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Stronger Hurricanes At The Margin

Al Gore told NPR this week that the typhoon in Burma "might be associated with continued global warming." The Cato Institute's Indur Goklany wonders how this can be possible, since sea-surface temperatures in the Bay of Bengal before the storm hit were about the same as they were at the same time last year, and were actually cooler than in 2005. So how can one say that warming contributed to the storm?

This is a common mistake that's made in thinking about global warming and hurricanes. The relevant claim here isn't that global warming causes hurricanes--there are any number of reasons, completely unrelated to climate change, why a big typhoon developed in the region this year as opposed to last year or in 2005. (It may or may not be true that warming increases the frequency of hurricanes; my understanding is that the evidence supporting that conclusion is pretty shaky. But leave that aside for now.) The main claim is that, at the margin, global warming will make already-existing storms more intense, because warm water is a central factor in determining how strong a given storm becomes.

So the relevant comparison isn't between this year and last year. The question to ask is, given that a typhoon developed in the Bay of Bengal this year, is there a good chance it would have been less intense in an alternate world with an atmospheric carbon dioxide concentration of 280 parts per million? That is, have hurricanes becomes more intense, on balance, as the world has warmed? And the answer to that question is almost certainly yes.

--Josh Patashnik