Guy Brasseur

Brysse:

This is Keynyn Brysse interviewing Guy Brasseur on June 25, 2009. Okay, so I’m really just interested in knowing everything you can tell me about your work to do with ozone depletion, science ozone depletion assessments. I’m interested in the role of heterogeneous chemistry, that’s one thing in particular, because it seems to me it was something that everybody was aware of but nobody really seriously investigated until the Antarctic ozone hole was discovered, and then it sort of became recognized as important again. I’m interested in that chronology.

Brasseur:

Okay, first of all about me. I started my research on the ozone in 1971. At that time, ozone was still a scientific problem, not necessarily a political problem or an environmental problem. It was becoming in fact an environmental and political problem because the U.S. had announced that they would produce a supersonic transport. At the same time, France and England had decided to build Concord, so the idea was, based on a paper by Hal Johnston and knowing what was really fundamental science with what Paul Crutzen did, that nitrogen oxide could destroy ozone. Johnston found out or indicated that half of the ozone layer could be destroyed by the supersonic aircraft. At that time we knew very little about the stratosphere, and in fact the nitrogen oxide had really never been measured, seriously at least, in the stratosphere. We didn’t even know there was nitrogen oxide in the stratosphere — we didn’t know much about the stratosphere. We were calling the stratosphere the “ignorosphere” at that time. So the Department of Transportation assembled a group of 500 scientists, supported it and put money on it, and a big program, that Climatic Impact Assessment Program of the Department of Transportation study, CIAP, and came to some conclusion after three or four years. There was a lot of work involved. It was interesting because it was an assessment in a way, but it was an assessment made at the time when knowledge didn’t exist. So, it suddenly became a boost for fundamental research on the stratosphere. We didn’t know much about the dynamics of the stratosphere. We didn’t know much about the chemistry of the stratosphere. We didn’t know much about the ozone layer about how it could be destroyed. We knew nothing about the halogen and the CFCs at that time. The major accomplishment of this assessment was the science increased tremendously. I was involved in modeling. At that time, we were operating with one-dimensional models that were just providing vertical distribution of chemical compounds. We were moving to a stage where we found out that well, we need two-dimensional models, because what happens at the equator, in the tropics, in the mid-latitude or in the polar region was different — insulation is different, the temperature is different, so we were just starting developing our two-dimensional models. This was a boost also. It gave us a good reason for doing that. CIAP came with some conclusions. They were probably quantitatively wrong because they were still missing knowledge, in particular on the chemistry of ozone in the upper troposphere and lower stratosphere. So, later on some people in the lab showed that some reactions were much faster than we had believed. Finally, the problem of the ozone depletion was not as severe as we had anticipated or was anticipated by the CIAP report. Science continued. Then five years later, and just because there was so much interest in the stratosphere, the problem of the CFC was raised by Molina and Rowland, then Cicerone and Stolarski have shown that chlorine could also deplete ozone. The problem of ozone was suddenly put on the table because of aircraft. You know, you send rockets, so NASA got involved: maybe if we send rockets we will also destroy the ozone. People started looking at that, and rockets were releasing chlorine, so that was the idea. Then the CFC issue came. That was in the mid ’70s. Then, the problem kind of was still going on but died off a bit, not so much activity. I was still improving the models and moving even to three-dimensional models and so on…

Brysse:

In the ’70s, 3D models?

Brasseur:

No, I was in Belgium at that time. We were really fully using our two-dimensional in the ’70s. But in the early ’80s, we started, or maybe mid ’80s, I have to look carefully. [Looks through papers for reference.] We started adding chemistry to general calculation models. In fact some work on that was going on at MIT and other places, but we were involved in Europe on these sorts of things also. Give me a minute, I might find it. [Looks through papers.] No I don’t think I can give it to you, but I could look more. Then, you’re talking about heterogeneous chemistry. When the ozone hole was discovered in 1985, the paper by Farman and Rowland, but in ’84 there was a meeting at Greece at Thessaloniki, and Chubachi from the Meteorological Research Institute in Tsukuba, Japan, had shown big depletion at the Japanese station of Showa, but he didn’t know why. Nobody really paid attention because it was one measurement, or at least several measurements made at one station. There was no explanation, and I don’t think the author himself had realized that there was a major problem coming up. He just said, “Well, I don’t know. I see a big depletion at our station and I don’t know why.” Then Farman and these people later published this paper in Nature that basically attributed the ozone hole to chlorine, but not a good explanation. I’m pretty sure it’s not correct. I remember that around that time, maybe before the paper by Farman was published, there was a meeting in Germany…

Brysse:

The Feldafing meeting?

Brasseur:

Yes, you know about it, where Rowland gave a talk and said, “We have those reservoirs. The question is, are they stable? Could they react themselves and release chlorine to gas phase reactions?” He had made some measurements in the lab and he had said, “Well, no. I don’t think a reaction between ClO and O₂ and HCl is of any danger because we measured it in the lab and it’s very slow in the gas phase.” Susan Solomon was in the audience, and she listened to that. Then when the paper by Farman came out she started thinking about it. She said, “Well, what if these reactions that Rowland believes are slow in the gas phase, what if they were accelerated in the presence of the particles that exist there,” and that the Langley people, McCormick and others, had been reporting also probably at that conference. She put those two pieces of information together: the possibility of the reactions between reservoirs, the presence of those PSCs that had been reported by McCormick. She said, “Well, what if this reaction was accelerated on the surface? What if we had a heterogeneous reaction?” She put that in a 2D model and found that, oh gosh, you could destroy ozone pretty, pretty rapidly, in months. That’s what’s happening.

Brysse:

This is fantastic. This is the clearest explanation of chronology I have gotten yet, thank you.

Brasseur:

Now, Susan Solomon did not have the catalytic distraction mechanism right in her model. She was using basically the chemistry that we knew at that time; she was just adding fake, if you want, reaction. Not fake, but she was using those reactions like ClO and O₂ + HCl. She said, “If we have clouds, let’s accelerate it and see what happens. I don’t know the mechanism, I don’t know exactly what’s happening, but we need to assume that the region that’s sufficiently caught where the PSCs are growing, this reaction is, for whatever reason, accelerating faster and releasing a lot of chlorine.” Then I could have the ozone hole. But she didn’t have the mechanism that really was destroying ozone. She had some, but not the major one that was still unknown. It is Molina and his wife, Molina and Molina, the first Molina is his wife…

Brysse:

This is the ClO dimer thing?

Brasseur:

This is the ClO dimer. They came up with that, and this reaction was then added in all the models, and then, boom, you could really destroy ozone rapidly. So Susan had half of the mechanism, and a good half, more than a half, because she said it’s due to the CFCs. We think that maybe on the clouds the reactions between reservoirs are accelerated due to a [???] mechanism. She had a mechanism for destroying ozone in the lower atmosphere that involved HOCl, but she didn’t have the mechanism that involved the dimer. That came a bit later from laboratory work, which shows, by the way, the importance of laboratory work in all that. Okay, now, when all that was said it was very simple to create an ozone hole in a model. You could say, “If the temperature is below a certain threshold, I release reactive chlorine from my reservoir and I destroy ozone.” The problem was what happens exactly. What are those particles? What are those PSCs? So a number of people started looking at that in the laboratory, in the atmosphere, and they were doing a lot of activities on those particles. One of the issues was that they were reporting particles at a temperature above the freezing point. You couldn’t see those particles but you could detect them because they were very, very tiny particles. You could detect them by measurements, I forget exactly the technology that was used, but they were not visible. They started realizing that there were different types of particles, what they call type I and type II. When you use type I and type II it means you don’t know exactly what it is. So type II I believe were the ice particles, and the type I particles basically included tiny liquid particles including nitric acids. So people started to better understand what was happening. But, the question was, is this theory reasonable? Is it a good theory? Can we trust it? There were other theories about the ozone that came out before any observation was made. Look, the dynamicists said, “Well, if for some reason you have some change in the dynamics, you could have upwelling just over these regions.” Then you bring in some air from the troposphere, which is poor in ozone, from the dynamical point of view what seems to happen is that somehow you have intrusion of air from the troposphere that comes in. If ozone is a trace — forget about the chemistry — you know, you have low ozone in the troposphere. This air is moving up. There might be a reverse in the circulation for whatever reason, so they started playing with their model to see if they could create that, and so on. A third theory was, well, we’ve known for a long time that if energetic particles coming from the space or from the sun penetrate into the upper atmosphere, they can produce nitrogen oxide. That had been known to happen. The nitrogen oxide can come down in the wintertime and it can destroy ozone, because we knew from Paul Crutzen that nitrogen oxide was a big destroyer of ozone. We were just in a period where the nitrogen oxide is very important, and maybe the chlorine, but nobody had any explanation of the chlorine. So you had those three theories. And they went to Antarctica; NASA went to Antarctica with university people. They made the measurements and they concluded that the right theory was the chlorine theory.

Brysse:

This was the AAOE right, not the NOZE expeditions?

Brasseur:

It was one of these NASA Antarctic expeditions, NOHR [NOAA?] Antarctic Expeditions. So this is like ’86 and ’87.

Brysse:

NOZE I was ’86. NOZE II and AAOE happened at the same time in ’87.

Brasseur:

Yeah, but the first experiment probably in ’86 concluded that it was due to the chlorine. Now, why? You can imagine. They could measure, for example, is the air coming from below? Well, they would measure that if the air is coming from below, you would have an increase of the chemical compounds that are very abundant in the troposphere. You didn’t see that. If the nitrogen oxide was coming from above, it should destroy ozone all the way down, not just between 20 and 25 kilometers. Of course, the reasoning of Susan Solomon was that the observation showed that ozone depletion was taking place up to 26 kilometers, not above. Not at 27 or 28, at 26 maximum. So something must happen there. What’s happening at 26? Well below 26 you have PSCs, above 26 you don’t have PSCs, so the PSCs must be involved somehow. That’s what she said. Then she said, “If the PSCs are involved, and the chlorine there is supposed to be under the reservoir, those PSCs must have destroyed the reservoir.” So it was as simple as that but you have to think about it. Okay, so I was involved in all that, since you’re asking me about myself. We did modeling, and we put the chemistry in the ozone and we did prediction and assessment and involving all this NASA and WMO and UNEP assessment.

Brysse:

Right. With the computer models, if the Antarctic ozone hole hadn’t been discovered for say another five years, but the models were continuing to get more sophisticated and incorporating more and more stuff, would you have seen something like the Antarctic ozone hole or something weird going on at the Poles?

Brasseur:

I don’t believe it, but you never know. I don’t believe it, because the modeling community knew about zero of heterogeneous chemistry. Maybe some chemist would have come and said, “You know I just did an experiment the other day, and I put ClO and O2 and HCl in my reservoir and I see that they are destroyed by the walls of the vessel. So these things must react on the surface of the vessels. I remember for example that at a very early stage we were talking about the CFCs. People were looking if the CFCs themselves could be destroyed on particles of dust from the desert. And people said, “No, it’s not destroyed.” Because we were looking for ways to destroy the CFC in the troposphere, so dust maybe. You might have people work on dust or you might say, “Oh, maybe those things were destroyed on the dust.” They might not think about the PSCs but on particles. Then maybe some people would check that in their model, but I don’t think there would have been a real discovery of the ozone hole from modeling without observations.

Brysse:

That’s good to know. Was there some simulation of the polar vortex though, or is that something else? That’s something that would only show up in a 3D model, or would you see something…

Brasseur:

Yes, you need a 3D model, and in the observation also, so we knew there was a vortex. We knew that this vortex was isolating the region from external influences. That helps, of course, in the explanation of the chlorine related cause because, you know, how come you have an ozone — I mean Farman said, “We see an ozone hole here. In our other station we don’t see it.” So, how come? Well, it has to be confined. Now, the PSCs were confined because the vortex was where the temperature is cold. Then there were a lot of studies on the dynamical barriers —you know, is that a real, complete 100% barrier or are there leaks? So the dynamicists started to study the vortex in much more detail, and in fact what you see is that there are small-scale processes that the models do not capture because the resolution is not good enough. You see the vortex kind of peeling off parcels of air. You can bring sometimes a blot of low-ozone air over Europe or over the U.S. So they were talking about those mini holes, thinking maybe these holes could happen anywhere. Could it happen where I live? Well, we’ve seen mini holes, but in fact these were kind of air that detached from the vortex somehow. So the vortex is not completely, 100% a barrier, but it’s a pretty strong one. There are other barriers, barriers between the tropics and the mid-latitude, for example. Then these barriers, they move. Suddenly you can have a wave like a tongue, and then it gets detached. That’s how it transferred. Now, what do the models represent? That’s another issue.

Brysse:

Great. Let’s see, what else.

Brasseur:

Yeah, why don’t you go to another question we don’t have to follow that completely.

Brysse:

I’m really interested in your work on scientific assessments and how you got involved in writing that 2007 thing that’s sort of assessing assessments.

Brasseur:

Okay, yeah. So the modeling community, in the beginning, was relatively small. We had like ten modelists in the world. In fact, Europe was a little bit ahead of the U.S. at the very beginning of all these problems. With American colleagues we were working on this, we were developing these models. Every time there was an assessment they needed the modelers, so we would go. These assessments started really with NASA. NASA was doing assessments, usually somewhere on the East Coast, so we would go there and we would write part of it and we would show our results. They would be added to the graphs that were prepared and all that. I’ve done that several times, and then it became more international with WMO and UNEP involved. I was lead author on one chapter in the ’80s, and then I didn’t do the next one and again did that — so I’ve been linked to these kind of assessments pretty often. Then I was involved in the last IPCC also as a lead author for Chapter 7 of working group one report. So the academy was asked, basically, at one point by CCSP, do you know what CCSP is? [No.] Okay, I forget exactly what it means, but it is the follow-up of the Global Change Research Program in the U.S. So, CCSP is something that the Bush administration put together to deal and not deal with climate change. They had decided to do an assessment in the U.S.

Brysse:

When was this?

Brasseur:

There was an assessment on the U.S. probably in the early ’90s, then CCSP — in fact there was a legal obligation to do an assessment every five years. It could be four, it could be six, I don’t remember. But is legal; it’s a law in the U.S. law. So under Clinton an assessment was made, and then Bush came into power and he changed everything. The Global Change Research Program, which was basically the place where all the U.S. agencies were coming together to look at the Global Change Climate Change Program, that was changing to something called CCSP. It was attached to the Department of Commerce. It was headed by Dr. Mahoney, who had been appointed by the administration and had been a specialist with acid rain. I think he tried to do his best, but he was sick and it was a difficult situation. So the second assessment that was expected was delayed, and the Bush administration was not providing the support, the finances to do it. So, what they decided also to do is rather than doing an integrated assessment, one volume, they decided to spread it into 20 or 21 small assessments (you should check if it’s 21, but I think its 21). 21 groups then were formed, and this report didn’t come out, and then few came out, but they were much behind the deadline. The staff of CCSP, not Mahoney because then he resigned his seat, but other people asked the Academy to look at other assessments, particularly international assessments, and see…

Brysse:

Sorry, that’s the National Academy of Sciences in the U.S.?

Brasseur:

Yes. It was asked and paid good money to do it by CCSP to look at other assessments made in the world and to see if there were any good ideas or recommendations that we could make for them to improve their approaches to assessments. I was asked by the Academy to chair that committee. Why, you can ask them.

Brysse:

Were you here by then?

Brasseur:

Yes. So the Academy assembled a group of experts and people. You had scientists, you had people from NGOs, you had people from even the private sector, the insurance companies and all these kind of things. So, we started thinking seriously about it, and we invited basically a number of people to brief us. We had scholars including university people, we had people who had been involved in assessments like Bob Watson, we had people who had been involved in more regional assessments as opposed to international assessments. People were asking us, “Do an assessment for me.” We had people from Congress, people from the White House, and I cannot remember exactly, but we had also users of assessments, or potential users of assessments. I always remember that we had a person who was in charge of providing water to the city of Phoenix, Arizona. So the city is growing like hell, they need more water in the desert. So this person had to really say, “What should I do to get more water? What are the projections?” So we asked him, we said, “You’re going to be affected by climate change. Are you getting any information from those assessments, like IPCC?” And he said, “No, nothing. Because IPCC is telling me the temperature of the U.S. will go up, but I need to know the temperature in Phoenix, Arizona, or more specific things.” So there was a bit of a limit of these assessments that are sometimes produced by scientists who believe they can answer all the questions but they have no idea what the real questions for the practitioners are. This is what the report was doing, so we made like 50 recommendations.

Brysse:

This sounds like the reasoning behind your recommendation to have nested assessments, regional, and then national and then international.

Brasseur:

Right, that’s right. So you saw the report? [Yes.] You see that we looked at eight or nine assessments, including the ozone assessment, but we also looked at basically the Arctic assessment, we looked at IPCC. We looked at practice that the Germans had been using. I don’t know how useful they will be, but there was a lot of discussion about how close should the policymakers and the scientists come? Should there be a firewall, a full firewall, a partial firewall? It’s a difficult question because you don’t want to be influenced too much by the people expect a response and tell you, “I hope you say this.” On the other hand, if you put a complete firewall, you don’t necessarily understand what questions they are after. The rules have to be clearly stated so that people understand exactly what the rules are. We need to know what the problems are that industry wants us to have an answer for or policymakers and so on. We don’t want them to be there and say, “Okay, we’re going to write a chapter for you.” Now in IPCC there’s a strong influence of the policymakers, because, for example, the last meeting is the discussion of the executive committee by the representative of the Nations, who are politicians, and they start arguing on every sentence that the scientists wrote. So the scientists need to fight that and say, “No, that’s not what we said. Maybe we didn’t say it clearly enough, maybe we should improve the way we say it; maybe we should be more explicit. But don’t change it.” And of course the discussion is always on both aspects. If you take the ozone assessments, there was very little connection with policymakers. It was really an exercise made by the scientists and then the report would be sent to the parties of the Montreal Protocol and then they would look at it.

Brysse:

That’s a really important point. My colleague Jessica, who’s looking at the IPCC, and I are coauthoring a paper right now about uncertainty has been handled in assessments, so she’s doing a case study on IPCC and I’m trying to do ozone. I’m finding it really hard, because although I’m sure uncertainty was something that a lot of people were thinking about and then it got discussed in meetings, you don’t really find explicit discussions of it in the assessment.

Brasseur:

You should also understand that the science of assessment or the practice of assessment has evolved dramatically over the years. The early assessments were really almost scientific papers, written by scientists who said, “Well, this might be of interest to the policymakers.” The IPCC is so much linked to policy that the scientists cannot escape answering some questions that are clearly stated. One of them is: how likely is this prediction? What is the error on that prediction? What is the error bar? Now, at the time of ozone, nobody was discussing this. Nobody was saying, “What is your error bar?” on an ozone prediction, because we didn’t even know. We would say, well my model provides this value. I don’t know what the error is! We could do sensitivity tests and see what happens if we change this, and this, and this, but there was no real discussion. In the IPCC there are even rules, codes, and vocabulary: very likely, not very likely. All of that is quantified. That didn’t exist at the time, in the ozone report.

Brysse:

Do you think that’s a helpful thing? Is the IPCC assessment better because it has that strict quantification?

Brasseur:

Yes. I think it’s important because it provides useful information to policymakers. Here, the difficulty is that if you make a prediction — For example, IPCC had 24 advanced models. They all give something slightly different. So you ask yourself why. Those ones are all different and you cannot say, “Okay this is wrong in this model, this is right in this model. Let’s take this.” It’s very complicated. There’s internal reliability in the system, the uncertainty on the emissions in the future, because it depends on the evolution of society and the economy. So you do an ensemble, basically, of predictions based on all these parameters, and then you provide kind of a distribution function. This distribution, then, it’s like when you hear the weather forecast they just say there’s a 60% chance that you’ll have thunderstorms. That tells you something. If you see there is 10%, it’s different. But nobody can say exactly if there will be thunderstorms or not. What they do, they take ten different models or whatever, and they say six of them show thunderstorms, therefore there’s a 60% chance. That’s how they do it. That’s how the climate community is doing it, also.

Brysse:

So that’s a good way of handling the random error from the different models, but what if there’s systematic error built into all the models?

Brasseur:

Yeah, you must assume first of all that all these models are independent to do this, which is not the case. Sometimes you use the same code. Sometimes you copy a neighbor, you say, “Oh, this is how he does it. Maybe I should do it this way too.” So, yeah those models are not completely independent. You might have systematic errors. If you don’t put the CFCs in the model because you don’t know they exist, you make a prediction, you might have the best distribution function, but maybe the solution is far away because you forget something. That’s science; that’s the way science works. There are a lot of things we don’t know, and we have to take measures and come to a solution in a world that’s not perfectly known. Something they call science. There are a lot of things we don’t know but we still have doctors who try to cure us.

Brysse:

Right. And there’s really no way of including things you truly just don’t know. What if there was something, like heterogeneous chemistry was for a while, where sort of in the back of your mind you think maybe it could be important somehow, but at the moment they’re not in the models. How would you put that in an assessment?

Brasseur:

If there is something that we know, I don’t think heterogeneous chemistry really knew much about it, because it could be known in another community.

Brysse:

Yeah, maybe not to the modelers.

Brasseur:

Right. But if there is something that we believe could happen, we do sensitivity tests. We might believe in one reaction that was measured by three groups. One group showed a very high value, five groups show a very low value. Who knows, you say, “Maybe this Army guy might be right, so we will take his value and we will do a new simulation. “ Then we’ll come back and we’ll say, “Look, if this is right, then this is a consequence.” So that’s sensitivity. We do that a lot. That helps us to look at limits a bit, that helps us also understanding the sensitivity of the system to a not very well known parameter.

Brysse:

Right, and that stuff makes it into the assessment chapter?

Brasseur:

It could go if something interesting is coming out of this, yes.

Brysse:

Like if it turns out to have serious climate consequences?

Brasseur:

Yeah, well okay, I’ll give you an example. Somebody in Germany recently, no in the U.S. has measured the ClO + ClO reaction and found that it was much lower. It had an explanation why the others found it. So suddenly the modelists were going, “Aha, maybe this reaction is much lower than we anticipated. Let’s put the low value in our model. We cannot produce ozone formula.” Now it becomes a very serious question, because maybe if this guy who made the measurements is right, we have been completely wrong in explaining the ozone hole. At least we know that if this guy is right, we cannot predict the ozone hole with our model and the current understanding of the chemistry in the atmosphere. So there are two possibilities: either the guy wrong or he is right. So quickly, other groups need to check and re-do his experiment. Or he’s right, and we have a much more serious problem because we don’t understand the ozone hole. It might not be coming from the CFCs, or if it’s coming from the CFC then there’s a different mechanism and all of our predictions are wrong. Suddenly you kind of get a heart attack almost and say, “Everything we have done the last 20 years is probably…” and that can happen. What happened, of course in this case, some people redid the experiment and found that something was wrong in the experiment. His measurements were wrong. Good, we didn’t waste our time.

Brysse:

In this example you don’t really need the involvement of the people who go out and measure the real world because you all already know that there is an ozone hole out there. If it was a different example with something that you didn’t already know for sure was out there, are all the people who do the lab work and the models and observations closely involved?

Brasseur:

It’s very, very important to have three categories of scientists talking to each other. In an institution like NCAR here we have experimentalists, we have modelists, we have lab people. For example, when I put a chemical scheme in my model, and you know I need hundreds of reactions. I’m a modelist; I am not a chemist. I need a chemist to check it. A chemist might say, “This reaction is really slow you shouldn’t put it in, but you forgot this reaction that could change it.” So when we build the models we get experimental people because they know the chemistry very well. Then every model needs to be evaluated and every observation needs to be understood, so the connection between modelers and observationalists is also very strong. So, you need the three of them. Sometimes there is a bit of a tendency to forget the lab people; you need them, they’re important. They also work with the experimentalists of course because they have experience about how the system works. Of course it works in their vessel, but then you have to translate it to how it works in the atmosphere.

Brysse:

I just realized something interesting. You said that in general the modeling community didn’t really know about heterogeneous chemistry, but Susan Solomon is a modeler isn’t she, and she was one of the first people to…?

Brasseur:

No, she didn’t know much about it either. She thought about it and she said, “I see the ozone depletion occurring where the PSCs are present. So I’m concluding that the PSCs can or must destroy — that’s the only way you can get active chlorine, you have to destroy somehow those reservoirs. So maybe the reaction that Rowland proposed in the gas phase as being slow might become fast on the surface of particles.” But nobody had ever measured or seen that in the lab. That triggered a lot of research in the lab by chemists to understand heterogeneous chemistry. She didn’t know heterogeneous chemistry. She knew it exists, but she had no idea that it would affect the problem. She really made a reasonable assumption, “Oh, it’s only happening with the PSCs so it must be linked with the PSCs. So what could it be? Maybe a reaction on the surface or a reaction involving the PSC?” It really opened a new field of atmospheric chemistry.

Brysse:

Do you know when people found out about PSCs? I’ve gotten different answers about stratospheric aerosols in general from people. Rowland says he didn’t know about them at all. He knew about heterogeneous chemistry but he didn’t think there were any surfaces in the stratosphere where ozone depletion was happening. Crutzen knew about the Junge layer because it was his predecessor who named it, but he didn’t think that it was high enough or that there were enough particles for it to really matter. Then of course Joe Farman knew about PSCs because he had worked in Antarctica since the 1950s, but apparently nobody else really knew about PSCs until the early 1980s.

Brasseur:

Well the PSCs, they had another name, I think nacreous clouds and had been observed in the 1800s. People, if they were going to Poles, they would see that when the sun was below the horizon, those clouds were beautiful, but at sunlight we could determine that they were higher because the sun already went below the horizon. Those clouds were known and people were taking pictures of them, but nobody ever was linking that to chemistry. This was like a beautiful meteorological thing that has been known for a very, very long time. I think it’s really Pat McCormick and the people at Langley who started looking at particles. They had these high peaks of polar stratospheric clouds. Independently of the ozone or the CFC problem, they reported those.

Brysse:

Was it Adrian Tuck? Dave Fahey yesterday morning, showed me a NASA report from 1983 and I think Pat McCormick was the lead author. That’s the one you’re talking about?

Brasseur:

Yes, but there were papers also. You know, I have a presentation on the history of ozone research. I can show you a few things. I don’t like to give it away yet because I want to write a paper on that. I have been giving a lot of presentations starting at the discovery of ozone. I have a few things that are interesting. [Turns on computer.] Okay, I have to find it now. If you want me to come to your group one day on the ozone history I have been giving several talks, and I’ve been doing a lot of research on the Internet, and I’m planning to write a book on it, but probably a relatively popular book with a lot of pictures. It takes a bit of time; it’s a huge file with a lot of pictures. You know, I have all of these old staff who discovered oxygen and so on, then the discovery of the stratosphere, and the discovery of ozone. And Shine, it’s interesting, he says in 1840, you know he has a principle which is in German. So I made this proposal to call this principle also, so it wasn’t even a gas at the time. But let me go to the more recent things.

Brysse:

Something that I think a lot of lay people find confusing nowadays is you know stratospheric ozone is good, tropospheric ozone is bad. You can’t simply move it somehow from the troposphere to the stratosphere.

Brasseur:

Okay, it’s right here. So here’s with Farman et al with the Dobson instrument. This is the original observation. So you can see the minimum, and it’s 11 days spring ozone Halley. You can see at 57 going down, so this is that paper at the station. So this is the paper. Then Shanklin here wrote an email to Mr. Blockson [?], “Our base at [???] is currently reporting a rather low value of ozone. (Well if you’re at 200 Dobson you need to discuss it, below then you’re on the average value. It would be interesting to know if this is confirmed by satellite data.”

Brysse:

Is this the letter that they never answered?

Brasseur:

Well they did give an answer, actually. If so it’s possibly connected with the [???] eruption. There is some evidence that an increased aerosol load has been detected by [???] measurements, and blah blah blah.

Brysse:

I talked to Jonathan Shanklin; I think he told me about this letter and either they didn’t respond promptly…

Brasseur:

Well yeah, here’s the response, October 10 of ’83. “Your ozone data has been forwarded to Mr. Holland for obligation directoratively. Our group is no longer involved in this activity. Good bye.” [Looks through document.] Then you have a cycle and then another cycle, the Molina cycle. So you have to recognize…

Brysse:

Can I ask you a question about the ClO cycle? What Molina discovered was that it breaks into ClO and ClO — no he discovered it breaks into that and not ClO and ClO.

Brasseur:

That’s important because it has to be. If it was ClO and ClO nothing would happen, so that’s the key. Because what happens is if it breaks into ClO…

Brysse:

It just stays like that.

Brasseur:

Ye. But it breaks into Cl which reacts also. There’s some stuff that’s interesting here. This is the modeling. Yeah, I don’t think I have it here but there were all these discussions about the impact of aircraft that was very interesting because they had meetings here in Boulder, and they were showing that if anything here to the water, so the hydrogen, because they didn’t know the work of Crutzen at that time. So, I have it somewhere else and a different version of this. Judas London made some calculation here, and he had four reactions related to nitrogen. He said that nitrogen is doing nothing. So Johnston said, “Well if you only have four reactions then you’re missing something, so your model is wrong.” But if you’re interested one day I could stop by for your group or something. I have several version of that talk on the history of ozone research.

Brysse:

That would be really great. I’ll talk to Michael and see if we can bring you out for that.

Brasseur:

I mean Princeton is on the way to Europe, or from Europe. So what are the other questions you have?

Brysse:

Well, another question about that 2007 about assessments. I really like the case study about ozone because it goes along with the ideas that I’ve started having. Like you said that they didn’t really do much to explicitly handle uncertainty, but the one exception to that is the EESC.

Brasseur:

This is the…?

Brysse:

Effective equivalent stratospheric chlorine.

Brasseur:

Oh yeah, and I don’t know much about this because this was a time when I got less involved in the ozone issue. Yeah, they were trying to get numbers. At one point it appeared that things needed to be better quantified instead of just saying, “Well we’re going to get a depletion here,” also because of the need for the industry to know what to do. They decided to put a number of — The one I remember most is the ozone depletion potential, saying each compound needs to have an ozone depletion potential, and it had also global warming potential later on, but it had an ozone depletion potential. This was then made so that you could say what a good product for the environment is and what a bad product is. Of course the way you calculated ozone depletion potential was a bit of a controversy, but there is of course more and more an idea that we have to give a simple number to the policymakers. These numbers might have to be revised sometime when we know more about it, but don’t tell them a very complicated story. Give them a number and then they say this product is bad.

Brysse:

Okay, so why was there a shift from the ODP to the chlorine loading potential and then the EESC?

Brasseur:

I don’t know exactly why that was. You should ask people — I was not so much involved in this. People like Fahey could be better in understanding that.

Brysse:

Yeah, and I have gotten some great answers; I’ve just been asking everybody.

Brasseur:

No, I’m probably not the right person to ask that.

Brysse:

All right. We’ve talked about sort of the state of computer modeling. Oh, here’s a question that Michael’s really interested in, this last one. I will just let you read it maybe.

Brasseur:

How would you describe the current state of computer modeling with respect to ozone depletion studies? Do models ever reach a point where they are done or good enough? And one can start improving them and just use them. Well, the models are nothing else than a representation of what we know. So the model should be really considered with that idea in mind. It’s not an absolute tool. It’s a tool that takes all the information that’s available, put in an equation or a parameterization form, links it with other processes, and then does basically what your brain would do. Just anticipate what’s going to happen with a situation, but does it for very complex and multiple stresses and processes. So if no more information shows up and we think that everything that we need to know is in the model, then we can believe that model is just good enough to be used. Now, this being said, at the moment there is an evaluation of the models going on in relation to chemistry and climate interaction in the stratosphere. One of the questions today was how will climate change affect ozone recovery. Now, the model that we have been using to do all these predictions we’re assuming the climate’s not changing. The CO2 will remain constant and everything will remain constant. Climate change was not an issue. Those models were not climate sensitive. You were fixing a number of things, you were not calculating climate. You were just assuming that climate is the same. And then suddenly comes a new question: how is climate going to affect the ozone recovery? And you say, “Oh, I’ve got to address that with my model because my model is not dealing with climate. I don’t have a climate model.” So we need now to go and talk to the people who do climate modeling and say, “Could you work with us? Could we put our chemistry of the stratosphere in your model, or can we at least get information about how the climate will change and see how it will affect our chemistry?” So suddenly we started building chemistry climate models, mostly for the stratosphere but also for the troposphere and for aerosols. At the moment I don’t know a number of models are running and SPARK, which is the international organization for climate and stratosphere, is really running an experiment under…it’s called CC validation organization. So they’re trying to run a number of cases where now they move from offline models, otherwise models in which you provide all the dynamics in the climate, to models that couple with the climate models, so online. What you see of course is that these models are very complex. The more complex they get, the more diverse they are, the more diverse answers they get. So the big issue now is not to develop models further but to understand why they give different answers. Because you have multi-model ensemble runs, you start again to have a probability distribution of your response and you have to understand what determines that. I believe, in a way, that the models are there to summarize the knowledge we have. But they are also built with a purpose: to answer a specific question. The configuration of the model will be dependent on the type of question you need to answer, and the questions change all the time. So we need all the time adapted models, even though we do not necessarily fundamentally change them, but we consider them in a different way. We add a climate component, and so tomorrow we might have a question about the impact of killing the trees on the chemistry of the atmosphere, just to think of a dumb example. Although, who knows? Then, we don’t have any beetle vegetation component in those models, we might have to add it. Then we might have to run scenarios where the climate changes and the beetles die or don’t die. Emissions by the vegetation is changing and all of that. Then, of course, the other thing is, moderately speaking, we are often limited by the computer capability that we have. I’ll give you an example: one thing that the climate modelists say is that they want higher resolution because they want to solve processes that are subscale. They say, “If we want to get clouds, we need a grid of 1 kilometer because that’s about the size of the clouds. Today we do 100 kilometers, maybe 50.” Now going from 50 to 20 is improvement, but it’s not a real change because you still don’t get the clouds. You have a number of thresholds like this. Now we’re more at a 10 to 100 kilometer resolution. Every time we get a new computer we improve the resolution; the grid gets smaller. We still haven’t addressed or hit the threshold where we start to replace the crude parameterization of clouds by an explicit representation of clouds. To do that we need a big quantum job. For the ocean, the eddies in the ocean, you need 10 kilometers to see them, or something like that. You don’t need 200 kilometers as you have in the models today. In this sense, the models are never finished because we’re always looking for the ability of representing small scale parameters that influence the last scale we just did.

Brysse:

Do the people who fund the computer models understand that? Like if you go to them and say, “Now we need to go look at climate,” or if there was another question like the beetle thing that you thought was important but nobody else had thought of it yet, would you be able to get funding?

Brasseur:

Well, if I wanted to do that and I was in a university I would send in a proposal to the staff for it to get reviewed. I don’t know what’s going to happen. It might be accepted, it might be rejected, who knows? On the other hand, if I’m in an organization like NCAR with base funding I can try new things without funding for a while at least. If it’s promising, if something comes out, maybe I’ll find funding. It’s always a bit difficult. The funding system is not necessarily open to completely crazy ideas. Farman would have never observed the ozone hole if they had been funded externally, because he started in ’57. He was looking at the ozone and he was seeing a little decrease but nothing dramatic first. Okay, so why do we need him? Just because the British Antarctic survey has money doing everything and will do ozone forever. They were not supported to do anything. Even NASA didn’t see the ozone hole because they had no funding for it. But in the European system it’s a bit more… there is routine monitoring going on and the funding is more attached to your salary and your base institutions and then you can do things like this.

Brysse:

That’s interesting. What do you think all the benefits are of assessments? Not just here’s the finished product, who reads it, I’m interested in that too, but for the scientists that come together and produce an assessment?

Brasseur:

Well the thing to say is that assessments are heavy, heavy. It takes a lot of your effort and a lot of your time. Everybody is busy with IPCC all the time, so that’s a negative thing. So we do perhaps too detailed assessments. Every time we do an assessment we say, “Please, only put what’s new in the last two years,” so the assessment should be 50 pages and it ends up to be 500 because everybody rewrites the full story and reinvents the wheel. So that’s a negative aspect because it costs a lot of time and effort for the scientists. On the other hand, it is a catalyst to do things that otherwise you would do later. It pushes the rate at which you produce things. Ed Carr, for example, just completed a new climate model. We would have never done it if we didn’t have the deadline offered by IPCC. Maybe in five years the model would have come slowly. So we have been under pressure, but on the other hand we get funding to do it because it’s needed. The funding has increased and is facilitated by the fact that we’re contributing to assessment. We really try to address a scientific problem under pressure, but we bring together the community and it does good to the community to be forced to contribute to all of that. I think it has accelerated the research. Sometimes it puts people so much under stress in a very clear and well-established framework that it doesn’t leave time for the completely original discovery. People are too busy going to all these meetings and writing text and so forth.

Brysse:

That’s a question I’m really interested in. I’ve had some people tell me that assessments stimulate scientific research by getting people together to exchange ideas, and especially with the ozone assessments being mandated every four years by the Montreal Protocol it sort of is freedom to say what you think is true now, knowing that in four years you can revise that if it needs revising. On the other hand, I’ve had people say that the assessment process is kind of stifling to scientific research because there’s this pressure to come together and produce a consensus whether the knowledge is ready or not.

Brasseur:

Both are true. You would hope that you have people who are involved in it and people who are not involved in it. Good people on both sides.

Brysse:

When you say involved and not involved you mean in the actual research, or…?

Brasseur:

In the assessment. I think that you don’t want everybody to work on the assessments. You want people to come up with completely different things that might challenge the assessment. I think we’re doing too many assessments too often, that’s for sure. I can see that here in NCAR. Everything is driven by IPCC in the climate division. The director of the climate division was telling me yesterday, “I need to keep things with the science also, and not just the assessment.”

Brysse:

Right, they’re not paid by IPCC to do this stuff it’s just that they’ve agreed to do it?

Brasseur:

No, no. We agree to do it because it’s a service to society.

Brysse:

Is there anything else you can tell me about the negotiating process of actually being at the assessment meetings and working together on a chapter? Is that like writing a scientific paper with a few colleagues and it’s just bigger, or is it a fundamentally different process to write an assessment chapter?

Brasseur:

Well, basically I think the first challenge is that when we have a chapter with maybe 15 or 20 people working on a chapter, we have to do an outline and then we agree who writes what. You have a coordinator person who is the lead author. Then you say, “Okay, we’ll meet again in two or three months,” and everybody would print his text or distribute the text and we would start discussing them. There’s a lot of discussion on the text. I think the challenge there is that you want to be fair and representative of not only of your science, the science of your neighbor, but also international science. It’s not easy, because when you write an assessment on ozone or climate, you don’t necessarily know very well what the Chinese, the Russians, what others have been doing. Some of the authors are very fair, while others, “Oh I’m going to report on my stuff and show what I did since I’m the best.” Okay, sometimes there might be disagreement over a very, very delicate issue. Let’s say some people were talking about trends. One person measured a trend going up another person measured no trend. Then the report needs to say something about that. So the report would say, “We think there’s a trend. We think the other observations are wrong for that and that reason.” The guy who would come to the meeting and say, “Wait a minute. You’re wrong! I can show you.” So sometimes there’s a fight. Then the report might say, “Well we have two views here. We don’t understand.” To give you an example, one of the questions is if water vapor is increasing in the stratosphere, which is very important because of greenhouse gases. Well the people here in Boulder at the Aeronomy Lab, they launched water sound and they see it continue straight. It’s very important for climate. But then if you take the satellites, they go up and down and up and down — no trend really. Then you have to put a subgroup, and the subgroup says, “Okay, why do they see a trend? Is there a drifting instrument?” So those guys get challenged. You’re the only one, so there must be something, so what about this or what about that. So those guys are like okay we’ll come back next week and we’ll show you why that’s not true. Then, when the chapter is put together it’s getting reviewed. You get a lot of comments because they’re sent to a lot of people.

Brysse:

The reviewers are other scientists, but not the ones…?

Brasseur:

Well it depends on the assessment. I think the ozone assessment would probably go to other scientists, but they have to be very unbiased. For IPCC, I forget the number of comments we got, but I think my chapter for 30,000 comments — a huge number. They send it to a number of people all over the world. Some comments are good and some are completely crazy. We have to respond to all of them. So I guess they do that in the ozone assessment. Then they have another meeting where they have to proof the chapter and finally the chapter comes together. There is a review that traditionally for the ozone assessment takes place in Les Diablerets, which is in Switzerland. It lasts a week, so several things are made there. I think chapters are being discussed, and then the executive summary is being discussed because that’s where you have problems.

Brysse:

Is that all the lead authors that come together?

Brasseur:

The lead authors come there and a number of reviewers. It depends a bit on which assessment. I’ve been to Les Diablerets maybe two or three times, but I haven’t been in the recent assessments. Usually they talk a lot about the executive summary, which is like five pages, but each word needs to be carefully looked at, and look if it’s got [???] in the text to finally release the text.

Brysse:

Good, that’s really helpful. I realize there are at least two different ways to look at the ozone regime, as a lot of people call it. The first few books I read on the subject when I was researching this present it as this wonderful, unmitigated success. Scientists figured out that there was a problem, and then regulation was put in place to deal with it and now ozone depletion is going away. From that point of view it’s a huge success. Then I realized there’s another way to look at it too when I read some other books and heard from some other people. You could argue that it took 15 unnecessary years between Rowland and Molina and others figuring out the problem to actually really starting to do something about it. From that point of view there was this unnecessary delay. Which of those is closer to you?

Brasseur:

Why was it unnecessary?

Brysse:

Well, you could argue that the science was certain enough and important enough early on that we knew CFCs were causing ozone depletion and therefore we should get rid of them.

Brasseur:

Yeah, but this is not the only thing that was happening. You had industry that was saying, “No, we don’t believe you.” Some of the governments were following industry. Before the scientists can make their point and the point is accepted by the decision makers, you have to make your case because of the implications that measures would take. The industry was trying to — it had a collaborative attitude. They said, “Okay, if there’s a problem we want to know about it. But as long as we’re not sure, don’t take any measures.” You should remember that when Molina and Rowland came up with their CFC business, there was no ozone hole. If you take the book that I wrote with Susan Solomon in the 80s, ’81, Aeronomy of the Middle Atmosphere, it was a textbook. There was a sentence in this book, and this is now in the early ’80s before the discovery of the ozone hole, but almost eight years after Rowland, we just said, “Although the potential for ozone depletion is real and it could be important, there has not been any report of substantial ozone depletion at this point.” So it’s still a theory; it’s still not proven, it’s still a hypothesis. It’s really when the ozone hole was discovered that people started realizing that the threat was real. If we didn’t have the ozone hole, we would have lost 2 or 3% of ozone, but that’s in the north. It’s really the ozone hole that created a psychological shock. When the Montreal Protocol issue was discussed, because I was a big part of that, and this was maybe ’85, we were discussing the Montreal Protocol before really the ozone hole was discovered. The ozone hole was not part of the discussion at the beginning. The threat was real but still based on assumptions and models, and there was no sign that this was really happening. Basically when the agreement was completed, the ozone hole had been discovered but not explained. So it was a strong push to do something. People said that we should not refer to that, maybe in a year it could be gone or it’s due to something else. If we say, “Oh, the ozone hole is there, therefore we have to get rid of the CFCs”, which you would say now, but at that time if you said it and then later on it was demonstrated that it was not due to the CFCs, you’re really in a bad, bad way. You will have made a decision based on a wrong scientific claim.

Brysse:

So it was having a psychological effect pushing people towards regulation, but they didn’t want to say that was…

Brasseur:

That’s right. They also said, “Okay, the science here. We don’t know. Let’s open the door for revising the agreement. Let’s do a scientific assessment again in two or three years and let’s do maybe more of them.” This is why the assessment continued to happen. In fact, the ozone assessment became a big obsolete. It was probably misunderstood. They start now to look at the climate, the recovery of ozone, and so on. There is no need to prove the case, well when the Montreal Protocol was signed there was still a need to prove the case. In fact, from a pure scientific point of view, the Montreal Protocol was signed too early, in a way. It was signed in a world of complete uncertainty still. Now we realize we did the right thing.

Brysse:

If you buy into the precautionary principle though, it’s not necessarily too early.

Brasseur:

From the pure scientific demonstration point of view, it was too early. When you see how slowly it was done, then you realize. Rowland and Molina come up — everybody’s skeptical. The model showed that indeed you can reduce a bit the ozone at 45 kilometer altitude maybe in the polar region, but in the lower atmosphere there’s no problem where the ozone is. So the U.S. government says, “Well, we should ban one of the sources, the sprays.” They do it. The Europeans resist because they say it’s not a spray problem; the spray is just a way to help DuPont. The Europeans said we should probably put a cap in the emissions not just stop something. It doesn’t matter how we do it. So there is a tension and the U.S. goes ahead. DuPont says, “We agree with the U.S. position.” So the other industries said, “All right, we’ll do it.” So Margaret Thatcher changed her mind and told the British ICI, “Stop it.” I always remember that I did once when I was in Belgium kind of a radio discussion on the CFCs at that time. You had me as a scientist, you had some ecological and environmental groups, and then the guy who was selling spray cans. He was upset, because he said, “We have been told by the CFC industry, by DuPont, ‘Don’t worry.’” These are small companies, these are not like DuPont or multinational companies. These are the small guys that sell cans, maybe not even with the CFC in there. Now suddenly they cannot use these cans and the guy goes bankrupt. He could have gone out of business earlier had he known that that would happen, but the company told him, “Don’t listen to these scientists. This is not really real. We will solve that, don’t wait. Just wait, sell your stuff. In two years the controversy is over.” I also remember once I was invited by Monte Santo in Italy, and I was sitting next to the CEO or some important guy at a dinner, and a professor asked a question, he said, “What do you think about that ozone theory?” And he said, “Oh, this is pure academic craziness. We know what’s going to happen. The atmosphere is much more robust. We just produce a limit of CFCs and there is more ozone than CFCs in the atmosphere. This is academic craziness.” And he looked at him in Italian, “Scusi, Professore.” So those guys believe that it’s a crisis among many others that they’re going to solve and they’re going to go off. Then the little guys in a lot of small companies that were using the CFCs and were expecting that the crisis would be solved. Then they were upset because these big companies misled them. You have a lot of aspects, and of course the government is listening to a lot of people. They look at how many jobs would be lost if we stop the production of CFCs and all these things.

Brysse:

Right, and that’s something pretty tangible to compare to the intangible possible increases in skin cancer or whatever.

Brasseur:

Well you could see that. When we had this discussion I was with a European delegation at a discussion in Geneva before the Montreal Protocol. There were American colleagues with NASA. You suddenly see people coming out of the ministry or the agencies in the U.S. and they take over, they do the negotiation; they don’t bother what the science is. But the scientists are completely playing a second role. The science is not the issue anymore, it’s in the background, but it’s not the issue very much. The issue is money, jobs, re-elections, and those kinds of things.

Brysse:

I guess the biggest purpose for what I’m doing is looking at past ozone assessments and trying to pull out lessons that maybe could be applied to climate change assessments. Do you see parallels between those two?

Brasseur:

Oh yeah, I think there are a lot of parallels. In both cases when the assessments started cases were not made. In both cases there was a lot of skepticism when you start, and you have to be scientifically very, very coherent and accurate. In both cases you repeat those assessments, and so they evolve because there is a certain degree of acceptance that is increasing. The assessment then becomes, in those cases, more towards solutions than towards the scientific problem. What do you do about it, now that we accept it? We see that in the climate issue. Five years ago, ten years ago you wouldn’t believe that the climate is changing. In the last IPCC assessment it was very clear it was changing and it’s going to continue to change. Now the question is don’t do a project — we believe you. What should we do? What are the solutions? It turns into the solution. In all cases the science is never finished before you study an assessment. So you have to allow a multiplicity of assessments going on that allows you to change your actions. Maybe it can be more relaxed or maybe you can be tougher. In both cases we have seen that as we understand more and more, the problem becomes more and more serious. The ozone problem was just a little thing at 45 kilometers, but then it became ozone and then it became a real issue of urgency. In the case of the climate issue, it started simple with CO₂ but now we have other greenhouse gases, aerosol, and you see what we believe is perhaps something is really going to happen. The solutions are much more complicated, but they’re also much more urgent. Now you hear from new studies that predict the warming is just irreversible. Even if you reverse the CO₂, it will take 3,000 or 4,000 years to come back to a normal situation, which means for us it’s irreversible. So the more you move, the more seriously you see the problem in both cases.

Brysse:

Right. That’s something I never thought of, that that is true that it does seem to get worse than we thought. Given that and given the precautionary principle and how careful we need to be, do you think scientists need to change the way they’re presenting or emphasizing uncertainties? You get a range of values for something like sea level rise. It might be really high and horrible but it might only be this much. Then when you want to present your results to the public, what do you say? Do you just give the middle number? Do you give the high one because you want to scare people into acting?

Brasseur:

In the beginning it didn’t matter so much what the uncertainty is it just mattered to raise the problem. That took years before people had become susceptive to this, “Oh, there is a problem.” Then you want to be more accurate about what’s going to happen, so you need to provide like an error bar and predictability. I think the IPCC scientists have done a good job in providing uncertainty. Sometimes I’m not sure that those uncertainties cover the systematic error that could be there, necessarily. What is interesting, in the last IPCC, Susan Solomon was leading it for the Working Group I, was really very careful that everything was strongly based and not just, “We think that,” but really documented. What you see is that perhaps we have underestimated a bit the future climate change. You see the melting of the Pole is faster than we’ve predicted, so there are systematic errors perhaps. We have to see if it’s an oscillation or if it’s really a trend. I think it’s good to have a clear way of presenting the uncertainties. I think that the IPCC approach, which I think is good, should be adopted by other assessments, including the ozone assessment.

Brysse:

Even though, in a sense, the ozone assessments are sort of over or routine now? [Yes.] That’s interesting. It’s a real concern how to present those uncertainties. On the one hand you could argue, as I was saying a minute ago, that you should emphasize the worst-case scenarios just to make sure enough regulation is done.

Brasseur:

Yeah, but then you are considered to be an alarmist.

Brysse:

Yeah, that’s the other problem that I’ve heard a few scientists says.

Brasseur:

You’re not credible. What I see now is that when we look at the early predictions we did like ten years ago, it seems that the more alarmist one is the one that has happened.

Brysse:

Right, and yet you do not now want to become an alarmist, even though that was true.

Brasseur:

I think you have to say the truth. You have to say what you know and what you don’t know, and when you say what you know you are already, in a way, an alarmist. When you look at the results of the last IPCC report — which was very, very carefully controlled and reviewed and all of that — it’s pretty serious stuff. The problem is if people realize that it’s so serious.

Brysse:

Right. Is that the kind of thing that people are going to say in scientific papers or the next assessment? “Look, this is what we’ve predicted, this is what has happened. It’s worse than we said it was going to be.”

Brasseur:

Some people do it. In one particular case there was a paper by Rahmsdorf that came out right after the IPCC that said, “The IPCC has been too optimistic.” He was an author of the IPCC report. But still he said, “The IPCC report has been a bit too gentle. It’s worse than that.” Of course you have to be careful, because you have also strong lobbies of skeptics, who if you make a single mistake by being a bit too alarmist here, they say well, “Oh, you’re not credible.” You lose your credibility. You can see that the press very often says, “Okay, let’s listen to what the other camp says,” and the other camp is three people. They put as much weight and interest into what those three guys who are not skeptics, they’re activists against it.

Brysse:

Yeah, that’s all hard decisions. I’ve heard that from several people though, that you can’t be an alarmist because you will lose your credibility. You’ll be accused of crying wolf.

Brasseur:

We’re scientists, so we have to stick to the truth as much as we can, if truth ever exists. But then of course, some of the people, the public, some organization, might of course show the consequences, and that might take a more alarmist side. But if we’re alarmists and it’s not justified… You know, we get all these questions what if this happened, we could be wrong also.

Brysse:

Great, I think that was everything I needed to ask you.