Global warming could decrease the number of Atlantic hurricanes by the end of the century, but it could simultaneously double the number of the most powerful (Category Four or greater) hurricanes, according to a study published in the most recent edition of the journal Science.

Computer modeling indicates that the annual number of Atlantic hurricanes will fall 30% by the end of the century, while the number of Category Four and Category Five hurricanes — storms with sustained winds of at least 131 mph — will increase by 81%. The largest increase is projected to occur in the western Atlantic, the researchers said.

The report is available at www.sciencemag.org.

Studies of the projected effects of rising greenhouse gas (GHG) levels have delivered a variety of results. For example, one study by the National Oceanic and Atmospheric Administration’s (NOAA) U.S. Climate Change Science Program found that intense hurricanes, heavy downpours, droughts and excessive heat are likely to become more common as humans continue to increase the atmospheric concentrations of heat-trapping GHG (see Daily GPI, June 2, 2008). A second NOAA study determined that global warming would not lead to an increase in Atlantic Basin hurricanes, and, in fact, might lead to fewer tropical storms and hurricanes (see Daily GPI, May 20, 2008).

Research by Florida State University climatologists found that rising ocean water temperatures are driving up the wind speeds of Atlantic Basin hurricanes and are likely to continue to do so for some time (see Daily GPI, Sept. 5, 2008). Maximum wind speeds of the strongest tropical storms have increased significantly since 1981, according to the study.

In one of the first long-range forecasts of the 2010 Atlantic Basin tropical cyclone season, Colorado State University’s hurricane forecasters recently said they expect above-average activity and a higher-than-average probability of a major storm making landfall in the United States and the Caribbean (see Daily GPI, Dec. 11, 2009).

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