Thawing permafrost may further increase climate warming: study
18/6/2006 10:21
Permafrost deposits in Alaska and Siberia containing dozens of times more
carbon than normal soils, could become a potent, likely unstoppable contributor
to global warming if it continues to thaw, scientists warned on Friday.
In a
paper appearing in the June 16 edition of the journal Science, scientists said
the permanently frozen ground or permafrost of the Northern Hemisphere
represents a large carbon reservoir, which was rarely considered in earlier
forecasts of the climate change.
Permafrost, full of grass roots and animal
bones, typically contains 10 to 30 times more carbon than deep, nonpermafrost
soils, the scientists said. The northeastern Siberian permafrost alone contains
about 75 times more carbon than is released by burning fossil fuels each year
all over the world.
If all the Siberian permafrost thawed, decomposed and
released its carbon in the form of heat-trapping carbon dioxide, it could nearly
double the 730 billion metric tons of carbon in the atmosphere presently- an
outcome that would have huge warming impact, the researchers
calculated.
Scientists have long known that permafrost, short for permanently
frozen earth, contains carbon. But the latest research, jointly conducted by
Russian and US researchers, is the first to examine in detail the huge swath of
permafrost soil blanketing northeast Siberia.
That soil is composed of layers
of frozen windblown dust, which fell from the air and accumulated as glaciers
advanced and retreated over hundreds of thousands of years. The dust is frozen
in the permafrost, which trapped layers of roots and other organic matter that
never decomposed.
In warmer regions, plants usually die, decompose and return
their carbon content to the atmosphere as carbon dioxide. When spring comes, new
plant growth takes up this carbon dioxide by photosynthesis, producing
oxygen.
The process repeats itself, with the amount of carbon consumed
roughly proportional to the amount of carbon produced. But in Siberia, the
deepest organic matter staying frozen becomes a huge build-up of undecomposed,
carbon-rich soil.
This soil contains from 2 to 5 percent carbon, 10 to 30
times more carbon than generally found in most deep mineral soils, according to
the researchers.
"It's another large pool of carbon on the list that could
move into the atmosphere with continued warming," said Ted Schuur, co- author of
the study and an assistant professor at the University of Florida.
"You start
thawing the permafrost, microbes release carbon dioxide, that makes things
warmer, more permafrost thaws and the process continues."
This soil appears
to shed its carbon relatively quickly when thawed, he added.
In laboratory
tests, the researchers found that the soil produced carbon dioxide at rates
roughly comparable to productive northern grassland soils as they thawed. Using
carbon dating techniques, they confirmed that the carbon dioxide was "ancient
carbon" dating back tens of thousands of years.
Today, permafrostis known to
be thawing. Depending on how much thaws, the result could well be a rapid
release of ancient carbon dioxide, the researchers concluded.
"If these rates
are sustained in the long term, as field observations suggest, then most carbon
in recently thawed (permafrost) will be released within a century, a striking
contrast to the preservation of carbon for tens of thousands of years when
frozen in permafrost," the researchers said in the Science
paper.
Xinhua News
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