Climate Number: 20 Fewer Hours
America’s costliest natural disasters are often North Atlantic hurricanes striking Florida, the East Coast or the Gulf Coast. While inland flooding, tornadoes, lighting and coastal storm surges account for the majority of monetary damages inflicted by these storms, the hurricane winds themselves also do a good deal of damage. How much structural damage winds inflict is directly proportional to wind speed, with no structural loss at low wind speeds and complete losses at high wind speeds. All other things being equal, monetary damages from hurricanes increase by about five percent for every two miles per hour increase in hurricane wind speed (starting at 74 miles per hour). Wind speed is generally a good proxy for the overall energy in the storm and the expected levels of heavy precipitation, lighting, storm surge damage, etc. How quickly a hurricane converts the heat energy at the surface of the ocean into energy of motion in the form of winds plays a major role in determining how fast winds will be when the hurricane makes landfall. As Earth’s oceans have warmed, this time has been reduced. This trend has been particularly pronounced in the North Atlantic basin, which has been the fastest warming ocean basin since the mid-1980s, when satellites began systematically monitoring hurricanes. The time it takes storms in the North Atlantic to accelerate from a 74 mile per hour Category 1 storm to a Category 4 storm with winds of 130 miles per hour or greater has been reduced by 20 hours.
Sources: Murnane, RJ and Elsner, JB. “Maximum wind speeds and US hurricane losses.” Geophysical Research Letters 39 (2012): L16707 and Kishtawal, CM et al. “Tropical cyclone intensification trends during satellite era (1986 – 2010).” Geophysical Research Letters 39 (2012): L10910.