In Annual Melt, Arctic Sea Ice Reaches Third-Lowest Point Ever Recorded

The 2009 melt did not reach the record melt of 2007, and the areas that melted differed. How to read this map of Arctic sea ice extent:

White: Ice remaining in 2009 only.
Dark gray: Ice remaining in 2007 only.
Light gray: Ice remaining in both 2007 and 2009.

Photo: NSIDC

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The annual summer melt in the Arctic is done, as ice begins to accumulate. And while 2009 didn't break the record set in 2007, it continued a trend of excessive melting that has exceeded scientific expectations for the effects of global warming.

This year marks the third-lowest extent of ice ever recorded, after 2007 and 2008. 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 (200 walrus carcasses just washed up in Alaska), and human use grows in the region -- for oil and gas drilling, and for shipping through once ice-locked channels. 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.

Even at its low point for the year, on Sept. 12, 2009, there's still a lot of ice in the Arctic -- 1.97 million square miles, or about 68% of the land area of the contiguous United States. The 2009 low point had 16% more ice than the record-low extent recorded in 2007 -- but it's 24% below the average recorded before 2000.

Chart: National Snow and Ice Data Center

"While the ice extent this year is higher than the last two years, scientists do not consider this to be a recovery," according to the National Snow and Ice Data Center, which tracks ice trends. "Despite conditions less favorable to ice loss, the 2009 minimum extent is still 24% below the 1979-2000 average, and 20% below the thirty-year 1979-2008 average minimum. In addition, the Arctic is still dominated by younger, thinner ice, which is more vulnerable to seasonal melt. The long-term decline in summer extent is expected to continue in future years."

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.

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