may include severe winter weather events on the North American and European continents.”
California Regional Weather Server provides up-to-date Jet Stream analyses, charts and archives. Excellent resource!! Here's a current shot:
Thomas Homer-Dixon has done a great job of explaining the changing climatic pattern in an article in the Globe & Mail: And now the weather: nasty and brutish.
Thomas Homer-Dixon writes:
"Jet streams
sometimes form huge loops over North America, with segments flowing from
north to south or south to north – what scientists call meridional
flow. These loops can even break into separate pieces. But meridional
flow is not the usual pattern, and such winds tend to have lower
velocity than their west-to-east counterparts.
Lately, though,
we’ve seen more north-to-south jet streams. These winds have dragged
cold air out of the Arctic and delivered it to populated regions of
North America and Europe.
Meanwhile, just as
cold snowy weather afflicts much of Europe and North America, parts of
the Far North are experiencing one of the warmest winters on record.
This month’s average temperature in Iqaluit, for instance, is 15 degrees
above normal."
Scientists at Germany’s Potsdam Institute for Climate Impact Research claim that warming of the Arctic Ocean and the subsequent melting of sea ice are, more likely than not, responsible for the cold winter weather.
