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 Antarctica hasn't warmed as much over the last century as climate models had originally predicted, a new study finds.
Climate
change's effects on Antarctica are of particular interest because of
the substantial amount of water locked up in its ice sheets.
Should that water begin to melt, sea levels around the globe could rise and inundate low-lying coastal areas.
The new study, detailed in
the April 5 issue of the journal Geophysical Research Letters, marks
the first time that researchers have been able to give a progress
report on Antarctic climate model projections by comparing climate
records to model simulations. (These comparisons have already been done
for the other six continents.)
Information about
Antarctica's harsh weather patterns has traditionally been limited, but
temperature records from ice cores and ground weather stations have
recently been constructed, giving scientists the missing information
they needed.
"This is a really important
exercise for these climate models," said study leader Andrew Monaghan
of the National Center for Atmospheric Research in Boulder, Co.
Temperature gap
Monaghan
and his team found that while climate models projected temperature
increases of 1.4 degrees Fahrenheit (0.75 degrees Celsius) over the
past century, temperatures were observed to have risen by only 0.4 F
(0.2 C).
"This is showing us that, over the past
century, most of Antarctica has not undergone the fairly dramatic
warming that has affected the rest of the globe," Monaghan said.
The
gap between prediction and reality seemed to be caused by the models
overestimating the amount of water vapor in the Antarctic atmosphere.
The cold air over the southernmost continent handles moisture differently than the atmosphere over warmer regions.
The
models did, however, correctly capture the increases in snowfall over
Antarctica in the late 20th century, followed by a decrease in the last
decade.
One reason that Antarctica hasn't warmed as much as other parts of the globe is the existence of the man-made ozone hole overhead:
It alters wind patterns, creating a swirling belt of winds around the
landmass that keeps comparatively warm air from seeping in, preserving
the continent's frigid temperatures.
One important exception to this rule is the Antarctic Peninsula, which has warmed by several degrees, in part because winds there draw in warmer air from the north.
Mixed verdict
The
Intergovernmental Panel on Climate Change has estimated that sea levels
could rise by 7 to 23 inches (18 to 59 centimeters) globally this
century, in part due to ice melt at both poles and from mountain
glaciers.
The new study, funded by the National
Science Foundation and the U.S. Department of Energy, suggests that
warming in Antarctica could offset this amount by about 2 inches (5
centimeters) if the continent warms by 5.4 F (3 C), as warmer air would
hold more moisture and generate more snowfall, which contributes to the
growth of the ice sheets, locking up any additional water in the these
large masses of ice.
That would mean a rise of only 5 to 21 inches (13 to 54 centimeters).
But
these projections are by no means certain — if melt from Antarctic ice
sheets outweighed the snowfall that contributes to their growth, sea
level rise could be higher.
"The research clearly
shows that you can actually slow down sea-level rise when you increase
temperatures over Antarctica because snowfall increases, but warmer
temperatures also have the potential to speed
up sea-level rise due to enhanced melting along the edges of
Antarctica," Monaghan said. "Over the next century, whether the ice
sheet grows from increased snowfall or shrinks due to more melt will
depend on how much temperatures increase in Antarctica, and potentially
on erosion at the ice sheet edge by the warmer ocean and rising sea
level."
The findings of the study don't call into question model projections for other parts of the globe, Monaghan said.
"The
models are really doing quite a good job at simulating the 20th-century
changes over the six inhabited continents," he told LiveScience. Source
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