Wednesday, September 21, 2005

Hurricanes and Global Warming

As Hurricane Rita gathers strength from the unusually warm waters of the Gulf of Mexico, some are finally beginning to consider the impact of global warming on tropical storms. Hurricanes intensify over warm water and weaken over cooler water. The oceans, like the atmosphere, have experienced a net increase in temperature as a consequence of global warming. But can we really predict whether global warming will produce more Category 5 hurricanes than we've experienced in the past?

Climate change scientists tend to be reluctant--and cautious--predictors. Most prefer not to make predictions without a great deal of observational data. Insurers, on the other hand, never have the luxury of waiting for all the data to come in before making predictions. Their profitability depends on the predictions they make about the risks they've assumed. And on the relationship between hurricanes and global warming, insurers are now making some interesting predictions.

Consider this exchange in onearth, the quarterly magazine of the Natural Resources Defense Council--an exchange that was in print before Hurricane Katrina struck the Gulf Coast:

Q: I've just lived through another hurricane season in Florida. Is it true that global warming could increase my insurance?

A: Scientists believe that global warming is making hurricanes and tropical storms more destructive, so as damage claims increase, it's likely that insurance will be more expensive, and perhaps more difficult to obtain. Over the past three decades, sea surface temperatures have risen, and today's average storm has higher wind speeds and lasts longer than those of the 1970s. Temperature isn't the only factor that controls storm frequency and intensity, but warmer water pumps more energy into the storm system, so its effect is pretty hard to ignore. Insurance industry risk analysts are just beginning to factor global warming into their assessments. Munich Re, the world's largest reinsurance company (an insurer of the insurance industry, in other words), believes that global warming is already taxing the insurance industry. Insured disaster losses totaled $44 billion last year--an industry record. Some say insurers are simply looking to global warming as an excuse to raise insurance rates; that increased coastal development is partly to blame. The Assocation of British Insurers predicts that global warming is likely to increase the worldwide cost of major storms by as much as two thirds over the next 75 years.