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Warmer Oceans Producing Stronger Hurricanes, Researchers Say

Rising ocean water temperatures are driving up the wind speeds of Atlantic hurricanes and are likely to continue to do so for some time, according to a study published in the journal Nature.

Maximum wind speeds of the strongest tropical storms have increased significantly since 1981, according to research by Florida State University (FSU) climatologists published in the journal's latest issue and available on its website. The strongest tropical storms are getting stronger, especially in the North Atlantic and northern Indian oceans.

The climatologists' analysis of satellite-derived data of cyclone wind speeds found hardly any increase in the average number or intensity of all storms, but did indicate a significant shift in distribution towards Category Four and Category Five storms. Rising ocean temperatures are thought to be the main cause of the observed shift, according to the FSU researchers. They calculated that a 1-degree centigrade increase in sea surface temperature would result in a 31% increase (from 13 to 17) in the global frequency of Category Four and Five storms annually. Since 1970, tropical oceans have warmed on average by around 0.5-degree centigrade, and computer models suggest they may warm by another two degrees by 2100, according to the FSU team.

Studies of the projected effects of rising greenhouse gas (GHG) levels have delivered a variety of results. In June a scientific assessment of observed and projected changes in weather and climate extremes in North American and U.S. territories by the National Oceanic and Atmospheric Administration's (NOAA) U.S. Climate Change Science Program and the Subcommittee on Global Change Research 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 NGI, June 23). That report concluded "that we are now witnessing and will increasingly experience more extreme weather and climate events."

In May, NOAA scientists said they had 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). In a paper published on-line by Nature Geoscience, the NOAA scientists explained how they simulated Atlantic hurricane activity in 21st century conditions -- during periods of an expected rise in GHG emissions. The simulations indicated 27% fewer tropical storms and 18% fewer hurricanes. The strongest hurricanes had slightly higher wind speeds.

Last year a study by National Aeronautics and Space Administration (NASA) scientists suggested that GHG emissions could raise average summer temperatures in the eastern part of the United States nearly 10 degrees Fahrenheit by the 2080s (see NGI, May 14, 2007). The NASA research found that eastern U.S. summer daily high temperatures that currently average in the low to mid 80s Fahrenheit will most likely soar into the low to mid 90s during typical summers by the 2080s. In extreme seasons, for example, if a drought occurred, July and August daily high temperatures could average between 100 and 110 degrees in Washington, DC, Atlanta and as far west as Chicago.

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