Living in a glass house
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By Douglas G.Cogan
Nineteen eightyeight may be remembered as the year the Earth struck back. Scorching summer heat had us flocking to the beaches, but medical waste and other tide-swept garbage kept us out of the water. Lack of rainfall parched crops, sapped hydropwer, even made washing the family car a luxury. While we waited anxiously for a change in the weather, NASA scientists informed us that more of the same-or worse-is in the long-range forecast. Within our lifetimes, they predicted, the climate will become hotter and the sun’s rays more deadly than at any time in human history. These twin atmospheric peril-the greenhouse effect and ozone depletion-are better u n d e r s t d if we envision the F.arth as a fragile glass house. It’s as if the planet were protected by a floating network of special window panes that filter out the sun’s harmful ultraviolet light while retaining some of its radiant heat. Spanning the globe in a seamless web, these window panes form a giant geodesic dome under which all life, save that in the deep oceans, has evolved. 20 Environ. Sci. Technol., MI. 23,NO.1. l W 9
Three years ago, an orbiting satellite known as Nimbus 7 provided the first tangible evidence that the exterior of the glass house is falling into disrepair. It revealed a gaping hole in the Eanhk basement window-the ozone layer over Antarctica-which spreads from the South Pole each year, at the beginning of austral spring, and engulfs the
Douglas G. Cogan
entire Antarctic continent by early October. Although the damage seems to repair itself as spring turns to summer, it is a patch-up job at best. Since 1979, all latitudes more than 60’ south of the equator have sustained ozone declines of 5% or more throughout the year. And at its worst, the hole covers an area twice the size of the continental United States, with depletion exceeding 50% at its center (I). In 1988, signs emerged of hairline fractures in window panes throughout the glass house-even around the main living quarters in the Northern Hemisphere. A careful review of nearly 20 years of ground-based and satellite instrument data confirmed a year-round ozone loss of 3 % across densely populated regions of North America, Europe, and the Soviet Union, and a wintertime loss of 4.7%. Perhaps more troubling is that sophisticated computer models had indicated that such a decline would not occur until well into the 21st century. A hole in the attic? As we enter 1989, the search is on for another ozone hole-this time in the attic of the glass house. One hundred
W13936WW09230020001.~/0 0 1988ArnericanChemical Society
atmospheric scientists and their support crew will be spending the next six weeks in and around Stavanger, Norway, a city of 85,000 inhabitants along the North Sea. Situated only 10" south of the Arctic Circle, Stavanger is strategically important for two reasons. First, it lies at the edge of a coldweather band that extends from Greenland to Russia, where stratospheric temperatures can plummet to below -80 "C-cold enough to gasify dry ice. Second, Stavanger has a large military airfield that can accommodate a specially equipped DC-8 and an ER-2, a modified U-2 spy plane. These NASA aircraft were the workhorses of the Antarctic Airborne Ozone Expedition (AAOE) of 1987. That expedition, in combination with extensive ground-based and satellite monitoring, identified three necessary elements for the development of an ozone hole. First, the atmosphere over one of the poles needs to wind itself up in a tight spiral-a polar vortex-that is virtually impenetrable by outside air masses. Second, stratospheric temperatures inside the vortex need to fall below -80 OC to freeze out droplets of nitric acid and below -85 OC to turn water vapor into ice. If the vortex is sufficiently cold and stable, the resulting particles-thought to be nitric acid trihydrate wrapped in a thick coat of icefall out of the ozone layer before evaporating in the troposphere several kilometers below (2). That leaves the lower stratosphere practically defenseless against ozone depletion, provided that the third element is in place: elevated levels of chlorine. Without nitric acid to sequester chlorine in inactive reservoirs of chlorine nitrate and hydrogen chloride, chlonne free radicals are able to amck ozone from the time sunlight returns to the pole at the end of winter until the polar vortex breaks up later in the spring. This heterogeneous (surfacecatalyzed) process allows one chlorine atom to destroy tens of thousands of ozone molecules before the carnage is over. An Arctic ozone bole is not likely to be as severe as the one in the Antarctic, however. The Northern Hemisphere is considerably wanner on average and the North Pole is less prone to the development of a well-contained polar vortex. Even so, the necessary elements exist for accelerated depletion of the Arctic ozone layer. Stratospheric temperatures there occasionally fall below -80 'C. This permits the formation of polar stratospheric clouds (PSCs) that freeze out nitric acid, although they appear 10 times less frequently than in the Antarmc. More importantly, tests conducted
last winter in the Arctic found abundances of chlorine dioxide, a proxy for the free radicals involved in omne depletion, at 10 times the level suggested in models of homogeneous chemistry. In addition, abundances of nitrogen dioxide, an inhibitor of chlorine's ozonedepleting capabilities, were among the lowest measured anywhere in the Earth's atmosphere. This strongly suggests that heterogeneous chemical reactions already are taking place in the Arctic (3). Nevertheless, this year's Arctic expedition may be unable to locate an ozone hole. The one in the Antarctic last year was weaker than expected, breaking up six weeks earlier than it did in 1987. Scientists attribute this to unusually dynamic weather patterns, which pushed the polar vortex offthe South Pole into regions with more sunlight, allowing the vortex to
warm up and diminishing the presence of PSCs. If the same kind of dynamic forces are at work in the Arctic this winter, PSCs there may not form at all-leaving scientists with the unwelcome prospect of having to repeat the Arctic experiments. Putting the house
Order
Sixteen months from now the Montreal Protocol will be reviewed. This international agreement, signed by nearly four dozen nations since September 1987, calls for a 50% cut in production of fully halogenated chlorofluorocarbons (CFCs) by 1998. But an analysis of the hotocol by the U.S. Environmental Protection Agency suggests that its implementation hardly WIII protect the ozone layer (4). On the contrary, EPA found that chlonne levels in the atmosphere are likely to tri-
Protocol: Baseline case
Low tract
Environ. Sci. Technol.. Val. 23,No. 1, 1989 21
ple-from 2.7 parts per billion in volume to 8 ppbv in 2075-even if all nations in the world were to abide by terms of the agreement (an unlikely proposition). The EPA study also concluded that stabilizing chlorine at its present concentration in the atmosphere (which itself may be too high) would require an immediate ban on production of CFCs and halons as well as a freeze on the production of methyl chloroform. (Halons are brominebased fire extinguishants. The Montreal Protocol calls for a freeze on production of these compounds by 1992. Methyl chloroform is a widely used chlorinated solvent; its use is not restricted by the Protocol.) Last October, scientists meeting at The Hague under the auspices of the United Nations Environment Program (UNEP) agreed to conduct a six-month assessment that may influence the outcome of the treaty negotiations in 1990. The assessment will be broken into four parts, reflecting the state of knowledge on: (1) the chemistry and physics of ozone depletion; (2) UV-B health effects on humans, plants, and animals; (3) the availability of substitutes for products made with or containing CFCs; and (4) economic impacts of more stringent controls. The UNEP assessment, due out this summer, may contain promising news. Several chemical companies expect to have commercial plants producing CFC substitutes by 1990. (Chronic toxicity tests are likely to delay market introduction of several substitutes until at least 1992, however.) The world's largest producer of CFCs, Du Pont, is optimistic enough about the development of alternatives that it has pledged to end production of fully halogenated CFCs
by the year 2000. In fact, companies that produce 60% of the world's CFCs have pledged their support for a complete phase-out of the ozone-depleting compounds. Other sections of the UNEP assessment may contain bad news, however. Beyond pointing out the inadequacy of present control measures, the assessment may take a longer look at the relationship between ozone depletion and the greenhouse effect. Past industrial activity has committed the Earth to at least 0.5 "C of warming over the next century (5).Since the warming will be accentuated at the poles, permafrost may thaw and release molecular methane hydrates from the soil. Oxidation of that methane, in turn, would increase the amount of water vapor in the atmosphere. The greenhouse effect also is likely to trap more heat in the troposphere and possibly reduce temperatures in the lower stratosphere. The combination of more airborne water vapor and reduced stratospheric temperatures could increase the presence of PSCseven in portions of the globe where they are not found now. Evidence also is mounting that sulfuric acid droplets, derived from power plant emissions and volcanic eruptions, could foster surface-catalyzedozone depletion away from the poles. The most sobering prospect of all is that efforts to limit future global warming may have their own adverse consequences on the ozone layer. EPA estimates that measures taken to hold global warming to an increase of 2 "C by 2075 could triple the ultimate rate of ozone depletion (4). This would result largely because of the reduced nitrogen oxide emissions and comparatively warmer stratospheric tempera-
tures, which, absent PSC considerations, facilitate ozone depletion. As more is learned about mankind's complex relationship with the sky, the perception is growing that Earth's dwellers do indeed live inside a glass house. This recognition may change the way society behaves inside the house and may promote new respect for its fragile exterior. The outcome of negotiations to revise the Montreal Protocol will tell whether this new perspective is shaping global environmental policy.
References (1)"Executive Summary"; Ozone Trends Panel Report, National Aeronautics and Space Administration: Washington, DC, March 1988. (2)Monastersky, R. Science News 1988, 134(16), 249-51. (3)Solomon, S . et al. Science 1988, 242, 550-55. (4)Hoffman, J. S . ; Gibbs, M. J. Future Concentrations of Stratospheric Chlorine and Bromine; U.S. Environmental Protection Agency. U.S. Government Printing Office: Washington, DC, 1988. (5)Jaeger, J. Developing Policies for Responding to Climatic Change; World Meteorological Organization: Geneva, Switzerland, 1988, WMOITD-No. 225.
Douglas G. Cogan is author of Stones in a Glass House: CFCs and Ozone Depletion, a chronicle of the development of regulations to protect the ozone layel: M K Cogan has coauthored reports on energy conservation and renewable energy and is presently engaged in a study of corporate responses to the greenhouse efect. He is a senior analyst with the Investor Responsibility Research Center, Inc. : (202) 939-6500. Stones in a Glass House is available for $35. Paid orders may be sent to IRRC, 1755 Massachusetts Ave., N. W , Suite 600, Washington,DC 20036.
Environmental Index Year the change in the ozone concentration over Antarctica was observed: 1977 Year the change in the ozone concentration over Antarctica was reported in the scientific literature: 1985 Year measurements of chlorofluorocarbons in the atmosphere were first made: 1970 Atmospheric lifetime of CFC-11 (CC13F): 75 years Atmospheric lifetime of CFC-12 (CClzF2): 110 years Definition of atmospheric lifetime of a chlorofluorocarbon: average time between release to the atmosphere and eventual destruction in the stratosphere
Sources are listed on page 26. 22 Environ. Sci. Technol., Vol. 23,No. 1, 1989
