Warming in Antarctic?

By Bill Scanlon
Scripps Howard

May 04, 2008 02:09 am

—

BOULDER, Colo. — The penguins are a bit chilly now, but once the ozone layer heals several decades from now, their Antarctic home is likely to be warmer — and that could spell trouble.

A new study says that when the hole in the stratospheric ozone layer recovers, the interior of the Antarctic will start experiencing the warming that the rest of Earth has experienced over the past 40 years.

Until now, the Antarctic interior has been spared the warming, and actually has been cooler than normal, likely because of the ozone depletion, a Colorado scientist said.

Judith Perlwitz of the Cooperative Institute for Research in Environmental Sciences in Boulder, said that when ozone levels return to their pre-1969 levels by the end of this century, the atmospheric patterns that now shield the Antarctic interior from warmer air will begin to break down.

Those seasonal circulation patterns are known as a positive phase in the Southern Annular Mode, or SAM.

As ozone levels recover, Perlwitz added, the lower stratosphere over the polar region will absorb more harmful ultraviolet radiation from the sun.

That could cause air temperatures six to 12 miles above Earth's surface to rise by as much as 16 degrees Fahrenheit. And that, in turn, would reduce the strong north-to-south variation in temperature that favors the SAM.

Perlwitz's institute, CIRES, is a joint venture of the University of Colorado and the National Oceanic and Atmospheric Administration.

Perlwitz is the lead author of an article on the research that appears in the latest issue of 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 ozone protects the Earth from harmful radiation, including skin cancer.

The hole in the Earth's protective ozone layer has been traced to the proliferation of chlorofluorocarbons, used in aerosol sprays and air conditioning, starting in the 1960s.

The CFCs climb into the atmosphere, latching onto the ozone and eating much more of it than their minuscule weights would suggest.

Most of the products that generate the CFCS now have been banned, but the ozone layer won't be healed for almost a century, scientists project.

The authors used a NASA supercomputer model that used interactions between the climate and stratospheric ozone chemistry to examine how changes in the ozone hole influence climate and weather near Earth's surface.

According to NASA's Pawson, 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 supercomputer also suggested that the ozone hole recovery would weaken the intense westerly winds that whip around Antarctica and block air masses from crossing into the continent's interior.

The seasonal shift in circulation patterns could have repercussions for Australia and South America as well. Australia could get warmer and drier, while southern South America could get wetter.

How big an influence a full recovery of the ozone hole will be on the Southern Hemisphere's climate depends largely on the future rate of greenhouse gas emissions.

"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."