Topsy-Turvy Weather Tied to Weaker Arctic ‘Fence’

http://www.nytimes.com/2011/01/25/science/earth/25cold.html?pagewanted=1&_r=1&ref=global-home

While people in Atlanta learn to shovel snow, the weather 2,000 miles to the north has been freakishly warm the past two winters. Throughout northeastern Canada and Greenland, temperatures in December ran as much as 15 or 20 degrees Fahrenheit above normal. Bays and lakes have been slow to freeze; ice fishing, hunting and trade routes have been disrupted.

The immediate cause of the topsy-turvy weather is clear enough. A pattern of atmospheric circulation that tends to keep frigid air penned in the Arctic has weakened during the past two winters, allowing big tongues of cold air to descend far to the south, while masses of warmer air have moved north.