INTENSIFICATION OF HURRICANES - The Climate Casino - page 117

THE EFFECT OF GLOBAL WARMING ON HURRICANES
A hurricane is the name given to the North Atlantic version of a
spectacular natural phenomenon known as a tropical cyclone. If sus-
tained winds from a North Atlantic tropical storm reach 74 miles per
hour, the storm is classifi ed as a hurricane. 1 Hurricanes are huge en-
gines that use the heat from warm waters to power churning winds.
They are fed by a reinforcing feedback loop in which stronger winds
lead to lower pressures, which increases evaporation and condensation,
which in turn causes stronger winds. The main factor generating hur-
ricanes is warm surface water in the oceans. To get one started requires
a sea surface temperature of at least 26 1 ⁄ 2 °C (80°F). The areal extent of
warm water will increase as the earth warms, which will probably in-
crease the areal extent of the spawning ground for hurricanes and will
make them more intense.
We can use basic physics and historical data to estimate the im-
pacts of global warming on hurricanes. The U.S. data are the most
complete, and I have gathered information about the characteristics
and economic damages for 234 hurricanes that made landfall in the
United States between 1900 and 2012. The data cover thirty storms
before 1933 and all storms since then. Figure 18 shows the trend in
annual normalized hurricane damages (dollar damages divided by
GDP) since 1900. 2 Hurricanes caused damages that averaged 0.05 per-
cent of GDP per year over this period, with the maximum being 1.3
percent of GDP in 2005 (the spike there is produced primarily by Hur-
ricane Katrina).
One interesting feature is that—unlike many other environmen-
tal impacts—the damages from hurricanes appear to have an upward
trend relative to the total economy. Statistical analysis indicates that,
after correcting for the number of storms and their intensity, damages
have risen around 2 percent per year faster than GDP. The reason for
this increased vulnerability has not been fully explained. It is clearly
not primarily due to global warming and is probably the result of peo-
ple's fondness for living near the coast. (I plead guilty to that syn-
drome.)