http://www.cnn.com/2007/TECH/science/07/29/tropical.storms.ap/index.html The number of tropical storms developing annually in the Atlantic Ocean more than doubled over the past century, with the increase taking place in two jumps, researchers say. The increases coincided with rising sea surface temperature, largely the byproduct of human-induced climate warming, researchers Greg J. Holland and Peter J. Webster concluded. ... The annual average jumped to 10 tropical storms and five hurricanes from 1931 to 1994. From 1995 to 2005, the average was 15 tropical storms and eight hurricanes annually. Even in 2006, widely reported as a mild year, there were 10 tropical storms. ... Hurricanes derive their energy from warm ocean water. North Atlantic surface temperature increased about 1.3 degrees Fahrenheit during the 100-year period studied. Other researchers have calculated that at least two-thirds of that warming can be attributed to human and industrial activities.