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Friday, September 23, 2005

Coming To The Arctic Near You: The Longer, Hotter Summer

difference in snow and vegitationFAIRBANKS,
AK--In a paper that shows dramatic summer warming in arctic Alaska,
scientists synthesized a decade of field data from Alaska showing
summer warming is occurring primarily on land, where a longer snow-free
season has contributed more strongly to atmospheric heating than have
changes in vegetation.

Arctic climate change is usually viewed as caused by the
retreat of sea ice, which reduces high-latitude albedo- a measure of
the amount of sunlight reflected off a surface - a change most
pronounced in winter.

"Summer warming is more pronounced over land than over sea ice,
and atmosphere and sea-ice observations can’t explain this," said Terry
Chapin, professor of ecology at the University of Alaska Fairbanks’
Institute of Arctic Biology and lead author of the paper which appears
in the September 22, 2005 advance online publication Science Express,

Using surface temperature records, satellite-based estimates of
cloud cover and energy exchange, ground-based measurements of albedo
and field observations of changes in snow cover and vegetation, Chapin
and co-authors argue that recent changes in the length of the snow-free
season have triggered a set of interlinked feedbacks that will amplify
future rates of summer warming.

"It’s the changes in season length rather than increases in
vegetation that explains this observation," Chapin said. Summer warming
correlates with a lengthening of the snow-free season that has
increased atmospheric heating locally by an amount similar in magnitude
to the regional heating expected over multiple decades from a doubling
of atmospheric carbon dioxide, say the authors.

"Snowmelt is 2.5 days earlier for each decade we studied, Chapin said.
eddy covariance towerTwo
mechanisms explain the pronounced warming over land during the summer.
First, the early snow melt increases the length of time the land
surface can absorb heat energy. Second, the increase in snow-free
ground permits increases in vegetation such shrubs and advances of

"Continuation of current trends in shrub and tree expansion
could further amplify this atmospheric heating 2-7 times," Chapin said.

"This mechanism should be incorporated into climate models,"
Chapin said. Improved understanding of the controls over rates of shrub
expansion would reduce the likelihood of surprises in the magnitude of
high-latitude amplification of summer warming.

Researchers were funded by the National Science Foundation,
Office of Polar Programs, ARCtic System Science program--the goal ARCSS
is to answer the question: What do changes in the arctic system imply
for the future?


High-resolution photographs are available for download at

F. Stuart (Terry) Chapin III, Professor of Ecology, Institute of Arctic Biology, University of Alaska Fairbanks. 907-474-7922,

Dr. Matthew Sturm, Research Physical Scientist, U.S. Army, Cold
Regions Research and Engineering Laboratory Alaska. 907-353-5183,

Marie Gilbert, Publications and Information Coordinator,
Institute of Arctic Biology, University of Alaska Fairbanks.


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