The ultimate positive feedback for global warming!
-- Roger
=-=-=-=-=-=-=
Most of Arctic's Near-Surface Permafrost May Thaw by 2100
December 19, 2005
BOULDER-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% 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.
[ . . . ]
The rest, and some pictures, are at:
http://www.ucar.edu/news/releases/2005/permafrost.shtml