Strongest Hurricanes May Triple in Frequency, Study Says

Mason Inman National Geographic News 21 Jan 10;

The U.S. Southeast, Mexico, and the Caribbean will be pounded by more very intense hurricanes in the coming decades due to global warming, a new computer model suggests.

Warmer sea surface temperatures—which fuel hurricanes—and shifting wind patterns are expected to strengthen the storms, the study says.

At the same time, rising temperatures should result in fewer weak or middling hurricanes in the western Atlantic.

The study considered what would happen if people kept emitting more greenhouse gases until about 2050 and then started cutting emissions.

"Some refer to this as a middle-of-the-road scenario" for tackling greenhouse gas emissions, said study co-author Thomas Knutson, a research meteorologist with the U.S. National Oceanic and Atmospheric Administration (NOAA).

In this scenario the world became about 4.5 degrees Fahrenheit (2.5 degrees Celsius) warmer than today.

In turn, the western Atlantic Ocean—from Mexico and the Caribbean Sea up to the Carolinas—saw a doubling of category 4 and 5 storms, the most powerful kinds, by 2100. The number of these very intense hurricanes jumped from 24 per decade to 46.

Category 4 storms have sustained wind speeds of 131 to 155 miles (211 to 249 kilometers) an hour. Category 5 hurricanes have winds exceeding 155 miles (249 kilometers) an hour.

"I was quite surprised," said Morris Bender, also a NOAA research meteorologist and the lead author of the new study, to be published tomorrow in the journal Science.

"I didn't expect a doubling. I didn't expect we'd see this much response."

What's more, the most intense hurricanes—category 5 storms—tripled by 2100 in the model.

"Unprecedented Results"

The new model is perhaps the most sophisticated yet to predict how hurricanes will change as the world warms, study co-author Knutson said.

The researchers combined state-of-the-art global climate simulations with "the hurricane prediction models used by weather forecasters and the [U.S.] Navy," he said.

Combining three models into one tool, the scientists were able to simulate the entire Earth's climate, with realistic hurricanes of all categories romping across the Atlantic.

The modeling method is a first, according to Judith Curry of the Georgia Institute of Technology, who was not involved in the study. "This is an important paper," she said.

Kevin Trenberth of the National Center for Atmospheric Research, in Boulder, Colorado, said there's still a lot of room for improvement in how all of today's climate simulations represent hurricanes and the oceans.

Even so, the new study does bolster an emerging consensus on how climate change will affect hurricanes, added Trenberth, who also was not involved in the research.

"The best information we have now supports the view that tropical storms will likely decrease in number," he said. "But the risk of category 4 and 5 storms could increase."