At the end of March, Arctic sea ice had re-frozen to an unusual degree there was more ice than average. The last three months have brought the story of Arctic sea ice back on depressing track. There's never been so little ice in the Arctic in June, and there's never been more ice lost during the month of June, not since humans started measuring it anyway.
Putting this into perspective, imagine the area covered by Mexico, the United States (including Alaska) and the westernmost province of Canada, British Columbia: That's the average amount of ice that covers the Arctic in June. Now cut away Texas, New Mexico and Arizona, and you have the extent of June 2010.
Compared to the last record-low for June, there's 73,000 fewer square miles of Arctic sea ice (roughly the size of New England).
Records for minimum sea ice extent would have been set in 2008 and 2009, compared to any other year on record, if it were not for 2007, when a dramatic record low was recorded.
The seasonal melt will continue into September, so the global warming litmus test will continue through the summer. As the National Snow and Ice Data Center, which tracks sea ice conditions, put it, whether or not we witness a new record-low this summer will depend largely on "weather conditions, atmospheric patterns, and cloud cover over the next month." Right now, it isn't looking good. Then again, most of the ice lost to this point was young one-year-old ice. Further melting will encounter thick, multi-year-old ice that is tougher to melt, so the rate of melting could well slow down.
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.
Chart at right: National Snow and Ice Data Center
Greenpeace has predicted that most summer ice could be gone in five years, and the summer could be completely ice-free by 2050. While that may be an extreme view, the trend is heading in that direction eventually, and the extent of melting in the past three years was to an extent not expected for decades, under mainstream scientific predictions of just a few years ago.
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. Environmental groups, galvanized by the catastrophic oil spill in the Gulf of Mexico, are warning that an oil spill in the Arctic could yield even greater damage, given the fragile ecosystem, harsh conditions for a cleanup and remoteness from rescue equipment.
More concerning for humans is this: As it becomes clear that the worst-case melting scenarios 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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