Forum hears storm alarm: Warming seas mean more hurricanes, researcher says

June 20 2006, The Post and Courier, Charleston SC
By Bo Petersen

More hurricanes and worse hurricanes making landfall in South Carolina are not far ahead, a leading climate scientist warned Monday, because sea temperatures are rising as humans continue to burn fossil fuels.

"There's been a lot of debate in the media. Unfortunately, the public debate has diverged from the scientific debate," said Judith Curry of the Georgia Institute of Technology. Scientists no longer are debating whether global warming is occurring or that sea temperatures are rising, she said. They are debating whether warming is a direct cause of hurricanes becoming more intense.

Curry's findings are supported by recent studies by Purdue University and the Massachusetts Institute of Technology that indicate global warming is causing stronger hurricanes.

But while scientific consensus is growing that a period of global warming is being spurred by fossil fuel emissions, not all scientists are ready to agree it's causing more hurricanes, or stronger ones.

Curry told a skeptical audience of about 50 area educators and professionals that a 5-degree Fahrenheit rise in sea temperatures is well within range over the next century. According to her interpretation of the data, every 1 degree rise correlates to five more tropical storms per year. The spike in sea temperatures correlates to the increase in carbon dioxide and sulfates in the atmosphere, she said.

Already in this period of what's seen as a multi-decade cycle of hurricane activity, 50 percent more hurricanes have occurred in the North Atlantic basin than the last active period a half-century ago. The number of more intense Category 4 and 5 hurricanes has also grown, she said.

The frequency of hurricanes spiked in the past 10 years, an increase that tracks the rise in sea temperatures, she said. Across the world, the number of hurricanes hasn't grown but the intensity has, she said.

By 2020, the average hurricane season could be 20-21 storms, more like the relentless 2004 season or the record-breaking 2005 season, she said. Seeing storms strengthen beyond Wilma's 180-mph winds in 2005 isn't out of the question.

While the multi-decade cycle suggests hurricane activity should subside by 2015, "if it's global warming, if things in 2020 are going 50 percent worse than they are now, that's a whole different ballgame. We need to get carbon dioxide out of the atmosphere so in 100 years people can live in South Carolina," she said.

"This is a very real risk. To wait until we're 100 percent sure of the science - and we're pretty darned sure - it doesn't make sense. The risk is rapidly accelerating. It could be much worse. Do you want Category 6? Category 7?"

Richard Lindzen, of the Massachusetts Institute of Technology, differed in a comment sent by e-mail.

"Historical data suggests that the trend she mentions is part of a long term cyclic pattern in hurricanes. The important policy question is whether any of this has much to do with global warming, and, as she says, there is some debate about this," Lindzen said.

"Actually, there is quite a lot of debate. There are also questions as to whether even Judith's claims hold for hurricanes making landfall, and it is these that are of concern for us land dwellers."

Lindzen did not take part in the school's recent stronger-hurricane study.

Chris Landsea of the National Hurricane Center, who worked as a climate researcher for 12 years and helped develop the multi-decade modeling of tropical storms, said, "I'm concerned that the conclusions Dr. Curry is drawing are due to changes in technology and technique to better identify the storms that are out there."

In the former busy period in the 1950s, there were no satellites to show how strong storms were out at sea.

While 2004 and 2005 were very active hurricane seasons, the average is about what forecasters would expect with the multi-decade cycle if the number of storms from the two seasons are averaged in with numbers over the past 11 years, Landsea said.

A recent study using Curry's data over the last 15 years rather than since the 1970s showed no change in the number of Category 4 and 5 hurricanes, Landsea said.

While there's no dispute that sea temperatures have risen and "without a doubt we're in a very busy hurricane period in the Atlantic," he said, "we're still learning what's going on."

Curry spoke as part of Charleston County's Project Impact, a federally sponsored program to help communities prevent and handle damages due to hazards such as hurricanes. The presentation was co-sponsored by the S.C. Wildlife Federation and Carolina Climate Network.

Landsea did not attend the presentation. He spoke from the hurricane center in Florida.