1. Gary Taubes' article ("The Ozone Backlash," Science, June 11, pp 1580-1583) refers to my commentaries as "purporting to shoot holes in the [CFC] theory of ozone depletion." This is hardly necessary; since March 1988 numerous press releases have announced ozone depletion to be "worse than expected" [from the theory]--thus effectively discrediting it.

My comments have pointed to the lack--so far--of convincing observational evidence for long-term ozone depletion:

• The data from ground-based observing stations are reported to be contaminated by UV absorption from atmospheric sulfur dioxide (1).

• The statistical treatment is inadequate, with the derived "trend" strongly dependent on the time interval selected for analysis (2).

• There is also the problem of disentangling any CFC effects from long-term ozone trends of natural origin, correlated with well-recorded trends in sunspot numbers (3).

2. While skeptical about the evidence for depletion, I consider the Antarctic ozone "hole" to be a genuine phenomenon, but have held a somewhat different view about its future. I have speculated (4) that--once there is sufficient chlorine present--the intensity of the hole is mainly controlled by the presence of polar stratospheric clouds (PSCs), and therefore by temperature and humidity rather than just atmospheric CFC concentration. Because the ongoing increase in atmospheric CO2 should gradually lower stratospheric temperatures (as a result of increased radiation loss), and the increase in methane should gradually increase stratospheric water vapor content (5), it is possible that the hole will persist--even if the chlorine concentration falls below the pre-1975 value. We don't know for certain where the chlorine threshold lies; it is possible therefore that an ozone hole could form in the Arctic if climate conditions favor the formation of PSCs there--even in the absence of CFC-produced chlorine (4).

3. Another controversial issue is covered by Taubes and in an adjacent article (6): What are the relative contribu- tions of natural and human sources to stratospheric chlorine? One side claims that the major sources are volcanic (7,8). The other side criticizes these estimates, arguing that nearly all of the chlorine emitted by volcanic and oceanic sources is washed out in the lower atmosphere, "with negligible quantities reaching the stratosphere" (9). A recent paper (10) claims removal of "up to" four orders of magnitude; but Taubes relates that El Chichon increased global stratospheric chlorine by 10 percent. I conclude that reliable statements about the relative effects of natural and human sources should be based on observed trends of stratospheric chlorine rather than on speculative calculations.

Rowland correctly quotes my views on sources of chlorine as of 1988 (11), but does not cite the relevant 1987 papers by Zander et al (12). They found that the total columns of HCl and HF (the major stratospheric reservoir gases for chlorine and fluorine) increased, from 1977 to 1986, at rates of (0.75 + 0.2)% and (8.5 + 1)% per year, respectively. Since HF is ascribed entirely to CFCs, the much lower trend for HCl would lead one to believe that there are large natural sources of stratospheric chlorine that overwhelm the CFC contribution.

This situation changed in 1991, however, when Curtis Rinsland et al, repeating Zander's measurements of solar IR spectra, reported increases for HCl and HF of (5.1 + 0.7)% and (10.9 + 1.1)% per year, respectively, for the period 1977-1990, thus suggesting CFCs as a major source (13). Nevertheless, Rinsland et al conclude--and I tend to agree: "...in contrast to HF, there are significant natural as well as anthropogenic sources of HCl."

According to Taubes, Rowland and others tag their opponents with "selective use of ...scientific papers and an equally discretionary choice of scientific results..." But in his "President's Lecture" Rowland quotes only papers that support his own view on CFC sources; the 1983 paper (14) he cites is in apparent disagreement with Zander's 1987 findings, and has been effectively criticized by Prinn (15).

I note in passing that the Montreal Protocol was signed in November 1987, and that production limits on CFCs were tightened in the period 1987 to 1991, when published scientific data indicated that CFCs were not an important source of stratospheric chlo- rine.

S. Fred Singer
Science & Environmental Policy Project

1. D. DeMuer and H. DeBacker, "Revision of 20 years Dobson Total Ozone Data at Uccle (Belgium): Fictitious Dobson Total Ozone Trends Induced by Sulfur Dioxide Trends," J. Geophys. Res., Vol. 97, pp. 5921-5937, April 20, 1992

2. S. F. Singer, "What Could Be Causing Global Ozone Depletion?" in Climate Impact of Solar Variability (K. H. Schatten and A. Arking, eds.) NASA Publication 3086, 1990

3. J. K. Angell, "On the Relation Between Atmospheric Ozone and Sunspot Number," J. Climate, Vol. 2, pp. 1404-1416 (1989)

4. S. F. Singer, "Does the Antarctic Ozone Hole Have a Future?" Eos (Transact. Am. Geophys. Union) Vol. 69, No. 47, p.1588, Nov. 22, 1988.

5. S. F. Singer, "Stratospheric Water Vapor Increase Due to Human Activities," Nature, Vol. 223, pp. 543-547 (1971)

6. F. S. Rowland, "President's Lecture: The Need for Scientific Communication with the Public," Science, Vol. 260, pp. 1571- 1576 (1993)

7. R. A. Maduro and R. Schauerhammer, The Holes in the Ozone Scare (21st Century Science Associates, Washington, D.C. 1992)

8. D. A. Johnston, Science, Vol. 209, 491 (1980). An even earlier publication is that of J. A. Ryan and N. R. Mukherjee, "Sources of Stratospheric Gaseous Chlorine" Rev. Geophys. Space Phys., Vol. 13, pp. 650-658 (1975).

9. F. S. Rowland, loc. cit., p. 1573

10. A. Tabazadeh and R. P. Turco, "Stratospheric Chlorine Injection by Volcanic Eruptions: HCl Scavenging and Implications for Ozone," Science, Vol. 260, pp. 1082-1086 (1993)

11. F. S. Rowland, loc. cit., p. 1576, Ref. 13: ["...evidence is firming up that volcanoes...contribute substantially to strato- spheric chlorine and thus dilute the effects of CFCs," quoted from S. F. Singer, Natl. Rev. 41, p. 37 (30 June 1989)]

12. R. Zander et al, "Monitoring of the Integrated Column of Hydrogen Fluoride Above the Jungfraujoch Station Since 1977--The HF/HCl Column Ratio," J. Atmos. Chem., Vol. 5, pp. 385-394 (1987); R. Zander et al, "Column Abundance and the Long-Term Trend of Hydrogen Chloride (HCl) Above the Jungfraujoch Station," J. Atmos. Chem., Vol. 5, pp. 395-404 (1987). Incidentally, the reported increasing trend for fluorine clearly demonstrates that CFCs are penetrating into the stratosphere; see also review by F.S. Rowland, "Chlorofluorocarbons, Stratospheric Ozone, and the Antarctic 'Ozone Hole'," in Global Climate Change (S. F. Singer, ed.) Paragon House, New York, 1989

13. C. P. Rinsland, J.S. Levine, A. Goldman, N.D. Sze, M. K. Ko, and D. W. Johnson, "Infrared Measurements of HF and HCl Total Column Abundances Above Kitt Peak 1977-1990," J. Geophys. Res., Vol. 96, D8, pp. 15523-15540, Aug. 20, 1991. W. G. Mankin and M. T. Coffey, "Latitudinal Distributions and Temporal Changes of Stratospheric HCl and HF," J. Geophys. Res., Vol. 88, pp. 10776-10784 (1983). They report increases of 5% and 12% per year, for HCl and HF, resp., based on aircraft observations between 1978 and 1982.

14. R. G. Prinn, "How Have the Atmospheric Concentrations of the Halocarbons Changed?" in The Changing Atmosphere (F. S. Rowland and I. S. A. Isaksen, eds.), pp. 33-48, John Wiley, New York, 1988. Prinn estimates that the results of Mankin and Coffey have a large 1-sigma uncertainty of +4.5% and +5.8 %, resp. Thus the rate of increase of stratospheric chlorine could well be close to zero, in agreement with Zander's 1987 result.

Dear Colleague:

The ozone situation is heating up again--just when we thought that there was nothing more that could be done to modify a string of policies based on uncertain and dubious science. A front page story in the April 15, 1993 Washington Post by science reporter Boyce Rensberger triggered this latest eruption. Quoting well-known environmental activists such as Michael Oppenheimer, it made the point that ozone depletion and the Antarctic ozone hole (AOH) are no longer a problem and would not have led to a catastro- phe in any case.

I commented on the Post article in a Washington Times op-ed, and Candace Crandall replied in the "Letters" column to a self-serving riposte from Oppenheimer. But the big guns came into play in a very long and detailed article by Pamela Zurer in the May 24 issue of Chemical & Engineering News and in a June 11 article in Science by Gary Taubes. Both articles gave the impression that I had dropped my skepticism about ozone depletion and the CFC-ozone theory. I invite your attention to my attached Letters of response, and to a supporting letter by Prof. Henry Linden, who serves on the SEPP advisory board and knows my publications and views.

I have absolutely no objection to phasing out CFCs--provided only that peer-reviewed scientific evidence supports such a policy. But many of us are concerned that CFC policy continues to be made instead on the basis of press release hyperbole. Let me quote some examples:

1. The ozone depletion "threat" actually goes back to the SST controversy more than 20 years ago. The skin cancer issue keeps being brought up, with copious confusion between malignant melanoma (which may depend on UV-A, and thus not on ozone) and the non- melanoma cancers (which do increase at lower latitudes and therefore have some dependence on UV-B intensity). Note however that UV-B increases by 5000 percent, just in going from the pole to the equator. This means that a 10% ozone decline increases UV-B exposure equivalent to moving about 100 miles towards the equator. [The skin cancer scare has now been joined by shrill claims about cataracts, immune system damage (raising the spectre of AIDS), plankton death and other ecological disasters. We even hear stories about blind sheep, etc., in Patagonia. There is no evidence to support such scares.]

2. A more recent example is the March 1988 press conference by the Ozone Trends Panel (OTP), the first to allege the existence of global ozone depletion. The underlying data were never fully published; what amounts to an internal report appeared some two years later. An independent analysis by Hill & Bishop, which showed that the depletion depended on the choice of time interval, appeared only in preprint form and was eliminated from their final published paper in the Journal of Geophysical Research. Evidently, the reported trend is at least partly an artifact of the analysis. My critique of the depletion claim was not accepted for publication because the OTP had not published its work--a real Catch-22. I finally put my objections into the proceedings of a NASA conference, rather than fight the referees. (Cf. enclosed Letters.)

3. The question of the relative contribution of human and natural sources to stratospheric chlorine has been treated cavalierly by both sides in the debate. My view is that it can only be settled by actual observations of long-term trends of stratospheric chlorine--not by calculations. The experimental situation has moved back and forth. Zander's results published in 1987 convinced many of us that natural sources were the most important. Rinsland's results published in 1991 suggested that CFCs were a major source, along with natural sources (see his paper and my Letter to Wash. Post). Will the situation change again?

   I note in passing that the Montreal Protocol was signed in November 1987, and that production limits on CFCs were tightened in the years 1987 to 1991--during a period when published scientific data indicated that CFCs were not an important source of strato- spheric chlorine. (Cf. enclosed review by Prinn and graph by Molina, from a 1988 volume edited by F.S. Rowland!)

4. Why was Zander's 1987 result ignored? The likely answer: Hype about the Antarctic ozone hole (AOH), which grew rapidly from the late 70s to the middle 80s--and was supposed to swallow us all. The AOH momentum proved to be so strong that all scientific evidence for natural sources of chlorine was pushed aside, as international bureaucrats achieved first a "framework convention," then a protocol to limit CFC production, then a production rollback, and finally a complete phaseout. You might recognize this pattern as the paradigm proposed for CO2 by greenhouse warming activists.

5. The final step was the five-year acceleration of the CFC production phaseout, from 2000 to 1996. It came about as the direct result of yet another press conference, the infamous February 3, 1992 NASA announcement of "record" levels of chlorine monoxide in the Arctic stratosphere. NASA scientists misled journalists into declaring an imminent Arctic ozone "hole." Al Gore even castigated Bush for allowing an "ozone hole over Kennebunkport." Within a few days, the Senate had passed a 96-0 resolution and Bush had advanced the phaseout date to December 31, 1995. After the completion of the experiment series on April 30, however, NASA finally admitted that no ozone hole had opened up over the United States. They had known--or should have known--at the time of the Feb. press conference that the ClO peak had passed--as was recently confirmed by the UARS (satellite) results (Nature, April 15, 1993).

Sincerely yours,

S. Fred Singer

• Rowland's well-known position in the CFC-ozone controversy, coupled with his prestige as past president of AAAS, might unduly influence the non-specialist.

• This is a classic case study of scientific data used for the purpose of advocacy.

• Simply, to put the record straight. (For convenience I have numbered the paragraphs of his Letter.)/ul>

  Para 1: Volcanic contribution to stratospheric chlorine Rowland quotes Mankin and Coffey (1983) to support: 1) a general, long-term increase in stratospheric chlorine, and 2) a less than 10% increase after El Chichon (1982). This is doubly wrong. 1) Their reported general increase has been shown by Prinn to be spurious -- in Rowland's own book, no less--and FSR apparently accepts Prinn's critique. 2) Also in this 1988 book--in the same review paper on "How Have the Atmospheric Concentrations of the Halocarbons Changed?"-- Prinn presents the actual data of Mankin and Coffey (cf. attached figure) showing a striking increase in high-latitude chlorine following the El Chichon eruption.

  Finally, Mankin and Coffey themselves do not agree with Rowland in their paper "Increased Stratospheric Hydrogen Chloride in the El Chichon Cloud" (Science 226, pp. 170-172, 1984). But Rowland does not cite this 1984 paper.

  Rowland has studiously avoided mentioning the main conclusion of Zander's (1987) papers, i.e. hardly any increase in stratospher- ic HCl over ten years. (FSR now admits this, but cf. below.) Nor has he mentioned evidence by Molina and by deZafra supporting Zander's result of natural chlorine overwhelming CFC-derived chlorine--again quoted in the same Prinn paper in FSR's book, which exhibits the attached figure (Molina 1985). One sees there clearly an upward trend of HF, proving that CFCs do penetrate into the stratosphere--no argument about that. But the absence of apprecia- ble upward trends of HCl and ClO suggests that the CFC contribution is swamped by other chlorine sources that are constant, i.e. natural.

  For good measure, Rowland distorts my 1988 quote about natural sources (taken from a popular article in National Review-- cf. here ref. 13 of Rowland's presidential address in June 11 Science) by failing to mention that it was in line with the scientific evidence then available.

  Para 2: Are CFCs the "only significant source"?

  Rowland completely misrepresents Rinsland's negative answer to this question; (cf. here my direct quote from Rinsland et al about "significant natural sources").

  Rowland finally quotes Zander (1992), but misleadingly. Unlike Zander's 1987 papers, his 1992 paper does not discuss trends at all but gives a 1985 "snapshot" of the vertical distribution of chlorine and fluorine compounds (from the ATMOS satellite experi- ment). Further, Rowland fails to tell us that Zander, on p. 172 of his 1992 paper, mentions the importance of natural sources for Cl (as opposed to F).

  Para 3: Rainout of natural sources of Cl.

  I have already commented on the folly of relying on the accuracy of calculations of removal by rainfall, when the natural emissions of chlorine exceed those from CFCs by such huge factors. (To render natural sources unimportant requires removal of over 99.99 %.) Therefore I would not put much faith in Rowland's (theoretical) conclusion of "negligible quantities reaching the stratosphere," particularly in view of the evidence from the Mankin-Coffey graph and Gary Taubes' statement in Science (June 11) about El Chichon's contribution.

  Para 4: No comment necessary

  Para 5: Global Ozone Depletion

  DeMuer and DeBacker, as careful scientists, talk first only about the SO2 corrections necessary for their own data. But elsewhere in their paper, and in their Abstract, they explain why their conclusion-- that the reported depletion is "fictitious"-- may hold throughout the northern hemisphere. They also criticize the "massaging" of data from the Dobson ozone network used by the OTP.

  Para 6: Temperature trends and heterogeneous reactions

  Rowland focuses on short-term temperature changes (i.e., over weeks), choosing to misunderstand my clearly stated point that both stratospheric temperature and humidity should gradually change (i.e., over years)--the former confirmed recently by the satellite observations of Christy and Spencer, the latter point suggested in my 1971 Nature paper (and restated by Blake and Rowland in Science 239, 1129, 1988).

  I was surprised to learn that it was Solomon (1986) who postulated heterogeneous reactions. That notion had been around for about 20 years but was avoided by theorists as being too diffi- cult to handle. (Cf. here, e.g., the attached 1975 exchange of letters with Cicerone.)

  Rowland quotes only what supports his position: Exactly my point!

  Those who want an insight into Rowland's general world view should study the attached "Morelia Declaration," of which he is signatory #2.

  One could of course go on and mention the economic impact of precipitous CFC removal, especially on the poor throughout the world; but this would take us beyond science. (See here the op-ed "Icons collapse, yet policy marches on" in the Washington Times, April 21, 1993.)