Increasing greenhouse gases could delay, or even
postpone indefinitely, the recovery of
stratospheric ozone in some regions of the Earth, a Johns
Hopkins earth scientist suggests. This
change might take a toll on public health.
Darryn W. Waugh, a professor in the Morton K. Blaustein
Department of Earth and Planetary
Sciences at The Johns Hopkins University, and his
colleagues report that climate change could
provoke variations in the circulation of air in the lower
stratosphere in tropical and southern
midlatitudes, a band of the Earth including Australia and
Brazil. The circulation changes would cause
ozone levels in these areas never to return to levels that
were present before decline began, even
after ozone-depleting substances have been wiped out from
the atmosphere.
"Global warming causes changes in the speed that the
air is transported into and through the
lower stratosphere [in tropical and southern
midlatitudes]," Waugh said. "You're moving the air
through it quicker, so less ozone gets formed."
He and his team present their findings in the Feb. 5
issue of Geophysical Research Letters, a
publication of the American Geophysical Union.
Dan Lubin, an atmospheric scientist who has studied
the relationship between ozone depletion
and variations in the ultraviolet radiation that reaches
the Earth, said that Waugh's findings could
bode ill for people living in the tropics and southern
midlatitudes. If ozone levels never return to
pre-1960 levels in those regions, "the risk of skin cancer
for fair-skinned populations living in countries
like Australia and New Zealand, and probably in Chile and
Argentina, too, will be greater in the 21st
century than it was during the 20th century," said Lubin,
who is at Scripps Institution of
Oceanography in La Jolla, Calif., and did not participate
in the research.
Ozone is a gas that is naturally present in the
atmosphere and absorbs ultraviolet radiation
from the sun that can harm living beings — for
instance, by causing human skin cancer. This protective
molecule has been in decline in the stratosphere since the
1970s due to an increase in atmospheric
concentrations of human-made substances (mostly
chlorofluorocarbon and bromofluorocarbon
compounds) that destroy ozone. Since the late 1980s, most
countries have adhered to the Montreal
Protocol, an international treaty to phase out production
of ozone-depleting substances.
Researchers at NASA Goddard Space Flight Center in
Greenbelt, Md., collaborated with Waugh
on the new study. The team forecast effects on ozone
recovery by means of simulations using a
computer model known as the Goddard Earth Observing System
Chemistry-Climate Model.
Not all regions face worse prospects for ozone
recovery as a result of climate change, the
scientists find.
Their projections indicate that in polar regions and
northern midlatitudes, restoration of ozone
in the lower stratosphere will suffer little impact from
increasing greenhouse gases. Indeed, in the
upper stratosphere, climate change causes a drop in
temperatures that slows down some of the
chemical reactions that destroy ozone. So, recovery might
be reached in those parts of the
atmosphere earlier than forecast, even decades before the
removal of ozone-depleting gases.
Although scientists have long suspected that climate
change might be altering the dynamics of
stratospheric ozone recovery, Waugh's team is the first to
estimate the effects of increasing
greenhouse gases on the recovery of ozone by region.
Waugh said that his study will help scientists
attribute ozone variations to the right agent.
"Ozone is going to change in response to both
ozone-depleting substances and greenhouse
gases," he said. "If you don't consider climate change when
studying the ozone recovery data, you may
get pretty confused."
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