BOSTON — WHEN the Du Pont Company announced it was shutting down its plants that make ozone-destroying chloroflurocarbons (CFCs), countries around the world started calling, asking to buy them. ``Since we announced this total phase out of CFCs, we have had number of inquires from developing countries that account for 60 to 70 percent of the world's population to buy our plants or to buy CFC technology,'' says Leo E. Manzer, a research manager at Du Pont, the world's largest producer of CFCs. Du Pont refused to sell the plants, giving as its reason that CFCs made in developing countries are as bad for the Earth's ozone shield as CFCs made in the United States.
The Du Pont action followed an international agreement three years ago, when 23 industrialized countries gathered in Montreal and promised to cut their production of CFCs by the year 1999. ``Five [CFC] plants have started up since the treaty was signed in 1987,'' says Dr. Manzer.
In his laboratory at the University of California at Irvine, F. Sherwood Rowland, an atmospheric chemist, analyzes samples of air from all over the world. He has found industrial chemicals like CFC-113, used almost exclusively in the electronics industry, in places as remote as Barrow, Alaska. ``There is no place in the world that people live that is free of this pollution,'' says Dr. Rowland.
Unlike smog or radiation, CFCs do not pose a direct threat to human health. The chemicals, which are used as propellents in aerosol-spray cans, to blow foam, and in refrigerators, eventually escape into the atmosphere where they contribute to global warming and break down the ozone layer that shields the surface of the Earth from the sun's deadly ultraviolet radiation. ``When they stop becoming a greenhouse problem, they start becoming an ozone problem,'' says Donald Blake, a postdoctoral research assistant in Rowland's laboratory.
Sixteen years ago, Rowland and Mario Molina published an article in the journal Nature, hypothesizing that CFCs might damage ozone in the upper atmosphere. Although Rowland and Dr. Molina lacked proof of actual ozone destruction, their argument was convincing enough that the United States, Canada, Sweden, and Norway banned the use of CFCs in most aerosol-spray cans.
In 1985, Dr. John Farman, a scientist with the British Survey, published a paper in Nature that said the ozone over the Halley Bay Station had been decreasing since 1957. Two years later, experiments aboard a modified U-2 spy plane flying over the Antarctic confirmed the so-called ozone hole and proved that chlorine released by CFCs was the culprit.
Companies like Du Pont are now hurriedly searching for ways of making CFC alternatives. But with $135 billion of equipment that uses CFCs in the United States alone, says Manzer, replacements must match the physical properties of the CFCs closely. If a replacement gas expands more when heated than does CFC-12, commonly used in automobile air conditioners, it might blow pressure relief valves in cars on a hot day, he says.
A second problem with the alternatives is their price: Because the substitute chemicals require three or four steps to manufacture, instead of the single step for most CFCs, they will probably cost three to five times as much. That cost will be especially difficult for developing countries - the countries now seeking to buy or build Du Pont's cheaper CFC technology. The Global Greenhouse
Scientists say, the problems and issues raised by the ozone layer are just a taste of what awaits the world on an even larger climatological problem: global warming.
The Earth's atmosphere acts like the glass in a greenhouse. Visible light from the sun passes through the atmosphere and heats the Earth's surface. But trace gases in the atmosphere, mostly carbon dioxide and water vapor, trap infrared radiation emitted from the surface and keep it from being reflected back into space.
``If we had no atmosphere, the temperature of the Earth would be around 0 degrees,'' says Blake. ``Because of carbon dioxide, water vapor, and ozone, we have an average temperature of about 60 degrees.''
Those trace gases have been steadily increasing since the Industrial Revolution began in the 18th century. Carbon dioxide (CO2) is on the rise thanks to the burning of coal, oil, and natural gas. Methane, another greenhouse gas, is on the rise because of increased agriculture. For developing countries, limits on greenhouse gas production - essentially bans on future development - might be even more unacceptable than limits on CFCs. A hundred years ago, the concentration of CO2 in the Earth's atmosphere was roughly 280 parts per million (ppm). Today, CO2 is at 340 ppm and rising.
In 1896, the Swedish chemist Svante Arrhenius predicted that doubling the amount of carbon dioxide would eventually lead to a 9 degree increase in the Earth's temperature. Most of today's computer-based climatological models forecast a 4 to 9 degree increase in global temperature, ``depending on how you represent the clouds,'' says Dr. Peter Stone, an atmospheric scientist at the Massachusetts Institute of Technology (MIT) in Cambridge, Mass.
Although some scientists say it may be years before increased greenhouse gases affect the Earth's temperature, the planet does seem to be getting warmer already. According to James Hansen, director of the NASA-Goddard Institute for Space Studies in New York, 1988 ``tied with 1981 as the warmest year on our record.'' The global average temperature for those two years was 0.63 degrees F. above the world's average between 1950 and 1980. Last year ``was warm, but it was not as warm as the previous year.... I think it was the sixth or seventh.''
Last year would have been warmer, says Dr. Hansen, except for a ``periodic up-swelling of cold water in the eastern Pacific,'' called the El Nino, that has been keeping temperature in that ocean cool. ``As we come out of that cool phase, we are going to get hotter temperatures in the next year or two which may rival or exceed the hottest years in the 1980s.''
But predicting the actual amount of warming - and how soon it will take place - is difficult, says Kerry Emmanuel, chairman of MIT's department of Earth and planetary sciences and a critic of many global climate models.
Models of Earth's climate
Scientists lack a comprehensive theory, or ``analytic understanding,'' of how the Earth's climate actually works. ``One would hope that we would at least have an analytic understanding some of the subprocesses, an understanding that is rooted in the physics of the phonemena,'' says Dr. Emmanuel. Even detailed understandings of the convection of air or the circulation of the oceans remain beyond the grasp of climatologists.
That understanding is vital, Emmanuel says, because ``water vapor is a much more important greenhouse gas than CO2.'' Like CO2 water vapor traps in the heat from the ground, but ``there is a lot more of it.''
Clouds move water around the globe. Since they can't be modeled directly, their effects must be inferred from other variables - which is where Kerry and other scientists feel that the models get shaky.
``There may be powerful negative feedback that are so strong that the amount of extra warmth is so small [as not to matter],'' he says. ``If you increase the amount of clouds by just a few percent, you could offset the warming. Clouds reflect sun back to space: They're white.''
Nevertheless, many scientists say the possibility for global warming should be reckoned with now. ``The numbers, to me, are worrisome, even given all of the uncertainties in the models,'' says MIT's Stone.
``One of the things that we really need to do is to improve our understanding of some of these processes that are important,'' he says. ``That requires getting lots of data.''
For example, says Stone, detailed measurements have to be made to determine the temperature of the ocean at different depths. One proposed experiment involves conducting underwater detonations and measuring the time it takes for the sound to travel to different parts of the world: Because cold water is denser than warm water, sound travels slower through it.
``This would be very valuable to tell us if we are getting a true global warming, and to tell us how rapidly it is coming about. The faster [the heat] penetrates into the deep oceans, the longer it will take'' to warm up the surface, says Stone. ``It is an important difference if we get a rise in 10 years or in a hundred, and that is the kind of uncertainty there is.''
But few scientists doubt that a warming is coming. ``The fact that the atmosphere is changing, that much is certain,'' says Rowland. ``CO2 is going up. Methane is going up. Those aren't questioned any more.''
``You hear a lot of people say, `I'm not sure that the greenhouse effect is real.' It is very real, in that there are driving forces: We can't change the concentration of these gases in the atmosphere without having a consequence on the climate,'' he says. ``The fact that we can't predict what that climate is going to be doesn't meant that it won't happen. We can't predict earthquakes, but we know that they happen.''
One of the most important developments in recent years has been the political agreement to cut the use of CFCs, says Stone: ``If nothing were done about CFCs, they would become the worst part of the warming problem in 20 years time.''
``The laws that were passed in the US and other countries [in the 1970s] did have a beneficial effect. The [warming] effect in recent years has not been as bad as it would have been if those laws had not been passed.'' That's because each CFC molecule traps more than a thousand times as much heat as each molecule of carbon dioxide.
One pressing problem, Stone says, is a shortage of scientists in the field of meteorology, a field that has perhaps less than 2,000 people engaged in research. ``A lot of this money that they are talking [about] spending in [NASA's proposed] Earth Observation System will gather data, but we don't have the manpower to make use of it. So we are going to need money for increasing the supply of scientists working on these problems.''