A friend recently recommended Russ Roberts’s Econtalk episode in which he interviews climatologists John Christy and Kerry Emmanuel in front of a large audience at the University of Alabama in Huntsville. I listened to it and followed along with the transcript and it is excellent.

In the area of global warming, it’s hard to find a civil discussion between two experts who disagree. This is one. Partly, I think, it’s because Russ does a good job of being even-handed and drawing out the facts and conjectures. But probably more important is that both Christy and Emmanuel are reasonable people.

Some excerpts follow.

From Christy’s opening statement:

3:00: 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.

From Emmanuel’s opening statement:

4:35: 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.

Here’s one of the most interesting parts:

27:20: Roberts: 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?
Emmanuel: M hmm. [Yes.]
Roberts: 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? What’s your position on it?
Emmanuel: Well, I would be dishonest if I told you I understood that. First of all, 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 whether 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) Susan 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.
Roberts: 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?
Emmanuel: Well, no. Not really. I think that range [2.5 to 9 degrees Fahrenheit] was generous enough that I would stick with it, until–maybe if we had 30 years of Pause. That would give me pause.

29:55: Roberts: What are your thoughts on the so-called Pause, John?
Christy: I have no idea why it happened, but my thoughts are 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.

40:50: On the ocean level:

Roberts: And what kind of magnitudes of sea level change do you think we are talking about here?
Emmanuel: 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.

48:48: Policy Views:

Christy: The risk of something bad happening by making energy expensive is real. People will suffer if energy prices go up; we already know that; there’s just no question about that–and as I said, living in Africa, I know what energy poverty does–it kills people. And so anything we can do to allow energy to expand into those areas that do not have it is going to enhance human life and welfare. So, solutions to–if you are really concerned about the carbon dioxide then how can you create energy that is affordable–that’s the only kind that really works in the economy–what choices are out there? And the big one that can answer the question is actually nuclear power. We’re sitting right here between a couple of big power plants, actually. And it’s difficult. It’s a bet-the-company move right now for the few that are trying to build nuclear power. And that’s probably got to change.
Roberts: Kerry?
Emmanuel: Well, I actually agree with that. I think it’s a mistake to do anything that increases world poverty. The history of this is very clear. Economic gains particularly in developing countries are largely, very strongly tied to the consumption of energy. So, we have to be clever about how we attack this risk. And I’m not of the camp that says, we should just go cold turkey on fossil fuels. We can’t do that. Nobody in their right mind would suggest we do that. But we should try to approach this risk as intelligent people by exploring all kinds of alternatives. The experts I talk to are–and I’m certainly not one–say it’s a question of doing a lot of little things that amount to a big thing, like building more energy efficient buildings, even in developing countries. It actually ends up saving people money because they are not consuming as much energy. Energy still costs something. Migrating away where it’s practical from fossil fuels toward renewables. So there are some parts of the world, including Africa, where it actually makes sense to have a supplemental supply. Can’t do everything with solar power, or maybe wind. I’m a big proponent, I get into lots of trouble with my colleagues over this, but like John, I’m a big proponent of nuclear energy. I’m so tired of being told we can’t do it. France went from almost no nuclear to 80% nuclear in 15 years. Are you seriously telling me that the United States can’t do, cannot do, what France did? I don’t think so. There’s one other piece of technology which would allow us to burn at least natural gas as much as we want to, if we could only get there, which is to capture the carbon from the atmosphere and sequester it. And I think it makes a lot of sense to put some money, not to jeopardize the economy, but some research and development money, into trying to develop this technology to the point where it might some day make economic sense to do that. We are not that far from being able to do it even today. So these are sensible things. We don’t have to bet the farm. We just do sensible things.

52:30: Both, surprisingly to me, were very down on geo-engineering.
At 53:25, Emmanuel says why: Someone, even an individual, might get the technology to geo-engineer.

55:30: Roberts asks if either of the guests is ever embarrassed by people on his side. They both answer emphatically yes.

1:01:00: Advice on what to read on climate.
1:01:25: Emmanuel says don’t read blogs on climate science. Read good books about the physics of climate.
1:03:20: Christy says read Congressional testimony of scientists–not of advocates or politicians, but of scientists.