updated 8/28/2007 7:06:19 PM ET 2007-08-28T23:06:19

Driving along the roads in Alaska's second-largest city is like riding a rollercoaster. Fairbanks was built on permafrost, and work crews are constantly repairing dips and bumps created when it thaws.

Eighty-five percent of Alaska is on permafrost, soil that has been frozen for at least two years. In the state’s far north it can be 2,000 feet deep, while in Fairbanks the typical thickness is around 150 feet.

The city is on the edge between frozen and unfrozen, says Matthew Sturm, an ice expert who makes his point by taking visitors for a walk in a tunnel dug into the side of a hill by his employer, the U.S. Army Corps of Engineers.

This worm’s-eye view of permafrost reveals bison bones, 40,000-year-old moss and, most important, ice. It doesn’t take long to understand how water from thawing ice seeps into the soil and destabilizes it.

Undermining oil, disappearing ponds
Even colder permafrost farther north is thawing, including the massive ice wedges on the Arctic coastal plain that had been hard as granite for thousands of years.

Computer models by the National Center for Atmospheric Research suggest that 90 percent of the top 10 feet of Arctic permafrost will have melted by 2100.

Already, and at a cost of $800 million, 400 miles of Alaska’s pipeline have been refrigerated and elevated to keep the relatively warm oil from causing more thawing.

Thawing permafrost is destroying ponds and lakes, which are absorbing more heat and warming the permafrost below. Ultimately, holes open up in lakebeds. Essentially, the process “pulls the plug on the bottom of the lake,” says Larry Hinzman, director of the International Arctic Research Center at the University of Alaska-Fairbanks.

Several of his Hinzman's colleagues compared aerial images from 1950 to 2005 and found that more than half of 10,000 ponds surveyed in interior Alaska had disappeared due to thawing permafrost, displacing untold numbers of waterfowl. Other ponds had shrunk by up to a third.

Defrosting carbon, methane

But the biggest impact of thawing permafrost could be to accelerate globalwarming by releasing carbon and methane that until now has been locked in the organic matter in the frozen soil. Both add to Earth’s greenhouse effect, which traps heat from the sun.

Permafrost may hold a third of all the carbon stored in soil worldwide, and it could hold even more of the world’s methane, which is 20 times as potent a greenhouse gas as carbon dioxide.

Carbon already is escaping from the top tier of permafrost, says Vladimir Romanovsky, a professor at the University of Alaska-Fairbanks who is tracking the trend with 60 monitoring stations across the state.

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