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

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    The European Space Agency's ENVISAT satellite captures the Arctic's shrinking summer sea ice in August. The red boundary outlines the ice boundary at the end of the melt season in 2007. It was the largest loss of summer ice on record.
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It's getting down to the wire: Will the Arctic ice cap's annual melt-off this year top last year's record?

In one sense, it's a trivial "horse race" question, because at this point in the summer, stats for the two years are sufficiently close and low to arch eyebrows yet again within the Arctic science community -- already out in force as part of the International Polar Year, which runs through next March.

So far, this year's decline has ensured that 2008 will at least rank as the second lowest year on record for summer sea-ice extent at the top of the world. Where Arctic scientists once spoke of virtually ice-free summers by 2070, and more recently by 2040, "the Arctic could be mainly ice free even earlier," according to Heinrich Miller, an Arctic scientist at the Alfred Wegener Institute in Bremerhaven, Germany, in an ESA press release that accompanied the satellite images.

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"Some notables had suggested '08 sea ice would probably not be another record-breaker or even close. What's going on up there now suggests the situation is indeed serious," writes Jonathan Overpeck, director of the Institute for the Study of Planet Earth at the University of Arizona in Tucson. Arctic science is one of its specialties.

The data on the Arctic ice cap come from the National Snow and Ice Data Center at the University of Colorado in Boulder. The European Space Agency chipped in today with a short "flip book" movie using images from its ENVISAT earth-observation satellite. Another useful website for taking part in Ice Watch 2008 lives at the University of Illinois at Urbana-Champaign. It's dubbed The Cryosphere Today.

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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