Global Warming Will Thaw Most of Arctic Perma-Frost by 2100
Boulder, CO - Global warming may decimate the top 10 feet
(3 meters) or more of perennially frozen soil across the
Northern Hemisphere, altering ecosystems as well as
damaging buildings and roads across Canada, Alaska, and
Russia. New simulations from the National Center for
Atmospheric Research (NCAR) show that over half of the
area covered by this topmost layer of permafrost could
thaw by 2050 and as much as 90 percent by 2100. Scientists
expect the thawing to increase runoff to the Arctic Ocean
and release vast amounts of carbon into the atmosphere.
The study, using the NCAR-based Community Climate System Model
(CCSM), is the first to examine the state of permafrost in a
global model that includes interactions among the atmosphere,
ocean, land, and sea ice as well as a soil model that depicts
freezing and thawing. Results appear online in the December
17 issue of Geophysical Research Letters.
"People have used models to study permafrost before, but not
within a fully interactive climate system model," says NCAR's
David Lawrence, the lead author. The coauthor is Andrew Slater
of the University of Colorado’s National Snow and Ice Data
Center.
About a quarter of the Northern Hemisphere’s land contains
permafrost, defined as soil that remains below 32 degrees F
(0 degrees C) for at least two years. Permafrost is typically
characterized by an active surface layer, extending anywhere
from a few centimeters to several meters deep, which thaws
during the summer and refreezes during the winter. The
deeper permafrost layer remains frozen. The active layer
responds to changes in climate, expanding downward as
surface air temperatures rise. Deeper permafrost has
not thawed since the last ice age, over 10,000 years
ago, and will be largely unaffected by global warming
in the coming century, says Lawrence.
Recent warming has degraded large sections of permafrost across
central Alaska, with pockets of soil collapsing as the ice
within it melts. The results include buckled highways,
destabilized houses, and "drunken forests"--trees that
lean at wild angles. In Siberia, some industrial facilities
have reported significant damage. Further loss of permafrost
could threaten migration patterns of animals such as reindeer
and caribou.
The CCSM simulations are based on high and low projections of
greenhouse-gas emissions for the 21st century, as constructed
by the Intergovernmental Panel on Climate Change. In both
cases, the CCSM determined which land areas would retain
permafrost at each of 10 soil depths extending down to 11.2
feet (3.43 meters).
For the high-emission scenario, the area with permafrost in any
of these layers shrinks from 4 million to just over 1 million
square miles by the year 2050 and decreases further to about
400,000 square miles (1 million square kilometers) by 2100.
In the low-emission scenario, which assumes major advances
in conservation and alternative energy, the permafrost area
shrinks to about 1.5 million square miles by 2100.
"Thawing permafrost could send considerable amounts of water to
the oceans," says Slater, who notes that runoff to the Arctic
has increased about 7 percent since the 1930s. In the high-emission
simulation, runoff grows by another 28 percent by the year 2100.
That increase includes contributions from enhanced rainfall and
snowfall as well as the water from ice melting within soil.
The new study highlights concern about emissions of greenhouse gases
from thawing soils. Permafrost may hold 30 percent or more of all
the carbon stored in soils worldwide. As the permafrost thaws,
it could lead to large-scale emissions of methane or carbon dioxide
beyond those produced by fossil fuels.
"There's a lot of carbon stored in the soil," says Lawrence. "If
the permafrost does thaw, as our model predicts, it could have a
major influence on climate." To address this and other questions,
Lawrence and colleagues are now working to develop a more advanced
model with interactive carbon.
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