Now you see it, now you don't (nearly as much)

And the concerns extend beyond polar bears and caribou. For instance, David Lawrence, with the National Center for Atmospheric Research in Boulder, Colo., published a study in the June 13 issue of Geophysical Research Letters suggesting that as the Arctic Ocean loses more of its reflective summer ice and the darker ocean captures more of the sun's warmth, those warmer waters can moderate temperatures over land as far as 900 miles inland. It's somewhat analogous to the Gulf Stream's effect on Europe's climate. Not surprisingly, during periods of rapid loss of sea ice, the modeling study suggested that temperatures over land would warm 3.5 times more than warming rates global climate models typically project for the 21 century. This additional warming could affect the amount of permafrost that melts, releasing CO2 and methane, the team noted.

Meanwhile, the loss of summer ice will open shipping lanes long dreamed of by many maritime countries. And it's already setting off a scramble for claims to natural resources under the UN Law of the Sea Treaty.

What's driving the Arctic to shed it's summer ice like this? Two major players, researchers say: Weather, and warmer water working its way into the ocean and under the ice from lower latitudes. These are reinforced by a shrinking amount of thick, multi-year ice, which serves as a foundation for the next winter's freeze. When the next spring arrives more of the existing ice is too thin to survive the spring and summer melt. But even the weather patterns feeding the trend look to have a climate-change connection, notes Joellen Russel, another University of Arizona researcher. She explains that in 2004, scientists at the University of Washington published work that tied heavy declines in sea ice to a mode of natural variation variously dubbed the Arctic Oscillation or the Northern Annular Mode. Essentially, when this mode gets stuck in overdrive, it strengthens prevailing-wind patterns in the Arctic in ways that help flush ice out into the North Atlantic. Other groups have since linked late-20th century trends toward this mode's more-muscular phase to global warming, perhaps with some help from an ozone hole that periodically sets up over the Arctic.

This year's great melt-off watch triggered something a tempest earlier this month when a blogger in Britain said he'd found a significant problem with the NSIDC's data that led the center to overestimate the melt-back. It triggered a round of hot bytes hurtling back and forth in the yes-it-is, no-it-isn't climate blogosphere. But said blogger retracted his conclusion after an NSIDC scientist pointed out the flaw in his analysis. The blogger now acknowledges that the NSIDC analysis is correct.

Note: Eoin O'Carroll is on vacation. He will return Sept. 2

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