Ozone Depletion

CFC-Ozone Puzzle: Question and Answer

Speakers: F. Sherwood Rowland and Mario J. Molina
Series: The John H. Chafee Memorial Lecture on Science and the Environment
1st National Conference on Science, Policy and the Environment
Date: December 7, 2000
Location: National Academy of Sciences, Washington, DC

Moderated by the Honorable Richard E. Benedick, President, National Council for Science and the Environment, Ambassador (retired), and Battelle Pacific Northwest National Laboratory:

Thank you very much, Sherry and Mario. It is really a remarkable story when you think of how close we came to not solving that problem and what the consequences would have been if it were not for courageous scientists like Sherry Rowland and Mario Molina coming at the right time and the right place, and finding their counterparts in the policy sector, in the Congress, and people like Senator John Chafee and his colleagues that together we were able to effectuate this marvelous success story. It’s truth being stranger than fiction. Mario and Sherry have offered to answer any question from viewing this history, this story. If you want to get something off your chest, this is the time to do it. And you have two Nobel Laureates to answer your questions. It would be good if you would identify yourself.

Question 1

Jonathan Patz, Johns Hopkins School of Public Health: We’ve very concerned about UV obviously, because of health effects. You showed a slide about the temperature sensitivity; showing that, in fact, it’s the cold stratosphere and the ice crystals that the reaction takes place. That’s a problem. I’ve been involved with the IPCC and global warming, and one of the questions that I have is, with global warming trapping the heat in the lower atmosphere, will the subsequent cooling of the stratosphere have any prolonging of the recovery of the ozone?

Rowland: Yes, it’s a possibility. The question that he has asked is, in the existing atmosphere with increasing concentrations of carbon dioxide, the effect is to warm the air at the surface and to cool the air at the lower stratosphere and because chlorine is most efficient at destroying ozone when the temperature is low, then the possibility exists that there will be an increased volume of air that exists at that low temperature.

But if you look closely, you will see that the temperature change is pretty rapid with altitude as you go above and below the region, so it’s going to be hard to cool very much more air. So my own feeling is that probably this will be overwhelmed by the reduction in chlorine from the removal of the CFCs. The other part of it is, that if something happens to put a large amount of surface, it doesn’t have to be ice, if a big volcano goes off, then there may be particles put into the air—that would make chlorine very much more efficient and we might get ozone losses then with that volcano.

This happened after Mount Pinatubo, the volcanic eruption in 1991 in the Philippines. It also happened to a much lesser extent in 1982. Those are the last two big volcanoes, but if there is a really big one that comes in the next 20 years, then there might be an effect.

Question 2

I’m Brian Goodman from Representative Vic Snyder’s office in Arkansas. My questions is, why do you think there is resistance from certain elements of the public in making changes that will protect the ozone layer?

Molina: In terms of protecting the ozone layer, I think the most important fact is that there is this international agreement so you might ask this question historically. But at present, in fact, even the developing nations that are not constrained to stop their production, many of them are moving ahead of schedule. The science is very clear. The International community is behind it.

In terms of the public, my own opinion, perhaps it’s just a lack of information. It’s a different story when you talk about all the other global problems where the science is more complicated. But I think we can use the CFC ozone depletion issue as a brilliant example. It’s a very important precedent that shows us that society can indeed solve these global problems.

Question 3

Mignon Bush Davis, United Nations Association: An enormous amount of chlorine is being used in our drinking water as well as in our swimming pools and is evaporating into the air. Need we be concerned to find alternatives?

Rowland: In order to get to the stratosphere, the chlorine needs to be in a form that will not dissolve in rainwater, won’t interact with sunlight. Hydrogen chloride dissolves in rainwater, and is removed from the atmosphere when it rains. Molecular chlorine (found in swimming pools) photolyzes in an hour. The CFCs, unfortunately, were beautifully designed to be stable and get to the stratosphere, but most other forms of chlorine don’t do that. The ones from your swimming pool won’t make it out of state, let alone to the stratosphere.

Question 4

Henry Tang, The George Washington University. The concentrations of CFCs have actually been decreasing since 1993, but the problem of ozone hole seems to become more and more terrible, especially this year. Can you tell us something about that?

Molina: Yes, the actual amount of chlorine in the stratosphere is rather well measured. It didn’t really decrease until very recently. It is beginning to level off. So it is the production that started really decreasing in those early years. And there are other compounds. We would not, of course, explain all the details, but there are compounds containing bromine whose concentrations are only now beginning to level off. So the fact that we have some years with more ozone depletion, or a larger ozone hole, has to do with the variability of the natural system, the weather, years that are colder. But we do expect that perhaps these coming years, the beginning of the century, are the worst ones from that point of view, and that, slowly, the atmosphere will recover with these natural fluctuations.

Rowland: The measurements that you saw were all made at the surface of the earth and there is a delay period which averages something like five to seven or eight years before there is a sort of equilibrium between the stratospheric chlorine and the tropospheric chlorine. So, if you go through a ground-level maximum in 1994, then 2000 to 2002 is about the time when you would expect the stratosphere to go through a maximum.

Question 5

I’m Ronald Pulliam from the University of Georgia. I know that you have been criticized for speculating, and you may have to speculate on my question, but I will ask it anyway. The question is very simple and largely aimed at Dr. Rowland. What if you had not been at that lecture of James Lovelock? How do you think these events might have unfolded?

Rowland: Well, Mario might have thought of this completely. But actually, a group of us did a calculation, and it was published in Nature in 1996, about what would have happened if Mario had decided that one of the radiochemistry problems was the most interesting. What we think is, the question is, if this situation was just lying there, when would somebody have noticed it? Well, probably that would have been when Farman noticed it. He was doing those measurements and as long as he was doing them, at some point he was going to say, “something crazy is going on here.”

Because we’d had ten years of thinking that it might be chlorine, we had an elimination contest in which the scientists around the world who were trying to measure chlorine in the stratosphere, some of them had succeeded, and they were the ones that were sent to Antarctica. If chlorine hadn’t been the suspect, then we wouldn’t have had the equipment ready to go. We wouldn’t have been able to have people there two years later saying this is what it is. So, probably, we’d say another ten years, and probably the amount of CFCs in the atmosphere would have been up by a factor of two, maybe two-and-onehalf, and we don’t know what that would have done.

Question 6

I’m John Mimikakis and I work for another Sherwood, Sherwood Boehlert, a Representative in Congress from upstate New York, and my question is–I’m not sure exactly how to ask this–but you saw how the science in terms of ozone destruction progressed from hypothesis to become more and more certain, and you saw the parallel with how serious your warnings were taken by the public and the government progress to a greater and greater degree of sincerity and action. I was wondering if you could compare now with climate change, the state of the science and the reaction you see from both the government and the public, and if you can compare that to the progress you saw?

Molina: The science, of course, with the climate change issue, as I mentioned before, is not nearly as certain. Perhaps it’s in the state that we had in the early 1980s. To me there is enough information for society to act, if nothing else, on the basis of some form of a precautionary principle. If nothing else, society should get ready. Let me clarify. The question you are asking is no longer science. It has to do with value judgments and attitudes but we scientists also have opinions, so I think it is very valuable for us to keep those opinions.

We just have to make it clear when is it we are speaking as scientists and when is it that we are expressing values. In my own opinion, when I am asked the question, “Do we have enough evidence that global warming is taking place and consequently should we do something about changing the way we go about consuming energy,” to me, the right question is, “Do we have enough evidence that we are not messing up the system?” It’s just too risky, and so it is imperative that at least we get ready, that at least we get prepared to do these changes, if nothing else because this is an analogy.

We don’t quite have the same situation as the ozone hole yet, but do we do have lots of indications and perhaps you can see that from the latest reports of the scientific groups, (which by the way, the IPCC is analogous to the scientific community reports that we had in the case of ozone depletion) that the consensus is there. We certainly need to worry about those issues.

Rowland: And we depend on people like Representative Boehlert who has been one of the strongest environmental participants, in the sense of trying to control things, so we rely on him in the House of Representatives to carry the ball for this group.

Question 7

Mimikakis continues—The two of you are scientists, you are chemists, and yet you made, I presume, a conscious decision to move out of the laboratory and out of the ivory tower, and into the arena of advocacy. Can you talk to us a little about the thought processes that you went through as you moved out and, obviously, then later in your careers, you’ve moved back and forth.

Rowland: If not us, who? If not now, when?



Environment, N. (2012). CFC-Ozone Puzzle: Question and Answer. Retrieved from http://www.eoearth.org/view/article/51cbf2e07896bb431f6ab10c


To add a comment, please Log In.