Stormy weather

Atlanta in a globally warmed world

In 1987, Kerry Emmanuel, a professor of atmospheric sciences at the Massachusetts Institute of Technology, published the first study predicting that global warming would intensify storms and hurricanes.Emmanuel's findings suggested that rising temperatures in the ocean would speed up evaporation, which would heat and strengthen the circular wind patterns that create severe storms. That churning would elevate tropical storms to hurricanes - and would make hurricanes even more powerful.

Eighteen years later, Mother Nature seems to have followed Emmanuel's cue. In 2005, a record has been set for the number of "named" storms to form in the Atlantic Ocean prior to July 5, according to the National Oceanic and Atmospheric Administration. (Storms get a name when winds reach at least 39 miles per hour, and are classified as hurricanes when winds hit 74 mph.)

Two of those storms, Tropical Storm Cindy and Hurricane Dennis, dumped more than 13 inches of rain on parts of the metro area - an all-time record for the first half of July. What's more, Dennis formed earlier in the calendar year than any Category 4 hurricane (with winds between 131 and 155 mph) to pass through the Caribbean basin.

Dennis also caused $30 million in damage to more than 100 structures in Atlanta. The storm knocked down more than 50 trees, one of which killed Ed Timmons, a 36-year-old husband and father of two, while he lay in his bed in his Decatur home.

Considering that the temperature of the Atlantic Ocean is between 2 degrees and 5 degrees above normal, it's tempting to say Emmanuel's predictions have come true - that global warming can be blamed for the severity of recent storms. After all, the number of annual Category 3 hurricanes (with sustained winds between 111 and 130 mph) has been on the rise. From 1967 to 1994, there were an average of 1.5 Category 3 hurricanes per season, according to a Florida State University study. From 1995 to 2004, the seasonal average increased more than twofold, to 3.5 Category 3 hurricanes. (Data on hurricanes before 1967 is too sketchy to be reliable, according to Emmanuel.)

But meteorologists and climatologists from the Weather Channel and Georgia Tech say it's scientifically impossible to blame global warming for a single weather event like a storm or flood. Earth's climate is way too complicated for that.

Still, the majority of climate experts agree that a buildup of fossil fuel emissions in the atmosphere is acting like the roof of a greenhouse, trapping heat close to Earth instead of letting it bounce back into space. Studies say the planet's surface temperature has risen 1.4 degrees over the last 100 years. The 1990s was the hottest decade on record. And 1998 was the hottest single year since accurate temperature recordings began in 1880, according to the NOAA. The years 2002 and 2003 are tied for the second hottest year. Last year was the fourth hottest.

The scientific community projects that temperatures will rise between 2.5 and 10.4 degrees in the next 96 years.

Some of the most powerful computers in the world are devoted to figuring out what those rising temperatures will do to the planet. But those computer models stink when it comes to predictions for specific areas, according to Robert Dickinson, a professor at Georgia Tech's School of Earth and Atmospheric Sciences. For instance, a study Dickinson authored in February 2002 predicts that a rise in temperatures will cause more evaporation, leaving some parts of the world soaked and others dry. But Dickinson says the computer model he used can't distinguish between Atlanta and New York City.

Last week, NOAA issued a report that supports Dickinson's wider predictions. The report says Texas, the Midwest and the Northeast were unusually dry for the month of June, while the Southeast, northern Plains states, and parts of the West were wetter than normal.

In addition to the July deluge, Georgia received more than 7 inches of rain - 2.6 inches above average - in June, making it the state's ninth wettest month on record.

And Georgia might get wetter. Recent computer models, based partly on Emmanuel's work, indicate that global warming could cause a 10 percent increase in hurricane intensity.

But Georgia Tech meteorologist Jim St. John says he'd need to study at least 100 years of data before he would acknowledge a relationship between recent hurricane intensity and global warming.

While the scientific and political debate on global warming rages, the NOAA predicts another above-normal hurricane season, the agency's eighth such forecast in the past 10 years. (Never has a single 10-year period seen so many above-average hurricane seasons, at least since the NOAA started tracking hurricanes in 1958.)

Some of those storms are likely to scrape part of metro Atlanta. Judging from the damage and misery Cindy and Dennis caused, global warming will pull no punches for Atlanta.

"The bottom line is, there's going to be winners and losers," says the Weather Channel's Climate Expert Heidi Cullen. "Hopefully we can get a heads-up as to who is going to be who, and try to deal with it."