Ozone Hole Recovery to Reshape Southern Climate Change Patterns?

Scientists have been citing evidence of links between greenhouse
forcing and the stratospheric ozone shield for some years. Here’s one
more.
Lance

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“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.”
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Public release date: 24-Apr-2008
University of Colorado at Boulder

Contact: Judith Perlwitz
judith.perlwitz@noaa.gov
303-497-4814

Ozone hole recovery may reshape southern hemisphere climate change
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.”

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NASA’s High-End Computing Program provided the Columbia supercomputer
resources at the NASA Ames Research Center in Moffett Field, Calif.

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