Arctic sea ice, that bellwether of global warming, has melted to a degree only seen once before in recorded history.
Before characterizing it, consider this recent history:
In 2005, the seasonal melting of the Arctic seemed to be running on steroids. Scientists were alarmed as a new record was set. Concern mounted that polar bears, and other life that relies on the ice, would suffer. Concern grew that we were nearing a tipping point, as a planetary air conditioner lost power.
Then, last year, the 2005 record was shattered. An additional 460,000 square miles of ice melted, the Northwest Passage opened, and the race among northern nations to develop oil infrastructure and shipping routes through the Arctic intensified.
This summer, ice hasn't melted to the extent seen last year, and early season predictions that the North Pole would become ice-free have not come to pass. Not quite. But the melting exceeds the level seen in 2005. It won't be as big a headline, but it ought to be.
Compared to the average, the Arctic has lost 760,000 square miles of additional ice this summer. That's about the size of Alaska and Colorado, the first and eighth largest states, combined.
Melting will continue into September. And the refrozen ice that replaces this ice next winter will remain thin, lacking that multiyear stability that gives the earth its air-conditioning.
National Snow and Ice Data Center
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