John Pyle

Brysse:

A little background on what I do. I’m a historian of science. I’m doing a post-doc at Princeton with Michael Oppenheimer. And another boss of mine is Naomi Oreski, a historian of science at UC San Diego. Together, and with another post-doc at San Diego, Jessica O’Reilly, we’re looking at the history of scientific assessments of climate change. I’m focusing on ozone depletion, and Jessica is looking at the IPCC especially to do with the west Antarctic ice sheet. The general idea is to see if we can draw out any lessons from these assessments that might be useful for ongoing and future assessments. A lot of people have written about the ozone depletion cases, but they’ve mostly been interested in how the policy was done. A good example would be Richard Benedick’s book, Ozone Diplomacy. Several people have said that they think the scientific assessments that were done and the process of creating those assessments has been important, but nobody has really written about the assessment writing process. So I’m trying to look a little bit at the ozone depletion science, then mostly how that science goes into the assessments, and what role the assessments have played. So what has been your involvement with ozone depletion?

Pyle:

I did a [???] in Oxford in the 1970s that involved building a two-dimensional model of the atmosphere, which I was doing with a guy called Bob Howard. My involvement became — I basically was the person who had to put ozone into the model. In the first instance because ozone is an important radiative gas, if you want to get the circulation of the stratosphere right you have to get ozone right. I started in 1972.

Brysse:

So it was initially not about ozone depletion?

Pyle:

It was not about ozone depletion. But very soon after that — I guess already at that time, although the aim was not to look at ozone depletion, an increasingly important issue was the question of depletion of ozone by supersonic aircraft. So there was a program involving the French and UK governments and their scientists called Covos/Comesa, which was specifically trying to look at the impact of aviation on ozone depletion, the SSTs. In a sense, that was the first problem I was starting from. Having said that, really what I did, I built a very simple chemical model of the atmosphere to put into this numerical model. In the first instance we were simply trying to reproduce the observed distribution of ozone, its seasonal variations and so on. This simple model did that pretty well. And that’s essentially what I did for my PhD. Toward the end of my PhD I started developing more complex chemistry schemes, which we were then able to use to look at ozone depletion. By the time we got those schemes ready, the issue was no longer the SSTs for a variety of reasons; it had become much more a question about chlorine initiated in those equations. From the late ’70s through the early ’80s I was involved in ozone depletion questions around the CFCs. The model that we had was, I think, the best that was around because of what our model could do and was actually designed to do. It could allow ozone to change, and that change of ozone then affected temperature and circulation. For example, I published a very early paper working out the impact of not just CFCs, but also CO₂, how that would affect stratospheric ozone and the kind of mutual interaction between those. So that happened through the ’80s. Now, one thing I’ve never been quite clear about is when the assessment process started, in a sense. There were books that were produced from the early ’80s onward. I’ve probably got some old copies up there. If not then we’ve got them downstairs.

Brysse:

There are even some from the ’70s depending on what you mean by assessment.

Pyle:

There’s a book here called, Stratesopheric Ozone, 1981. There were the famous three blue books. This is ’85. I was kind of lead author… I led the chapter on — I think we had a chapter on models, chapter 12, which I led that. That was a phenomenal amount of work.

Brysse:

Was that the first big one you were involved in?

Pyle:

I think I was involved in the ’81 model. There’s one that — I can’t, to be honest with you, I can’t remember. I can’t actually remember whether I was on this one or not. There’s probably a list of people on the back.

Brysse:

Is that just a UK one?

Pyle:

No, no, no. Yeah, so here we are. I was involved in the workshop for that. I think it probably happened at Hampshire.

Brysse:

Oh, that’s the WMO with NASA.

Pyle:

That’s the WMO. So if you’d like, there’s an even earlier one, which I think was a meeting that came out of a meeting at somewhere like — There’s an earlier brown one. It’s a buff colored thing like that, which I was not involved in. I think that could possibly claim to be the first of these attempts to consolidate our information. I wasn’t involved in that, but I’ve been involved in every one since then. I was involved in all of these blue, 1988 Ozone Trans Panel. And then presumably in the early ’90s they started being the assessments. Well, I don’t know. When do you think the assessments started?

Brysse:

It depends what you mean by assessments? There’s the SMIC and SCEP from the early 1970s. I think they’re early 1971 and ’72, but they’re just American. If assessment means an international assessment process, that I don’t think starts until the 1980s. In fact Edward Parson wrote a book, one of the four called Protecting the Ozone Layer, he says the first truly international authoritative assessment was the 1985 blue books.

Pyle:

I think that 1981 book is actually pretty important. But certainly, what I recall about that, hazily, is that we went to a meeting in Hampton, Virginia and got a lot of people together and presumably people were told to go write bits and pieces of it and so on. But what happened in ’85 was that there was a very deliberate attempt to say, “We’re going to deal with all of these issues.” So, a chapter on modeling, a chapter on this, and a chapter on that. Teams were assembled. My team met a couple of times. But it was done very differently. I’ve been lead author several times on these assessments. And the 1985 assessment I actually wrote the chapter myself, and then all the other people tore the chapter apart and reassembled it. I don’t think anybody would dream of doing that now. It was a great exercise for me at the stage in my career that I was at. It didn’t do me any harm. Although one of the things that the assessment has not done — I mean the people who are involved in the assessment get a lot out of it. But I just noticed I was looking at the IPCC report here, which says, “This chapter should be sighted as Johnston, blah, blah, blah.” We’ve always had a kind of problem of actually giving credit to the people who have written the chapters in terms of referencing. It’s a minor thing, but the people of the IPCC are aware of it. They solved that problem, which I don’t think we have. One of or two of the chapters got turned into papers, so it’s clearly citable because there are lots of people citing, but they tend to cite the whole report rather than the individual chapters. But at some stage they became the official assessments.

Brysse:

Official like the ones that are called for by the Montreal protocol?

Pyle:

Of course the protocol was in ’87. But I don’t think the ’88 thing was — was that necessarily an assessment in that sense?

Brysse:

It was an assessment. It wasn’t tied directly to the Montreal protocol.

Pyle:

Here’s the ’89 book, which is called, Scientific Assessment of Stratospheric Ozone.

Brysse:

By 1988 you mean the Ozone Trans Panel Report, right?

Pyle:

Yes. The ’88 thing is the Ozone Trans Panel Report, which presumably was our start.

Brysse:

That’s the impression I got.

Pyle:

So I’ve been involved all the way through. Certainly there was a time when I think I’d been a lead author more than anybody else. The last assessment I was on the — There are a group of co-chairs, who at that stage were Dan Albritton, Bob Watson, Ajete Alvamon [?]. There was a guy from South Africa as well whose name I’ve forgotten. The two lead players had been Bob Watson and Dan. And frankly, Bob, in the last couple hasn’t really done very much.

Brysse:

That’s what he said.

Pyle:

I remember talking to Bob a couple of years ago, and he kind of indicated that he wanted to stand down. But Dan had said, “Politically, it might be a good idea if you stick around, Bob, because we don’t know who might replace you.” And I don’t know whether Bob said that’s it.

Brysse:

Yes, that’s pretty much exactly what he said.

Pyle:

In the last assessment, that was the team of co-chairs, but the only person who was really active was Dan. And Dan was already starting to edge toward retirement.

Brysse:

So that would be 2004 and 2006?

Pyle:

This is the 2006 report I’m talking about. I can’t remember what we were called. We were either called a steering group or advisory panel or something like that. Basically, they created this sub-structure underneath the co-chairs, which was Paul Newman, me, Ravishan Kara [?], Ted Sheppard, I think Suzanne Diaz, and Marilee Channel [?]. We did a lot of the work certainly at the very end of the process. The way the process works is — So we’re kind of going through this now for the next one. I’m now co-chair, so I’m going to be talking to the other co-chairs on Friday and we’ve already sent out a straw man for the structure of the report. And we’ve got reviews in. This has been sent to some governments and to interested scientists, people we think will make constructive comments, and we’ve had a whole series of comments back. So we’ll be talking on Friday about how the report might work, whether we got the structure right. We’ll also be trying to identify the people to be the lead authors. Then the lead authors and co-chairs will meet in probably June in London to kind of agree things and make sure we haven’t missed things or that there isn’t too much of an overlap between the chapters, which is always a bit of a problem. Where do different things go? Then the convening lead authors with the co-chairs will decide their author lists, who the authors they want to get involved should be. Then it’s up to the convening lead authors to then have as many meetings as they need to put together a chapter. They will need to have a rough outline of a chapter by November when we’ll have a first very informal review. Then depending on how we play it, they have to have at least one pretty decent chapter, which is sent out for review. So the meeting in November will just be, “This is what we’re doing. This is where we’ve got to so far. These are the kind of topics we’ve got so far. Here are some key figures we expect to have in.” We don’t expect to see a lot of really good joined text at that stage. There might be some, but it doesn’t always happen. By end of January and early February they have to submit their first draft, which then gets sent out for review. And then that comes back. Last time we actually had a second iteration. Then we meet in Switzerland in Ladealbolrae [?] usually in June. All the assessments have gone through this kind of process, met in the same place in Switzerland. And during that week the chapters are agreed — they’re not finished, but they are agreed. The other thing you do is you finish the executive summary at that stage. There’s a huge job on usually the co-chairs, but last time, in fact Dan didn’t go to that last meeting, so it was really this kind of structure underneath. We were up most nights trying to reconstruct what had happened during the day to prepare for the following day. It’s really hard work, but the report gets essentially finalized. The chapter authors go away, but they are told clearly what they are to do. So there are no rabbits that are going to be pulled out of a hat after that.

Brysse:

How do you choose authors, lead authors and other authors?

Pyle:

This is the first time I’m a co-chair. What I should have said is three of that team from last year, three of this team kind of underneath, Ravi, Paul Newman, and I are now co-chairs along with Ajevon [?] from TOGO [?]. We have to do this. What we’ve done this time, which I think is what they’ve done every time, is to send out to program managers and especially scientists to say, “This is what the structure looks like. Can you please make recommendations for which you think might be good people to be involved with the chapters? And if you’d like to suggest people, whom might be lead authors, please do that? And don’t be shy about saying you want to do it yourself.” I think what then happens is that the lead authors will be decided with a lot of regard to geographic balance. You wouldn’t want all your lead authors to be North American, nor would you want them all to be European. You want a mixture of lead authors from all over the world if you can do that. The two areas where there’s a lot of this science still going on are North America and Europe. There have been lead authors from Australia and New Zealand in the past. We’d obviously like to spread the geographical spread even wider. The other thing is gender balance as well. We try to see whether we can get a number of women involved in writing the assessment. I’m sure those will be things we deliberate about when we speak on Friday. First and foremost, you’ve got to get people who you think will write the chapters or will lead the writing of the chapters. They need to have expertise, but they also need to be people who if they’ve got a team working underneath them, will actually get the best out of that team. Sometimes it works well and sometimes it doesn’t. Some people are great scientists and not very good at working with somebody else.

Brysse:

How about the reviewers? Do the co-chairs choose the reviewers or do you find them anonymously somehow?

Pyle:

There’s a two-stage review. Partly the review is done by — Again, I’m not quite sure what’s going to happen this time, but some of the reviewers are scientists involved in the field. So you’d send it to people particularly if you think you’re going to get some kind of sense back from them. They are selected. But they are also sent to governments. Again, I don’t know how many governments this gets sent to, to be perfectly honest. In Europe it definitely gets sent to the Department of the Environment in the UK. It also gets sent to the Secretary of the European Union, so the Directorate for Research. They would either review it themselves or they might ask scientists to review it. They may be asking the same scientists. They can choose what they want to do with it. That, as I understand it, is how the process works. As I said, this is the first time I’ve actually been right on the particular side of the fence that I’m set on at the moment.

Brysse:

You’ve had a lot of experience with the assessments in general. Have you seen an evolution, not just in the way the meetings are handled and the people are chosen, but the way the finished product actually looks? For example, Bob Watson said his big regret with the blue books is that it didn’t have an executive summary. He told me exactly what the difference between an executive summary and the introduction that it does have is. So something that’s changed is the addition of an executive summary. Has anything else evolved over time?

Pyle:

So the blue book didn’t have an executive summary. It probably just had individual chapter headings.

Brysse:

There is an introduction that says, “This is what chapter one is about. This is what chapter two is about.” And Bob pointed out that there’s a big difference between what’s going to be discussed in the chapter and what the conclusion of the chapter is.

Pyle:

I guess there are two things. One is that every report we’ve ever written we’ve said we must make this really succinct, and in fact they are always pretty big. And we’re saying exactly the same thing this time. I was actually reading the comments on our draft outline yesterday, and a number of people were saying, “Great if you can get it small.” But I’ve heard this kind of thing before. Maybe nothing’s changed there. What has changed is the question and answer things. The 20 questions and answers about the ozone layer.

Brysse:

When did those start?

Pyle:

I don’t know if we’ve had three of those or two. Certainly the very first one was done by Jared Majee [?] and then David Fahey. There may well have been three. I think David Fahey has done two. That would be my guess. I guess the community is used to doing assessments now. People by and large want to be involved. People want to be involved for a variety of reasons. I want to be involved because for me it’s a good way of keeping in touch with everything that’s going on. Things are synthesized for you. I run a fairly large research group here and I’ve got administrative responsibilities in the department, and this is a really good chance to be on top of that particular bit of science, because I have to be. I’ve got to be reading the papers that everybody’s talking about. Lots of people want to do it for that reason. There are other people who want to do it as well because they want to push their particular agenda, push their research agenda or whatever: “Here’s my bit of work. I want to get it in the assessments.” There are a couple of things like that. But the community is now pretty good at doing this. So I think in terms of the operation we’re safe. It’s interesting that one of the things about the process rather than the final product is that several of the comments we had from these first reviewers just of the outline were saying I think you ought to get your executive summary sorted earlier than you’ve done in the past. That’s a good point. I think the executive summary still tends to be something that we pull together at this big meeting at Ladealbolrae. We say to the lead authors early on, “You really must tell us what you think you’re highlights are,” but nobody really sits down and writes that. That might be partly because I think, in a sense, the co-chairs have always seen themselves as the custodians of the assessments. They’re not writing the assessments — the assessment is being written by the scientists. It wouldn’t be our job as the co-chairs to sit down and say, “Well, here’s a draft executive summary. Let’s kind of tinker with that.” So there’s a question about who owns the intellectual input of the assessment and so on. I was saying the co-chairs really need to be seen as people who are the surface of the assessment in a way.

Brysse:

You’re scientists yourselves though.

Pyle:

Absolutely. My group has done work recently, which will certainly be featured in the assessment. There’s no doubt about it. In a sense what we’re not doing — As I said, there is a danger that people want to push their own particular research angle. I think the leadership of the assessment must be done by people who are trying to be as scientifically impartial as they can be. That’s to say it’s not about my science versus your science. It’s about somebody doing the assessment of the science, and then we point together for scientists everywhere.

Brysse:

Do you find there is a tension between on the one hand you want the people who are actually experts in the field to be writing the chapters, but on the other hand if they are always busy writing chapters for assessments they may not have time to continue their work and they’ll no longer be experts in the field?

Pyle:

I don’t think that’s as big a problem as it is in IPCC. I don’t see a fatigue in the same way as there is with IPCC. Ted Sheppard and I were the convening lead authors of a chapter and there was a special report on ozone depleting gases and climate change.

Brysse:

Special report for the IPCC?

Pyle:

And for TEAP. It’s this one here. Safeguarding the Ozone Layer in the Global Climate System. So it was a special report for the IPCC and TEAP. So I was a convening lead author on a chapter on chemistry climate interactions for that. It was a really interesting experience. IPCC is much more formal than the WMO assessments. They are very strict about what is admissible and what is not. That’s not to say that the ozone assessment isn’t strict, but I think we’re aiming for is the best possible assessment. I think IPCC says we have to produce assessments within these very, very constrained set of rules. Even if everybody agrees something should be in, if it doesn’t satisfy the criteria of when it was published, etc. then we can’t do it. What that means is the IPCC process, so we had three or four meetings for the chapter that I was involved in. And the first chapter was fantastic because we were coming together and saying what’s going to go into this and what’s the stuff that’s out there. And then the succeeding two or three meetings were really polishing that original chapter; no new material was really coming forward. Intellectually it was — You were honing your arguments and making sure that it came across really well and was successful and so on, but you couldn’t bring new information in really because the rules said there’s this great new paper coming out, but it’s not out yet so you can’t have it. The rules for the ozone assessment are supposed to be somewhat similar, although I guess we’ve got a little bit more time with the ozone assessment in terms of when that kind of — If we know something has been accepted for publication, then it can go in. The IPCC assessment seems much more cautious about that. It may not appear; okay, it’s in review. So I find the IPCC process much less stimulating toward the end of the process than the WMO assessment. I also find it quite political. For example, this is not news to anybody, every single comment that comes in from a scientific reviewer or government reviewer has to be addressed. Even if you say, “Done. Done. Done. Didn’t do.” You’ve got to say something. Temperamentally, that doesn’t suit me. Once I’ve done something, I just want to move on to the next thing. The idea of spending ages saying why you didn’t address a particular issue when it was because it was a stupid comment, it’s just a waste of time for me. I know other people who have been involved in the IPCC assessments who find that sort of pointed thing quite tedious. On the other hand, all the people I know who went to Paris for the IPCC in 2007 all obviously thought, as they were doing, something really important, and were on a high because of that. It swings around about, but for me a lot of the snakes are kind of worse than the ladders, are not compensated for by the ladders.

Brysse:

Can we talk a little bit about modeling? I should have refreshed myself on chapter 12 of the blue book assessment, but I didn’t have a copy with me. I remember that I enjoyed reading it because you included a really big discussion of some of the kinds of assumptions that have to go into models, these are the different kinds of models, and these are the things we can get right for sure and these are things that are…Can we talk a little bit more about uncertainties?

Pyle:

The game has changed tremendously since the mid-1980s. Then we were using simple, simple. At that stage they were the bee’s knees, but these were two-dimensional models of the atmosphere where you describe the average of the flow around circles of latitude. So you’re looking at the atmosphere from pole to pole and from the surface too. Some height. When you do that, inevitably you have to parameterize some of the processes; a kind of so called eddy processes that are going on. There was a lot of discussion at that time about that. Two new models were the workhorse, really, until in the 1990s what started to be used by a group of people were three-dimensional models where the models were driven by specified winds and temperatures. The advantage of these models is that if the specifications of winds and temperatures is good, and you get these from the weather services (I forgot what they call them in the States; European centers is what we in Europe would traditionally use, or the meteorology office or somebody else), and they produce these global analyses every day that you can use to drive your model. When we ran our models with these things and we could reproduce the kind of observations that the people were seeing in polar latitudes, for example, can structure across the vortex edge and so on. So those models were really good at describing what’s going on. They’re not very good at predicting what’s going to happen in the future because you are doing a kind of post-hoc analysis — you’re looking at what happened last week or last month or last year. We don’t have the analysis for the future although models can make projections about the future. Certainly I think a lot of the science about what was going on was tied down because we had these sophisticated models to use. We could look in detail day-by-day the ozone levels fell off.

Brysse:

Including the ozone hole?

Pyle:

Yes. For example, we can run models that reproduce the observed decline of the ozone at a particular location.

Brysse:

To get the Antarctic ozone hole in the models, did you have to do anything else besides this inclusion of the specified winds and temperatures? Did you have to start including heterogeneous reactions?

Pyle:

Oh yes, of course. There are two developments in models. The whole point about polar ozone depletion is that we had a huge argument in the late ’80s about what to do, and there were kind of camps saying, “It’s chemistry,” and there were other camps saying, “No, it’s meteorology.” Basically, it’s a chemical process that happens there because of the meteorology. It’s not chemistry versus physics — all of these processes are coming together. Clearly if you want a model to reproduce the observations, then that model has to have the best description of chemistry you can possibly have, but it also needs to have the best description of meteorology that you can have as well. Indeed, one of the problems that we had in the late 1980s was that people were starting to realize that heterogeneous chemistry was important and we started putting that in our new working models. Those two-dimensional models were not very good about reproducing the peculiar dynamics of the polar vortex because essentially it is a three-dimensional phenomenon. It’s really difficult to — You know, the idea of having an enclosed vortex, which is what happens here, air inside strongly isolated from air outside, is difficult to do in those two-dimensional models. We got around it by playing around again with diffusion co-efficiencies and so on, creating barriers to transport. But the models had to be adjusted. So there was this big increase in understanding about the role of heterogeneous chemistry. And that happened. With that we got improved meteorological models by using the weather service models, places like the European center. We were suddenly able to do a pretty good job of describing the observed ozone loss of the seasonal cycle. There are still in some models you will find some vices, but the basic structure was reproduced during the 1990s.

Brysse:

So it took maybe three or four years after the discovery of the ozone hole and getting the ozone hole to be fairly reliably reproduced in models? Maybe a little more?

Pyle:

I would have said it was probably ten years before we had good three-dimensional models that were doing a really good reproducing job. But that’s not to say that there weren’t some excellent simulations going on even in the 1980s with these simple models. The whole point is it’s a process of evolution, so there isn’t a day when you say everything is perfect. It’s kind of incremental. But what certainly happened was a shift over a decade more towards these three-dimensional models. I think it was the late ’90s, which bit of engineering, the kind of three-dimensional model, forced by observed winds and temperatures became kind of the norm. And then what happens since is that the problem has changed. Certainly the scientists are not arguing anymore about ozone depletion. There have been little ripples of arguments about whether the kinetic data is right. But by-and-large we’ve got a pretty good description of what is going on. The problem has changed to being one about can we understand now how ozone will change in the future in response to the Montreal protocol, but also in response to changing greenhouse gases in the atmosphere. It comes back to this thing that I said I did some work on in 1980, but because we had this model that would allow us to look at some of those interactions in a kind of simple way. Now people are trying to look at those interactions in climate models. So you’re adding the chemistry of the ozone layer to climate models to see what happens. It’s also about how will ozone recover given these various factors? But what will that change in ozone do to surface climate? It’s a kind of two-way thing. The way that climate changes, matter of fact ozone, because of reactions that destroy ozone tend to be temperature dependent. The winds move ozone around, so you change the wind distribution and then you change the distribution of ozone in the stratosphere. But also ozone is an important radiative gas. It’s a greenhouse gas. It also absorbs much of our radiation strongly, so it can affect the heating of the atmosphere in complex ways. The question is as ozone changes, what’s that going to do to the surface? Those have become the big research questions. The issues there, we’re running climate models which have their limitations like all models. There are questions about can you run the models with sufficient resolutions, sufficient special resolution to capture the kind of features that we might be interested in. If we are running for long periods of time, we are not dealing with an initial value problem. We’re dealing with a problem that is inherently — the kind of system is chaotic. So you want to run not just one simulation, but you’d like to run twenty or fifty or something so you have an ensemble. You understand how that ensemble of calculations behaves. You can be much more confident. So can we do that? Have we parameterized those processes that need to be parameterized properly? For example, in most numerical models, convective transport has to be parameterized because convection is happening on very small spatial scales. The climate models we’re talking about, if the sizes of your grid boxes were 100 kilometers by 100 kilometers, which would be a pretty good resolution. And convection is happening kilometer-by-kilometer or less. So we have to parameterize those processes. And those processes are important in terms of moving the material that could destroy ozone from the lower atmosphere to the upper atmosphere and so on. There are a number of other examples like that that you could pick out. There’ve been long-standing issues of how well does your model reproduce the behavior. The thing particularly about polar ozone is that the depletion is all or nothing. If the temperature doesn’t drop below about 195 Calvin, you don’t get depletion. This is a slight caricature, but if it’s 196, nothing happens; if it’s 194, everything happens. What you’re asking then is how good is your model at reproducing the temperatures to two degrees? If you have a bias that you’re two degrees too high, then you’re not going to get the depletion. If you’re model is biased two-degrees too low, then you’re going to get too much depletion. And that’s a real challenge. There are lots of issues associated with that. In some ways moving from models of the 1990s, which are still being used, where we take the observed winds and temperatures and going to the climate models where we are predicting everything — you know, we just throw it all in, churn the equations and out the other end comes the answer. That’s a much more difficult problem to get everything absolutely right.

Brysse:

I want to pull together a couple of things you said a few minutes ago. On the one hand you said the ozone question that by and large the science is pretty good. Everyone pretty much agrees that ozone depletion is happening. It’s being caused by CFCs. We’ve got regulations in place about that. Then on the other hand the direction we are moving in now is the connections between climate change and ozone depletion. With those two things in mind, where are the ozone assessments going? Are there going to continue to be ozone assessments or will they get folded into the IPCC assessments?

Pyle:

That’s a question that all the scientists are asking as well. I think scientifically, then, those assessments have got to come much closer together. There isn’t an argument about it.

Brysse:

The IPCC assessments?

Pyle:

The IPCC and the WMO assessments, in a sense, need to come closer together. That’s to say, if you like, they should be folded into each other. On the other hand, there are still some questions which are intrinsically for the chemical industry that they might say, “Well…” It’s interesting, there are territorial questions as well, and some people think if I — It’s a bit like scientifically at the moment, there is a lot of talk about Earth system science. Everything is part of the Earth system so all our things go in there. Some of the scientific communities are saying, “Well, actually if I’m part of this much bigger community, I may not get some of the resources that I want to do the things that I want to do.” If atmospheric chemistry becomes just a tiny bit of the Earth’s system, it may not serve me as well in terms of trying to pursue my research agendas if it’s thrown in with this, because another community might be bigger and for whatever reason able to pull in more money. I think what happens to the assessments will partly be dictated by — First of all, clearly you’re under Montreal and its amendments; there’s still a need to report. And whether the IPCC process can do that adequately would need to be decided. I think there will also be questions on the part of the scientists. Some of them will say, “Yeah, we don’t need these anymore. They can just be folded in.” They are different to IPCC assessments. The other thing about the IPCC assessments is that they are getting bigger and bigger and bigger and bigger. So there will be a question about is the best thing to throw everything in together or is it still, even though there’s a large overlap, and it’s important that that overlap is recognized increasingly, is it still right that for certain audiences we’re better off producing a small report that deals with particular things? That might be more effective. One of the things that I’ve heard people talk about is what, in assessment terms, should we think about HFCs? These are compounds that don’t destroy ozone. They are replacements for compounds that did. And they have greenhouse gases. Should the ozone assessment consider these gases? Because the replacement for the CFCs and the HFCs are these… you know some people were using these as replacements. Should we say, “Not our problem?” I’ve heard arguments either way. So on the one hand people are saying, “HFCs are purely and simply a problem for IPCC.” But on the other hand, if you don’t recognize that HFCs are really part of the solution to the ozone depletion problem, it’s a new problem for somebody else. I don’t think the ozone depletion people could say, “Well, actually that’s somebody else’s problem now.” There are some people who say we should definitely do that. And there are other people who would say, “Oh, you’re being a bit territorial because it has nothing to do with ozone depletion.” They are not simple questions. That isn’t a simple question. There are scientific issues and they will be clearly. I think having just articulated that, the ozone assessment can’t ignore the HFCs. It would be a bit irresponsible if we did. That’s clearly an area where you’d expect to see overlap with IPCC.

Brysse:

Slightly different question. There was a period, I don’t know exactly when this was, but I’m hoping you do, when the discussion in the assessments and I think in the scientific papers shifted from talking about the ozone depletion potential of chemicals to the chlorine loading potential. I’m interested in exactly when and why that happened and who started it.

Pyle:

There are one or two people who you should speak to. Susan Solomon has been somebody who did a lot of work on ODPs, but she would have her own view of what happened there. And you might want to speak to other people as well. This is an important question because it comes to the question of how we get messages across to policy makers. The problem with ODPs and the reason why these other metrics were kind of invented is because they are not actually very good numbers in some ways. Let me rephrase that. It’s clear that some compounds are much bigger ozone depleters than other compounds. And if something has an ozone depletion potential of 1,000 and something has an ozone depletion potential of 1, the thing with 1,000 is the thing that you don’t want to get in the atmosphere rather than the thing with 1 if they are going to be emitted in similar quantities. ODPs are useful for that. What became clear in the area that I got involved in is that when you are looking at replacements with short lifetimes, you are looking at short lifetime replacements. We did some work on n-propyl bromide, and we showed that the effective ozone depletion potential varied depending on where you emitted it. In other words, this is not an intrinsic property of the compound, but it depends on circumstances as well. I think similarly if you talk to the IPCC community they’d say, “We use global warming potentials, but people are trying to invent other metrics which might be better.”

Brysse:

Like CO₂E.

Pyle:

Whatever. Yes, a variety of different metrics that they want to use. And a problem with any metric is there’s a danger that it’s over simplified, because you are trying to do something laudable, which is to say to users, to politicians, to regulators, etc., “This compound is worse than that compound. I’ve got a number that tells you how much worse it is.” That’s very laudable; it’s just that under certain circumstances those numbers start to break down. I often get phoned up by people saying, “I want a compound that has an ODP of 0.0. Is that all good?” You actually think, “Frankly, I’d rather you didn’t use the compound that had an ODP at all.” That’s clearly the best of all possible worlds. But you’ve got to accept that small contents of a compound which has a very low ODP so long as there’s nothing else bad about it. It’s clearly better than large compounds with large ODP. But actually deciding on, “Do I feel confident enough in my metric to say that there ought to be a break-off point somewhere?” Whatever you decide about the break-off point, below ODP it’s okay, above it it’s not. It’s just a bit arbitrary; it’s got to be. There is not an intrinsic ODP value that below that it’s good and above that it’s bad.

Brysse:

It depends on the quantities you’re planning to emit.

Pyle:

Exactly! It depends on both of those things. Small quantities of varying ODP are clearly less bad than large quantities of a larger ODP. I’m not really answering your question. The bottom line was that those changes were brought about because people recognize that there were limitations in ODPs, and that they depended on other things. We now know that ozone depletion doesn’t just happen because of chlorine compound it happens because of bromine compounds. And the amount of depletion you’re going to get in the future will depend on the two trajectories of chlorine and bromine to the future. Bromine and chlorine interact together in different ways in the middle latitudes to the high latitudes. Susan Solomon introduced the so-called empirical ODPs, where she used some of the information that you’ve got from making measurements. That also recognized the fact that the effective ODPs varied with latitude as well. So not just latitude. The work that I did said, “If you emit these compounds in the tropics but then lift it very quickly into the stratosphere by convection…” So convection the stuff up on the time scale of hours, it might get into the stratosphere, then it could have a high ODP. If on the other hand you emit it in northern Europe in the winter under an inversion, then these compounds are much more likely to take a long time to get anywhere dangerous and they may well have been killed off by then. So the ozone depletion could be different.

Brysse:

Will that happen with CFCs though?

Pyle:

No, CFCs are just so long-lived. The CFC lifetime is 100 — many, many decades. We’re talking about replacements. The whole point of going to short-lived replacements is that you hope they don’t get into the stratosphere. But we now realize that some of them can get into the stratosphere under certain circumstances.

Brysse:

Did the ODP to CLP have anything to do with heterogeneous chemistry? I thought I’d read that part of it was the reactions were getting so hard to calculate and model that you couldn’t take the calculations all the way to ODP anymore. So they were sort of stopped at chlorine loading potential.

Pyle:

I think the feeling was that chlorine loading potential was more effective because of this complexity about the chemistry that goes on. It depends where your chlorine is, how effective it’s going to be, and what the background bromine is, how effective that depletion is going to be. I think chlorine loading was a kind of slightly simpler message in that it wasn’t trying to say, “This is how much depletion we get,” but basically the more chlorine in the stratosphere the less good that is. So something that’s going to put a lot of chlorine in the stratosphere is less desirable than something that’s going to put no chlorine in the stratosphere, or the tiniest amount in the stratosphere.

Brysse:

So it’s safe to conclude that switching from ozone depletion potential to chlorine loading potential means that it’s sort of a signal that at that time, there is a consensus, that ozone depletion is happening, it’s being caused by chlorine. The fact that you can talk about chlorine loading potential…

Pyle:

It certainly wasn’t backing away from the idea that these things were depleting ozone. It was more recognizing the fact that ozone depletion potentials were under some circumstances difficult to calculate and potentially misleading at the margins. So again, the point I’m making is that nobody’s going to say that a compound with a very large ODP is better than a compound with a very small ODP. But it’s when you start arguing what exactly is the ODP of this compound that you can start getting into difficulties.

Brysse:

We go back to talking about the assessment process. Let me know if you think you covered this already. If you imagine writing a scientific paper with two or three colleagues versus working on an assessment with a large number of authors working together, is the assessment process just a scaled-up version of writing a paper with colleagues, or is it actually a qualitatively different process as well? And I guess the other question I’m asking is what’s the difference between assessments and papers?

Pyle:

The assessment, first and foremost — There’s an expression that I used, which Dan Albrightson said I was the first one to say, I don’t know that I was, one of the problems with the assessment process is that you want lots of new information, but what the assessments are supposed to be about is saying, “Let’s assess the information that we already have.” So there’s a tension in the assessment between saying, “We must find something else new, because here are some interesting questions that we don’t quite know the answers to, but with a bit of work we can do.” And on the other hand, say the IPCC model is very much — you know, “If it’s not in the literature, then we can’t do it.” This idea of doing science on the hoof, you’re making it up as you go along — you’re not actually making up, you’re doing it as you go along — is something that I said to Dan, you know, the assessment was asking for all these new calculations, and I said, “That’s fine, but it’s not just a matter of doing the calculations. Somebody needs to think about the results of the calculations to make sure…” What you don’t want to do is go into an assessment with something that is half-baked. So what the assessment is supposed to be about, as opposed to writing papers, is saying, “This stuff is in the literature, and there is a strong consensus in this area where we can see several people have done this from different angles and they are all saying the same thing. This is go.” And then there might be other areas where we say, “Actually there seems to be a bit of disagreement between scientists about this part of the process.” And you might say this is something that we also think about much more. “This is where we stand at the moment, but we’re not really so clear what the impact of this bit is.” That’s the difference. Whereas when I write a scientific paper we’re doing calculations and we get that stuff out. I’m assimilating that information and I’m digesting that information, analyzing, and then we write the paper. But the assessment is supposed to be one step beyond that. It’s at a higher level in that we’re really working largely from published papers. There are new calculations that are done for the assessment. You’ve got to be careful to make sure that they’ve been worked out carefully. That’s the difference between assessments and writing scientific papers. Is it different writing in — I think people have the same pride of authorship as when they are writing their own papers. But what now happens is that the lead authors will have their chapter meetings soon for the assessment, and they’ll say, “We’ve been told to keep this down to 20 printed pages. Here are six different things that we want to go in it. And you and you can write two pages on that…” It’s not normally micromanaged at that level, but, “This is the bit you’re doing and this is the bit you’re doing,” and you can kind of write it and do it. So at that level you are breaking into much smaller teams; all thirteen people are not writing on the whole thing. What they do is they will all review that thing. So the first set of reviews, the authors do themselves, because they’ll read that their colleagues will have written two pages on something or other. Actually that’s okay. I don’t like that as it sort of conflicts with what I’m saying somewhere in the report. So it’s different. But it’s not really different to when I write a scientific paper. I’m always writing papers with people in my group, so I tend to write something, they do some work, I write it up and then we iterate it. So it’s not fantastically different. As I say, the very first model that I use in that blue book, I actually sat down and wrote that chapter myself. And I don’t think people would do that now.

Brysse:

Well it sure sounds like a lot of work.

Pyle:

It was fantastic. As I say, at that stage in my career it was a great thing to do. I can’t imagine anybody at an equivalent stage of his career wanting to do that. You want to make sure that your footprint is visible in the report. It just got too big.

Brysse:

Either as a lead author of a chapter or as a co-chair of the assessment as a whole, how would you handle uncertainty? If you are trying to present a consensus on whatever is supposed to be in the chapter or the assessment, and there just isn’t a consensus, “These scientists say this, these say that,” and you somehow have to present all of that information together.

Pyle:

I don’t think that’s too difficult. I think you just have to say, “These are areas where we still are not sure about the process so we need more data. We need more laboratory data or whatever.” There have been arguments in the past about things, which — Again, I’m not the best person to talk to about. But for example, how methylbromide was handled. I know that caused a lot of angst amongst the practitioners. In methylbromide where there was an argument about how much of the methylbromide was anthropogenic and how much of it was natural. There was a strong disagreement there. I think the way the chapter came out, the chapter decided to go kind of one way, and a couple of the people involved with it were very unhappy with it.

Brysse:

Which report was that?

Pyle:

I can’t remember. It would again be in the mid-’90s, but I really can’t remember.

Brysse:

Well, that’s a good thing for me to look at. I led a group discussion with a bunch of people yesterday, and we had a really great talk about handling uncertainty in estimates. For example, the IPCC if they are trying to predict sea level rise it might be six meters plus or minus three and trying to tie both the probability or certainty of that…

Pyle:

You mean in terms of the language?

Brysse:

Yes. Like the IPCC has come up with…

Pyle:

Likely, very likely.

Brysse:

Yes. And they go with particular numbers. Somebody pointed out that the ozone assessments haven’t really ever done that with the numbers. There was some discussion of why, and Peter Brysiker [?], a post-doc, said… or maybe it was someone in response to him. Anyway, somebody said that they didn’t really think that the ozone assessments ever really needed to do that because there wasn’t the level of uncertainty that there is in the IPCC report. So the underlying idea there would be the more uncertain you are, the more quantification you need. What are your thoughts on that?

Pyle:

I guess there’ve been stages in the past when we’ve not known things. When the ozone hole was discovered in 1985, we still didn’t know if the same thing would happen in the Arctic at that stage. So there have been times when we’ve not known about things. I think it’s different in that the ozone assessment process started off in a quite different way than the IPCC process. Firstly, industry was kind of involved, so industry funded some of the research. They wanted the research to say these compounds are good for the atmosphere; they’re good for everybody, obviously. But they funded research that was carried out and demonstrated that in fact they weren’t good for the atmosphere in terms of their ozone depletion. I think it’s actually quite interesting that if they hadn’t depleted ozone, these gases would have been such a disaster for the climate system. It’s kind of ironic, but it’s a good thing they were ozone depleters. But that’s another matter. I think that the people that needed persuading for the ozone reports were essentially industry and regulators. I think climate is a different question altogether. It’s so much wider. I find the IPCC language — two things. It’s not clear to me how in IPCC they actually decide that something is likely as opposed to very likely. You can put numbers on it, but for every time they use that word — I don’t think somebody’s done a numerical assessment to decide that really it is 90% not likely. So it’s not clear to me that going — I think that it is important for IPCC. I think they need to try to show that people have at least sat down and argued about where they put things. However, you have to say, “I’ve got a bit of a concern about how it’s not obvious to me how you’re quantifying your level of certainty.” From my point of view, I think climate change is happening. I don't think it's very likely, I think it's absolutely without doubt that we’re putting something into the atmosphere that is affecting the climate system. For me saying it’s 90% likely to be due to human activity I think kind of underestimates it. I’m not sure if I’ve answered that question very well. I think the IPCC reports have a much wider audience than the WMO reports. I think that’s one of the reasons why you need to persuade the general public. The general public didn’t need persuading about ozone depletion quite frankly.

Brysse:

What do you think the role or impact of the assessments has been? Obviously, I suppose the simple answer is politicians don’t have time and aren’t willing to read scientific papers so you have to give them something they are going to read. Is there more than that that the assessments have done?

Pyle:

I think for the scientific community the assessments have been a very strong kind of focal point for the community. So I think they’ve actually strengthened the community. So I think being involved in the assessment and working for the assessment has actually been good for the science. So ultimately it’s been good for the assessment because we’ve had more good science to talk about.

Brysse:

In a networking kind of way and stimulating more research?

Pyle:

Yes, in lots of ways. Certainly networking. It has helped to develop a very strong — The ozone community has been a pretty strong and coherent community for 20 years. I think that’s been one of the advantages of it. And that’s one reason, as long as you think the science is worth doing, that maintaining an independent assessment is a good idea.

Brysse:

What role do the assessments play in the policy-making?

Pyle:

It’s clear they’ve played an important role. Which bit of the assessments have played a role? I think just the process of producing them. There’s no doubt politicians don’t sit down and read a total nothing. Somebody who works for a politician will read the executive summary, and they might dip into it a bit, depending on how interested they are or not. But the process of producing it has been important, and I think what it has done — If you look at the subsequent amendments that have been made, the faster phasing out of HFCs and so on, that’s continuing to happen because of the assessment process. I think it’s very beneficial.

Brysse:

Thank you very much for meeting with me.

Pyle:

It’s a pleasure.