We’ve on occasion discussed a paper that we did in 2000 on the relative contributions to future damage of changes in intensity of hurricanes (called tropical cyclones worldwide) and changes in societal vulnerability, under the assumptions of the IPCC to 2050. Our paper found that the independent effects of changes in societal vulnerability are larger than the independent effects of changes in storm intensity by a factor of between 22 to 1 and 100 to one. The ratios are far larger the further one goes into the future. This would seems to provide pretty compelling evidence that even if scientists are underestimating the degree to which hurricane intensity will change in the future, energy policies simply are not going to be an effective tool of hurricane policy. Thus we have often recommended keeping separate the issues of greenhouse gas reductions and hurricane policy.

For obvious reasons some people find this argument inconvenient. One response to a talk I gave on this last week was, “if we don’t have the imagery of hurricane damage it is going to make the task of selling greenhouse gas reductions that much harder” (see also the recent discussion at Kevin’s NoSeNada blog, and thanks to Brian S. for motivating this further discussion). Below is some simple math that should make the point inescapable, drawn from the analysis in Pielke et al. 2000 (PDF). Have a look, and play around with the numbers yourself.


A = hurricane damages today = $1

B = increase in hurricane damages in 2050, according to high end of IPCC TAR = 10% increase = $1 * 0.10 = $0.10

C = increase in hurriane damage in 2050, according to low end of IPCC TAR in Pielke/Landsea normalization method = 220% increase = $1 * 2.20 = $2.20

D = combined effect of B and C = $2.20 * 0.10 = $0.22

E = Total increase in costs = B + C + D = $0.10 + $2.20 + $0.22 = $2.52

F = Total costs in 2050 = A + E = $3.52

Of E the part that can be addressed by intentionally modulating the intensity of hurricanes (a dubious proposition, but lets assume) is $0.32 (B + D), and the part that can be addressed by addressing vulnerability is $2.44 (C + D) (note: does not equal E because D is counted twice because it is influenced by both factors).

So if you focus on energy policies as a way to modulate hurricane behavior as a tool of disaster mitigation, and assuming that (a) you can instantaneously reduce GHGs to pre-industrial, and (b) that we are not committed to change already, then you can at best reduce the increase in future damages from $3.52 to $3.20, still representing a 320% increase from today.

But lets be slightly more realistic, how about Kyoto? Assuming that the effects of GHG reductions on hurricane intensity are instantaneous and exactly proportional to emissions concentrations (also dubious assumptions, but lets go with them) under full and successful implementation of Kyoto, including the participation of the US, the reduction in projected damages would be about $0.03. (Assuming: increase 2005-2050 = ~120 ppm, Kyoto’s effects = ~12 ppm, $0.32 * 12/120 = ~$0.03, but substitute numbers as you wish, I just made these up.) Now before people start writing to tell me Kyoto is a first step, please go ahead and substitute second, third, and fourth steps as you wish and see what effects they get. Then get back to the political realities such as Kyoto is not meeting its targets, and the subsequent steps look a long way off (not to mention the incorrect simplifying scientific assumptions above about the close connections of GHG reductions and corresponding reductions in hurricane intensity) .

Again, it is important for me repeat that I support emissions reductions, and I even think Kyoto makes good political sense for the U.S. to be a part of, however, it stretches credulity to think that Kyoto or any emissions reductions policy makes sense as a tool of hurricane (or more generally, disaster) mitigation. The important policy question is not whether or not global warming affects hurricanes, it probably does, but rather, what outcomes can be expected from different policies in response to hurricanes related to the things we care about, like property and life?

Moving on, if you focus on reducing vulnerability as a tool of disaster mitigation, then you can at best reduce the increase in future damages by $2.42 to $1.10, representing an increase of 10% from today. And of course mitigation need not stop at the level of damages we see today, and in principle can cut into that original $1.00 of losses, which proportionately reduces the increase related to changing storm intensity. It seems obvious that achieving the same $0.03 reduction in future losses from the $2.42 expected due to increasing vulnerability would be a much more tractable and cost effective approach to hurricane mitigation than an indirect effort to modulate storm behavior. Put another way, 100% success in implementation of Kyoto is the equivalent of about 1% success in addressing vulnerability. This is a huge difference in both the politics and the practicality.

Note that all of the above are calculated using the most favorable ratio toward emissions reductions of 22 to 1. The other end of the scale is 100 to one, so keep that in mind. Alos keep in mind that this anaysis goes to 2050, if you’d like to extend it to, say, 2085, probably should at least quadruple the vulneability numbers and increase the intensity numbers by a percent or three.

The bottom line: For advocates of emissions reductions, asserting a hurricane-energy policy linkage is tempting, very tempting. But it does not make good policy sense. It is a bad argument, perhaps even an abuse of science or immoral. If scientific accuracy is of concern, then look elsewhere for your justifications.