CHAPTER 4l
“Atmospheric scientists are struggling to explain one of the strangest mysteries ever to confront them: a widening and potentially dangerous hole in the ozone layer over the South Pole.
“Putting forward a series of theories, and unsatisfied by all of them, the scientists are making final preparations for a rare research expedition that will fly into the dead of the Antarctic winter next week.
“At the same time, biologists are reporting heightened concern over the possible dangers to human beings and ocean life from even small increases in ultraviolet radiation, which the ozone layer blocks.
“Concern has intensified steadily since last fall, when scientists were stunned by satellite data showing the magnitude of the hole, which appears each September and October. The depletion is many times worse than has been predicted over the last 15 years amid concern over the global effects on ozone of manmade gasses, such as fluorocarbons.
“By flying four teams with advanced instrumentation into the American base at McMurdo Sound, ordinarily closed to traffic in winter except for maintenance flights, the scientists hope to distinguish two extreme possibilities.
“The hole could be a transient climate phenomenon that will go away by itself. Or it could be caused by manmade pollution, in which case it could continue to widen, reaching populated areas of South America, Australia and southern Africa, and appear at the North Pole as well.
“It’s like rolling dice,” said Michael B.Elroy of Harvard University’s Center for Earth and Planetary Physics. “The big money question is: If what’s happening in Antarctica is likely to be a foretaste of what might happen in the northern region.
“The mystery has renewed worldwide interest in the ozone issue, which began in 1971 with fears over gasses released by supersonic jets and spray cans. the United States banned fluorocarbons in spray cans in 1978, and a few European countries followed suit, but global production for uses ranging from air conditioners to foam has continued to grow.
“All the predictions assumed that such gasses in the stratosphere would result in a steady, gradual, global depletion of ozone. Now scientists find themselves forced to confront a sudden, highly localized hemorrhaging effect of ozone that none of their calculations predicted. Instead of declining a few percent over decades, the Antarctic ozone has plunged 40 percent since 1979.
“On the one hand, it’s very exhilarating and challenging, and on the other – scary because it’s hard to place your bets with any confidence,” said Ralph J. Cicerone of the National Center for Atmospheric Research.
“Ozone is an unstable form of oxygen with molecules of three atoms instead of two. In the upper atmosphere, it forms and breaks down continuously in chemical processes that have proved sensitive to the presence of other rare gasses” The Antarctic hole appears 8 to 10 miles up, at the end of winter as the spring sun rises briefly over the horizon. By the end of November, the ozone levels recover. Each year, though, the hole has expanded. In 1985, it reached a size equivalent to the United States.
“When the ozone is thin, the ultraviolet radiation reaching the ground in Antarctica would produce a tan (brunfarge) even in the low, pale October sun, a level that over populated areas would sharply increase the incidence of skin cancer.” The initial report of the hole by British scientists in March 1985 caused little excitement, partially because the British team in Antarctica was not well-known among atmospheric scientists.
“But later last year, scientists at the National Aeronautics and Space Administration produced satellite data confirming the British findings and showing how big the hole was, NASA scientists found that the depletion of ozone was so severe that the computer analyzing the data had been suppressing it, having been programmed to assume that deviations so extreme must be errors. The scientists had to go back and reprocess the data going back to 1979.
“Just as an earthquake precedes volcanic eruptions, this could be a signal of something worse,” said Mark Schoeberl, a NASA scientist at the Goddard Space Flight Center in Greenbelt, Md. “It could be the leading edge of something More detrimental. It could expand outward to more-populated areas. We just don’t know right now.”
“As the Antarctic expedition prepares for departure, new theories are emerging, all speculative and none convincing. Some use chains of chemical reactions to link the hole to the gradual depletion already observed. others explain the hole in terms of cyclical atmospheric processes that have no relation to manmade gasses.
“The atmosphere high over the Antarctic is the coldest place on Earth, 15 to 20 degrees colder than over the North Pole. The difference comes from asymmetries in the flow of the atmosphere weather systems.” Some climate experts think a change in the ordinary dynamic motions of waves and cyclones in the upper atmosphere might cause the hole. For example, an upwelling of air over the pole could push aside the layer of the stratosphere with the most ozone, replacing it with low ozone air from lower altitudes.
“Such an explanation implies that the hole may have come and gone in the past before it could be measured. Even so, to be convincing, such an explanation needs to answer the question: why now? “One theory ties the hole to volcanic particles that have built up in the polar atmosphere. The particles could be heated by the sun, causing the upwelling. Another theory suggests that the dynamics could be affected by a change in solar activity.
“Jerry Mahlman, director of the Geophysical Fluid Dynamics Laboratory in Princeton, N.J., is one of those who favor a dynamical explanation, although he thinks all of the existing theories suffer from a level of evidence “somewhere between minuscule and nonexistent.” The hole points to shortcomings in the existing computer “models” used to make predictions about the Earth’s climate, he said, but it does not necessarily confirm the worst ozone warnings of the last decade.” You could say, ’Aha! We’ve found the great smoking gun, – Mahlman said. “But the chemistry does not really match up. So far, there’s a lot of wishful hand waving.” He has bet a Chinese lunch that ozone levels will rise again this year.
“On the other hand, Elroy of Harvard favors a chemical explanation and he put one forward last month in the British journal nature. The manmade gasses that break down ozone include, most prominently, chlorine, formerly released by spray cans and now by a host of industrial processes. McElroys theory relies on another element as well: bromine, a much rarer gas used in specialized fire-extinguishing equipment. “In the sequence of chemical reactions he proposes, little bromine produces large ozone depletion. If this theory is correct, policy-makers might find that strictly controlling bromine would be more effective than controlling chlorine.
“All of the theories make specific predictions about the polar atmosphere that should be testable – hence the Antarctic expedition, announced by the National Science Foundation.
“You know how much excitement this is causing in scientific circles and industry and government,” said Cicerone of the National Center for Atmospheric Research. “But so far, the only people who are sure of themselves are not convincing their colleagues. most of these theories will bite the dust.”
“Thirteen researchers will join the 130 people spending the winter at the McMurdo base. They will launch a series of 33 balloons with high-atmosphere measuring instruments. And they will use an assortment of advanced ground instruments, including various spectrometers, caw able of detecting the minute quantities of various chemical byproducts whose existence is predicted by the various theories. The spectra meters measure the scattered wavelengths of sunlight and moonlight, in effect, letting the sun and moon, interrogate the atmosphere.
“The scientists come from the State University of New York at Stony Brook, the University of Wyoming, NASA’s Jet Propulsion Laboratory in Pasadena, Calif., and the National Oceanic and Atmospheric Administration’s Aeronar Laboratory in Boulder, Cob.
“This is one of the most challenging things we1ve ever come across in atmospheric chemistry.” said Susan Soloman of the Aeronomy Laboratory, then leader of the expedition. “whatever the source is, we need to understand it because this is a change in the ozone that’s of absolutely unprecedented proportions. We’ve just never seen anything like what we’re experiencing in the Antarctic.”
“Her own theory, also put forward in NATURE, is chemical, relying on some complicated interactions of chlorine and sunlight.