Permafrost Threatened By Rapid Melt Of Arctic Sea Ice
Pastor Dale Morgan
Permafrost Threatened By Rapid Melt Of Arctic Sea Ice*
Simulations by global climate models show that when sea ice is in rapid
decline, the rate of predicted Arctic warming over land can more than
triple. The image at left shows simulated autumn temperature trends
during periods of rapid sea-ice loss, which can last for 5 to 10 years.
The accelerated warming signal (ranging from red to dark red) reaches
nearly 1,000 miles inland. In contrast, the image at right shows the
comparatively milder but still substantial warming rates associated with
rising amounts of greenhouse gas in the atmosphere and moderate sea-ice
retreat that is expected during the 21st century. Most other parts of
the globe (in white) still experience warming, but at a lower rate of
less than 1 degree Fahrenheit (0.5 Celsius) per decade. Image by Steve
Deyo, UCAR.
by Staff Writers
Washington DC (SPX) Jun 12, 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. 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 the National
Center for Atmospheric Research (NCAR).
The study will be published Friday, 13 June, in Geophysical Research
Letters, a journal of the American Geophysical Union (AGU).
The research, conducted by scientists from NCAR and the National Snow
and Ice Data Center (NSIDC), 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 2 degrees
Celsius (4 degrees Fahrenheit) 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 finds 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 1500 kilometers (about 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 5 degrees C (9 degrees F) 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.
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 0 degrees C (32 degrees F) 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
NSIDC co-author Andrew Slater. "The loss of sea ice can trigger
widespread changes that would be felt across the region."
The study was funded by the U.S. Department of Energy and by the
National Science Foundation, NCAR's sponsor.