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By Brenda Ekwurzel
Rapid population growth in coastal regions has placed many more people and structures in the path of storms, increasing the potential for casualties, property damage, and financial hardship when these storms make landfall. And as reported by the media in the wake of hurricanes Katrina and Rita, global warming may be making matters worse. Recent scientific evidence suggests a link between the destructive power (or intensity) of hurricanes and higher ocean temperatures driven in large part by our changing climate.
Meteorologists use the term “tropical cyclone” to denote a closed atmospheric circulation that forms over a tropical or subtropical ocean. Three factors must be present for such a storm to intensify: warm ocean temperatures (hurricanes can occur when surface temperatures exceed about 79 degrees Fahrenheit or 26 degrees Celsius), low wind shear, and high water vapor content. By the same token, there are several natural factors that can put the brakes on a storm: moving over or churning up colder ocean water, strong wind shear that can diminish or destroy the vortex, dry air migrating to the hurricane’s core, and moving over land, which creates high frictional drag and deprives the storm of the warm ocean “fuel” it needs to thrive.
An Unnatural Disaster
Human activities such as the burning of fossil fuels and the clearing of forests release carbon dioxide and other heat-trapping gases into the lower atmosphere, where they act like an insulating blanket that raises land and ocean temperatures alike. Since the dawn of the industrial age, these heat-trapping emissions have increased exponentially, and the world is now warming at an alarming rate. Nineteen of the hottest 20 years on record have occurred since 1980, and the world’s oceans have absorbed about 20 times as much heat as the atmosphere over the past half-century.
Scientists have recently looked at potential correlations between ocean temperatures and storm trends worldwide over the past several decades. One study, which combined each storm’s duration and maximum wind speed, found that the destructive power of storms has increased around 70 percent in both the Atlantic and Pacific Oceans over the last 30 years. Another study revealed that the percentage of hurricanes classified as Category 4 or 5 (the most intense storms) worldwide has increased over the same period, correlating with the concurrent rise in sea surface temperatures in the regions where storms typically originate (see the figure below).
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