The Ozone-CFC Debacle: Hasty Action, Shaky Science
By international agreement, the manufacture of chlorofluorocarbons (CFCs) is supposed to cease in the United States and most other developed nations by the end of 1995. Motorists will face shortages when they try to recharge their air conditioners, with the cost for repair or retrofit likely in the multi-hundred dollar range; the 10-yr cost for U.S. automobiles is estimated as between $24 and $49 billion (1). The U.S. Environmental Protection Agency (EPA), anticipating a potential consumer revolt, had to persuade a reluctant DuPont Corporation to rescind its voluntary commitment to close down its production line by the end of 1994 (2). (Hoechst AG actually closed down its CFC production in Germany on April 16, 1994)
Yet in spite of the hardships caused by the hasty phaseout of CFCs and other suspected ozone-depleting halocarbons, the EPA has never questioned the adequacy of the science that forms the basis for its phaseout policy. The facts are that the scientific underpinnings are quite shaky: the data are suspect; the statistical analyses are faulty; and the theory has not been validated (3,4). The science simply does not support this premature and abrupt removal of widely used chemicals -- at great cost to the economy. This fact seems finally to have been recognized by legislators; in early 1995, Republican Congressman from Texas, Tom Delay, introduced a bill, H.R. 475, to repeal the provisions in Title VI of the 1990 Clean Air Act regulating the production and use of CFCs.
If one examines the history of governmental CFC policy, one finds that it is based mainly on panicky reactions to press releases from EPA, National Aeronautics and Space Administration (NASA), and National Oceanographic and Atmospheric Administration (NOAA) about skin cancer and possible Arctic ozone holes -¬ stimulated and amplified by environmental pressure groups and the media ¬- rather than on published work that has withstood the scrutiny of scientific peers. Credence has been given to EPA "estimates" of millions of extra skin cancer deaths, to lurid stories about ozone depletion leading to blind sheep, to the travails of whales in the Antarctic, and to the worldwide disappearance of frogs and toads. It is perhaps characteristic of this topic that so many of the scary announcements have led off with some statement like: "The depletion of ozone is worse than expected" -¬ starting with the March 1988 press conference by the Ozone Trends Panel (5). Yet since "expectation" must be based on theory, the discrepancy with observations means, logically, that either the theory is wrong or the data are wrong, or both are wrong!
For the general public, and even for the trained scientist, these scientific controversies are difficult to sort out. It is indeed a multi-faceted problem, a chain with many links connecting the release of CFCs into the atmosphere with the occurrence of skin cancer. Briefly, the steps are postulated as follows (6):
1. CFCs with lifetimes of decades and longer become well-mixed in the atmosphere, percolate into the stratosphere, and there release chlorine.
2. Chlorine, in its active form, can destroy ozone catalytically and thereby lower its total amount in the stratosphere.
3. A reduced level of ozone results in an increased level of solar ultraviolet radiation reaching the surface of the earth.
4. Exposure to increased UV leads to increases in skin cancer.
Each of these four steps is controversial, has not been sufficiently substantiated, and may even be incorrect (7,8). One can reasonably conclude that policy is rushing far ahead of the science.
Scientific Uncertainties and Controversies
It is generally agreed that natural sources of tropospheric chlorine (volcanoes, ocean spray, etc.) are four to five orders of magnitude larger than man-made sources (9). But it is what gets into the stratosphere that counts. The debate has degenerated into arguing about how much chlorine is rained out in the lower atmosphere (10) rather than measuring whether stratospheric chlorine is actually increasing.
Contrary to the claims of some skeptics, CFCs do indeed reach the stratosphere; the secular increase of fluorine, in the form of HF, as reported by Belgian researcher R. Zander, may be sufficient proof (11,12). But as late as 1987, Zander found no long-term increase in HCl, suggesting that stratospheric chlorine comes mostly from natural sources, which are not expected to increase over time. The situation changed in 1991, however, when NASA scientist C. Rinsland published data showing HCl increasing at about half the rate of HF, suggesting both natural and man-made sources (13). Yet the Montreal Protocol to freeze CFC production and roll it back to lower levels was signed in 1987, at a time when published work still indicated little, if any, contribution from CFCs.
(Earlier aircraft-based observations of HCl increases between 1978 and 1982 by NCAR researchers Mankin and Coffey (14) were used to justify a CFC phaseout, even as late as 1993 (15,16), in spite of the fact that their data series was judged to be of poor quality and too short; according to MIT Professor Prinn, their published rate of increase of stratospheric chlorine could well be close to zero, in agreement with Zander's 1987 result (17). In any case, Mankin and Coffey themselves ascribe their observed 1982 increase to the volcano E1 Chichon (18) rather than to CFCs).
The question of global ozone depletion has been bedeviled by doubts about the quality of the data. Readings from Dobson ground observatories can be contaminated by long-term trends in SO2 pollution of the lower atmosphere. DeMuer and DeBacker have demonstrated that the Dobson ozone meter can misinterpret the downward trend of SO2 pollution, giving rise to a "fictitious" ozone trend (19). (Their finding was confirmed by a task group, chaired by Robert T. Watson, in a Joint Workshop of the IPCC and the International Ozone Assessment Panel in May 1993).
Another, quite separate problem is produced by the extreme noisiness of the ozone record. To establish the existence of a small, long-term trend it is necessary to eliminate the large natural variations, especially also those correlated with the 11-yr sunspot cycle. This is an impossible task given the shortness of the record and the virtual absence of data on long-term variations of the solar far-UV radiation that produces ozone in the upper atmosphere. The analysis fails a simple test: The "trend" is found to depend strongly on the choice of time interval (20). An additional problem in identifying a man-made trend arises from long-term trends in sunspot number, and therefore long-term ozone trends of natural origin (21).
Thus, the issue of whether the global ozone layer shows a steadily depleting trend is still controversial. Satellite data on global ozone content are not subject to interference from low-altitude pollution, but long-term calibration drift presents a problem; the TOMS data from satellites appear to have a calibration drift due to nonlinearities in the photomultiplier (22). In any case, the shortness of the record, 1979 to present, makes the solar-cycle correction problematic (23).
The Antarctic ozone "hole", an annual short-lived thinning of the layer first identified in 1985, is a genuine phenomenon whose intensity has increased markedly since about 1978. Its proximate cause is unquestionably stratospheric chlorine, but its fate may be controlled more by climate factors and the presence of particulates than by the concentration of chlorine itself (24); the hole may persist even if the chlorine level were to drop below the 1978 value. In any case, no theoretical predictions exist that can be tested by future observations.
Nor is the CFC-ozone theory itself in good shape. Over the years, its predictions for long-term, global ozone depletion have varied widely; during the early eighties the National Academy of Sciences published values that gradually decreased from 18% down to 3%. Since the discovery of the ozone hole, there have been no further quantitative predictions published because it was recognized that the existing theory could not cope with the heterogeneous destruction processes that depended more on particulate surface area than on the level of chlorine (25,26).
The theory could not describe ozone variations caused by the (heterogeneous) reactions on particulates (volcanic debris, aerosols, etc.) in the lower stratosphere and therefore was not able to predict the Antarctic ozone hole.. In the upper stratosphere, where only gas-phase (homogeneous) reactions take place, the theory predicts larger changes than are actually observed (27).
There is marked disagreement also among the satellite ozone data (28): In the upper stratosphere, trends seen by the SBUV instrument are negative, while SAGE I and II data show slightly positive trend values; in the lower stratosphere SAGE shows much larger decreases than SBW¬up to 3%-6%/yr in the equatorial region, a result that is difficult to explain from CFC theory.
In the lower stratosphere, recent model calculations and observations indicate that chlorine-based ozone destruction may be rate-limited by the amounts of OH and HO2 radicals (29,30). If borne out, then increasing stratospheric water vapor -¬ as a result of rising tropospheric methane from human activities, such as cattle raising and rice growing ¬- could play a significant role in ozone chemistry (31).
Concerns About Skin Cancer
The major public concern about a possible depletion of ozone comes from the fear that solar UV-B (280-320 nm) radiation reaching the surface will increase, typically by 10%. Yet UV-B intensity increases naturally by about 5000% between pole and equator; there is less ozone traversed when the sun is closer to the zenith (32). Hence a 10% increase at mid-latitudes translates into moving 60 miles (100 km) to the south, hardly a source for health concerns.
There has been, of course, a determined search for a secular increase in UV-B to match the presumed depletion of ozone. But no such trends had been observed (33) until publication in November 1993 of a startling increasing trend, between 1989 and 1993, over Toronto, Canada (34). Close examination, however, revealed that this "smoking gun" was mostly smoke. The authors confused a short-lived increase at the end of their record with a long-term trend (35).
The driving force behind the policy to phase out CFCs has always been the fear of skin cancer, particularly malignant melanoma. The EPA has predicted 3 million additional skin cancer deaths by the year 2075 as a result of ozone depletion (36,37). But unlike basal and squamous cell skin cancers, which are easily cured growths caused by long-term exposure to UV-B, melanoma does not show the same characteristic increase towards lower latitudes (38) (Surprisingly, European data on melanoma incidence show a reverse latitude effect).
It is clear therefore that the rising incidence of melanoma over the past 50 yr cannot be due to any changes in the ozone layer. Non-melanoma (basal cell and squamous cell) skin cancers are clearly linked to chronic exposures to UV-B, as judged from the increasing incidence towards lower latitudes; melanoma exhibits a different epidemiology and often occurs on areas of the body not chronically exposed to the sun. Yet the clear link to solar exposure suggests that changes in lifestyle leading to greater exposure to the sun may be the main cause of melanoma.
A breakthrough in our understanding of the mechanism of melanoma induction came with the experiments of Dr. Richard Setlow and colleagues at the Brookhaven National Laboratory. To measure the action spectrum of UV radiation for melanoma induction, they exposed hybrids of the fish genus Xiphophorus to specific wavelengths in the UV-A and UV-B range. The animals had been back-cross bred to have only one tumor-suppressor gene; inactivation of this gene in a melanoblast or melanocyte then permits the melanoma to develop (39).. The experimenters found that the action spectrum (sensitivity per quantum) was reasonably flat across the UV-B and UV-A regions. Because of the much greater number of UV-A photons, they conclude that 90%-95% of melanomas are caused by UV-A (40).
But UV-A is not absorbed by ozone at all, and therefore melanoma rates would not be affected by changes in stratospheric ozone. This important finding undercuts one of the main reasons for the Montreal Protocol and all subsequent regulations (41).
A final point should be emphasized: If people exposed themselves to sunlight using sunscreens that merely prevent sunburns (produced by UV-B), they will increase their exposure to melanoma-inducing UV-A radiation. While long-term tanning may be somewhat protective, episodic or recreational exposures expose melanocytes to exceptionally high levels of dangerous UV-A (42). The best protection may be clothing or avoiding the sun altogether.
Policy Actions: Dumping the Montreal Protocol
The above discussion demonstrates that the scientific evidence does not support the Montreal Protocol and all subsequent efforts to phase out CFCs, haloes, methyl bromide, carbon tetrachloride, and other important chemicals. Substitutes will surely be found, but much testing will be necessary to establish their safety and effectiveness (43). Then there is the huge cost, estimated at over $200 billion worldwide, of replacing capital equipment that cannot accept the substitutes (44), plus the as yet unquantified additional costs of regulatory uncertainty, as activists attack many CFC substitutes as "ozone-unfriendly" and demand their early phaseout. The American public may not take kindly to those who are imposing a $1000 burden on every household with no obvious benefit. It will be interesting to see whether the new scientific results, and a scrutiny of the older ones, will force also a re-examination of existing policies.
This scrutiny has already begun. California Congressman John Doolittle, in an October 18, 1994 letter to EPA Administrator Carol Browner, suggested that EPA revise its 1987 cost-benefit analysis in light of the new scientific results on melanoma. In reply, EPA seems unwilling to accept Setlow's results until confirmed in a mammalian species, and raised various other objections. In a private communication to me, dated November 29, 1994, Setlow points out that both fish and humans have melanocytes that produce the pigment melanin, whose absorption of a UV-A photon is presumed to lead to DNA damage within the melanocyte cell. In dealing with the other EPA objections, Setlow states that "one cannot use epidemiological data that relate skin cancer to latitude to determine what wavelengths are important in skin cancer induction. If the EPA does not understand this simple point, it should not be involved in cost-benefit analysis."
Might the U.S. withdraw from the Montreal Protocol? "Scientific evidence indicates that CFCs are causing no substantive damage to our atmosphere," Congressman DeLay has stated in introducing his bill. From his frontal assault on the Clean Air Act it is but a short step to call for U.S. withdrawal from the international agreement entered into in 1987, ostensibly to "protect" the global ozone layer (though at the time there was no hard evidence that it needed protecting). Withdrawal from the Protocol and canceling the ban on CFCs may seem improbable at this late stage, however -¬ in view of the physical, political, and emotional investments that have been made. International bureaucrats, federal regulators, environmental zealots, and especially chemical manufacturers are all counting on governments to abolish these chemicals in favor of substitutes that are often unproven or nonexistent.
Yet momentum against Montreal is building. In addition to Representatives DeLay and Doolittle, other members of Congress, on both sides of the aisle, are raising concerns about the precipitous phaseout of CFCs (freons), fire-fighting bromocarbons (halons), and the near-irreplaceable agricultural fumigant methyl bromide. The concerns could sky-rocket when motorists find themselves without airconditioning -¬ short of paying extortionary prices.
Less satisfactory than dumping Montreal, but more likely as a first step, might be a delay in the phaseout date of halocarbons, perhaps returning it to the year 2000. That was the date in effect in 1992 before President Bush advanced the phaseout, stampeded by a misleading NASA press conference, which raised fears of an "ozone hole over Kennebunkport," and a panicky Senate resolution, spearheaded by then-Senator Al Gore. Michigan Democrat John Dingell initiated an inquiry into the press conference that started it all, but has failed to follow through. Perhaps the time has come to complete his investigation into the events of February 1992.
The absence of a sufficient scientific base for the ozone issue is not yet widely recognized, and a halocarbon phaseout is by now well supported by entrenched constituencies, including even some scientists who have staked their reputation and research budgets on this issue. Nevertheless, it is important for the future of scientific inquiry to permit free and open debate on the shortcomings of the CFC theory and the other scientific "facts" that have been used to shore up the Montreal policy. This will take time, however, and some attention by the Congress.
The trend in recent years has been towards stifling debate by various means: denial of research funds to younger academic researchers who hold "unconventional" views; the muzzling of senior scientists in government service; even the dismissal of federal appointees who boldly suggest that theories be validated by measurements. It is in this climate of intimidation and ad hominem attacks that Congress has been vainly trying to get at the facts. Yet with the federal research budget for "global change" now at the level of $2.1 billion a year -¬ topping even the budget of the National Cancer Institute -¬ it should not be too difficult to find the answers.
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