IRA FLATOW, host:
You're listening to Talk of the Nation, Science Friday. I'm Ira Flatow. A little bit later, we'll be talking about tracking the melting of the Greenland ice sheet. But up next, a lesson in science as a moving target. In studies released over the past few years, several researchers studying the relationship between global warming and the weather have concluded that global warming may create more powerful hurricanes, if not more of them. But now research out in the Bulletin of the American Meteorological Society questions whether that view may be too simplistic, and what adds weight to the paper is that the lead author was one of the first to point out the hurricane/global warming connection. He joins us now. Kerry Emanuel is a professor of Atmospheric Science at MIT. Welcome back to the program, Dr. Emanuel.
Dr. KERRY EMANUEL (Professor of Atmospheric Science, MIT): Nice to be back.
FLATOW: Let me just refresh all of our memories back in Nature, a paper in 2005, you wrote, my results suggest that future warming may lead to an upward trend in tropical cyclone destructive potential. Now, with this new paper, are you changing that position and revising it? Give us some idea of what you're talking about now.
Dr. EMANUEL: Well, I think the new study certainly modifies that instead of looking at past data and drawing conclusions directly from that, what we've done is to develop a new technique which allows us to infer from the course output of climate models what their hurricane climatology should be, And what that study suggests going forward is that globally the changes we expect to see while we do still expect to see an increase in hurricane power somewhat less than what one would do simply from extrapolating what happened over the past.
FLATOW: So, would that explain why we haven't seen the strong hurricanes predicted by the last couple of seasons?
Dr. EMANUEL: No, because both of these techniques - looking at the past climate change and also looking at the future, look at sort of long-term variability and ignore the year-to-year variability. So, we really can't - nothing we've done that really does address the year-to-year fluctuations.
FLATOW: Now, in this new paper, you developed a new way to model hurricanes in conditions of global warming. What does this model do better that the previous ones?
Dr. EMANUEL: Well, the previous study that I did was not a model at all. It was simply an analysis of hurricane data and showed that hurricane power is very strongly correlated with measured ocean temperature. There are studies on the other hand which have looked at global climate model projections. And the problem with global climate models themselves is they're far too coarse to resolve hurricanes. Their grid points are maybe 100 or 200 km apart. And the intense core of a hurricane may be 10 km or 20 km across. So, our technique gets around that by running very detailed specialized, very highly-resolved hurricane models embedded within the climate model. And so, we can essentially get the best of both worlds. We can get the global climate models to produce what they're supposed to do, which is to predict global climate and the hurricane models do what they're supposed to do which is to suggest how hurricanes ought to react to that.
FLATOW: So, you have two separate models here that have to be reconciled? Would that be accurate?
Dr. EMANUEL: Well, I think the thing that we're all puzzled about is that, you know, we saw something like a 60 percent increase in hurricane power globally. And when we use this new technique run on past climate data sets, that gives a result which is very consistent with what we saw in the hurricane data themselves. That is we saw the 60 percent increase over the last 25 years. But now, when we apply that technique going forward over the next hundred years, we see much more modest increases and that is a dilemma. It might be - that one interpretation is that maybe what we've seen over the last 25 years really isn't due to global warming. It's due to something else. Another possible interpretation is that there's something systematically wrong with these climate models which isn't capturing the global warming signal that we're seeing in nature. But we don't know which of those two it is yet.
FLATOW: So, you're keeping an open mind about this.
Dr. EMANUEL: Yes, yes, I think we have to.
FLATOW: And what do you need to see, to change your mind one way or the other, the third way?
Dr. EMANUEL: Well, I think we need to try to get to the bottom of why the changes that we're observing this two new techniques, happen. That is what aspect of the physical changes in the atmosphere being predicted by global climate models, are driving the changes that we see in hurricane activity. If we can get to the bottom of that, we can begin to understand whether how much confidence to place in these projections or whether there might be something we discovered that's systematically wrong with the way these models are working.
FLATOW: So, to just sum up in the last minute or two that we have, you're not backing away from your prediction that there will be stronger hurricanes?
Dr. EMANUEL: No, I think both the data and the models suggest qualitatively that hurricanes should become stronger, they may become less numerous globally. But what we see in this technique is a lot of variation from one model to the next, and from one place to the next. So, we're really talking about numbers here. The indications are hurricane power will go up, but we need to know whether it's going to go up by a trivial amount that we shouldn't worry about or by enough that we do need to worry about it.
FLATOW: And because you can't predict the immediate from these models, it doesn't really affect us one way or the other in this hurricane season.
Dr. EMANUEL: No, no, nothing that we're doing really has any bearing on what's going to happen next year or even in the next 10 years. I mean, we have to be looking out much further than that.
FLATOW: That's typical science, we'll stay tuned. Thank you, Kerry, for taking time to be with us.
Dr. EMANUEL: You're quite welcome.
FLATOW: Kerry Emanuel is professor of Atmospheric Science at MIT in Cambridge talking about a new data about hurricanes.