Katey M. Walter Anthony, a scientist, investigated a plume of methane, a greenhouse gas, at an Alaskan lake. Dr. Walter Anthony is a leading researcher in studying the escape of methane. Josh Haner / The New York Times

By JUSTIN GILLIS
16 December 2011

FAIRBANKS, Alaska – A bubble rose through a hole in the surface of a frozen lake. It popped, followed by another, and another, as if a pot were somehow boiling in the icy depths.

Every bursting bubble sent up a puff of methane, a powerful greenhouse gas generated beneath the lake from the decay of plant debris. These plants last saw the light of day 30,000 years ago and have been locked in a deep freeze — until now.

“That’s a hot spot,” declared Katey M. Walter Anthony, a leading scientist in studying the escape of methane. A few minutes later, she leaned perilously over the edge of the ice, plunging a bottle into the water to grab a gas sample.

It was another small clue for scientists struggling to understand one of the biggest looming mysteries about the future of the earth.

Experts have long known that northern lands were a storehouse of frozen carbon, locked up in the form of leaves, roots and other organic matter trapped in icy soil — a mix that, when thawed, can produce methane and carbon dioxide, gases that trap heat and warm the planet. But they have been stunned in recent years to realize just how much organic debris is there.

A recent estimate suggests that the perennially frozen ground known as permafrost, which underlies nearly a quarter of the Northern Hemisphere, contains twice as much carbon as the entire atmosphere.

Temperatures are warming across much of that region, primarily, scientists believe, because of the rapid human release of greenhouse gases. Permafrost is warming, too. Some has already thawed, and other signs are emerging that the frozen carbon may be becoming unstable.

“It’s like broccoli in your freezer,” said Kevin Schaefer, a scientist at the National Snow and Ice Data Center in Boulder, Colo. “As long as the broccoli stays in the freezer, it’s going to be O.K. But once you take it out of the freezer and put it in the fridge, it will thaw out and eventually decay.”

If a substantial amount of the carbon should enter the atmosphere, it would intensify the planetary warming. An especially worrisome possibility is that a significant proportion will emerge not as carbon dioxide, the gas that usually forms when organic material breaks down, but as methane, produced when the breakdown occurs in lakes or wetlands. Methane is especially potent at trapping the sun’s heat, and the potential for large new methane emissions in the Arctic is one of the biggest wild cards in climate science.

Scientists have declared that understanding the problem is a major priority. The United States Department of Energy and the European Union recently committed to new projects aimed at doing so, and NASA is considering a similar plan. But researchers say the money and people devoted to the issue are still minimal compared with the risk.

For now, scientists have many more questions than answers. Preliminary computer analyses, made only recently, suggest that the Arctic and sub-Arctic regions could eventually become an annual source of carbon equal to 15 percent or so of today’s yearly emissions from human activities.

But those calculations were deliberately cautious. A recent survey drew on the expertise of 41 permafrost scientists to offer more informal projections. They estimated that if human fossil-fuel burning remained high and the planet warmed sharply, the gases from permafrost could eventually equal 35 percent of today’s annual human emissions.

The experts also said that if humanity began getting its own emissions under control soon, the greenhouse gases emerging from permafrost could be kept to a much lower level, perhaps equivalent to 10 percent of today’s human emissions.

Even at the low end, these numbers mean that the long-running international negotiations over greenhouse gases are likely to become more difficult, with less room for countries to continue burning large amounts of fossil fuels.

In the minds of most experts, the chief worry is not that the carbon in the permafrost will break down quickly — typical estimates say that will take more than a century, perhaps several — but that once the decomposition starts, it will be impossible to stop.

“Even if it’s 5 or 10 percent of today’s emissions, it’s exceptionally worrying, and 30 percent is humongous,” said Josep G. Canadell, a scientist in Australia who runs a global program to monitor greenhouse gases. “It will be a chronic source of emissions that will last hundreds of years.” […]

As Permafrost Thaws, Scientists Study the Risks

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