|
Ozone Hole
Recovery May Reshape Southern Hemisphere Climate Change
April 24, 2008
A new study by CU-Boulder, NOAA and NASA shows the recovery of the
Antarctic ozone hole may amplify warming in the continent's interior.
Photo courtesy Ted Scambos/ University of Colorado at Boulder
A full recovery of the stratospheric ozone hole could modify climate
change in the Southern Hemisphere and even amplify Antarctic warming,
according to scientists from the University of Colorado at Boulder, the
National Oceanic and Atmospheric Administration and NASA.
While Earth's average
surface temperatures have been increasing, the interior of Antarctica
has exhibited a unique cooling trend during the austral summer and fall
caused by ozone depletion, said Judith Perlwitz of the Cooperative
Institute for Research in Environmental Sciences, a joint institute of
CU-Boulder and NOAA. "If the successful control of ozone-depleting
substances allows for a full recovery of the ozone hole over Antarctica,
we may finally see the interior of Antarctica begin to warm with the
rest of the world," Perlwitz said.
Perlwitz is lead author
of a new study on the subject to be published April 26 in Geophysical
Research Letters. Co-authors include Steven Pawson and Eric Nielson of
NASA's Goddard Space Flight Center in Greenbelt, Md., and Ryan Fogt and
William Neff of NOAA's Earth System Research Laboratory in Boulder. The
study was supported by NASA's Modeling and Analysis Program.
The authors used a NASA
supercomputer model that included interactions between the climate and
stratospheric ozone chemistry to examine how changes in the ozone hole
influence climate and weather near Earth's surface, said Perlwitz.
The study authors
calculated that when stratospheric ozone levels return to near pre-1969
levels by the end of the 21st century, large-scale atmospheric
circulation patterns now shielding the Antarctic interior from warmer
air masses to the north will begin to break down during the austral
summer. The circulation patterns are collectively known as a positive
phase of the Southern Annular Mode, or SAM.
The scientists found that
as ozone levels recover, the lower stratosphere over the polar region
will absorb more harmful ultraviolet radiation from the sun. This could
cause air temperatures roughly 6 to 12 miles above Earth's surface to
rise by as much as 16 degrees Fahrenheit, reducing the strong
north-south temperature gradient that currently favors the positive
phase of SAM, said the research team.
The supercomputer
modeling effort also indicated that ozone hole recovery would weaken the
intense westerly winds that currently whip around Antarctica and block
air masses from crossing into the continent's interior. As a result,
Antarctica would no longer be isolated from the warming patterns
affecting the rest of the world.
NASA's Pawson said ozone
recovery over Antarctica would essentially reverse summertime climate
and atmospheric circulation changes that have been caused by the
presence of the ozone hole. "It appears that ozone-induced climate
change occurred quickly, over 20 to 30 years, in response to the rapid
onset of the ozone hole," he said. "These seasonal changes
will decay more slowly than they built up, since it takes longer to
cleanse the stratosphere of ozone-depleting gases than it took for them
to build up."
The seasonal shift in
large-scale circulation patterns could have repercussions for Australia
and South America as well. Other studies have shown that the positive
phase of SAM is associated with cooler temperatures over much of
Australia and increased rainfall over Australia's southeast coastline.
During late spring and
early summer, the positive phase of SAM also is associated with drier
conditions in South America's productive agricultural areas like
Argentina, Brazil, Uruguay and Paraguay, said Perlwitz. If ozone
recovery induces a shift away from a positive SAM, Australia could
experience warmer and drier conditions while South America could get
wetter, she said.
But just how influential
a full stratospheric ozone recovery will be on Southern Hemisphere
climate largely depends on the future rate of greenhouse gas emissions,
according to the GRL authors. Projected increases in human-emitted
greenhouse gases like carbon dioxide will be the main driver for
strengthening the positive phase of SAM.
"In running our
model simulations, we assumed that greenhouse gases like carbon dioxide
would double over the next 40 years and then slowly level off,"
said Perlwitz. "If human activities cause more rapid increases in
greenhouse gases, or if we continue to produce these gases for a longer
period of time, then the positive SAM may dominate year-round and dwarf
any climatic effects caused by ozone recovery."
NASA's High-End Computing
Program provided the Columbia supercomputer resources at the NASA Ames
Research Center in Moffett Field, Calif.
Contact
Judith Perlwitz,
303-497-4814
Judith.Perlwitz@noaa.gov
Lynn Chandler, 301-286-2806 (NASA)
Adriana Raudzens Bailey, 303-492-6289
Jim Scott, 303-492-3114 |
