Evey summer, ice melts in the Arctic. And every winter it re-freezes. That hasn't changed, but the rate of melting has accelerated and the rate of refreezing has decelerated, leading to a steady loss of ice in the Earth's air conditioner.
Case-in-point: February 2011. Satellites monitored by the National Snow and Ice Data Center measured as little ice as has ever been seen in the Arctic for that calendar month. It's a tie with the winter of 2005:
Sea ice extent averaged over the month of February 2011 was 5.54 million square miles. This was a tie with the previous record low for the month, set in 2005. February ice extent remained below normal in both the Atlantic and Pacific sectors, particularly in the Labrador Sea and the Gulf of St. Lawrence.
While ice extent has declined less in winter months than in summer, the downward winter trend is clear. The 1979 to 2000 average is 6.04 million square miles. From 1979 through 2003, the February extent averaged 6.02 million square miles. Every year since 2004 has had a mean February extent below 5.79 million square miles.
The records set or tied this winter (January set a new record, too) is being driven by the phase of the so-called Arctic Oscillation, a description of pressure gradient that affects weather patterns across the northern latitudes. While the Arctic has been unusually warm, the icy air (and snow) has been pushed farther south, as residents of the U.S. well know.
And while the extent of ice in any given month varies widely from year to year, the trend line is clear. Satellite records date to 1979, but ice cores and other data indicate that the rate of melting is unprecedented and can only be explained by the heat-trapping accumulation of greenhouse gases in the atmosphere. As ice melts, the darker water that is revealed absorbs more heat than the reflective ice, reinforcing the melting trend.
As the ice melts, polar bear, Pacific walrus, ribbon seals and other species struggle for survival. Meanwhile, the potential for human use grows -- for shipping through once ice-locked channels, and for oil and gas drilling.
More concerning for humans is this: As it becomes clear that the worst-case melting scenarios of climate change in the Arctic are taking place, does that mean that the worst-case predictions for other aspects of global warming are inevitable? Wildfires, droughts, crop failure, sea-level rise, massive rates of species extinctions ... each could appear more quickly, and have more severe impacts than the public expects.
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