Most of Arctic's near-surface permafrost may thaw by 2100
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.
|Regions containing permafrost within the top 11 feet of soil could decrease by as much as 90% across the Arctic over the next century, based on simulations by the NCAR Community Climate System Model. Shown are areas with near-surface permafrost in the CCSM simulations for 1980-1999 (light blue) and 2080-2099 (dark blue). The latter projection is based on the Intergovernmental Panel on Climate Change's A1B emissions scenario, often called the "business as usual" scenario. (Photo: David Lawrence)|
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.
"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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