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December 2005 - January 2006

CGD research shows that permafrost may thaw in this century

Dave Lawrence

Dave Lawrence. (Photo by Diane Fritz.)

New research indicates that global warming may decimate the top 10 feet (3 meters) or more of perennially frozen soil across the Northern Hemisphere. This would alter ecosystems as well as damage buildings and roads across Canada, Alaska, and Russia.

The study, by CGD's Dave Lawrence and Andrew Slater of CU's National Snow and Ice Data Center, appeared online in the December 17 issue of Geophysical Research Letters.

Dave and Andrew analyzed computer simulations to find that over half of the area covered by this topmost layer of permafrost could thaw by 2050 and as much as 90% 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.
"People have used models to study permafrost before, but not within a fully interactive climate system model," says Dave, the study's lead author.

"If the permafrost does thaw, as our model predicts, it could have a major influence on climate."

—Dave Lawrence

About a quarter of the Northern Hemisphere's land contains permafrost, defined as soil that remains below 32°F (0°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, Dave says.

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.

Thawing permafrost

Thawing permafrost: 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. (Image courtesy David Lawrence.)

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 (labeled "A2" by the IPCC), the area with permafrost in any of these layers shrinks from 4 million square miles (10.4 million square kilometers) to just over 1 million square miles (2.6 million square kilometers) by the year 2050 and decreases further to about 400,000 square miles (1 million square kilometers) by 2100. In the low-emission scenario (B1), which assumes major advances in conservation and alternative energy, the permafrost area shrinks to about 1.5 million square miles (3.9 million square kilometers) by 2100.

The changes may affect the circulation of water in the oceans. Andrew notes that runoff to the Arctic Ocean has increased about 7% since the 1930s. In the high-emission simulation, runoff grows by another 28% 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.

"There's a lot of carbon stored in the soil," Dave explains. "If the permafrost does thaw, as our model predicts, it could have a major influence on climate."

To address this and other questions, Dave and colleagues are now working to develop a more advanced model with interactive carbon.

One of the challenges, says Dave, will be to properly simulate the growth of vegetation at higher latitudes. Also, he hopes to collaborate with cryosphere experts elsewhere to depict the influence of the deeper, colder permafrost, which could slow down the projected thawing of the topmost layer.

• by Bob Henson


This sinkhole near Fairbanks, Alaska, formed due to the melting of a large ice pocket within permafrost that is gradually thawing as temperatures warm. (Photo courtesy Vladimir Romanovsky, Geophysical Institute, University of Alaska Fairbanks.)

Also in this issue...

The 2005 Outstanding Accomplishment Awards

Offsite but not unseen:
UCAR's non-Boulder staffers stay in touch

A TWERLE reunion

Predicting hurricane damage

Atmospheric science books for all ages

CGD research shows that permafrost may thaw in this century

New CG library

Just One Look: Santa


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