0:33 Intro. [Recording date: March 3, 2014.] Russ: Welcome to a special edition of EconTalk, recorded live at the College of Business Administration at the U. of Alabama in Huntsville.... Our topic for today is climate change, and I'll be moderating a conversation in front of a live audience between two scientists with different perspectives on the issue. Climate change reminds me a lot of macroeconomics. We have a complex system, many causal factors, and we're often interested in the impact of one key variable. In macro, it might be fiscal policy or monetary policy or a change in taxes. With the climate, we are interested in temperature or how rainfall or hurricanes respond to human activity, and in particular increases in carbon dioxide in the atmosphere. In both the climate, and the economy, there are experts on both sides of the issue. We are highly confident they understand how these complex systems work. Everyday citizens--those of us who are not experts--we struggle with finding out where the truth lies. How do we evaluate which expert is credible? Who can we trust? Is that the wrong model? Is it possible for anyone to figure out where the truth lies? And what I'm interested in discovering today is where there is agreement, where there is disagreement, and why does disagreement persist in this very important area of public policy and science. Now, to introduce our guests. John Christy is.... Kerry Emanuel is....

2:43 Russ: We're going to start with each guest making a brief statement, one to two minutes, about what we know and don't know about the climate, to get us started. John Christy, go ahead. GuestC: Thank you, and it's a delight to welcome both of you here at the U. of Alabama in Huntsville. Ultimately the question before us is a moral question, not a scientific question. Is it good to enhance and [?] human life. Today and for the foreseeable future, the reliable energy that enhances human life and which is economically viable comes from burning carbon. That will continue no matter what our country decides to do. Does extra CO_2 cause climate problems? The observations tell us not much is happening to the climate that hasn't happened before. Now, a fundamental aspect about the scientific method is that when we understand a system, we can predict its behavior. That has not happened for our climate system. It is true that we have an expensive climate modeling industry that shows scary changes. But they are unable to replicate the actual climate system today. In fact, 100% of the latest climate models overshoot the key target variable of climate change detection. And there is no model that has been rigorously validated for reliability. We are not bad people for burning carbon. Indeed, from my experience from living in Africa, I can say with conviction that we are good people, because of the immeasurable enhancement to human life that carbon now provides.

4:18 Russ: Kerry Emanuel, what is your view, what we know and don't know? GuestE: Well, thank you for inviting me here. It's delightful to be with you all this evening. In the middle of the 19th century, the gifted Irish physicist, John Tyndall, made a remarkable discovery using a laboratory apparatus--it was [?]--that is that all of the absorption of infrared radiation that takes place in our atmosphere is done by a tiny amount of gas that makes up less than 1% of the atmosphere. That was quite a shocking revelation at the time. And not long after that, the Swedish chemist, Svante Arrhenius, found out that the climate is heavily regulated by one of the greenhouse gases, carbon dioxide, whose mass represents four ten-thousands of our atmosphere--a tiny trace. And calculated that without that four ten-thousands part of our atmosphere that is carbon dioxide, the earth would be a snowball. We wouldn't be here. We couldn't survive. This is not in dispute, this finding of the scientific community. It was not made with supercomputers. It was made with pencil and paper, and it can be replicated today. If that tiny amount of greenhouse gas is what is making our planet habitable, then there would be no surprise that if we double or triple it, we are taking a risk with the climate system. And that's how it has to be viewed. It's a risk. So, going forward, we are taking a risk. Not with ourselves--not with me. I'm old enough that it doesn't matter. But with future generations. And a rational people deal with a risk rationally. And my whole program is to try to de-tribalize this debate. You know, it's not about this is going to be a climate catastrophe on the one side, or nothing on the other. And it's also not about trying to do something about it--it will be an economic catastrophe on one side or won't have any effect on the other. That's not the way the world works. The world is more complex. We have a set of poorly quantified risks for action, and a set of, maybe, as poorly quantified risks in taking action. That's the problem we have to deal with. And that's what I'm here tonight to talk to you about it.

6:29 Russ: So, I want to start us off by talking about the idea of climate models. John, you said that climate models have been poor predictors. I want to get your opinion on that, Kerry, in a second, but before we talk about the quality of these models, Kerry, I wonder if you could start us off by explaining how these models are actually constructed. So, in economics what we do, we have a lot of data, say, about a macroeconomic variable--GDP (Gross Domestic Product) or labor, the amount of unemployment, the number of hours. And we know it's a factor of a lot of different variables, so we try to use very statistical techniques--typically multiple regression analysis, a fancy term--to try to hold other things constant while one thing changes, and look at the impact of that one thing. And the statistical techniques that do that are pretty good. And then there are issues: Have you measured things correctly? Have you controlled accurately for these variables as legitimate, is there correlation going in both directions? Etc. Is that what we do in climate modeling, or is it a little bit different? GuestE: Let me just preface my answer here to your important question by saying that a lot of what we know about the climate system was predicted long before there was such a thing as a climate model. It's a mistake to think that everything we knew about climate or predictions about climate are based on complicated models. Having said that, we have built over the years a hierarchy of increasingly complex models that really are some of the most complicated pieces of software that the human race has ever constructed. They have their origins in models that were built for a much more pedestrian but important purpose, which is weather forecasting. And they are very complex. In the case of weather forecasting, arguably you can test them twice a day and see how well they are doing. With climate, it's much more difficult to test them because we don't have that many climate states. But we do experiments that are much along the lines of what you had just described as done with economic models. We try to hold certain variables constant, like sunlight. And vary another external factor, like carbon dioxide, to see how the system responds. Russ: In the case of economics, what we typically do is we take, say, data up to the present. And then we say, based on the relationship between these variables in the past, here's what's going to happen in the future. Is that the same idea in climate modeling? GuestC: Uh, no, it isn't the same. Because there is a huge difference between climate modeling and economic modeling. We know the equations. You guys don't. Okay? And we actually know the equations we are trying to solve. And the problems come with actually trying to solve them. And arguably our computers aren't nearly powerful enough to really solve them exactly; and they won't be for generations, unless there is some unbelievable breakthrough in computation. So, that philosophy is very different. We are actually solving or trying to solve known equations, for the most part. Russ: So in economics--I don't want to miss a chance to get in my favorite joke in economics, which is: How do you know a macroeconomist? And the answer is because a macroeconomist uses decimal points. And that's clearly an illusion of precision in the case of macroeconomics. Whereas, here, the isn't the precision of the underlying equations. It's: How do the underlying equations interact? Is that a correct way to summarize what the issue is? GuestC: It's a fair way to summarize the issue.

9:53 Russ: Let's talk also about--and we are going to get into the implications of these models in a second. Before I do that, one more bit of foundation-laying, which is: John, I'd like you--you talk about how we actually measure the raw variables we want to talk about. Because John has done a lot of work on that here at the U. of Alabama in Huntsville. And I think most of us who are not climate scientists tend to think, Well, there's a thing called 'The Temperature.' But of course the world's a big place. And 'The Temperature', the thing we are trying to explain and measure, is not so straightforward. So, talk a little bit about what--the amount, the level of complexity involved in that is. GuestC: Well, it's quite a bit, I think. Let me first of all say that we don't have a thermometer that can tell us how much warming is due to human effects and how much is due to Mother Nature. We just don't have a thermometer to do that. And so it comes down to, a lot of times, about opinion. About how much is one way or the other. Now, to measure at least what the temperature is doing, the way Roy Spencer and I have done it is through is through the fact microwaves in the atmosphere from atmospheric oxygen, up well and are captured by satellites and the intensity of that radiation is proportional to the temperature of the atmosphere. That's fairly straightforward. And you are talking about measuring the thermometers on the surface--it's a much more murky process because a thermometer is commonly go[?], the instruments change, a lot of places aren't monitored, the setting around the thermometer changes with parking lots or farms or so on. So that's kind of a bit more of a complication there. Russ: Kerry, is there any dispute about the underlying data to be explained? Is there any--how precise is that? GuestE: In science, there is always a dispute about the underlying data. You never get around it, nor should you get around it. Um, however, the surface temperature record for the last 80 years or so was pretty robust. How do we know that? Well, we can take the analyses that are based on the observations, and arbitrarily throw away about 70% of the data--just throw it away, to review the analysis. And we see the same long-term trend. Versus the little wiggles from year to year and decade to decade. It's a pretty robust record. But it is not by any means the sole piece of evidence, observationally, for the fact that the earth is changing. Now.

12:14 Russ: So, let's get into that. We'll start with John. John, you have just said in your opening remarks, and you've written recently in the Wall Street Journal, that climate models have consistently over-predicted the amount of warming. Correct? GuestC: Yes. We looked at 100 into the latest simulations. That's all that we were able to download. And in every single case, we saw that the portion of the atmosphere that is most sensitive to greenhouse forcing, in the models at least, over-predicted by at least a factor of 2, what has actually happened in the world of the past 35 years. So we are not talking about just 10 or 15 years. This is over a third of a century that we can see these models are over-projecting what is actually happening on the planet. Russ: Do you agree with that, Kerry? GuestE: Not particularly. I would say--I actually share with John an inherent distrust of complicated models. I don't like them particularly. It's one of the necessary evils. And I want to get back to the point that we base projections, even projections along more than models. Yeah, it depends very much on where you look, when you look, and the time period over which you look. If you look at Svante Arrhenius's prediction about what would happen in 1897 he said that doubling CO_2 would give rise to about 4 degrees Centigrade change in temperature. Russ: Four. GuestE: Four. Today, with all of our supercomputer models we estimate that doubling would result in a temperature increase of between one and a half and four and a half. See, that's not bad for 19th century when you were doing things with paper and pencil. If you look at the temperature records and natural logarithm of CO_2 content over 100 years, it's a spectacular correlation between the two. Is it perfect? No, because there is natural variability. There always will be. And it's poorly quantified. I don't think we understand it very well. I will say that as predicted, most of the heat that you are putting into the system from excess greenhouse gases actually goes in the ocean. It's much more massive and has a higher heat capacity. We haven't been able to measure the ocean nearly as well as the atmosphere until quite recently. But in the last few decades it's very clear that the heat content of the ocean is going up. So we have lots of different, completely independent pieces of evidence, none of which I would argue--here I agree with John--is a smoking gun, but all of which together amounts to a very compelling case that the climate is changing and we're doing it. Russ: Do you agree, John? GuestC: Not exactly. No. I'm not going to argue about the fact that the temperature has risen. Well, here's a news flash: The temperature has always risen, and fallen, in the earth's history. It has been warmer than it is today. It has been cooler than it is today. Without the impact or the influence of mankind. And so, I go back to that other point: We don't have a thermometer that can tell us: this much is due to humans, this much is due to mother nature. And so someone can make the case that it's all due to human effects, or someone can say it's all due to mother nature, because you don't have a way to separate that. I can say from the models, though-- Russ: Kerry, do you agree with that? GuestC: that the hardcore evidence we have, and anyone can repeat this, is that every single one of the models overpredicted what happened over the past 35[?] years. Russ: I want to focus on two issues here. One is the overprediction of the particular--the sophisticated--models, not the back of the envelope. And 2, do you agree with his statement, which I know you don't, that we cannot disentangle any actual increase between human and natural causes. GuestE: Well, let me first say that clearly the climate has always varied. And one of the spectacular successes of climate science is to begin to understand how it's varied in the past. I'm not going to get into it here; we pretty much understand the root cause of the great glacial cycles. There have been roughly ten in the last 3 million years. So, there is something about climate science. But, the fact that it's always changing, right, does not mean we shouldn't be concerned about the change that's going on now. Saying that it's always changed in this context is rather like a defendant in a murder trial saying, yeah, well, people are always dying. Right? It's true, but we're concerned about this change and what it portends for the future. So, I'm afraid I've lost track of the[?]-- Russ: So back to the--the specific question I want to challenge John's claim is that: Well, there's been some warming. And in a minute I'm going to press each of you to talk about how much, because magnitudes matter a great deal, I think, particularly when you get to the policy implications. I think there is a [?] real, genuine consensus from people that the climate is warmer today than it was 40 years ago. And then the crucial question is: how much warmer and why? John says we can't measure why it's warmer, dividing between, disentangling human versus natural causes. I don't think you agree with that. GuestE: I don't agree with that. I agree with that on the 10 or 15 year time scale. I don't agree with that on a 50 year time scale. The fact is that most of the changes we see in climate on these longer time scales are forced, and there are a variety of things that force--it's not just greenhouse gases. There is solar variability. There is cooling of the planet, demonstrably when volcanoes erupt. And there's cooling of the planet that's caused, demonstrably I think, by us, through aerosols and things. The fact of the matter is that solar output, which has been measured very carefully for a few decades has if anything been going down. This warming that we've seen in the last 40 years, I would say with 95% confidence, and 95% of my colleagues agree, has been caused by greenhouse gases building up. Now, is there a chance that John is right and it's not? Or whether regardless of how John feels about it, it's not going? Yes, there is. This is what risk is. If you sit here and say, I need a complete guarantee that we are taking a risk before I do anything, you are not treating this part of risk the same way you treat any other part of risk. If I said to you, I'm going to let my toddler cross the street unless you can guarantee with 98% certainty that that toddler won't get run down, I'm not going to be very comforted. Right? That's the problem we are dealing with. Can I prove absolutely in a court of law? Probably not. But to the satisfaction of 97% of my colleagues, yes. Russ: John? GuestC: That 97% is a canard, I think. That is a very simple question about do humans contribute to climate change at the root, the meaning of that question, which I would agree with. So I'm in the 97%. But like I say, we can't tell why it is warming. But one of the tools that you can use to untangle this is the climate model. And so we can put CO_2, extra CO_2, in the model and see how it warms. Well, using the same amount of CO_2 putting in the model that is actually in the real world turns out to produce, on average, models that are three times warmer than what has actually happened. So my claim is: Whatever is happening in the world, at least the climate models are over-doing it. It's very clear they are. There's no question about that. Because that's what the evidence and the numbers show. And so I don't see, the real prominent things that probably are happening with negative feedback and internal variability--just the way the internal physics of the thing works--can lead to rises and falls in temperature. And so they have happened in the past. And it's hard to convict carbon dioxide of committing a crime if he can look back and say this has happened before and I wasn't there. Russ: What's your answer to that, Kerry? GuestE: Well, I think it's relatively easy, and the fact Svante Arrhenius did it in 1897 without big supercomputers--my students do it after taking a couple of semesters with models they've built themselves. I don't think it's that difficult. But I would agree that internal random variability is there. And the climate would change even if all the forcing agents I talked about before were constant. We're confident of that. We're not terribly confident that we know this noise quantitatively. For example, it might be that if it weren't for carbon dioxide increasing that the climate of the earth would cool, would have cooled over the last 15 years. We don't know that that's not true. These fluctuations occur on top of the forcing. So it's a little bit like, you know, here in Alabama you can have a day at the end of April which is colder than a day at the beginning of April; and you wouldn't conclude from that, that summer isn't coming. Weather, superimposed on the seasonal cycle. I will say that climate models have been wrong in a lot of different regards. And there, John and I agree. Their predictions aren't particularly good. But it's not one-sided. For example, no climate model predicted the demise of summertime marking CIs[?] at the rate it's actually occurring. It's going much faster than the models--any model--predicted. And I'm in the field of hurricanes, and I actually made predictions back in the 1980s about how fast hurricanes would respond to climate change. In at least the Atlantic, they've been responding much faster than I can account for. No, I don't know why. Okay. So, these models aren't particularly good. But all the evidence points to a pretty compelling picture of risk here.

22:05 Russ: I want to come back to the economics point. We just passed the 5-year anniversary of the American Reinvestment and Recovery Act--the so-called stimulus package. And proponents of the stimulus package would tell you that it worked. And they'll point to historical examples where stimulus worked. But they won't point to the examples where it didn't work. And they can't predict the impact--they did not accurately predict the impact on [?] unemployment, which is they grossly underestimated the impact on employment. The question is: what do you do about that. You concede that the models are inaccurate, but you don't concede that there is inaccurate in only one direction. Would that be a correct way to summarize that? John, you want to say anything else in response to that? GuestC: I would just say, yeah, none of the models predicted that the Antarctic sea ice would increase, either. GuestE: That's right. GuestC: So that Arctic one needs to be balanced by that. But in terms of this fundamental parameter of the bulk atmospheric temperature, every single model went the wrong direction. Russ: Is that accurate? Do you agree with that? GuestE: Not entirely. I'll tell you why. Because these models are not just run once. They are run many times, to try to account for their own internal random variability. And you can find 15, 20, 25 year stretches in all of these projections where the temperature not only flattens out but it actually goes down a little bit. So, if you take the ensemble mean, then it's correct that the last 30 years, the models have overpredicted the temperature. I might add that 30 years before that, they underpredicted it. And this is what happens when you superimpose natural variability on forced variability.

23:42 Russ: So, in your book, you suggest that over the next 100 years--and I'm addressing Kerry now, for those of you listening at home who can't see us up here and can't tell the voices apart as well as you might--you suggest the next 100 years, "if nothing changes"--and of course that's a, it's hard to, you didn't really mean that literally if you said that. It meant if we don't do anything radical to slow down the accumulation of carbon dioxide in the atmosphere--that the temperature would grow by approximately--not by approximately--it would grow in a range of 2.5-9 degrees Fahrenheit. So, the low estimate of the impact would be 2.5 degrees. The high estimate would be 9 degrees. How confident are you of that range? And we'll talk about the implications of it in a sec. But how confident are you of that? GuestE: Well, if you choose the range large enough it's easy to be confident. Russ: More confident. You can get more confident. That's a large range, but it starts with a--the lower end is pretty high. So that's why-- GuestC: Is this Fahrenheit? GuestE: Fahrenheit. Yeah. This is something that any serious climate scientist--and I think the two of us on this stage represent this, in this respect--would immediately tell you, is that we are very uncertain about these projections. Nobody pretends to be certain about it. But there just isn't much certainty in that. To say it's between 2.5 and 9 degrees for a doubling or more of CO_2, Fahrenheit, it's to confess that we don't know. All right? And so what we are dealing with is a problem of the[?] t-curve. Okay? The near end, it doesn't morph, it's 2.5 degrees--we don't have to worry very much, I would argue. And I don't think many of my colleagues would suggest we do. If it's in the middle range, there will be problems. Probably we'll adapt to them. If it's up at the higher end, that could be catastrophic. And the question for me is: Do we do nothing to avoid, even a small risk of catastrophe for our grandchildren? To me, that's the moral question. Russ: We're going to come to that in a second. Maybe a little more than a second. Toward the end I want to talk about what ought to be done, if anything, to cope with this. But I want to get John Christy's reaction to the 2.5-9. It's a modest claim on the surface because it's a large range. It's like when the CBO (Congressional Budget Office) says things about the impact on employment. They are very often vague. Which gives it an unscientific air. It does raise the question of the precision of the estimate. But again, it's a large range. You'd think that would engender confidence. Does it engender confidence in you, John? GuestC: Well, I would go with the very low end part of that range. We have, you know, 35 years period that has a couple of volcanoes that helped tilt the trend a little bit higher. But it is rising at about 2.5 Fahrenheit per century right now. So that's some evidence that that's about the rate it wants to go. Russ: He can't make you more nervous for your grandchildren? GuestC: No, I love my grandchildren. I think I am more nervous about something the government might do that would harm them more than anything the climate might do. Russ: It's a cynical approach. It's a cynical remark that I am of course sympathetic to. But we are going to put my sympathies to the side until we get to the discussion, discussion of policy.

27:15 Russ: I want to bring up another issue, in terms of what we know and don't know. What is your feeling, Kerry, about the apparent--and you can challenge the claim if you like--the apparent pause in temperature rise over the last 15 years? Again, as a crude, empirical--a mere social scientist, yes, I confess. When I look at the raw numbers of the temperature nominally over the last 15 years, it looks awfully flat to me. Is that correct? And given that the rise in CO_2 over that period has been the same as before--it's been rather dramatic--how do you explain that and what's your position on it? GuestE: Well, I would be dishonest if I told you I understood that. First of all, just [?], yes. The temperature, the global mean temperature, is pretty flat for 15 years. It was also pretty flat from about 1952 to the 1970s or so. So it's not the first time it's flattened out. And what we're--I don't think the community of scientists is very sure about, is we're seeing a manifestation of internal variability, natural oscillations that happen to be working against the radiatively[?] forced signal at the moment, or whether there is something about the radiative forcing that we haven't understood. For example, my colleague at MIT (Massachusetts Institute of Technology), Citizen Solomon[?], just last week published a paper--I think it was in Science, I don't know if you saw it--suggesting that the fact that we've had a large number of relatively mild volcanic eruptions in the last 10 or 15 years may have put enough aerosol[?] collectively into the atmosphere to affect the temperature. Now I haven't had a chance to digest that. I think the scientific community does have to get on top of this. And in fact all the other periods of reduced and enhanced warming in the past. Russ: Does the Pause give you pause? You were confident that there is a small chance of a large rise, based on the rough science and some of the models. Does it cause you to be a little more conservative? GuestE: Well, no. Not really. I think that range was generous enough that I would stick with it, until--maybe if we had 30 years of Pause. That would give me pause. Russ: We'll be back in 2029. Perhaps. Go ahead. GuestE: What would we all be saying if the next 15 years is rising at twice the rate the models predicted? Would we be trying to revise our estimates? I would have to say that I probably wouldn't revise my estimate upward, either, in response to that. There's a certain amount of natural variability that goes on. Russ: What are your thoughts on the so-called Pause, John? GuestC: I have no idea why it happened, but my thoughts back to what I have said in the introduction. When we understand a system in a scientific way, we can predict its behavior. I know of no one who predicted a flat temperature trend for the past 15, 16, 17 years. We were all under the belief--me, included--that CO_2 forcing would cause even more warming. And yet it did not happen. Russ: However, we do see--and I notice this elsewhere, on this platform, that people who are worried about global warming and climate change will point out there have been many plateaus in the past; that the underlying trend is what matters; small, short-term variability, of again--15 year's is one person's eon and one person's blink, another person's blink. You are suggesting it's closer to an eon. Kerry thinks it's a blink. Can't really make any conclusion from it. Past times, we've had plateaus. Is that just the difference here? Just a question of [?]-- GuestC: Well remember [?] when we talk about 120-30 years, we are starting at one of the coldest periods in the earth's history in the last 10,000 years. So the fact it's warming at all could be completely due to the natural variations. I happen to think the actual carbon dioxide, there is no way you could say it is not a forcing mechanism. It is doing something. And it turns out, and from what I gather and from what I can understand, is that there are ways that the earth's system itself actually feeds back in a negative way, so that that heat energy is not being stored like a climate model stores it. And so therefore the temperature is rising much more slowly, if at all. Russ: Kerry, can you convince him? Can you try to take a shot? Here's what I think. You can't argue with his basic point, because you conceded it, that of course, in any one year, any 5 years, maybe 15 years things happen we don't fully understand. The world is a complicated place. But the underlying science, which [?] back to 1897, which seems very convincing: Why can't John Christy see that this large increase in carbon dioxide accumulation is inevitably going to cause significant warming? Why do you think you can't convince him of that? GuestE: Well, because I'm a climate scientist and not a psychiatrist. I guess. Russ: A cheap shot. But go ahead. But an amusing one. The crowd really liked it. Go ahead. GuestE: I could have said something better [?]. Russ: Uh, I join you on most of that. [?] GuestE: You really do, I think, to look at, when you look at the earth's history, the response to forcing as at long time scales, I think you really do have to look at the 100 year time scale. That's very hard for us. We're much more interested in what's happening today and tomorrow, and very early on. When you look at the very long term, let's say not even that long by geological standards, 3 million year record, of climate, on the earth, and you see the spectacular fluctuations of climate--yes, and they were natural. And yes, in the case [?] usually--carbon dioxide itself, content itself fluctuated. In fact, most climate scientists believe that the tropics cooled and warmed was because of changes in CO_2. What you see, when you look at that record, is the last 7 thousand years, up to about 100 years ago, was remarkably stable. Sea levels remarkably stable. The climate was remarkably stable. We were very blessed to generate civilization in that 7000 years. Okay? And yes, if we didn't do anything at all, the orbital forcing suggests that we would be slowly cooling. As we in fact were, up until about 100 years ago. I agree with that. And we would continue to cool until maybe in 10 or 20,000 years--that's really a long time away--we would plummet, and probably will plummet, into another ice age. This thing is short. What we are doing now is short by geological standards. But still fairly long on the human time scale. I can't convince myself, as much as I would like to, that we aren't running a risk. I think we are running enough of a risk with our grandchildren that we should pay attention to that. Russ: John? GuestC: Um, was I supposed to be convinced by that? Russ: I don't know. Yeah. You could invoke, you could mention psychiatrists if you want. Or anything else you can think. GuestC: No, I, you know, I just go back to the hard numbers of the data. We just do not see these kinds of changes that are dramatic, that are hard[?], that were predicted. They are not happening. And so I am just am rooted in what's really happening in the planet.

34:39 Russ: Well, let's move on to a different area. Which is sometimes as far as I can see goes under the name of 'extreme climate events.' This would be hurricanes, droughts, famines, etc. Kerry, your specialty is hurricanes. Have hurricanes and other extreme events gotten worse over the last 40 or 50 years, and can we attribute that to climate--to human activity? GuestE: I'm sorry to have to give a nuance. Russ: I like nuance. GuestE: In the Atlantic, demonstrably hurricane power has increased over the last 30 years by a big factor, too. I don't profess to understand that. It's gone up hand in hand with the tropical Atlantic surface temperature in the summer time. It's a tiny piece of the globe. And maybe some of that is global warming. I don't honestly know. I don't want to try to give you the illusion that I understand this. When you look globally, the problem there is a problem with data. The data are very poor outside the Atlantic. In the Atlantic we fly airplanes. I've done that. We fly airplanes into hurricanes. But we don't do that anywhere else in the world. 90% of the world's hurricanes occur outside the Atlantic. And so we are forced to rely on data which is not particularly suited for this. There is some indication of an upward trend in the most intense hurricanes, but I wouldn't want to put my money on that. Russ: Did you say you've flown airplanes into hurricanes? GuestE: Yes. Russ: What was that like? GuestE: Better than some flights I've had on Delta Airlines. Seriously, it's not as bad as you might think. Russ: As someone who doesn't want to take a lot of risk, that would make me a little bit nervous. It sounds like it was probably a pretty exhilarating experience. As a scientist. GuestE: Everybody should see the eye of a hurricane. When I retire, I'm going to start a hurricane safari operation, seek paying customers. Russ: That would be awesome. John, what do you think about hurricanes? GuestC: Dr. Emanuel is the expert on that. And I think he gave a terrific answer there. I look at other kinds of climate variables that are more readily available to us in terms of longer data sets, and those are things like droughts and floods and so on. And we are nowhere near the kinds of extremes that have occurred in the past thousand years in this country, for sure, where we have had mega-droughts. These are hundred-year kind of droughts, out West, and the periods of dryness and in fact the temperature here in Alabama has actually declined in the past 103 years. So when you look at those kind of extreme events, you don't see any change, really. Russ: Do you think there is hope of modeling hurricanes more precisely? GuestC: That's not a question I can answer. I always hope we can get better tracks because we are exposed on our Gulf Coast and it would be a terrific advancement to have. Russ: Are we getting better at it? GuestC: Over the last 40 or 50 years we've gotten substantially better at forecasting hurricane tracks. Really demonstrably better. Not much improvement at all in hurricane intensity. Russ: The tracking thing--they have a band of uncertainty around it. And I remember as a kid they were always off. And now they are really pretty good. I'd always say, when I'd look at the picture: Who knows? But they are pretty reliable now. Seems that way.

38:00 Russ: Let's talk about another thing people care a lot about, you've mentioned briefly, which is sea level and Arctic ice. It's an issue that came up in a recent EconTalk episode with Judith Curry. What's going on with ice in the north and the south? How much do we know about it? How much uncertainty do we have about its impact on sea level? Kerry, you go first. GuestE: So, sea level is going up. And apparently at an accelerating rate. Russ: Can I ask, before you go on: How do you measure that? The sea is in a lot of places. GuestE: That's right. So, before the satellite era, it was measured with tide gauges. There's a real sampling problem with that. By the way, most people think the sea level rises uniformly around the globe. It doesn't. You can actually find places where it is going down. Just like temperature. [?] that's because it's affected by wind and things. In the satellite era, we've been able to measure the absolute altitude of the sea level globally, with absolutely stunning accuracy. The magicians at NASA (National Aeronautics and Space Administration) somehow figured out how to do this. And there's no question that it's going up globally, now, with those measurements. The ice is more complicated. First of all, sea ice, which we see a lot of changes, it doesn't affect sea level, when it melts it doesn't change sea level. Russ: [?] In general? GuestE: No. The sea ice doesn't change it at all. Russ: That's not an issue? GuestE: No. In fact, if you don't believe me, right after this talk go and mix yourself a nice Scotch on the rocks; I highly recommend it; and watch the ice melt. Tell me what happens to the Scotch. Russ: It's simple science. GuestE: Or if you are a teetotaler you can use Coke; that's okay. That's allowed. Anyway-- Russ: People don't talk about it that way, though. They talk a lot about the ice melting affecting the sea level. Is that-- GuestE: Well, the land ice, when that melts, it does affect it. So when ice melts that's sitting on land, like Greenland or Antarctica, melts, that affects the sea level. When it melts, the sea level goes up. The sea ice doesn't really change things. The Arctic sea ice in the summertime has been in decline since we've been able to measure it, which isn't terribly long. Antarctica is mixed, but in general, actual sea ice is increasing in Antarctica, not decreasing. Mountain glaciers, which are another[?] form of ice, almost all of them in retreat now, and we see big changes historically in glaciers. It's much harder to measure what's important for your sea level with[?] the big ice sheets in Greenland and Antarctica. And we are getting better and better at measuring those, but I think it's a little too soon to say what's happening to them. In both[?] the weight of the evidence is that they are losing mass, but they are certainly not losing mass everywhere. Russ: And what kind of magnitudes of sea level change do you think we are talking about here? GuestE: Well, this is--the best estimates from the last IPCC (Intergovernmental Panel on Climate Change) reporter on the order of a meter or so--3 feet by the end of the century. But everybody who is in that business says there is much more uncertainty about that than anything else. And one of the problems is that we don't actually understand the physics very well. You'd think we would by now. If I'd written a book called "What We Don't Know about Climate Science," it would have been an encyclopedia. Russ: Longer book. GuestE: But we don't really understand the physics at which ice slides off of big continents, like Greenland. It's not just melting and the water trickling into the sea. There's actually glaciers that flow off the ice sheets and calve into icebergs. That's what did the Titanic in, in the ocean. And we don't know whether that will accelerate. Here's what we can say: is that there were various times in the geological past, in previous interglacial periods, where apparently most of the Greenland ice sheet was gone--not all of it. If you did melt it all, somehow, and it would probably take a long time to do that, you are talking about 7 meters of sea level rise. You know, 25 feet or so. It's a big number. And Antarctica, if you melted that, I can't remember the exact number but it's much more. It's 50 meters or something like that. That's an awful lot of ice, and everybody I know in the field thinks it would take an awfully long time to do that. Russ: The implication is that small or potentially large parts of currently inhabited parts of the world would be under water. GuestE: So, if we go into an extreme-- Russ: I'm sorry, I just want to say, I've seen these, you may have seen these where Florida drops off the face of the earth and becomes an underground island. My attitude on that is partially--well, overnight it would be really bad. Over 150 years, not so bad. If it happened over 10 years, much harder to deal with. Might not be our best thing. What are your thoughts? GuestE: Well, the time scale is everything. It certainly won't happen--we don't think it will happen--in 10 years. But here's some food for thought. I think, and I'm now speaking a little more philosophically, that historically science and scientists have been very concerned with it in their estimates of risk. We didn't predict that there could be a magnitude 9 earthquake off of Japan that caused that huge tsunami. The largest estimates were for 8.3, which is way lower, actually. There are a lot of things that we haven't predicted. What we do know from the ice core records in the past, particularly in cold periods, the earth was capable of rather sudden changes, flips if you will, in the climate, at least locally, and we don't understand those flips. So, you know, what keeps us awake at night are the risks that we are missing. Okay? And we don't think that Greenland ice is going to go very fast. But there are a few models on it that say, yeah, once it gets going, it's really going to go. Nobody attaches a lot of importance to that, and we've put a very low probability on that, but we are frightened by what we don't know about that problem. Russ: John, talk about your thoughts on ice and sea level. GuestC: Well, the sea level is rising. And it will continue to rise because there is more land ice to melt. If you go back to the last interglacial, about 130,000 years ago, we find that sea level reached 6 meters higher than it is today. So, that should go on about an inch per decade just on that. Remember that out West in the Rocky Mountains and so on, those glaciers only appeared between a period of 3700 and 1900 years ago. So they are relatively new in the sense of our most recent climate. When I advise people about sea level, I say it's going to go up about an inch per decade, and if you are on the Gulf Coast, that's not your problem. It's the 15 feet in 6 hours when the next hurricane comes. That's your problem. Russ: For sure. GuestC: So that's the attack and that's the vulnerability you have there on the coast. Russ: So, you don't think there is a social or civilization issue that over the next hundred years we are going to lose some important things. GuestC: Well, it would happen very slowly. When people are building infrastructure on the coast and I have to do some kind of reports for those, I tell them: Look, if you are going to be there 100 years, plan for a meter of sea level rise. And if you build your infrastructure for that way, that much I think you are okay with. The hurricanes are what are going to hit you. Russ: Do you think we can do something about that meter? In other words, can human, can public policy, human behavioral changes, reduce the threat of the meter increase? GuestC: No. I presented evidence in Federal court before Congress and so on that the legislative action being planned and so on just will have no impact on that. Russ: Do you agree with that, Kerry? GuestE: I don't think it will have a direct impact, but I think it could have a pretty big indirect impact. Like all movements that go on, it starts small and it starts with something doable whose direct effect is probably not measurable. So in that sense I agree with it. But we have to start somewhere. You can't start with solving the whole problem in one day. That doesn't work. You have to start somewhere. I suppose at some point we'll talk about solutions to that. Russ: In about a minute. But I want to go back to John's claim, because the way I understood John's claim is that the rise in the sea level over the last century and the expected rise over the next century is overwhelmingly driven by a large trend that has nothing to do with human change, human activity, which is the recession of the ice age and glaciers, where carbon dioxide has virtually nothing to do with it. GuestE: Well, right now, the carbon dioxide influence hasn't had a whole lot of time to build up. It's only been around a few decades, really. And these are big blocks of ice, and they take a lot of effort to melt. And so it takes thousands of years for these things to melt. Is carbon dioxide adding to that? I think so. I think it is adding a little more. That's why I say an inch per decade instead of the 3/4 of an inch from last century that we experienced. Russ: One of the greatest things in the world that I didn't know about till recently is that until refrigeration people made money carving out large blocks of ice, putting them in the holds of ships, and taking them to very hot places so they could have a cold drink. Which now is not a viable economic enterprise because of refrigeration. But it does take a long time for a big piece of ice to melt, which is rather remarkable.