In the destructive heart of hurricane season, climate scientists have come out with some alarming news: the most powerful storms have gained wind strength over the past 25 years as a result of gradually warming ocean waters, and global warming is likely to continue that trend. It’s hardly welcome news, as Gulf Coast residents are still recovering from this week’s close call with Hurricane Gustav and Caribbean islanders are warily eyeing several new tropical storms gaining strength over the Atlantic.
The new study is likely to renew the debate over global warming’s effect on major storms: [T]here has been controversy about whether these hurricanes will get more intense and numerous, with many claiming the data are not good enough to discern a real trend upwards in recent years…. Today’s study, by Prof James Elsner of Florida State University, concludes that the strongest tropical cyclones – the general term for intense storms such as hurricanes and typhoons – are getting stronger, with the greatest increase recorded in the North Atlantic and northern Indian oceans [Telegraph].
Elsner’s study, published in the journal Nature [subscription required], examined all the cyclones, typhoons, and hurricanes that have formed around the world over the past 25 years, and looked at the maximum wind speed attained by each storm. While he didn’t find a change in the overall number of storms, he did determine that the peak wind speeds of the most intense storms has increased over the decades; the strongest North Atlantic hurricanes in the 1990s had peak wind speeds about 10 kilometers per hour faster than those in the region’s strongest storms of the 1980s [Science News].
Researchers believe that rising ocean temperatures provide more energy that can be converted into cyclone wind, and say the strongest storms are best able to take advantage of this energy boost, overcoming dampening atmospheric conditions to reach their full potential strength. The study found that the strongest storms gained wind speed in all of the world’s storm basins except the South Pacific. The apparent reason is that the South Pacific is already the warmest sea region, and thus has seen less of a relative increase in temperature compared to the Atlantic, Indian Ocean and North Pacific [AFP].
This trend is not promising, says Elsner. The team calculates that a 1 ºC increase in sea-surface temperatures would result in a 31% increase in the global frequency of category 4 and 5 storms per year: from 13 of those storms to 17. Since 1970, the tropical oceans have warmed on average by around 0.5 ºC. Computer models suggest they may warm by a further 2 ºC by 2100 [Nature News].