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Public Radio's Environmental News Magazine (follow us on Google News)

Update on Ozone

Air Date: Week of

David Baron examines the current debate over the state of the planet's thinning ozone layer. Although the hole in our atmosphere continues to grow, scientists say it's doing so more slowly these days, and the global phaseout of chlorofluorocarbons may have prevented a real disaster. Still, controversy remains about current damage, and most scientists agree that this is no time to stop worrying.


CURWOOD: Among the chlorinated chemicals which industry has agreed to stop using are chlorofluorocarbons, CFCs. Nearly two decades ago, scientists found that CFCs were destroying the Earth's protective ozone layer in the stratosphere, and in 1987 the world's nations agreed to phase out CFCs. Even after the phase-out began, though, for years studies of the ozone layer kept showing it to be getting worse. But recently, scientists have begun saying that the worldwide CFC ban may be working, and that the worst of ozone layer depletion may soon be over. David Baron of member station WBUR reports.

BARON: Two atmospheric chemists at the University of California first alerted the world to the potential danger of ozone depletion 20 years ago, in a paper published in the British journal Nature. One of the authors was Mario Melino. He now teaches at MIT, and he keeps a copy of that historic article in his filing cabinet.

(Filing cabinet being opened, files riffled through)

MELINO: There we go. Destruction of ozone, Nature, 1974.

BARON: This seemingly unexceptional technical report contained a profound message. It suggested that common manmade chemicals called chlorofluorocarbons, or CFCs, used at the time in aerosol spray cans, refrigerators, and air conditioners, could migrate to the upper atmosphere and destroy ozone. Ozone is a naturally-occurring gas that shields the planet from deadly ultraviolet radiation. Without this ozone layer, scientists said, the Earth would likely suffer an ecological and human health disaster. But after 20 years of fearing dire consequences, Melino now believes a disaster will be averted.

MELINO: The worst is not over yet, but it's not going to get a lot worse.

BARON: In fact, the situation should start to improve before long. Sherwood Roland was Mario Melino's coauthor on the 1974 paper.

ROLAND: The worst, as far as ozone depletion, might pass within the next 10 or 15 years.

BARON: Such forecasts have led some politicians and journalists to claim that scientists have backed down from their earlier doomsday predictions, and that perhaps ozone depletion never did pose a major threat. But atmospheric chemists like Roland and Melino are adamant that their warnings were justified. That serious consequences could have resulted, and that health and environmental problems from ozone depletion could still lie ahead. Scientists say the outlook is better now only because the world heeded their warnings, and implemented agreements to phase out CFCs.

PRINN: Clearly the policies are working. We are now going to reach the peak a lot sooner than most people expected.

BARON: MIT chemist Ron Prinn has monitored ozone-destroying CFCs in the atmosphere since 1978. For most of that time he's found concentrations of the chemicals steadily rising with no end in sight. Prinn says CFC levels are still rising but things have changed.

(Papers being flipped)

PRINN: Looking at this graph you see very good news. You see that for the two major chlorofluorocarbons, the rate of increase has been flattening out.

BARON: Prinn says a little after the turn of the century, CFC concentrations should begin to fall. But World Meteorological Organization calculates that the Earth has already lost about 10% of its ozone. By the time CFC concentrations peak, the WMO predicts that number could rise to 12 or 13%. That's a significant loss, which could cause higher rates of skin cancer and cataracts in people, and could harm plants and animals. Recent research suggests increases in ultraviolet radiation may have already reduced the growth of plankton in the ocean around Antarctica, and a new study hints that loss of ozone could be partly responsible for a worldwide decline in frog populations, which maybe be highly susceptible to ultraviolet light. But the world has in some ways been lucky; ozone depletion has occurred in a way that has minimized risk to life. Ozone has been lost mostly over the poles, where few people live, and in the winter when there's naturally more ozone to begin with and thus the loss has a smaller impact. And some early reports of harm from ozone depletion haven't withstood scientific scrutiny. Several years ago there were reports from southern Chile, an area that for part of the year sits below Antarctica's ozone hole, that increased ultraviolet radiation had blinded thousands of sheep and rabbits and had caused skin diseases in people. Dr. Oliver Schein of Johns Hopkins University traveled to southern Chile a year and a half ago to examine the region's people and animals.

SCHEIN: I believe the reports in the lay press did not have a basis in reality. We could not see any evidence of unusual eye disease or skin disease in these populations.

BARON: But Michael Oppenheimer, a scientist with the Environmental Defense Fund, says it's too soon to conclude that ozone depletion hasn't caused substantial damage to natural ecosystems.

OPPENHEIMER: We are so profoundly ignorant about the way ecosystems operate that we don't know what we've done.

BARON: And much remains unknown about how ozone depletion occurs. In many years, ozone loss has been worse than scientists had predicted. Harvard researcher Jim Anderson, in New Zealand for a study of the ozone layer above Antarctica, stresses that the ozone layer will continue to deteriorate before it starts to recover. And any prediction of what will happen in the next few decades is nothing more than an educated guess.

ANDERSON: 1992 and 1993 were the two worst years for ozone erosion over the Northern Hemisphere, and we don't have the key evidence that defines why that occurred. We didn't predict the Antarctic ozone hole. So I think history speaks to us to be very careful about making assumptions.

BARON: Even the most optimistic scientists point out their forecasts depend on a central assumption, which could turn out to be invalid. That is, that the nations of the world will continue their strict adherence to agreements to protect the ozone layer. Optimism may be warranted, scientists say. Complacency is not. For Living on Earth, I'm David Baron.



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