Two recent scientific findings conclude that there has been an increase in hurricane intensity and attribute this trend in part to climate change.

• Emanuel, Kerry. "Increasing Destructiveness of Tropical Cyclones Over the Past 30 Years." Nature 436: 686-688. 4 August 2005 at www.nature.com

• Webster, P. J. et al. "Changes in Tropical Cyclone Number, Duration, and Intensity in a Warming Environment." Science 309(5742): 1844-1846. 16 September 2005 at www.sciencemag.org

While scientists have yet to conclude whether the number of hurricanes per year is correlated with climate change (Trenberth, Kevin. 17 June 2005. “Uncertainty in Hurricanes and Global Warming.” Science 308(5729): 1753-1754. 17 June 2005 at www.sciencemag.org), these two recent studies demonstrate that there has been an increase in hurricane intensity and attribute this trend to climate change, among other factors.

Emanuel developed an index based on factors associated with hurricane  destructive power. It includes sea surface temperature (which has been rising in part due to climate change and is correlated with hurricane intensity), as well as interannual and interdecadal swings in storm frequency, wind shear, sub-surface ocean temperatures, and tropospheric temperatures. Emanuel coupled the projected trends for hurricane intensity with the observed trends, and concludes that the observed increase in hurricane intensity far exceeds the pace of the predicted increase; he also concludes that climate change can be expected to further increase the intensity of hurricanes in the future.

Webster et al. shed additional light on the relationship between hurricane intensity and climate change, examining the upward trend in the number of category 4 and 5 hurricanes over a 30-year period. Their findings are consistent with climate models that attribute more intense storms to higher levels of greenhouse gases, which contribute to climate change.

Implications: There has been almost a doubling of hurricane power dissipation over the period on record, and future climate change, according to these analyses, can be expected to bring a greater number of intense storms. Given damages associated with intense storms over the recent past (for example, reports by Munich Re and others indicate weather-related damages over the past 25 years at about $1.5 trillion), we will need to increase our capacity to deal with damages to coastal communities and ecosystems.