Hurricanes and Global Warming
Hurricanes or tropical cyclones are formed when a tropical wave or disturbance develops into a large cluster of towering thunderstorms. If the conditions are right - sufficiently high water temperatures (80 F+) in a deep enough layer of the ocean; high humidity in the lower troposphere; low wind shear (change in wind speed & direction with height); and enough Coriolis effect (to allow for spin-up), there is a potential for the cluster to develop into a tropical depression. If the conditions continue to be favorable, a tropical storm (sustained 39 mph or higher) can develop. Further strengthening can lead to a hurricane (74 mph or higher). The Saffir Simpson Scale is the way meteorologist's categorize storm intensity and possible impact.
There are certain
favorable areas for development.
where the aforementioned conditions are most likely to be met.
More on the actual mechanics of these storms can be found
Global warming is expected to impact tropical cyclones in certain ways, although there is uncertainty as to exactly what the effects will be. Studies by Kerry Emanuel, the IPCC, and others suggest that although the number of tropical cyclones may not increase, the number of "major" tropical cyclones will increase. Intensity is directly related to ocean water temperatures (all else being equal) and the warming atmosphere will continue to lead to an increase in average sea water temperatures. The warm, moisture-laden air provides the energy as the air moves upward quickly in the updrafts, cools, condenses, and leads to precipitation and latent head release (the fuel of these storms) which leads to further strengthening in a "feed back" loop (the warmer air rises, leading to lowering pressure, stronger pressure gradient leads to more air rushing into the center, forced upwards, further lowering pressure and strengthening wind some more).
Further study out of NOAA's GFDL reached some main conclusions:
1) It is not possible to tell the effect on current tropical cyclones due to global warming as the signal is too small, as compared to natural variations;
2) Anthropogenic warming by 2100 will likely cause an increase in average intensity of tropical cyclones from 2 to 11%;
3) Model results predict a doubling of the frequency of very intense (category 4-5) hurricanes in the Atlantic basin by the end of the 21st century;
4) The overall number of tropical cyclones will likely change very little;
5) Warming due to the activities of mankind is expected to lead to an increase in rainfall rates of up to 20% (within 100 km of storm center);
6) There is an expected 30% increase in potential damage in the Atlantic Basin by 2100.
The graphic shows the correlation between sea surface temperature and hurricane development. Notice how well correlated the two parameters are.
In summary, there can be no doubt that eighty years of CO2 increases of 1%/year (compounded) will lead to more extreme weather and effect tropical cyclones in some way. The tropospheric warming will lead to an increase in sea surface temperatures which fuel these monsters. Even with the other "ingredients" still not sorted out (in terms of global warming's effects), even with "all else being equal" there will simply be more available potential energy. More warm, moist air will rise in these towering thunderstorm towers leading to more condensation and latent heat release - the key to energizing these storms.
Tropical cyclones are the greatest storms on earth. Time will tell if they become an even greater threat when extreme weather becomes more common.