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Tuesday, August 26, 2008

Arctic Tundra Holds Global Warming Time Bomb

by Michael Reilly, Discovery News, August 25, 2008

Aug. 25, 2008 -- Locked away in the frozen soils of the Arctic tundra, there lies a ticking time bomb.

Nothing more than accumulated leaves, roots and other plant matter, the unassuming detritus is rich in carbon, giving it the power to dramatically enhance the effects of global warming should it ever get into the atmosphere. But for now it mostly lies dormant, in cold storage in the permafrosts of Siberia, Alaska, and Canada.

That's starting to change, according to some scientists. The planet has already begun to warm as a result of humans pumping billions of tons of carbon into the atmosphere each year. The permafrost is starting to melt, and that pent-up carbon is already leaking into the air in the form of carbon dioxide and methane, powerful greenhouse gases.

Even worse, there may be more of the stuff than anyone ever thought.

Chien-Liu Ping and a team of researchers at the University of Alaska, Fairbanks spent the last 13 years meticulously sampling tundra soils across North America. In a study published this week in the journal Nature Geoscience, they estimate there may be almost 100 billion tons of carbon in the first meter of soil alone.

That's equivalent to about a quarter of the amount currently in Earth's atmosphere, or 10 years' worth of global emissions from human activity.

It also nearly doubles previous estimates of carbon content in Arctic soil. Despite decades of work, such approximations are rough at best, because land in the far North is vast, remote, and inhospitably cold. Even in the height of summer, soil scientists can rarely dig deeper than 50 centimeters before they hit rock-solid permafrost.

But worst-case scenario climate projections from the Intergovernmental Panel on Climate Change (IPCC) suggest Arctic temperatures could climb as much as 6 degrees centigrade by the end of the century.

If that happens, the Arctic region, which has already shown signs of thawing, will change dramatically. Already scientists have begun seeing areas where permafrost tundra has melted into muddy bogs called 'thermokarsts.' In other places, steep hillsides, no longer supported by rigid ice crystals, are giving way in landslides.

As the land melts bacteria intrude, decomposing the plant matter that has built up over thousands of years. They release methane and carbon dioxide into the air as byproducts, gases that warm the planet by trapping heat energy from the sun.

"Permafrost temperatures in Alaska have gone up about 1 degree Centigrade over the last 50 years," Ping said, pushing soils to within a fraction of a degree of freezing temperature. "In Russia, they've been monitoring permafrost for over a century. It has warmed 2 degrees Centigrade, so almost 5 degrees Fahrenheit."

It's not all bad news though. The warmer temperatures should allow plants to grow vigorously, and they can suck up huge amounts of carbon out from the atmosphere through photosynthesis -- perhaps even enough to cancel out greenhouse gas emissions from the soil.

In fact, many scientists say the jury is still out on whether or not the thawing Arctic could quicken the pace of global warming.

"The carbon losses you have to have from soil to affect climate need to be fast and big," David McGuire of the University of Alaska, Fairbanks said. "There are two ways do that: mass erosion from slumping or along the coasts and rivers, and through fires."

Last year, McGuire, who was not involved with Ping's research, ran computer simulations of what would happen if catastrophe struck vast swaths of Arctic tundra in the form of wildfires and massive erosion.

"The most carbon we could get into the atmosphere was about 50 billion tons," he said, or about half of what Ping's team thinks is stored in the soil.

That's not enough to make much difference by the year 2100, but Ted Schuur of the University of Florida thinks we need to look further into the future.

In a paper to be published in the September issue of the journal Bioscience, he estimates that 1,672 billion tons of carbon are locked in Arctic permafrosts, much of it in Siberia. The carbon leak is slow -- he estimates it could only be as high as 1 billion tons each year worldwide, or about 10 percent of what is emitted today through human activity emissions. But over the next four centuries it could end up in the atmosphere, drastically altering Earth's climate.

"The Ping paper is great so far as it goes, but it's only dealing with this one zone: North America," Schuur said. "That's like describing what an elephant looks like by talking all about its foot. We're trying to describe the whole elephant."

If Schuur's estimate is right, Arctic soils harbor two to three times more carbon than is currently aloft in Earth's atmosphere. If it were to be released as greenhouse gases over the course of the next few centuries, the effect on the climate might not be noticeable by the year 2100. But by the year 2400 or 2500 it would be tremendous.

"Right now there's about 780 billion tons of carbon in the atmosphere. And now you say you're going to take and slowly put much of 1,600 billion tons from the soil up there. That's going to have a huge effect on the heat-trapping capacity of the Earth," Schuur said.

"Say you look at Earth in 500 years," he said. "It's probably going to be a very different place."

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