Sorry for the hurricane-induced delay in replying, Sam. You've got a major conceptual error in the above paragraph. NOBODY is saying that the entire amount of CFCs leaked is concentrated in the upper atmosphere. Only a very small amount of CFC molecules reach the upper atmosphere (compared to the amount released)! But in the upper atmosphere the CFC molecules are broken down by energetic reactions (cosmic rays, free oxygen), which releases the chlorine and fluorine, which are highly reactive. Cl and F react with ozone, breaking it down. In the normal stratosphere, this has resulted in a slight (5%) ozone concentration reduction. But in the polar vortex, ozone breakdown reactions are catalyzed on polar ice cloud particles, resulting in a much larger decrease in CFC concentration.
Does your Web site refute that scenario? Or does it merely refute erroneous models?
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).
Obviously, one cannot exclude the possibility of a long-term depletion of ozone due to anthropogenic causes, and specifically due to CFCs. But with each cause producing its characteristic "finger prints," proof must rely on a longer time series of more detailed observations (of CFC-specific altitude, latitude, and seasonal dependence). 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 --------------------------------------------------------------------------------