Tropical cyclones are one of Earth’s mechanisms for distributing heat from the sweltering tropical regions to the frigid poles. Once the winds inside these cyclones reach 75 miles per hour, they are classified as hurricanes. There are five categories of hurricanes, with category five hurricanes being the most severe. Warm ocean water is necessary to power these cyclones, and records from the twentieth century show that high sea surface temperatures (SSTs) correspond to more tropical cyclone activity. Global SSTs are the warmest that they have been since at least 1870. During the last thirty-five years, there has been an increase the number of tropical cyclones in the North Atlantic and globally the number of hurricanes (or typhoons) that fall into categories four and five has nearly doubled. Category four and five storms produce winds that exceed 136 miles per hour.
Seasons: Summer
(Source: Webster PJ, et al. 2005: Changes in Tropical Cyclone Number, Duration, and Intensity in a Warming Environment. Science 309, 1844-1846. and Hoyos CD, et al. 2006: Deconvolution of the Factors Contributing to the Increase in Global Hurricane Intensity. Science 312, 94-97 and Is Global Warming Impacting or Expected to Impact Hurricanes. October 20, 2007. United States Senate.)
