A Cycle of Warming Spirals in the Arctic

More bad news from the Arctic.

Not only did the extent of sea ice this summer decline to a record-low, exposing the fabled Northwest Passage for the first time in history, but even the thickest, most permanent ice that typically doesn't melt in summer declined by 23%, according to a new NASA study. This study goes beyond other, similar studies that have been released in recent days because it characterizes not only the extent of sea ice versus open water, but also characterizes the thickness and type of ice that remains.

The two forces could indicate that a so-called global warming "positive feedback loop" is in effect that will lead to ever-greater declines in ice year after year. That could lead to a tipping point -- after which the loss of ice accelerates and can not be reversed.

"The reason so much (of the Arctic ice) went suddenly is that it is hitting a tipping point that we have been warning about for the past few years," James Hansen, director of NASA's Goddard Institute for Space Studies, told Reuters last week.

From the 1970s through the 1990s, perennial ice declined by about 193,000 square miles each decade. Since 2000, that rate of decline has nearly tripled.

NASA uses satellite measurements, coupled with observations from buoys and a complex computer model, to map different classes of sea ice, including older, thicker perennial ice and younger, thinner seasonal ice.

That thinner, seasonal ice has been declining at a rapid rate this decade, with 2007 exceeding what had been a record loss in 2005. In 2007, the extent of perennial ice shrunk by an area the size of California and Texas combined. The loss of so-called perennial ice is what caused the record loss of the ephemeral floating summer ice, according to a NASA study to be published tomorrow in the journal Geophysical Research Letters.

The trend will likely continue in years to come, as the dark open ocean waters absorb additional heat that would have been reflected by ice, leading to more ice melting, which will only increase the extent of open water and heat absorption. This "positive feedback loop" is described by NASA this way:

The Arctic Ocean's shift from perennial to seasonal ice is preconditioning the sea ice cover there for more efficient melting and further ice reductions each summer. The shift to seasonal ice decreases the reflectivity of Earth's surface and allows more solar energy to be absorbed in the ice-ocean system.

Sea ice melt in the Arctic is a harbinger of other global warming consequences to come.

The rate of melting ice far exceeds what the United Nations had predicted for this time period. The amount of ice melting in the Arctic wasn't expected for decades -- raising the prospect that other warnings in the U.N. Intergovernmental Panel on Climate Change's reports will meet reality more quickly than expected.

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