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Global Warming and Polar Ozone Depletion

Professor Bruce E. Johansen

When chlorofluorocarbons (CFCs) were banned in the late 1980s under the “Montreal Protocol,” most experts expected ozone depletion over the Antarctic to heal rather quickly. By 2005, however, ozone depletion was still a major problem and an ozone ‘hole’ was starting to open over the Arctic as well. As the science has evolved, we are now better able to explain how the capture of heat near the Earth’s surface by greenhouse gases speeds cooling in the stratosphere, and plays an important role in continuing ozone depletion at that level. Thus, the healing of the stratospheric ozone layer depends, to some degree, on reduction of greenhouse-gas levels in the lower atmosphere.

Greenhouse gases warm the atmosphere near the surface like a blanket, holding heat where we live. Deprived of emitted warmth, the stratosphere above cools. The cooler stratosphere, in turn, accelerates the chemical reactions that drive ozone depletion, which accounts for why — despite a two-decade-long ban on CFCs — the restoration of the ozone layer has proceeded so slowly.

But what’s so important about stratospheric ozone?

It protects people and other animals from damaging ultraviolet radiation, which can lead to dangerous forms of skin cancer in humans. The probability that DNA can be damaged by ultraviolet radiation varies with wavelength, with the shorter wavelengths being the most dangerous.

Ozone ‘Hole’ Continues to Expand

The coupling of global warming near the surface with cooling stratospheric temperatures continued in 2006, as loss of ozone over Antarctica reached a new record, according to scientists with the European Space Agency. “Such significant ozone loss requires very low temperatures in the stratosphere combined with sunlight,” said ESA atmospheric engineer Claus Zehner. “This year’s extreme loss of ozone can be explained by the temperatures above Antarctica reaching the lowest recorded in the area since 1979,” the beginning of recordkeeping. Late in September 2006, the World Meteorological Organization reported that the size of that year’s ozone hole had expanded to 10.6 million square miles — an area of depleted ozone larger than the surface area of North America.

Chloroflourocarbons initially sounded no environmental alarms when they were first marketed by Dupont Chemical during the 1930s under the trade name ‘Freon’ for use in air conditioning. The building in which I work, the University of Nebraska’s Arts & Sciences Hall, made news at that time as the first fully air-conditioned college classroom building in the United States. Freon was introduced at a time when environmental questions usually were not asked. At about the same time, asbestos was being proposed as a high-fashion material for clothing, and radioactive radium was being built into timepieces so that they would glow in the dark.

By 1976, manufacturers in the United States were producing 750 million pounds of CFCs a year and finding all sorts of uses for them — from propellants in aerosol sprays, to solvents used to clean silicon chips, to automobile air conditioning, and as blowing agents for polystyrene cups, egg cartons and containers for fast food. “They were amazingly useful,” wrote Anita Gordon and Peter Suzuki in It’s a Matter of Survival (1991). “Cheap to manufacture, non-toxic, non-inflammable, and chemically stable.”

By the time scientists discovered, during the 1980s, that CFCs were thinning the ozone layer over the Antarctic, they found themselves taking on a $28-billion-a-year industry. The ozone shield protects plant and animal life on land from the sun’s ultraviolet rays, which can cause skin cancer, cataracts and damage to the immune systems of human beings and other animals. Thinning of the ozone layer also may alter the DNA of plants and animals.

By the time their manufacture was banned internationally in 1987, CFCs had been used in roughly 90 million car and truck air conditioners, 100 million refrigerators, 30 million freezers and 45 million air conditioners in homes and other buildings. Because CFCs remain in the stratosphere for up to 100 years, they will deplete ozone long after industrial production of the chemicals ceased.

The Ozone ‘Hole’ of 2000

The Antarctic Ozone ‘hole’ formed earlier and endured longer during the September and October of 2000 than ever before — and by a significant amount. Figures from NASA satellite measurements showed that the hole covered an area of approximately 29 million square kilometers in early September, exceeding the previous record from 1998. These record sizes persisted for several days.

Ozone levels, measured in Dobson units, fell below 100 D.U. for the first time. The area cold enough to produce ozone depletion also grew by 10 to 20 percent more surface area than any other year. The ozone-depletion zone was coming closer to New Zealand, where usual springtime ozone levels average about 350 D.U. During the spring of 2000, ozone levels reached as low as 260 D.U. when atmospheric circulation patterns nudged the Antarctic zone northward. Scientists usually regard an area of the stratosphere as ozone-depleted when its D.U. level falls below 220. ‘Ozone warnings’ were issued in southern Argentina and Chile.

During early September 2003, the area of depleted ozone over Antarctica approached near-record size again. By the end of the month, the area of severely depleted ozone was the second-largest on record, at about the size of North America. This record size was exceeded in 2006, and changed little in 2007 and 2008.

A Scary Game of ‘What If?’

Scientists now realize that it will take more than a ban on CFCs to heal the ozone shield. A ‘fix’ for stratospheric ozone is part of the tougher problem of mending the natural imbalance that we have created by interjecting ancient stores of Earth’s carbon dioxide and other greenhouses gases into the atmosphere as fossil fuels.

The world community, however, just got a scientific ‘heads-up’ about the importance of taking timely action on climate change in a newly released NASA study. Curious about what might have happened if the world community hadn’t acted to ban CFCs 22 years ago, a group of NASA scientists created a computer model to predict the effect on the planet.

Had the earth’s 193 nations not adopted the Montreal Protocol, we’d have been well on our way to what atmospheric scientist Paul Newman called a “bizarre world.” By 2065, he stated, two-thirds of the protective ozone layer would have vanished and the ozone ‘hole’ would have covered the Earth. The additional CFCs would have pushed the world’s temperature up an extra 4 degrees F. By implementing the 1987 ban, what was a bad situation was kept from getting worse, he said. That experience, Newman continued, provides hope that the world can do the same thing on the looming and even tougher problem of global warming.

Frederick W. Kayser Professor of Communication at the University of Nebraska at Omaha, Johansen is the author of the three-volume “The Global Warming Combat Manual” (Greenwood Press, 2008).