Ohio State University
COLUMBUS , Ohio – A new report on
climate over the world's southernmost continent shows that
temperatures during the late 20th century did not climb as had been
predicted by many global climate models.
This comes soon after the latest report by the Intergovernmental
Panel on Climate Change that strongly supports the conclusion that
the Earth's climate as a whole is warming, largely due to human
It also follows a similar finding from last summer by the same
research group that showed no increase in precipitation over
Antarctica in the last 50 years. Most models predict that both
precipitation and temperature will increase over Antarctica with a
warming of the planet.
David Bromwich, professor of atmospheric sciences in
the Department of Geography, and researcher with the Byrd Polar
Research Center at Ohio State University, reported on this work at
the annual meeting of the American Association for the Advancement
of Science at San Francisco.
"It's hard to see a global warming
signal from the mainland of Antarctica right now," he said.
"Part of the reason is that there is a lot of variability there.
It's very hard in these polar latitudes to demonstrate a global
warming signal. This is in marked contrast to the northern tip
of the Antarctic Peninsula that is one of the most rapidly
warming parts of the Earth."
Bromwich says that the problem rises
from several complications. The continent is vast, as large as the
United States and Mexico combined. Only a small amount of detailed
data is available – there are perhaps only 100 weather stations on
that continent compared to the thousands spread across the U.S. and
And the records that we have only date
back a half-century.
"The best we can say right now is
that the climate models are somewhat inconsistent with the
evidence that we have for the last 50 years from continental
"We're looking for a small signal that represents the impact of
human activity and it is hard to find it at the moment," he
Last year, Bromwich's research group
reported in the journal Science that Antarctic snowfall hadn't
increased in the last 50 years.
"What we see now is that the
temperature regime is broadly similar to what we saw before with
snowfall. In the last decade or so, both have gone down," he
In addition to the new temperature
records and earlier precipitation records, Bromwich's team also
looked at the behavior of the circumpolar westerlies, the broad
system of winds that surround the Antarctic continent.
"The westerlies have intensified
over the last four decades of so, increasing in strength by as
much as perhaps 10 to 20 percent," he said. "This is a huge
amount of ocean north of Antarctica and we're only now
understanding just how important the winds are for things like
mixing in the Southern Ocean."
The ocean mixing both dissipates heat
and absorbs carbon dioxide, one of the key greenhouse gases linked
to global warming.
Some researchers are suggesting that the strengthening of the
westerlies may be playing a role in the collapse of ice shelves
along the Antarctic Peninsula.
"The peninsula is the most northern
point of Antarctica and it sticks out into the westerlies,"
Bromwich says. "If there is an increase in the westerly winds,
it will have a warming impact on that part of the continent,
thus helping to break up the ice shelves, he said.
"Farther south, the impact would be modest, or even
Bromwich said that the
increase in the
ozone hole above the central Antarctic continent may also be
affecting temperatures on the mainland.
"If you have less ozone, there's
less absorption of the ultraviolet light and the stratosphere
doesn't warm as much."
That would mean that winter-like
conditions would remain later in the spring than normal, lowering
"In some sense, we might have
competing effects going on in Antarctica where there is
low-level CO2 warming but that may be swamped by the
effects of ozone depletion," he said. "The year 2006 was the
all-time maximum for ozone depletion over the Antarctic."
Bromwich said the disagreement between
climate model predictions and the snowfall and temperature records
doesn't necessarily mean that the models are wrong.
"It isn't surprising that these
models are not doing as well in these remote parts of the world.
These are global models and shouldn't be expected to be equally
exact for all locations," he said.