Cambridge Seminar Group Session

Brysse:

I’m working with Michael Oppenheimer at Princeton University. I’m a post-doc; he’s a scientist there. It occurred to him to study the history of scientific assessments that he’s been heavily involved with in the past, with the idea that if you can learn something, if you can analyze past scientific assessments, hopefully you can learn from them and apply those lessons to ongoing and future assessments, the IPCC ones being a perfect example. So I was brought on board to look at the ozone depletion case, and there is another post-doc at UC San Diego in California named Jessica O’Reilly who is looking at the history of the IPCC assessments, particularly in connection with changes to the west Antarctic ice sheet. And we’re working with another professor at San Diego, Naomi Oreskes. She is a historian of geology. As Neil said, I typically do history in paleontology, so for the last six months since I started at Princeton I’ve been having to teach myself a lot of atmospheric chemistry, which has been very exciting, trying to understand the ozone depletion situation. Does everyone in the room know what I’m talking about when I say ozone depletion? I assume you’re all involved in the chemistry. You probably know much more about it than I do. Obviously the Antarctic ozone hole that was discovered by some people in this room in 1985 and the connection of CFCs to the ozone depletion, I’m looking at that. So I guess one of the first questions to start with is a lot of the books that I’ve read that have talked about the history of the ozone regime, as people call it, have presented it as basically an unmitigated success story. They’ve said scientists beginning in 1974 discovered that there was this problem. They told people about it. International bodies came together to try to come up with regulations about it, and those regulations were put in place with the Vienna Convention and the Montreal Protocol. So it’s been presented as this huge success story that climate change policy, for example, should look to to try to emulate. However, if you ask other people, particularly a lot of the scientists who were involved with ozone depletion, they describe it as something that took five or ten or even fifteen years longer than it should have for the regulations to be implemented after the science was first presented. So maybe we could start with that, folks’ thoughts on: is the ozone case a case of successful science and successful policy, or is it something else?

McIntyre:

I think we should remember that the discovery of the ozone hole, the scientific paradigm change that was so painfully achieved so long after the first suggestion of a possibility of ozone depletion, was the very first time that a scientific assessment actually influenced gigantic commercial and political organizations on a question of global environmental change. Now, if you can’t call that a success, I think we should all give up and commit suicide.

Farman:

It was an unmitigated disaster, which has been replicated in the IPCC and which has achieved nothing in the world yet.

McIntyre:

You’d prefer to go back to the old days when it would be taken for granted that what a few scientists talked about couldn’t possibly have any relevance to the real world and the global environment.

Farman:

No one is denying that. All one is claiming is that its effect on policy was not as great as it usually may have it. By all means, we should have an effect by what we get up and say. You’ve got to find the right people, and unfortunately, the right people are neither the politicians nor the heads of industry. What has actually produced progress has been the non-governmental bodies, the NGOs, who have worked very hard and have actually managed to get somewhere when they get a little help from the electorate, such as putting in the Green Party in Germany in balance of power for three years, which did more than anything any other politician has ever done. I’m sorry, I…

Shanklin:

I’ll go along with that to some extent in that it’s the public that has made the difference, and it’s to do with the nomenclature. The ozone “hole”—holes are bad, we don’t want ozone holes. Skin cancer, that’s bad, we don’t want that. So there’s a huge public ground swell that says this is an issue that we don’t want, we’ve got to do something about. And once you’ve got that, the rest is relatively easy.

Brysse:

Wasn’t there such a ground swell with aerosol can banning at least in the US?

Farman:

That started beforehand, and that was a nice piece of someone saying, “Enough is enough.” But it didn’t really have any great effect, did it? I mean what did it do? All the production from that just vanished into other things. It’s a bit frightening. Take fast freezing of food, it was even worse than the aerosol. What did you use? You used CFC-12 to be chilled and blow through the food, and you just let it out the other end into the air — you didn’t even recycle it. The trouble is these things became so cheap, and there was no pressure from the market on any of it; it was just something you could dispose of as you saw fit.

Shanklin:

That’s the reason the climate change problem is the same, that energy is cheap, so I worry about it. Where it’s different is that greenhouse warming sounds quite nice, so there isn’t such a knee-jerk public resistance.

McIntyre:

Can we afford the impression the ozone problem and the climate change problem have a similar scientific status? In the case of ozone, the scientific particular [paradigm?] understanding has been relatively clear, and the need for action relatively clear, and the political arc of the possible therefore made some progress on it. In the case of climate, the uncertainties are enormous. They range all the way from the greenhouse planet, the lifeless planet at the one extreme in a few millennia from now, to a relatively modest effect. That is the size of the uncertainty. It is a completely different scientific situation.

Brysse:

I would like to talk about similarities and differences between climate change and ozone later. Could I ask you for a point of clarification on what you said? You mentioned a paradigm shift. What was the shift from and to?

McIntyre:

From gas chemistry to heterogeneous; that was a relatively technical point. But the scientific community was slow to pick it up, and it took the observations of Farman and Shanklin and Gardner to actually force the community to pay attention to it. That’s the usual thing in science: a key observation changes the paradigm.

Cox:

My perception of what happened in the ’70s and ’80s, I would in a way confirm earlier speakers’ sentiments, a good deal of resistance for I would guess at least ten years led by industry and industrial representatives. I do remember some of that because I sat on some committees. But eventually I guess the case was accepted, with the chair’s observations, and from that point on maybe it has been a success story because it does appear the hole is mending. I agree with earlier speakers, I think climate change for all sorts of reasons is a more difficult problem.

Farman:

And it shouldn’t be, because we’re not at all interested in what the actual predictions are in 100 years’ time. We all know in our heart of hearts that hope of forecasting the atmosphere in 100 years’ time in this stage of human knowledge is just rubbish. So we’re not really interested in that at all. But what we can say is if you keep putting carbon dioxide in at this ever-accelerating rate, things ain’t going to be good. So at the very least we ought to get to the stage where we try to hold the wretched stuff constant, but we haven’t even achieved that.

Smith:

I wouldn’t disagree with that, but I think it’s a much more complex problem than national and political area to tackle climate change than it was to tackle CFCs. Fairly quickly people — and I know it wasn’t the only use of CFCs — could do without aerosol cans driven by CFCs, so that was an easy starter, as it were. This I think is much more difficult to get people out of their cars and get the cars driven in different ways, etc. I think it is a much bigger problem.

Farman:

I’m sorry, you’re confusing two things. You’re confusing insufficient evidence to force us to take action at the moment, and then the answer is yes there is, if you explain that to people properly.

Smith:

Joe, I never said anything about the evidence. Yes, I would agree with the evidence. I don’t say the evidence is shaky in this time.

Grad student:

I would say the fact that it was so easy to stop using CFCs while it’s quite hard to stop using your car is a big thing that drove the change in policy, the fact that it was quite an achievable thing with alternatives to using CFCs, rather than being some great policy thing on how all the world acting together was actually just a quite simple thing today.

Brysse:

Right. And industry certainly tried to present it as difficult at first, but when they were given less of a choice, they were coming up with alternatives. Yes, I agree with you.

Cox:

They didn’t really give up until September 1987. That was the first airborne expedition. solution.

Brysse:

And the signing of the Montreal Protocol.

Cox:

Well, they’d signed the Montreal Protocol by then, because I think they considered the regulations that were talked about at that stage were not going to be too perfect. But once the scientific case was proven in September 1987, well, I don't know whether the chairman of the CMA represents all industry, to be certain. Because he publicly threw the towel in at the meeting we had that year with the CMA science group.

Harris:

Commitments weren’t started I think until January the following year when DuPont backed up the letter from earlier that if there were proofs given that CFCs were involved, then they would rein in production. I’ve forgotten if they said ban or rein in.

Brysse:

Ban.

Cox:

That was prior to September ’87.

Harris:

No, it was following. It was subsequent.

Farman:

Actually it was ’87. The press release was in October. They formulated the protocol to meet this deadline by a fortnight. And what did they do? Well, I’ll tell you what they did. They said, “Well, we can’t decide what to do, but we’ll come back in 1990, and by that stage we might have a better idea of what we can do.” That was the sum total of their legislation.

Harris:

And in the meantime, DuPont had made this single-company policy, which was very unpopular with the other companies because DuPont had the replacement gases ready to go, and the other companies didn’t, so the other companies thought it was a commercial advantage.

Unknown voice:

Which indeed it was.

Harris:

Partly. But equally, DuPont was much better informed than other companies because they had Mack McFarland directly in the loop.

Farman:

But a lot of what actually triggered the DuPont advantage was Mack McFarland, who was sitting in on this, and he just got fed up and he went back to them and said, “I’m sorry, I’ve been convinced, and I think you ought to be.” It was as simple as that. It was just an honest man doing his job, and suddenly deciding we had presented a case that was beyond dispute.

McIntyre:

That’s right, beyond dispute. There’s no such thing as absolute proof in science, but the uncertainty was very, very small. In fact it was pretty clear the year before from less evidence that we had chemical depletion due to the manmade CFCs. But the airborne expedition produced several lines of confirming evidence that left no real room for doubt. Now we’ve never been remotely near that with climate change.

Brysse:

You mentioned heterogeneous chemistry. As you said, it is a highly technical point, but it is still something that I’m very interested in.

McIntyre:

You could get a tutorial from anyone here on that afterwards. It’s a mere technicality. Basically solid surfaces versus just gas, that’s all.

Brysse:

I do understand what it is. I’m interested in the fact that Molina and Rowland mentioned it in their 1974 paper as something that could possibly be a factor in ozone depletion, but they weren’t considering it. And then no one appeared to do much with heterogeneous chemistry until the early to mid-1980s. The Antarctic ozone hole was discovered, the paper came out in 1985, and then suddenly everyone is considering heterogeneous chemistry. I’m interested in the reasons for those shifts. I’ve discussed this with everyone I’ve interviewed so far and they have given me some excellent answers on the subject. But again, I’d like to hear everyone’s thoughts on that sort of timeline.

Cox:

A further thought on that, why they said that. I can’t remember the particular phrase in their paper, but the thing that was really radical about their paper was the fact that the CFCs had no removal mechanisms in the atmosphere except for this photochemistry in the ozone layer. But most people assumed that if things hung around long enough in the atmosphere that they would attach to dust and get removed, and I suspect they wanted to cover themselves that if the CFCs were absorbing onto dust and got removed from the atmosphere, then it would obviously ameliorate the impact on the ozone layer. By that time, there were people at NBS, they were all plugged into this kind of atmosphere chemistry, and they were looking at this absorption of pollutants onto the surfaces, stuff like sar [sulfur??] and dust. You know, it’s been going on for years. I think they were really covering that possibility. But as I told you this morning, if you did the sums on the surfaces, it really didn’t make sense.

McIntyre:

Tony, just be clear, Molina and Rowland did not suggest heterogeneous chemistry for ozone depletion reactions but only as a possible reservoir for CFCs. Is that what you’re saying? It’s a way of scavenging CFCs.

Cox:

No, it’s a way of scavenging CFCs. I suspect that’s why they flagged it. They weren’t thinking of it in terms of this funny redux reaction that was going on in the stratosphere.

McIntyre:

In other words, their suggestion was totally irrelevant to the actual…

Harris:

No, it’s not very clear, Michael.

McIntyre:

It’s simply vague and ambiguous — well no wonder it didn’t have much influence, yes?

Farman:

There’s no reason to have an influence unless you’ve disproved the homogeneous reactions don’t work first. You’ve got to deal with chlorine nitrate plus water and chlorine nitrate plus HCl as gas phase relations, come to the conclusion they can be of no significance unless you’ve got something else going on.

McIntyre:

That’s true. There was a huge effort on gas phase, wasn’t there. An absolutely huge effort.

Farman:

Yes, but sorry, I was about to bring in an extra red herring, just for fun. Although several of us knew and had measured PSCs and written papers on them by scientists in ’63, and Wilson observed them in 1912, and so on and so forth, it wasn’t really until the American ER-2 flew into the damn things that they hit the public consciousness. There were a few of us that were slow in putting various bits together. Once the ER-2 found them, flew through them, then all things began to be possible.

Cox:

Surely the change from gas phase to this pulse of heterogeneous chemistry occurred — I mean Rowland and Molina suggested, if you like, a global mechanism for removal of those in the upper atmosphere.

Farman:

You will find in the Farman, Gardiner, and Shanklin paper a remark about the chlorine nitrate plus water reaction, and Sherry Rowland, and Molina were asked to comment on this and they refused to. They wouldn’t say yea or nay. Brian Thrash told it to me as a personal communication which he had overheard in America.

Cox:

I don’t think that would count as what I’m saying. But it was when you made discoveries of very serious ozone depletion in very particular parts of the atmosphere, which has heavy amounts of particulate and so on. But I think the heterogeneous chemistry, if you like, flagged off.

Farman:

I’m sorry, I don’t agree. The real thrust which brought it into wider attention was certainly the ER-2 — well first of all, the fact that it turned around the first time it flew down because its fuel was going solid, and this brought home to people like Sherry and so on that -90 is not an unheard of temperature in the atmosphere. And it did bring home to them the fact that they were flying through soup.

Cox:

Sure. But it only reaches -90 in fairly particular parts of the atmosphere.

Farman:

Of course, yes indeed. That’s all we need, to start with.

Harris:

I think while it was known about the Antarctic atmosphere was cold, it wasn’t necessarily related to the existence of PSCs as a sort of conscious thing. Yes people knew there were PSCs, they knew the atmosphere was cold, they knew there was ozone depletion, but I don’t think all that came together until the aircraft saw it.

McIntyre:

Can someone remind me whether the NOZE expedition the year before, which was a ground-based remote sensing expedition, actually had a—I mean they saw products of heterogeneous chemistry already, didn’t they.

Farman:

But they didn’t know at that stage it was a product of heterogeneous chemistry.

McIntyre:

Did they not even know whether PSCs were present or not?

Farman:

They didn’t know if they were present or not.

Harris:

No, no, no. The special issue of GRL on the ozone hole came out in 1986, before the ER-2 went down, and that’s where the first papers, I think the Sullivan paper and the other two papers on heterogeneous chemistry was put forward. It also included earlier references to the SAGE I study by Pat McCormick et al from 1982 or something, which showed the vortex-wide presence of PSCs. This was known before the ER-2 went down. Well what happened when ER-2 went down? There were chemists there, there were analysts there who hadn’t particularly followed this. So to me, it was always a breaking down of barriers between the communities who hadn’t followed it rather than anything else. But the timing, those papers came out before the ER-2 went down.

McIntyre:

Wasn’t there chlorine monoxide? That’s the smoking gun. No real doubt anymore. The PSCs and so on from McCormick’s group and so on, as you remind us correctly, was kind of well known. And Susan Solomon, with whom I was in correspondence in ’85 or so, was thinking about heterogeneous chemistry, being well aware of the McCormick groups, and that’s why the NOZE expedition happened—because she was pretty sure it would have to be heterogeneous chemistry, and she was going to go down and look for the evidence.

Brysse:

The NOZE I expedition, the 1986 one?

McIntyre:

Yes. Susan Solomon led it. They had a few ground-based sensors for nitrous oxide and things.

Brysse:

I’ve read about NOZE I and II, ’86 and ’87, and AAOE, which was at the same time as NOZE II. I don't know that I read about SAGE.

Harris:

SAGE was a satellite. It’d been up since 1978. SAGE I was there for two or three years.

Cox:

The guy I couldn’t remember when you asked me about it this morning was Pat McCormick, and he led a satellite mission which showed that the polar vortices had PSCs, and in the southern hemisphere they were extremely widespread. And we knew about that, and that’s really why we could start worrying whether this heterogeneous chemistry — Because the reason people didn’t worry about it before is they didn’t think there was any sufficient surface area in the stratosphere to support these sorts of processes.

Brysse:

Several of you have said some people knew about polar stratosphere clouds, some people didn’t; some people knew about particles, some people didn’t. That’s what I’ve been hearing from everyone that I’ve talked to, depending on what the researcher’s background was. If it was atmosphere chemistry, if there was chemistry at all, if they were coming in from some other discipline. Some of them were taught that there were no particles anywhere in the stratosphere. Rowland, for example, I talked to him last week, and he said that’s what he was taught — there are no particles in the stratosphere, therefore there’s nothing on which to have heterogeneous reactions. So your explanation about dust makes perfect sense to me.

Cox:

Except after a major volcanic eruption, then there’s a lot of dust. There’s some evidence in the early ‘90s after Pinatubo there was more ozone depletion. We haven’t had a major eruption since.

McIntyre:

It’s exactly the Balkanization of science. One group knows the thing very well, it’s studying bomb debris and aerosols from volcanoes and all of those things, and they have a big infrastructure studying this with airborne LiDARs and satellites. That’s Pat McCormick and company. On the other hand, you have the chemistry community focusing on modeling gas phase chemistry, and by god those models are complicated. I remember when I started to read about [???] just how many reaction equations they have to study. So you can imagine the attention being focused on all that and not wanting to bother with extra complications. Is that fair, Tony?

Cox:

Yes, it is. I mean by and large, for most of the atmosphere the gas phase theory was pretty good.

McIntyre:

After a large number of — you know, for years and years, “Oh, we forgot this reaction. We forgot that reaction.” The model kept on being built up, and they were seriously complicated.

Harris:

I think the chlorine nitrate plus HCl reaction wasn’t nailed down in the kinetic assessments until 1976 or 1978, so it wasn’t nailed down by the time of the original papers. Was it chlorine nitrate plus water or chlorine nitrate plus HCl? One of them was re-measured and had a huge effect on the models in the late ’70.

Cox:

Well, it must have been guesswork what people put in for it, because the first published paper on that reaction wasn’t…

Harris:

I mean gas phase. It was one of the chlorine nitrate reactions. It wasn’t then measured, so people were looking at the gas phase reactions at that point. It wasn’t well known, so you certainly don’t go to heterogeneous until you know the gas phase.

Brysse:

Maybe we could talk about scientific assessments of ozone depletion now. I know many of you have been involved in working on scientific assessments of ozone depletion. I’m very interested in the process of coming up with those, how it’s similar to and different from say writing a scientific paper with two or three colleagues. Obviously in the assessment process there’s going to be a lot more people involved. But is it simply a matter of scaling up the same process, or is there something different going on? Another thing that interests me is you could say, and several authors have said, that scientific assessments in general do not present novel scientific claims. Instead they are collating or synthesizing or collecting, or some word like that, they are bringing together novel scientific claims that have already been published in separate peer reviewed scientific papers. But I’m not sure that that means that there is nothing new in a scientific assessment. For on thing, there’s the audience. You’re not going to find all of the policy makers reading those individual peer-reviewed scientific papers. And also, perhaps there’s something new going on in that synthesis. For example, if you have ten papers talking about the projected level of ozone depletion over the next 50 years, and they’re all giving different numbers, and you synthesize those in a report and put the average, for example, maybe that synthesis might be something new. So I’d like to hear everyone’s thoughts on the assessment process, and is a scientific assessment new science or no.

McIntyre:

No. It can’t be. It has to be the consensus. The most a scientific assessment will ever say about something genuinely new is, “So-and-so has speculated that the following might be important, but we have not yet had a chance to assess it.” Is that a fair summary? I mean you can’t do anything else.

Cox:

I would like to think that the process of scientific assessment is just one other way in which scientists talk to each other. Because whenever you get experts together, grappling with a problem which everybody recognizes we don’t know what’s going on here, that people stimulate each other and learn about the thoughts of others. That happens in this forum just the same as it does in every other forum where scientists meet. In that respect I think it can produce new ideas…

Brysse:

But they won’t necessarily be in the assessment, or they will?

Cox:

They won’t necessarily be in that assessment, but probably by the time the next bloody assessment comes, people have gone away and thought about it and had a paper published on it. Then it’s fair game for putting in the assessment.

McIntyre:

Of course assessments are a good thing in that sort of way, and also in de-Balkanizing — they force different communities to talk to each other, and that’s an excellent thing. But let me just mention a perfect example of what I’m saying. In the last IPCC report, the assessment of ice flow rates essentially said, “We don’t understand ice flow, therefore we don’t dare say very much about it.” But if certain speculations were true about them, then sea level rise rates might be quite a lot more than we say. And since then, of course, we’ve had the terrifying prospect of that kind of thing is actually quite on the cause.

Shanklin:

They were saying, at least in the past, that sea level rises were going to be higher than the assessment said, because there was no consensus.

Farman:

That’s a question of uncertainty again. IPCC says sea level rise over the next century could be anything between 10 and 70 centimeters or something. I’d say you can easily double that. There’s a joker in the deck called ‘West Antarctica,’ and it’s not understood at all. That’s still true today — it really isn’t understood. Except there’s now observational evidence showing that most of the models are greatly underestimating ice depletion rates.

Brysse:

That’s a fantastic example of not saying anything about uncertainty doesn’t make it go away. As you said, they weren’t modeling catastrophic ice sheet destruction, so they weren’t putting it in the model because they didn’t understand it well enough to put it in the model. But you could say that’s the same thing as including it in the model with a value of zero. And the value of zero is not necessarily what’s going to happen. The contribution of the melting of the west Antarctic ice sheet, if you don’t include it in your model, you could say that’s the same thing as including it with a value of zero, zero contribution. So not talking about something doesn’t mean that it’s not going to have an effect, I guess I would say.

Shanklin:

I think these assessments have to be conservative. It’s politically impossible to be anything else. And if something is highly speculative, and I’m certain the most you can say is that it’s highly uncertain. They didn’t even quite say that!

Harris:

It depends on the consequences of the bit that’s speculative. If it has no significant consequence politically, then it probably goes in quite happily. If on the other hand the consequences are such that politicians have to take significant actions, then it’s less likely to go in until it is certain.

Shanklin:

Yes, which is a pity because the assessment should focus on the whole balance of probabilities and the scientific picture. What do you think IPCC should have said about ice flow?

Harris:

It should certainly have emphasized the uncertainties, and made some estimate of what an upper limit to those uncertainties were. So if you looked at the worst case rather than the consensus or best case, if we’ve got it all wrong, what in the worst circumstances might befall us? And I think that is important as well.

Shanklin:

They should have at least said that. And it’s very hard to say even that because we don’t have an accurate idea.

Harris:

We don’t really know what the uncertainties are, but you can have something of an idea that yeah, we might be a bit out; how much out can we be? And you’ve got the upper bound. So it’s sort of like looking at the quartiles.

Grad student:

Sorry, just to ask a question. In terms of ice melting in Antarctica, aren’t we expecting the temperature of Antarctica to cool in the future atmosphere?

McIntyre:

Are we?

Grad student:

I thought that the temperature will at least cool in the stratosphere.

McIntyre:

We don’t know.

Harris:

Surface temperatures over Antarctica certainly warming certainly on the century time scale. At the moment, perhaps slight cooling over east Antarctica, but the chance of that continuing for 100 years are not zero, but they’re pretty slim.

McIntyre:

We don’t know. And above all, we don’t know accumulation rates. We don’t know what the storm tracks and precipitation is doing in the region. The climate models are no where near good enough to begin to talk about that.

Harris:

The simple temperature forcing has been warming from greenhouse gases, including from stratospheric ozone depletion to date. The chances are with stratospheric ozone depletion turning around that they will start adding together. What that means in terms of the actual local temperatures in meteorology is different, as Michael said. But the basic forcing is that they will both start adding rather than canceling, as they have been in the last 20 years.

McIntyre:

And ocean currents.

Harris:

Absolutely. In terms of the atmospheric changes, the forces are to combine in warming rather than offset in cooling and warming as it’s been in the past.

McIntyre:

It could be. You could have a high rate of ice depletion with a very high rate of deposition.

Harris:

Absolutely. And all that can complicate it enormously, yes.

McIntyre:

We might yet save the planet, we don’t know!

Brysse:

I think in the case of something like climate change and ozone depletion, a unique situation arises in which the term conservative, which you used a few minutes ago, can be interpreted a couple of different ways. If you’re talking just about science, not necessarily the climate science but science in general, if you have a range of values, the conservative side might be the one that is less astonishing, less shocking compared to what we’re used to, less different from the current value. That’s one interpretation of conservative, the one that is least different from known or present values. But on the other hand, if you’re talking about things like climate change in which you might be applying the precautionary principle where it’s better to err on the side of safety, then it might be conservative to go with the estimates in which there is greater damage, greater loss of ozone, greater loss of ice sheets. So you could use the word conservative to mean…I’m not sure how to express this.

Shanklin:

Well you said precautionary principle, didn’t you, which is a completely different thing. And probably admirable but let’s just be clear. When scientists say conservative, they mean solidly supported by evidence, preferably several different independent lines of evidence. That’s the situation we had in 1987 with the ozone hole. So conservatively you could say there’s an overwhelming probability that this is due to manmade chlorofluorocarbons, it’s a simple account of those.

Brysse:

But suppose we’re talking about estimates of sea level rise, and you come up with a projected estimate of rise over the next 20 years of 6 meters (I’m just making these numbers up), with an uncertainty range of ± 3 meters. If you’ve truly got that uncertainty range, 9 meters is no less likely than 3 meters, but there might be a sense in which 3 meters could be considered more conservative than 9.

Farman:

I think with the sea level rise problem, there is only one scientifically sensible thing to say — this is my personal opinion—and that is it’s a probably distribution function that we can estimate as far as we can, and it’s not enough to say where the quartiles are or the standard deviation or anything like that. The shape of that distribution is probably not Gaussian, so you can’t describe it by just a few numbers. So the best we can do is have a shot at seeing what it’s like, and unfortunately, it’s got a long tail of catastrophic extremes. And I actually think that on the political side, scientists ought to be talking more about that, because it’s perfectly plain that our politicians are not getting this. They’re talking in one breath about, “Oh, let’s get low carbon…and build more runways.” That summarizes the way their thinking.

Harris:

And we must grow the economy.

Farman:

They have not thought, they have not taken on board even that simple probability distribution function.

Cox:

Plus the aircraft industry, it’s not the first time they’ve had a little juxtaposition with the scientists, because before Molina and Rowland we had the NOx issue, the supersonic transport, and the CIAP report, which was actually an extremely professional report put together by scientists and administrators, albeit not an international group because was in the US. And that, of course, led to the demise of the US SST. The exact circumstances I don't know. That it would stop the program probably because of the economic factors more than anything else.

Brysse:

That’s the story I’ve read, that the report certainly wasn’t encouraging, but they’d already decided not to go ahead for economic reasons. I don’t know if it was that report, but there was one where the report actually concluded that supersonic transports would cause serious ozone depletion, but they weren’t actually going to be — the US had decided not to build the large fleet that they projected, and the ones that already existed weren’t flying as high as the future ones would have. So in terms of what’s actually going on, there wasn’t serious ozone depletion. And the way they presented this conclusion was so muddled that the report was completely misunderstood. Was it that report?

Cox:

Yes, the CIAP report.

Farman:

You should, I think, also have a quick look at the assumptions they made. They were going to exchange the population of New York and London in the matter of about half a year I think, and I don’t think we’ve succeeded in doing that. It was a very curious… [chuckles]

McIntyre:

At least it greatly stimulated the development gas phase chemical models. They were about half way done by the time of that report, weren’t they? [Laughs]

Harris:

But going back to your point on concerns on assessments, I think it’s inevitable. Because scientists when we publish, we’re used to publishing where we hope we’re at 80-95% certainty, we always use 2 sigma error, etc., etc. — that's our comfort zone. In an assessment, what I think you should really be doing is giving your best guess at what would actually happen, and that's not the same as a 95% confidence limit. So you’re inevitably more cautious as a group in an assessment, and I think that has hurt…

Shanklin:

I think it’s probably worse than that, but the best guess of what will happen is not necessarily what you put in your report. I think the best guess for many of these were actually worse than those in the report.

Harris:

As I was going on to say, I think that is actually what’s happened, especially with the IPCC report, and there’s always been veering to worst consequences over the last 15 years. Not just because the emissions have been going up faster, but because of the science, I think, the more extreme possibilities have been underemphasized in each report as it goes up. Part of this is sociological, because if you back to the 1995 report, Ben Santer was the lead author on the chapter of attribution of climate change, and it was the first time that any statement was made that what you could attribute changes in the past record to climate change, it’s the first time that that had been made, and he was absolutely vilified by the industry in America. And you see that happening, and what are scientists going to do the next time? It’s sort of what I was saying earlier where industry learns, and I think that happens. And I think you now in the assessments are sticking to ’97 criteria implicitly. In your judgment; I don’t mean the terms of probability distribution. And I think it’s a major point with the assessments is they are inevitably conservative in the sense of you don’t want to be wrong in what you say. It may be bigger, but you don’t want to be wrong.

McIntyre:

There a political pressure to give us the answer, so this “best guess” thing is kind of a natural response, isn’t it, to that. I think we’ve got to try and get beyond that and talk about ranges of uncertainty more.

Shanklin:

Well you are, but I think you’re still being conservative in doing that. They do that at IPCC, they do a lot of ranges and are conservative. But are you conservative in assessing those? I still think that in an assessment you inevitably are, and I think it’s a real shame because it’s giving bad advice, or not the best advice.

Brysse:

In your assessment, what you said just a minute ago, you say what you think might happen, but it could be worse than that. Why could you not say what you think is going to happen and it might be better than that? Why don’t people go that route in assessments?

Shanklin:

That’s why I say, I think it’s just sociological—we don’t like doing that as a community. Logically you should.

Cox:

Then you’ve got the problem of scare tactics. It sends everybody in a spin. Scare tactics can be extremely destructive, as we see all around us.

Shanklin:

It’s sort of the “crying wolf” principal: if you cry wolf too often then nobody believes you anymore, and the sky does fall in.

Brysse:

Whereas if you say I think it’s going to be this bad and it turns out to be worse, you might be listened to even more. [Yes, yes.] Anyone else have thoughts on that issue?

Grad student:

I think definitely the conscious effect of this is credibility, when you see these graphs of the sea level rising so high, much higher than it ever really would rise. And I think definitely when people say that, it does lose credibility.

Farman:

Much higher than it would rise? You know the upper limit, do you?

Grad student:

All I can say is I’ve seen non-reputable graphs where the sea level rises many, many meters, and going over much greater time spans than we can possibly predict.

Farman:

I would say there is a significant probability that it will go up several meters, with of course disastrous geopolitical consequences.

Grad student:

[Inaudible phrase] many graphs there have confirmed that say that sea level is going to rise tens of meters.

Cox:

That’s perfectly plausible if you take the time scale of several thousand years.

Grad student:

Yes, but you can’t really say what’s going to happen over the next thousands of years.

Harris:

I think there are two points. One is that one. The other one is you said they are from non-reputable sources, and there have been a lot of plots I have seen on a number of issues which the public doesn’t distinguish from the ones in the assessments. So it’s to pull those two apart, I think is desired.

Shanklin:

So getting the impression that you might have several meters in a hundred years’ time, when even the worst case scenario would say it is a longer time scale. So certainly for all of Greenland and all of west Antarctica going, which would give you 14 meters…

McIntyre:

Sorry, that’s 5 or 6, isn’t it, West Antarctica?

Harris:

I don’t think we should get into a discussion of the sea level rise here. [Laughter]

McIntyre:

The question is will it take one century, five centuries, or ten centuries.

Harris:

No, here we’re talking about the role of science in assessments, so you can come back to that after. We’re not trying to get a number here, Michael.

McIntyre:

My point is there is no upper bound as you get into the tens of meters. As was said, it could take millennia. It is part of a huge uncertainty. That’s all I’ll say.

Shanklin:

In many ways with the ozone case, although the damage that could have been done was going to be much more global, the actions that have been taken have actually given us an upper bound on ozone depletion.

McIntyre:

Yes, because that’s relatively well understood.

Brysse:

How about the handling of uncertainty in assessments? For the assessment to be useful for the government and policy community that it’s meant for, you have to give them some sort of solid or semisolid information that they can use to make decisions based on. But there are quite likely to be some things in the science of the assessment that just aren’t known yet. So how should that be handled? Should you simply say “I don't know”? Or what’s the solution for handling stuff like that?

McIntyre:

I think you have to say IPCC has made good progress. They’ve set some quite good examples. They set a standard: very likely, likely, etc. They say what they mean in terms of estimated percentage probabilities. So I think we have to keep trying to develop that and make it as consistent as we can, difficult though that may be.

Graf:

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Brysse:

Does any of that make it into the summary for policy makers, or just in the individual chapters?

Graf:

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McIntyre:

In the IPCC it did, didn’t it? There was a lot of this probability language. There was a table saying what it was meant to mean.

Braesicke:

It’s quite interesting, what you said. I think you’d better be bothered as something very positive that you have basically language which maps on numbers. Sometimes it worries me, actually, and I think it’s also a little bit of weakness in the IPCC report, because again, you give people a sense of certainty that likely, and I’ve forgotten the exact number, that many percent likelihood.

McIntyre:

Well, but what else can you do, Peter?

Braesicke:

I actually quite more enjoy reading the ozone assessment, where basically the language isn’t really nailed down to a number and there is a bit of fluffiness about. Because fluffiness also gives you more…at least for [???] I think fluffiness gives also a feeling of uncertainty. If you nail that word down with a number, policy makers look at it, “Oh, it’s just a 50-50 chance. Oh! Don’t care!”

Cox:

Well you see, the ozone does have a far small answer, so it can afford to be less fluffy.

Braesicke:

But they don’t. In the ozone report you never find any mapping between words and numbers. Every chapter basically tries to find the balance by getting the bullet points right, as Hans highlighted, saying these actually are things we are quite certain about, and they are weaknesses in the whole thing. And I think that for me as individual is much easier to appreciate, and I think it’s fairer on the topic than trying to nail down the exact numbers, when we know that most of these exact numbers are actually some kind of illusion. I would basically really say, “Yes it’s likely,” 50% somehow derived from some kind of model average or whatever, and there are a lot of good reasons and a long discussion why they settled for this combination of words and numbers. I don’t really think it’d help in policy maker in understanding where there are properties.

McIntyre:

I actually sympathize with what you say, Peter. But I emphasize again the ozone problem is a much easier case than the climate problem. The ozone problem you can say quite a lot of things without bothering with numbers because they’re practically certain. There are some weaknesses, you can say. In that kind of problem, practically everything is highly uncertain, you’ve got to say.

Harris:

I think you’re pushing that too far. In terms of the past, you can say a lot of things very clearly about either problem. Ozone has gone down; CO₂ has gone up. There’s a lot of past explanation you can do on both.

McIntyre:

You can say some things on the climate problem, but you can’t say very much in terms of predicted scenarios.

Harris:

But in terms of the past, for both of them you’re on firm ground. In terms of the future…

Shanklin:

Climate you can argue that it’s all due to the sun…

Harris:

There’s not a lot of room for those types of arguments.

Shanklin:

…and people do argue that.

Harris:

Not in the scientific community, there’s not a lot of room for that type of argument.

Shanklin:

I agree the scope is small.

Cox:

The point of having scientific assessment is to actually get some science into the policy arena, and then in a way in which the policy maker can make what you hope is his best decision. And I think it’s an interesting point you raise, is whether the policy maker makes a better decision confronted with a number of which one side is right and one side is wrong, or is presented with fuzziness. Again, it depends on how he responds to the problem he’s facing, which is a different one to you as a scientist.

Graf:

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Harris:

Not necessarily.

Graf:

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Harris:

It depends what their electoral system is.

Graf:

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Brysse:

This is something that I’ve read about. A few people have done studies discussing the efficacy of the policy of the IPCC to try to assign numbers to their probabilities. And they’ve come up with at least two problems with it, although I think they generally agree, and I certainly think it’s a move in the right direction. But one problem has been that although the IPCC report clearly states this number means this, and it’s right there in a table, one group of authors who did a survey of readers of that report found that readers were interpreting the numbers the way that made the most sense to them in their heads, whether or not that matched the term that the report says goes with that number; they were simply reinterpreting it in the sense most intuitive to them. Then the other problem goes with what you were just saying. The numbers presented in the IPCC report were probabilities, but a lot of people were reading them as risks. I myself am not an economist or statistician, but the way I understand it, risk is probability times consequence. So people were reading the number and interpreting it to mean not only the probability of the event, but also trying to include the consequence in that, and that in fact is not what the IPCC was doing. So if you have something that’s only got a 30% likelihood, but it is something that would kill every human being on the planet, 30% looks a lot worse than something that has a 30% probability of happening but nobody would care if it did happen. People were interpreting these numbers according to those risks when they were not meant to be interpreted that way. So it sounds like there is a little bit more work to be done with this quantification, if that’s the direction IPCC wants to go in. But what else are they supposed to do? The policy makers need something on which to base their decisions. And should they have words they can interpret the way they want to, or should they have numbers?

Graf:

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Brysse:

That’s even harder!

McIntyre:

The bottom line is you can’t escape that. We’ve got to avoid getting into the deep philosophical differences surrounding the theory of probability and its various interpretations, which I could talk about all day actually, but let’s not do that. Let me just say that I think the IPCC got another thing right when they separated the scientific assessment report working group one from the risk assessment and litigation and all of those things in the other working groups. So if you know what you’re talking about, you should say risk belongs to the second or third working groups, doesn’t it, and that’s helpful, isn’t it.

Brysse:

That leads me to another question, actually. It has generally been the case, certainly with assessments lately, and I talked to Bob Watson who said he deliberately made this a principle in the assessments he was in charge of, is that many people agree that scientific assessments should be policy relevant, but not policy prescriptive. In other words, they should give policy makers information on which to base their decisions, but they shouldn’t tell the policy makers what those decisions should be. So I’d like to hear everyone’s thoughts on is that a good idea? Is it not a good idea? And why?

McIntyre:

I think it’s a very good idea, because the one thing we’ve got to do to the extent possible is to say science is one thing and politics is another. They obviously get entangled. We can’t help that. But we should try and keep prying them apart.

Shanklin:

I think what you have to do is give policy options on the consequences, and then the politicians can choose from a menu as to what they see as the least worst from their perspective. Obviously they will have very different perspectives because the bottom line is what will get me reelected.

Cox:

How much better are scientists than politicians qualified to make that judgment as to what the policy options should be? Because policy options are not just scientific. They include all sorts of other things in them.

McIntyre:

That’s getting the two things tangled, isn’t it? The scientists should say what the facts are as far as we can tell; the policy makers should look at policy options.

Shanklin:

But science can say if CFC levels are held at this value, the consequences are this; if they’re allowed to rise to this value, the consequences are this.

Brysse:

So maybe we’re just using the wrong word in policy options.

Cox:

It’s the consequences. If the consequence is something that’s testable scientifically, then a scientist can give you a value judgment and probably a good answer. But if it is not something that is essentially intrinsic to the system that the scientist has commented on, then it can be something different.

McIntyre:

I think Jonathan put it well. I think policy semantics should come after the word “if”. In scientific assessments, if you do this, then we think the range of possibilities is that. End of story. Leave the rest to the other working groups. Because if we don’t do that, we are immediately open to the charge that many, many, especially the more loony post-modernist academics ought to say, is that there is no such thing as objective science. All scientists are totally influenced by cultural and political considerations. If that were true, science would be valueless, so we ought to try and fight it off.

Harris:

Coming back to the modern rather than the post-modern, you have to be slightly careful making such a clean distinction, though. And I don’t mind what you call them, but you need people to work in this area who are scientifically knowledgeable and literate. You may not want to call them scientists. They may not be the practicing research scientists in the various universities or government labs, but if they don’t have the science input that they’re working in this intermediate area, then it’s not going to be that effective work. So you need that. Like the science advisors to the government, you need people in that who know what the science is and can talk knowledgably about it. Whether we call them scientists—and I think this is semantic rather than anything else personally. But you can’t avoid having talented people in that region.

Shanklin:

I don’t think it is entirely semantic, because you can have people that know the words but not the meaning of them. And that certainly happens with some advisors. They can spin a very good story and from the words it all sounds good. But they don’t understand the underlying science.

Harris:

That’s my point—you need real scientists, but not necessarily practicing research scientists in this area. It’s got to be real, or it just goes haywire in the transition.

McIntyre:

Perfectly true. But of course somebody in that dual role simply has to say which hat he or she is wearing. “Speaking as a scientist, my judgment is the following. In terms of the policy responses, you might consider this and that.” But keep the two modes separate.

Harris:

Agreed. I agree with that part. The way you put it before sounded a bit like a no-go area to scientists.

Farman:

They have to talk to one another, it seems to me. I mean one way is to have the assessment entirely scientifically based, and the politicians who are leading this assessment, if it’s that kind of assessment we’re talking about, have then got to talk to maybe some of the scientists who created the report, in my view.

Brysse:

And there may need to be some consideration of the political audience when the scientists are writing the assessment, because it may not be read, or certainly won’t be understood. The summary: not the whole thing.

McIntyre:

That’s one of the reasons for being very conservative. Once you say something that sounds dramatic, the tabloid newspapers grab it and it’s totally — You know, like the crop circles. You cannot stop people believing it’s due to aliens, even though the people who made them wrote a book explaining how they did it. You’ve got to try and stop that genie getting out of that bottle.

Harris:

But why, if that means you’re giving the wrong advice to government? Why is that the case?

McIntyre:

No, no, it should be correct, but it should be said in a very conservative and careful and cautious and nondramatic way.

Harris:

And that might mean it’s wrong. You can’t always have correct, conservative, cautious on the same thing you’re saying.

McIntyre:

I could say the runaway greenhouse might in several millennia produce a lifeless planet, but not in a dramatic way. I say it is simply a possibility whose probability we are hard put to estimate at the present time. There’s a good reason, by the way, we don’t know enough about the continuum of the water vapor irradiative properties.

Brysse:

But you will be reported simply as having said there will a lifeless planet. [Laughter]

McIntyre:

The other reason is we don’t know how much carbon is locked up in the permafrost and under the ocean and so on. There is a huge, huge uncertainty there.

Harris:

Are there any other comments or questions people would like to make?

Graf:

[Graf's responses are restricted without his permission. Please contact the Niels Bohr Library & Archives if you wish to view them.]

Harris:

Before you go too far back… [laughter]

Graf:

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Harris:

Any other comments? We’ll be around for a little bit more for tea if anyone wants to talk individually.

Brysse:

That would be great. And I just want to reiterate that I did record our discussion. I’m not planning on writing anything and attributing it to anyone because with very few exceptions I don’t know anyone’s name. But if anyone who spoke this afternoon has decided they are uncomfortable with the fact that I recorded this and you don’t feel like shouting it out right now, just come on up quietly and tell me after and I’ll get rid of my tape. And thank you all very much.