The press often prints dire predictions of the consequences of global warming when reporting damage from land-falling hurricanes. (For instance see stories here, and here, and here, and here) and some insurance companies are raising their rates (see here.) However, the increased storm damage is an artifact of our tendency to build more stuff in the historical path of storms rather than an increase in storm frequency or intensity.
A new paper takes a look at hurricane frequency: Historical global tropical cyclone landfalls, Jessica Weinkle, Ryan Maue and Roger Pielke, Jr., Journal of Climate (in press). They present the following graph:
You can see that in the last 40 years there has been no increase in hurricane landfalls. The paper abstract reads:
In recent decades, economic damage from tropical cyclones (TCs) around the world has increased dramatically. Scientific literature published to date finds that the increase in losses can be explained entirely by societal changes (such as increasing wealth, structures, population, etc) in locations prone to tropical cyclone landfalls, rather than by changes in annual storm frequency or intensity. However, no homogenized dataset of global tropical cyclone landfalls has been created that might serve as a consistency check for such economic normalization studies. Using currently available historical TC best-track records, we have constructed a global database focused on hurricane-force strength landfalls. Our analysis does not indicate significant long-period global or individual basin trends in the frequency or intensity of land falling TCs of minor or major hurricane strength. This evidence provides strong support for the conclusion that increasing damage around the world during the past several decades can be explained entirely by increasing wealth in locations prone to TC landfalls, which adds confidence to the fidelity of economic normalization analyses.
The paper above speaks of land falling hurricanes. The total number of detected hurricanes, land falling or not is also not increasing. (Maue, R. N. (2011), Recent historically low global tropical cyclone activity. , Geophys. Res. Letts. VOL. 38, L14803, 6 PP., 2011).
The intensity of hurricanes is also not increasing as the planet warms.
Dr. Christopher W. Landsea, the Science and Operations Officer at the National Weather Service’s National Hurricane Center in Miami, FL., explains the relationship between global warming and hurricanes as follows:
Hurricanes are natural heat engines. They extract energy from the moist, warm air over the tropical and subtropical oceans, liberate this energy in the process of forming clouds and rainfall, but lose most of this energy in the cold exhaust of the cyclone in the upper part (~8 mi, or ~12 km) of the atmosphere. A very small percentage (less than 1%) of this released energy is used to warm the air within the hurricane, drop the air’s density and pressure, and cause the swirling winds to spin faster and faster.
It’s also important to point out that ocean temperatures are not the only factor that is crucial in knowing which disturbances will develop into a tropical storm and which systems will intensify to become extremely strong hurricanes. Other physical “ingredients” in the hurricane “recipe” include moist air and numerous thunderstorms, weak vertical wind shear (the difference in winds near the ocean versus the upper part of the atmosphere), and a triggering disturbance (in the Atlantic this is often from an African easterly wave in the atmosphere). All climate models predict that for every degree of warming at the ocean that the air temperature aloft will warm around twice as much. This is important because if global warming only affected the earth’s surface, then there would be much more energy available for hurricanes to tap into. But, instead, warming the upper atmosphere more than the surface along with some additional moisture near the ocean means that the energy available for hurricanes to access increases by just a slight amount. Moreover, the vertical wind shear is also supposed to increase, making it more difficult (not easier) for hurricanes to form and intensify.
The bottom line is that nearly all of the theoretical and computer modeling work suggest that hurricanes may be slightly stronger (by a few percent) by the end of the 21st Century, even presuming that a large global warming will occur.
Looks like another global warming scare story is not supported by facts.