Poles Apart in Climate Response
NOAA-While the Arctic
and the Antarctic experience similar greenhouse gas levels and
solar radiation, each region responds in a dramatically
different way, especially in temperature and loss of sea ice,
says an international team of scientists that includes a NOAA
oceanographer. While the Arctic is warming, most of Antarctica
is not, largely because of the ozone hole, but projections
indicate that is likely to change.
“While some people would
say this is a paradox, these different responses are mostly
consistent with what we know about how the climate system
works,” said James Overland, lead author and an oceanographer
at NOAA’s Pacific Marine
Environmental Laboratory in Seattle.
The findings, based on
an October 2007 polar climate workshop, will be published in
the May 6 issue of EOS, a publication of the American
Geophysical Union. Co-authors are John Turner and Gareth
Marshall of the British Antarctic Survey, Jennifer Francis of
Rutgers University, Nathan Gillett of the University of East
Anglia, and Michael Tjernstrom of Stockholm University.
attended the Seattle workshop that looked at the Polar Regions
from 1987 to 2007. The scientists concluded, based on new
research since the 2007 Intergovernmental Panel on Climate
Change Report, that a combination of factors is responsible
for the recent dramatic sea ice loss in the Arctic as well as
masking some of the effects in the Antarctic.
Experienced seasonal temperatures that at times were more
than four degrees Fahrenheit
warmer than usual.
For most of the Antarctic, temperatures were not unusual,
except on the Antarctic Peninsula, a finger of land and ice
about 1,000 miles south of the tip of South America, which
had the largest increase in temperatures of any location in
the Southern Hemisphere. Temperatures warmed by three
degrees Fahrenheit. Warming temperatures and exposure to
ocean waves were cited by the National Snow and Ice Data
Center as the cause of the collapse of a 160-square-mile
segment of the Wilkins Ice Shelf on the Antarctic Peninsula,
which began collapsing in late February.
Summer sea ice loss was greater and declining more rapidly
than climate models projected.
The amount and stability of the sea ice was not unusual.
There are multiple causes for change.
“In the Arctic, there
is a combination of factors, such as warming of the air
because of more greenhouse gases, an unusual wind pattern,
and warming of the ocean water in regions with reduced sea
ice,” said Overland.
Story is clearer.
Gillett, a climate
dynamics scientist, said, “In the Antarctic, the changes in
winds and temperatures are consistent with how we would
expect them to respond to increased greenhouse gases and
depletion of stratospheric ozone.”
The depletion of ozone
has strengthened the atmospheric circulation, called the
Southern Annual Mode, or SAM. As the ozone hole recovers,
the winds that currently whiz around Antarctica and block
air masses from crossing into the continent’s interior would
weaken, and Antarctica would no longer be so isolated from
global warming patterns.
Sea ice losses will continue. The study says that a
combination of factors has sent the Arctic into a new state
of sea ice loss, which is occurring much earlier than
projected by climate models subject to greenhouse gases
of the ocean and an overall thinning of the sea ice makes it
difficult for the Arctic to now return to earlier
conditions,” says Overland.
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Scientists project that the ozone hole should fully
recover by 2070.
“As the ozone hole recovers, we expect that warming will
appear on the central plateau of Antarctica and we will see
a reduction in sea ice area,” said Turner.