This year's unusually intense period of destructive weather activity could be a harbinger of what is to come as the effects of global warming grow even more pronounced, according to a briefing at the Center for Health and the Global Environment at Harvard Medical School.

The recent onslaught of four major tropical weather disturbances that did so much damage in the United States and Haiti have prompted questions about the relationship between hurricanes and global warming. Although experts cannot say that climate change will result in more hurricanes in the future, growing evidence suggests that the tropical storms that do happen will be more intense than in the past.

“Scientists cannot say at present whether more or fewer hurricanes will occur in the future,” said Paul R. Epstein, M.D., associate director of the center. “However, even if the number of storms remained constant, more powerful hurricanes with stronger winds, higher storm surges, and heavier downpours would have an even greater potential for damage, including increased risks to human life and public health, more floods and mud slides, increased coastal erosion, and damage to coastal buildings and infrastructure. This is the pattern that we already may be seeing related to the overall increase in extremes.”

Precipitation from hurricanes also is likely to increase, leading to flooding and mud slides. In addition, hurricane storm surges could be larger due to sea-level rise from melting ice and snow, and the thermal expansion of ocean waters, the panel warned. In the United States, the areas at greatest risk are low-lying lands along the Gulf Coast, such as Florida's Panhandle, Alabama's Gulf Shores, southern Louisiana, and eastern Texas. More intense hurricane activity also poses a risk to such vulnerable sections of the United States as Georgia, South Carolina, and North Carolina.

One of the consequences of global warming appears to be not only an increase in sea surface temperature, but a rising of the overall energy flux at the tropical ocean surface. Some experts think that this increased surface disequilibrium may lead to more intense tropical storms. In the Pacific, a large ocean water area two degrees warmer than average spawned 20 typhoons this season. Eight hit Japan, and meteorologists there have openly attributed that nation's battering to global warming, according to the center.

The insurance industry is feeling the effects of heightened hurricane activity. From the 1980s through the 1990s, damages from catastrophes (primarily weather extremes) rose exponentially, from $4 billion to $40 billion annually (when calculated in 1999 dollars), with about one-quarter of that amount insured. In the 1990s, Federal Emergency Management Agency payouts for disasters quadrupled.

With the possibility of more problems to come, the United Nations projects that weather-related property and casualty costs from extreme events will reach $150 billion worldwide this decade. In the United States, some companies already have withdrawn coverage from Cape Cod and the southern coast of Massachusetts. After this year's season, the center expects that Florida homes and businesses will face higher deductibles.

“Not since 1886 have four hurricanes hit one state in a single season,” said Matthias Weber, senior vice president and chief property underwriter of the U.S. Direct Americas division of Swiss Re. “This year, 22 percent of Floridians were affected, and 2 million claims generated by hurricanes and tropical storms. In 2005, we expect the demand for catastrophe reinsurance to continue to rise. Over the last 10 years demand has increased about 10 percent per year.”

Special Reports /

Global Warming Accelerates Hurricane Activity

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