Monday, September 15, 2008
A June 27 letter to Nature 455, 92-95 (4 September 2008) | doi:10.1038/nature07234 from James Eisner, James Kossin, and Thomas Jagger, suggests that Atlantic tropical hurricanes are getting stronger due to increased ocean temperatures. While the same phenomenon is observed throughout the world, the effects are strongest in the tropical Atlantic. Their study does not indicate necessarily that there are more hurricanes or stronger hurricanes in terms of average wind speed; instead, it is the maximum intensity of the hurricanes that is increasing -- in other words, their destructive potential.
Atlantic tropical cyclones are getting stronger on average, with a 30-year trend that has been related to an increase in ocean temperatures over the Atlantic Ocean and elsewhere1, 2, 3, 4. Over the rest of the tropics, however, possible trends in tropical cyclone intensity are less obvious, owing to the unreliability and incompleteness of the observational record and to a restricted focus, in previous trend analyses, on changes in average intensity. Here we overcome these two limitations by examining trends in the upper quantiles of per-cyclone maximum wind speeds (that is, the maximum intensities that cyclones achieve during their lifetimes), estimated from homogeneous data derived from an archive of satellite records. We find significant upward trends for wind speed quantiles above the 70th percentile, with trends as high as 0.3 0.09 m s-1 yr-1 (s.e.) for the strongest cyclones. We note separate upward trends in the estimated lifetime-maximum wind speeds of the very strongest tropical cyclones (99th percentile) over each ocean basin, with the largest increase at this quantile occurring over the North Atlantic, although not all basins show statistically significant increases. Our results are qualitatively consistent with the hypothesis that as the seas warm, the ocean has more energy to convert to tropical cyclone wind.