from http://www.livescience.com/24377-weather-climate-hurricane-sandy.html Hurricanes and tropical cyclones are fueled by warm water evaporating into the air. Ocean surface temperatures are up 0.9 degrees Fahrenheit (0.5 degrees Celsius) from about a century ago, a fact that may boost storm intensity. A recent study released in September in the journal Geophysical Research Letters, for example, found that hurricanes and tropical cyclones ramp up faster than they did 25 years ago. Globally, these storms reach Category 3 status, with winds up to 129 mph (208 kph), nine hours earlier on average than they used to, the study found. With warmer ocean surfaces comes warmer air above the oceans, Trenberth said. With warmer temperatures, this ocean air now holds about 4 percent more moisture than it did in the 1970s. "In general, we estimate it increases the risk that the intensity of hurricanes can be somewhat greater and particularly the rainfall from hurricanes is about 5 to 10 percent greater than it otherwise would be," Trenberth said. [Video: Hurricane Sandy's Intensity] In the case of 2005's Hurricane Katrina, which dumped at least 10 inches (25 centimeters) of rain along its track on the Gulf Coast, that means about 1 inch was attributable to climate change, Trenberth said. Sandy could dump similar levels of moisture over the Northeast. Trenberth added that "there are signs" that storms of Category 3 and above are becoming more common, but warned that hurricanes show tremendous natural variability from year to year, driven largely by climate patterns set up by El Niño.