Notes: From Climate Central: "Arctic Paradox: Warmer Arctic May Mean Cold Blasts for Some"
"Blasts of cold and snow have gripped Europe and the United States in recent weeks, from Minneapolis to Paris. These weather conditions are leading to speculation about the role climate change may be playing in altering such extreme events.
"Recent scientific studies have shown that the dramatic warming that has been occurring in the Arctic during the past few decades, along with the associated loss of sea ice cover, may be changing atmospheric circulation patterns throughout the northern hemisphere. This could be contributing to the recent outbreaks of unusually cold and snowy weather."
"Cold air is normally trapped in the Arctic in winter by strong Polar Vortex winds, which circle the North Pole from west to east and the strong pressure field that is shown in purple/blue colors in Figure 1a, below left. This pattern broke down in December 2009, and in February 2010. North-south winds increased, allowing cold Arctic air to spill southwards."
Additional notes (from John Russell):
this analogy has been used several times by different scientists during different talks and on different websites (for instance here, by John Cook).
The exclamation by people in Northern Europe and North America that, "how can there be global warming when we're experiencing such cold and snowy winters?", is very common. The explanation is simple.
There's a given amount of heat in the weather system and when the Arctic warms up—due in part to the 'sea ice blanket' covering the sea gradually reducing, thus allowing heat to escape from the ocean—the cold air is pushed further South. It's made worse, of course, by the fact that a warmer planet has more water vapour in the atmosphere, more clouds, and when it's cold enough, water vapour falls as snow.
Update 2-9-12: Three more studies confirm the "Refrigerator Door" hypothesis.
2-28-12: Even Judith Curry's latest research points in the same direction, as does nnew research by a U.S.-Chinese team.
Bite Source: Jeff Masters, Weather Underground. Variation and additional notes by John Russell.
Image Source: here and here