Earthsky Interviews
Private: Hurricanes and Climate
12-28-2004 - Earth
_JB:_ And scientists are coming closer to predicting how much stronger and how much rainier. An earlier study predicted dramatic increases in hurricane strength as Earth’s climate warms. A recent study, published last September by climate researchers in Princeton, New Jersey, shows changes that are less dramatic – but still cause for concern.
_DB:_ The researchers used a computer model that simulates how a single hurricane evolves over several days. In some simulations, they used today’s climate conditions. In others, they used climate conditions that might exist 80 years from now. Tom Knutson is a climate modeler and study co-author.
_Tom Knutson:_ The model simulated more intense hurricanes under warmer climate conditions. And the size of the change that we simulated was roughly half a category more intense for these conditions.
_JB:_ Increasing a hurricane’s intensity by half a category means slightly faster winds and about 20 percent more rainfall.
_DB:_ Hurricanes get their energy from evaporating water at the surface of an ocean. As Earth warms, the sea surface will become warmer. This allows more evaporation – and more intense hurricanes.
_JB:_ That’s our show. With thanks to the “National Oceanic and Atmospheric Administration”:http://www.noaa.gov/ and to the “National Fish and Wildlife Foundation”:http://www.nfwf.org/, we’re Block and Byrd for Earth and Sky
More Resources:
“Climate Prediction Center – Background Information: The North Atlantic Hurricane Season”:http://www.cpc.noaa.gov/products/outlooks/background_information.html#NOAADEF (NOAA)
Author’s Notes:
This past year’s Atlantic hurricane season was unusual. In a typical year, about 6 hurricanes form in the Atlantic. This past year, 7 hurricanes formed. Six of those were considered “major hurricanes” with maximum winds over 110 miles per hour. Over 1,000 people died when Hurricane Jeanne hit the island of Haiti.
The paths of this year’s Atlantic hurricanes were also unusual. Four hurricanes hit Florida in six weeks. This is the first time four hurricanes have hit one U.S. state in one season since four hurricanes hit the Texas coast in 1886.
The experts we spoke with said that it’s still not known whether climate change would affect the number of hurricanes that form in a season. So far, the easier problem of hurricane intensity is the one that has received the most attention and produced the most trusted results. Dr. Knutson would like to try to answer the harder question of hurricane frequency, though.
So what does a half category increase in intensity mean? Let’s say a storm goes from a class four and a half hurricane to a class five hurricane. In their model, the hurricane would have about a six to nine percent increase in wind speeds. It would also have about 20 percent more rainfall. It also means changes in what’s known as the “surface minimum pressure” – the low-pressure zone at the center of a hurricane. These differences make the storm more destructive.
Dr. Knutson wanted to clarify that there is a lot of uncertainty about what climate might be like in 80 years. In an email, he wrote that this is “due to uncertainties in climate model projections (which we try to address to some extent in our study by using 9 different climate models) and due to uncertainty in the future radiative forcing (there we only used a single, fairly strong radiative forcing scenario: +1%/yr CO2 compounded increase).” In other words, they assume that carbon dioxide levels in our atmosphere will increase by one percent each year. That would increase the amount of greenhouse warming we experience.”
The following people were interviewed for today’s show. Our thanks to:
Tom Knutson
Geophysical Fluid Dynamics Laboratory
NOAA
Princeton, New Jersey
Adam H. Sobel
Department of Applied Physics and Applied Mathematics
and Department of Earth and Environmental Sciences
Columbia University
New York, NY