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Permafrost melt poses long-term threat


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Author Topic: Permafrost melt poses long-term threat  (Read 48 times)
DazzaMc
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« on: May 29, 2009, 09:41:45 am »

Melting permafrost could eventually disgorge a billion tonnes a year of greenhouse gas into the atmosphere, accelerating the threat from climate change, scientists said Wednesday.
Their probe sought to shed light on a fiercely-debated but poorly-understood concern: the future of organic matter that today is locked up in the frozen soil of Alaska, Canada, northern Europe and Siberia.


The fear is that, as the land thaws, this material will be converted by microbes into carbon dioxide, which will seep into the atmosphere, adding to the greenhouse effect.

This in turn will stoke warming and cause more permafrost to thaw, which in turn pushes up temperatures, and so on.

But how and when this vicious cycle could be unleashed is unclear.

Indeed, some voices have argued that it will not present a significant threat, as plants will start to grow on the soggy, warmer earth and suck in carbon dioxide (CO2) from the atmosphere through photosynthesis, thus blunting the problem.

A team led by University of Florida ecology professor Ted Schuur investigated an area of tundra at Eight Mile Lake in central Alaska, where permafrost thaw has been monitored since 1990 but had begun to start many years before.

Schuur's team used hand-built, automated chambers, which they deployed at three sites that represented minimal, moderate and extensive amounts of thaw.

From 2004 to 2006, the chambers measured how much carbon was escaping from the soil and how much was being absorbed by any vegetation.

In areas that had thawed for the previous 15 years, there was a net uptake of carbon, meaning that the newly-established plants sucked up more CO2 than was lost from the soil.

But in areas that had begun to thaw decades before, the reverse was true.

There was a net loss of CO2, the principal greenhouse gas blamed for global warming, as older stocks of carbon were gradually released to the atmosphere.

"At first, with the plants offsetting the carbon dioxide, it will appear that everything is fine, but this actually conceals the initial destabilisation of permafrost carbon," Schuur said in a press release.

"But it doesn't last, because there is so much carbon in the permafrost that eventually the plants can't keep up."

Most of the 13 million square kilometres (five million square miles) of permafrost remain frozen, but thawing is already under way around the region's southern fringes and is thought likely to expand this century.

In that scenario, the permafrost could release around a billion tonnes a year of carbon, roughly equivalent to the contribution to greenhouse emissions each year by deforestation in the tropics, the paper said.

Even as the Arctic greens, the rising loss of older carbon "could make permafrost a large biospheric carbon source in a warmer world," it said.

Burning fossil fuels adds about 8.5 gigatonnes of emissions each year, but it is a process that can theoretically be controlled.

Permafrost thaw, though, would be self-reinforcing and could be almost impossible to brake.

"It's not an option to be putting insulation on top of the tundra," Schuur said.

"If we address our own emissions either by reducing deforestation or controlling emissions from fossil fuels, that's the key to minimising the changes in the permafrost carbon pool."


http://www.terradaily.com/reports/Permafrost_melt_poses_long-term_threat_says_study_999.html
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DazzaMc
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« Reply #1 on: May 29, 2009, 12:46:40 pm »

Greening Arctic Not Likely To Offset Permafrost Carbon Release

As the frozen soil in the Arctic thaws, bacteria will break down organic matter, releasing long-stored carbon into the warming atmosphere.

At the same time, plants will proliferate, nurtured by balmier temperatures, more nutrients from decomposing soil and the increasing abundance of the greenhouse gas they depend on for growth.

These connected but contrasting changes have raised a question for scientists who study the causes and consequences of global climate change: Will the shrubs and incipient forests spreading across the Arctic compensate for the permafrost's rising release of carbon, blunting its impact on a warming planet? Or, with twice as much carbon locked up in the permafrost as now present in the atmosphere, will the lush growth become overwhelmed -- like a kitchen sponge put down to stem a water main break?

Researchers led by a University of Florida ecologist may have an answer. In a paper set to appear May 28 in the journal Nature, the team reports experimental results suggesting tundra plant growth may keep up with rising carbon dioxide initially.

But if thawing continues in a warmer world, the permafrost will spew carbon for decades, and the plants will become overwhelmed -- unable to sop up the excess carbon despite even the most vigorous growth.

"At first, with the plants offsetting the carbon dioxide, it will appear that everything is fine, but actually this conceals the initial destabilization of permafrost carbon," said Ted Schuur, a UF associate professor of ecology and lead author of the paper. "But it doesn't last, because there is so much carbon in the permafrost that eventually the plants can't keep up."

Schuur noted most of the 13 million square kilometers, or roughly 5 million square miles, of permafrost in Alaska, Canada, Siberia and parts of Europe remain frozen. However, thawing already occurring around its southern edges is expected to expand this century.

Should that occur, this study suggests the permafrost could lose in the range of 1 gigaton of carbon, or 1 billion tons, per year – about the same order of magnitude as being added by current deforestation of the tropics, another large biospheric source, Schuur said.

While burning fossil fuels contributes considerably more carbon, about 8.5 gigatons annually, that process can at least in theory be controlled – whereas once the permafrost thaw begins, it sets up a self-reinforcing loop far from human activity and potentially difficult to stop.

That highlights the urgent need to address human-caused emissions now, Schuur said.

"It is not an option to be putting insulation on top of the tundra," he said. "If we address our own emissions, either by reducing deforestation or controlling emissions from fossil fuels, that's the key to minimizing the changes in the permafrost carbon pool."

Researchers from UF used hand-built, automated chambers to trap and measure carbon dioxide losses in Alaska year-round from 2004 through 2006. Thawing at the research sites near Denali National Park, in central Alaska, varies considerably, with some plots much more extensively thawed than others.

The researchers determined how long each spot had been thawing using long-term data from permafrost-monitoring instruments combined with historical aerial photographs. With a total of 18 of the automated chambers, they measured the release and uptake of carbon between the tundra and the atmosphere. This resulted in a measurement of net ecosystem carbon exchange – the total carbon each spot lost, or gained, due to thawing permafrost.

The results were clear.

Tundra sites that had thawed for the past 15 years gained net carbon, as increasingly verdant plant growth was greater than the permafrost's carbon losses. However, radiocarbon dating of carbon dioxide showed that old carbon from the permafrost was already being released in higher amounts due to thaw – signifying that all was not well with the permafrost carbon even in that time period. The site that began thawing decades before gained net carbon emission to the atmosphere, revealing that more thaw caused significantly more old carbon loss -- despite greening of the vegetation, including more shrubs.

Said Jason Vogel, a UF postdoctoral associate and author of the paper: "The plants are still growing faster in the extensively thawed area, but that's not enough to keep up with the greater microbial activity releasing old carbon from deeper in the soil."

As a result, even as the Arctic greens, its escalating old carbon loss "could make permafrost a large biospheric carbon source in a warmer world," according to the paper.

The other authors are Kathryn Crummer, a UF lab technician; Hanna Lee, a UF doctoral student; James Sickman, of the University of California, Riverside; and T.E. Osterkamp of the University of Alaska, Fairbanks. The research was funded by the National Science Foundation, NASA and a cooperative agreement with the National Park Service.

http://www.sciencedaily.com/releases/2009/05/090527130826.htm
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