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Phil. Trans. Royal. Soc. A doi:10.1098/rsta.2007.2083 (2007)

Credit: © NCAR

The frequency of North Atlantic hurricanes has more than doubled in the past century — a trend primarily driven by climate change — a new study finds. Researchers have identified three distinct climatic periods, or regimes, in the region since 1900. In each successive one, the number of tropical cyclones and hurricanes (extreme cyclones) increased by about 50% compared with the previous period and then stabilized.

Greg Holland of the US National Center for Atmospheric Research and Peter Webster of the Georgia Institute of Technology in the USA analysed North Atlantic Ocean tropical cyclone activity in relation to sea surface temperature from 1855 to 2005. They found two sharp transitions to periods of elevated activity, occurring in 1930 and 1995, which followed increases in sea surface temperature in the eastern North Atlantic. The first period from 1990 to 1930 saw an average of six tropical cyclones per year, whereas the most recent, from 1995 to 2006, saw an average of 15 per year. Regardless of the number of cyclones each year, about half became hurricanes.

Similar, or higher, levels of storms and hurricanes are expected in the future, resulting from continued warming of the Atlantic and the Gulf of Mexico.

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