Interview with Kerry Emanuel

Question: Where do you stand in the controversy on hurricane’s behavior changing or not, do you look at a particular pool or are you leading a more global research?

Answer : There are differences for sure. The clearest signal that we see  and that could be related to global warming is in the Atlantic, which you have to remember is only about 12% of the global number of storms. But we have by far the best data there. This is where it gets tricky., when you look at the metrics, the metrics which have the clearest signal is power dissipation. When calculating the power of dissipation one needs to know the wind speed of storms. Now, it’s not widely understood that estimating wind speed from satellite is very dicey. You can get two different expert groups looking at the same satellite data and coming up with completely different estimates of wind speed, whereas the Atlantic has the advantage of nearly continuous aircrafts observations beginning in the 1940’s, although the really good measurements didn’t begin until about 1958. But even in the Atlantic only a roughly a third of the storms are surveyed, although they tend to be the more powerful ones and contribute disproportionally to this power dissipation. So, one reason to look at the Atlantic is that we have by far the best data there, but the other is that it seems that in the Atlantic there is a clear relationship between ocean temperature and hurricane power.

Q : You mentioned that you sometimes work with economists. What are their role in this research?

A : Well, so I just published a paper in Nature Climate Change in January with an economist, quite a good one. His name is Robert Mendelsohn. And, there was  a project funded by the World Bank and I ran this synthesis hurricane event sets for different climates using downscaling from different global climate models. He basically converted the meteorological advance into a human advance, estimating the amount of damage that each of these synthetically generated storms would do to existing infrastructures and also to infrastructures that are projected to exist a 100 years from now.

Q : Is it joining the thesis of Pielke?

A : Roger Pielke’s point has always been, for the US, that demographic changes overshadow climate changes. We look at the whole world, we look at future climates, we came to the conclusion that it’s more like half and half. That is, if you look at damage increases in places where damage does increase, (it doesn’t increase everywhere by the way), about half of it is just simply due to changing wealth in infrastructure, and about half of it due to changing climate. The reason that we have much more emphasis on climate than Roger did is that the US is almost unique in having policies in places with people moving to the coast. Even if the population and economy are stable, there’s still this huge migration from inland to coastal region, which you don’t see in other parts of the world. So it’s not surprising that the demographic signals have been stronger in the US than elsewhere.

Q : Would that also explain the fact that reinsurance companies have an increasing role in the research for hurricane behavior?

A : Oh I think so. I think there are a lot of differences between insurance companies and reinsurance companies. The big one is that most reinsurance companies are global, that is their clients are global. Whereas insurance companies, their clients are local, I mean I sit in the board of an insurance company in Massachusetts and in Connecticut, that’s pretty local. Any change in activity globally shows up immediately as a signal in their business so they are much more interested in funding the research.

Q: If scientists disagree in the fact that frequency and intensity vary or not, or only frequency or only intensity, is it a matter of methods that they use ?

A : I think it’s to some extent a matter of methods, it’s also a matter of metrics. One thing I’d like to draw your attention away from is the classical frequency/intensity dichotomy. It’s not a very good one, and the reason for it is for a concern about the social impact of hurricanes. You have to be cognizant of the fact that it’s 80% of hurricane damage is caused by only 30% of the storms, most of it are the high categories ones (the 3, 4, 5). So advances that dominate that frequency are advances that really don’t matter for us. So what we should be concerned with is the frequency of intense hurricanes. That’s a very different matter. More power dissipation is something that varies with the frequency of intense hurricanes.

Q : And you think that only a few scientists look at this problem this way ?

A : Yes, that’s the problem nowadays. They are focused on this frequency/intensity problem… So, many places in the world where global warming is expected to decrease the frequency of storms. And yet, we see that destruction by the storm is increasing. There’s no contradiction there, it’s because the frequency of the intense events is going up.