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The Arctic Thaw Could Make Global Warming Worse

The melting Arctic is releasing vast quantities of methane. How big is this greenhouse threat? What can be done?

That same spring Walter’s colleague at Fairbanks, Vladimir Romanovsky, whose computer simulations are some of those predicting a dramatic thaw this century, made an unrelated visit to Cherskii and observed Walter swimming in the icy lakes: “She’s a tough girl,” he says simply. By summer Walter found herself in the hospital with pneumonia. “But a couple of months later, and with a good dose of Russian antibiotics, I was back in the lakes,” she recalls. When winter came again, the drill changed from snorkeling to shoveling. For hours at a time Walter dug away at the snow atop the ice, clearing paths above the seeps and marking them with flags as she went. “The Siberians were laughing their heads off at how much money we were spending to come to Siberia to shovel snow off the frozen lakes,” she says. But no one was laughing when the world learned about her hard-won findings.

Proof for a Spike
Walter’s intimate relationship with a handful of Siberian lakes initially brought lake emissions into the limelight, but it was her analysis of their global importance, which she reported in two major scientific journals in 2007, that really turned heads. The potential for emissions to increase dramatically became clear through her work with paleoecologist Mary Edwards of the University of Southampton in England, who has studied the life histories of Arctic lakes. Together they showed that methane bubbling out of Arctic lakes could have been responsible for up to 87 percent of the spike in methane emissions that helped the planet warm from the most recent ice age. At that time, roughly 11,400 years ago, global methane concentrations rose 50 percent in less than 200 years.

Many scientists are keen to determine whether such a dramatic spike might happen again. A steady march of global warming, spread out over hundreds or thousands of years, could set off the gaseous Arctic time bomb slowly. But a quicker thaw could ignite a runaway outgassing of methane.

For about a decade it has been clear that the ongoing loss of sea ice is accelerating the Arctic’s rapid warming, says climate modeler David Lawrence of the National Center for Atmospheric Research in Boulder, Colo. When summer ice retreated to a record minimum in 2007 and again last year, the outlook seemed to worsen by the month. New estimates, published in April by the National Oceanic and Atmospheric Administration, predict nearly ice-free summers by 2037—three times sooner than earlier models indicated. The prospect of more open water has nations scrambling to stake oil and gas claims to the Arctic seabed [see “Arctic Landgrab,” by Jessa Gamble; Scientific American Earth 3.0, Vol. 19, No. 1, 2009], but the backlash for climate change could be severe. Dark seawater absorbs more of the sun’s heat than white ice does, thus warming the region’s air and thereby the soil, putting permafrost at risk. Lawrence’s newest global climate simulations predict that warming associated with spells of particularly rapid loss of sea ice could lead directly to faster permafrost thaw. During such episodes, which would last five or 10 years, autumn temperatures might increase by as much as nine degrees Fahrenheit along Arctic shorelines, and the heat penetrating inland would more than triple the average warming rates previously assumed.

Rising inland temperatures are fueling another dramatic change “potentially as profound as the loss of sea ice,” says Matthew Sturm of the U.S. Army’s Cold Regions Research and Engineering Laboratory in Fort Wainwright, Alaska. Shrubs are taking over great swaths of the tundra. During the summer, shrubs absorb more sunlight than does the mossier, grassier vegetation they replace, warming the ground further. And in the winter they create snowdrifts that help the ground hold on to summer heat. Sturm’s extensive comparison of 6,000 aerial photographs taken across northern Alaska for oil exploration during the 1940s to present-day surveys of the same locations shows significant shrub expansion, now covering 77,000 square miles.

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