Magazine article E Magazine

Extreme Weather: Is Global Warming to Blame?

Magazine article E Magazine

Extreme Weather: Is Global Warming to Blame?

Article excerpt

Climate experts warn us that the first sign of a shifting climate will be turbulent, unpredictable weather. So when Hurricane Jeanne crashed ashore in Florida in September of 2004--the fourth hurricane to blow through the region in less than six weeks--environmentalists couldn't help but wonder if this was it: climate change in action. It seems as though the past few years have been characterized by all sorts of weather extremes--driest, hottest, coldest, wettest. We know that the planet has warmed 1.8 degrees Fahrenheit in the past 100 years, but is there really a link between our weather and climate change?

The devastating 2004 hurricane season can only partially be attributed to climate change, experts say. "There are a number of factors that go into making hurricanes," says Ruth Curry, research specialist at Woods Hole Oceanographic Institute. Those factors include El Nino cycles, upper stratospheric circulation patterns and the amount of rainfall in the Sahel region of Africa. Sometimes they combine to create conditions ripe for hurricanes and sometimes they work against each other. The 2004 hurricane season is primarily attributed to alignment of these three critical elements.

Does climate change play any role? "You can't attribute one storm to climate change, but you can look at how the phenomenon fits into a pattern," says Ross Gelbspan, author of the book Boiling Point. "You can't attribute one case of cancer to smoking, but you can look at the epidemiology."

The general scientific consensus on climate change and hurricanes is this: Hurricanes won't necessarily become more frequent, but they will become more intense. While ocean and atmospheric circulation is the engine of a hurricane, heat is the fuel. "In order to form, a hurricane must have ocean temperature of at least 80 degrees down to a depth of 164 feet," says Curry. "Sea surface temperatures all over the tropics are running 1.8 to 3.6 degrees above normal. This is due to global warming." Thus, when other factors line up to form a storm, a warmer ocean means it will be all the more powerful and destructive.

The five-year (and counting) drought afflicting the western states has also stirred murmurings of climate change. Again, climate change is just one factor among many. The relationship between heat and moisture is the key to understanding most weather patterns. While most of us tend to think heat waves cause drought, it is actually the reverse: dryness creates heat.

"The first thing that happens after a rain storm is that the sun comes out and the puddles dry up," explains Kevin Trenberth, head of the Climate Analysis Section at the National Center for Atmospheric Research. Only when the majority of surface water is evaporated does heat begin to kick up. Climate change may contribute to more erratic rainfall, creating conditions ripe for heat waves in some places, but it is difficult to distinguish how much of a heat wave is due to a warmer planet versus natural variation in rainfall.

The current droughts in the western states are reinforced by shorter winters, result a possible of climate change. In the mountains, there are several weeks each year when precipitation that once fell as snow now falls as rain. "In the Sierra Nevadas all of the peak run-offs are now occurring one to two weeks earlier than 30 years ago," says Trenberth. "As you go into the summer there is less snow, so there is less soil moisture and less water to evaporate. Then you get a feedback process; since there is no moisture for clouds to form, there is no further rainfall." Trenberth is, however, cautious about blaming it all on climate change. …

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