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: January 2011. Satellites monitored by the National Snow and Ice Data Center measured less sea ice in January 2011 than ever before for that calendar month:
Arctic sea ice extent averaged over January 2011 was 13.55 million square kilometers (5.23 million square miles). This was the lowest January ice extent recorded since satellite records began in 1979. It was 50,000 square kilometers (19,300 square miles) below the record low of 13.60 million square kilometers (5.25 million square miles), set in 2006, and 1.27 million square kilometers (490,000 square miles) below the 1979 to 2000 average.
At 5.3 million square miles, that's still a lot of ice (the United States covers a territory of about 3.8 million square miles). But the hole in the ice, if you will, is big: Take the Western U.S. (California, Montana, New Mexico, Arizona, Nevada, Colorado, Oregon, Wyoming, Idaho, Utah and Washington) and throw in North Dakota for good measure, and you get at total area equal to the difference in ice extent measured this January compared to an average January.
The record in January 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 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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