The Economy and Hurricanes

Donald Sensing might be on to something. Last month saw the creation of 337,000 new jobs. Guess where a big part of that number came from?

Part of the pick-up in jobs was down to the worst hurricane seasons for many years. About 71,000 new construction jobs had been added - the most since March 2000.

If President Bush can be blamed for the hurricanes, he ought to get full credit for it as well.

Now, I know Rev. Sensing is jesting. But, I want to address something which his post brought up: the notion that global warming is responsible for or will lead to an increase in hurricane activity or strength. This is "demonstrably false". Hurricanes deliver heat from the equator to the poles. That's why they originate in the tropics and move to the colder polar regions, losing energy on the way. As George Taylor, a climatologist at Oregon State's College of Oceanic and Atmospheric Sciences, puts it:

And there is no reason to expect increases in hurricanes due to greenhouse warming. Climate models, for all their problems, are unanimous in at least one respect: they predict that most of the future warming will be in high latitudes, in the polar regions. This will reduce the north-south temperature gradient and make poleward transfer of heat less vigorous -- a task in which tropical storms play a major role. All other things being equal, a warmer world should have fewer, not more, hurricanes.

Furthermore, other issues can be raised with the climate models which predict such increases in hurricane strength.

While I will admit that, ultimately, such computer models are a necessary tool to help answer questions related to global warming, we must always keep in mind that there are a wide variety of assumptions that are necessary to perform these modeling experiments. First of all, the assumed 1% per year increase in atmospheric carbon dioxide concentration, while widely used by modelers for its simplicity, is considerably above what has been experienced in the last 30 years. The resultant 2.2-times increase in carbon dioxide over 80 years, as assumed in the models, would actually take 280 years if we extrapolate the real, observed upward trend over the last 30 years out in time. Of course, no one knows whether we'll even be using carbon-based fuels in another 100, let alone 280, years.

Secondly, the model-predicted warming in the tropics is strongly tied to how those models handle moist convection (showers and thunderstorms). All models have greatly simplified schemes for how this convection transfers heat and moisture from the surface to the atmosphere. Any warming in the models leads to moistening of the atmospheric humidity throughout the troposphere (where our weather occurs), and since water vapor is by far the most important greenhouse gas, this leads to further warming and moistening. It is not at all obvious that this strong of a water vapor feedback will occur in response to carbon dioxide increases. An increase in precipitation efficiency (how readily clouds convert water vapor into precipitation) is one possible negative feedback which isn't understood well enough to include in models yet. Furthermore, a mixture of surface thermometer, weather balloon, and satellite data over the last 25 years suggests that the tropical atmosphere might not behave as simply as the models assume. The satellite and weather balloon data suggest little, if any, warming of the tropical troposphere during that time, the reason for which remains a mystery, since all models suggest any surface warming should, if anything, be amplified with height.

As it is, Florida got hammered pretty badly this summer, and I feel for those affected. After all, I've been through a hurricane myself (Andrew in 1992), and most of my family still lives in South and Central Florida. I spent a good bit of time this summer on the phone checking in on them. It isn't fun to be without the conveniences of daily life. We so often seem to take them for granted. But I'll save my own experience with a hurricane, for a future post.