[Platform-fossilfuels] Permafrost Threatened, say Scientists

[John Andrews]

[More alarming evidence that we nearing a tipping point.  This comes just
days after Congress killed global warming legislation for this year. - John]


< http://www.sciencedaily.com/releases/2008/06/080610112628.htm>

Permafrost Threatened By Rapid Retreat Of Arctic Sea Ice, Study Finds

ScienceDaily (Jun. 11, 2008) — The rate of climate warming over northern
Alaska, Canada, and Russia could more than triple during periods of rapid
sea ice loss, according to a new study led by the National Center for
Atmospheric Research (NCAR). The findings raise concerns about the thawing
of permafrost, or permanently frozen soil, and the potential consequences
for sensitive ecosystems, human infrastructure, and the release of
additional greenhouse gases.

"Our study suggests that, if sea-ice continues to contract rapidly over the
next several years, Arctic land warming and permafrost thaw are likely to
accelerate," says lead author David Lawrence of NCAR. The study is by
scientists from NCAR and the National Snow and Ice Data Center.

The research was spurred in part by events last summer, when the extent of
Arctic sea ice shrank to more than 30 percent below average, setting a
modern-day record. From August to October last year, air temperatures over
land in the western Arctic were also unusually warm, reaching more than 4
degrees Fahrenheit (2 degrees Celsius) above the 1978-2006 average and
raising the question of whether or not the unusually low sea-ice extent and
warm land temperatures were related.

To investigate this question, Lawrence and his colleagues analyzed climate
change simulations generated by the NCAR-based Community Climate System
Model. Previous analysis of these simulations suggested that a sustained
period of rapid ice loss lasting roughly 5 to 10 years can occur when the
ice thins enough. During such an event, the model revealed, the minimum
sea-ice extent can drop by an area greater than the size of Alaska and
Colorado combined.

The team found that during episodes of rapid sea-ice loss, the rate of
Arctic land warming is 3.5 times greater than the average 21st century
warming rates predicted in global climate models. While this warming is
largest over the ocean, the simulations suggest that it can penetrate as far
as 900 miles inland. The simulations also indicate that the warming
acceleration during such events is especially pronounced in autumn. The
decade during which a rapid sea-ice loss event occurs could see autumn
temperatures warm by as much as 9 degrees F (5 degrees C) along the Arctic
coasts of Russia, Alaska, and Canada.

Lawrence and his colleagues then used the model to study the influence of
accelerated warming on permafrost and found that in areas where permafrost
is already at risk, such as central Alaska, a period of abrupt sea-ice loss
could lead to rapid soil thaw. This situation, when summer thaw extends more
deeply than the next winter's freeze, can lead to a talik, which is a layer
of permanently unfrozen soil sandwiched between the seasonally frozen layer
above and the perennially frozen layer below. A talik allows heat to build
more quickly in the soil, hastening the long-term thaw of permafrost.

Potential impacts on greenhouse gases

Arctic soils are believed to hold 30 percent or more of all the carbon
stored in soils worldwide. Although researchers are uncertain what will
happen to this carbon as soils warm and permafrost thaws, one possibility is
that the thaw will initiate significant additional emissions of carbon
dioxide or the more potent greenhouse gas, methane.

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. Recent warming has degraded large sections of permafrost, with
pockets of soil collapsing as the ice within it melts. The results include
buckled highways, destabilized houses, and "drunken forests" of trees that
lean at wild angles.

"An important unresolved question is how the delicate balance of life in the
Arctic will respond to such a rapid warming," Lawrence says. "Will we see,
for example, accelerated coastal erosion, or increased methane emissions, or
faster shrub encroachment into tundra regions if sea ice continues to
retreat rapidly?"

The study sheds light on how interconnected the Arctic system is, says
co-author Andrew Slater, a scientist at the National Snow and Ice Data
Center (NSIDC). "The loss of sea ice can trigger widespread changes that
would be felt across the region."

This research was funded by the U.S. Department of Energy and by the
National Science Foundation, NCAR's sponsor.

Journal reference:

   1. David Lawrence, Andrew Slater, Robert Tomas, Marika Holland, and Clara
Deser. Accelerated Arctic land warming and permafrost degradation during
rapid sea ice loss. Geophysical Research Letters, June 13, 2008