Hurricane intensity linked to global warming
mongabay.com
August 15, 2006


A new study says climate change is affecting the intensity of Atlantic hurricanes and that hurricane damage will likely worsen in coming years due to increasing ocean temperatures. Unlike recent studies that have linked higher sea temperatures to an increase in the number of hurricanes, the new research shows a direct relationship between climate change and hurricane intensity.



In early August, forecasters at the National Ocean and Atmospheric Administration's National Hurricane Center revised downward slightly their early-season predictions of the 2006 Atlantic hurricane season. Citing atmospheric and oceanic conditions less conducive to hurricane formation than they initially expected, the center decreased its predictions of named storms (12-15 instead of 13-16), hurricanes (7-9 instead of 8-10), and major hurricanes (3-4 instead of 4-6). The revised prediction is still above-normal compared to the long-term average.

This pair of images from Japan's Advanced Microwave Scanning Radiometer for EOS Aqua satellite shows areas where sea surface temperatures were hurricane-ready on August 14, 2006 (top), and August 1 (bottom). Sea surface temperatures warmer than a threshold of about 28 degrees Celsius (about 82 degrees Fahrenheit) are one of the required ingredients for hurricanes to form. Areas where waters have reached the hurricane-ready threshold are yellow or red in these images, while areas where waters are generally to cool to support hurricanes are blue. Coastal areas where temperatures were not measured are light gray.

The study, published by James Elsner of Florida State University in the August 23 issue of Geophysical Research Letters, the journal of the American Geophysical Union, found that a correlation between average air temperatures during the June through November hurricane season and sea surface temperatures that help fuel hurricanes winds. Elsner says his work "helps provide verification of a linkage between atmospheric warming caused largely by greenhouse gases and the recent upswing in frequency and intensity of Atlantic hurricanes, including Katrina and Rita."

"The large increases in powerful hurricanes over the past several decades, together with the results presented here, certainly suggest cause for concern," he said. "These results have serious implications for life and property throughout the Caribbean, Mexico, and portions of the United States."

"I infer that future hurricane hazard mitigation efforts should reflect that hurricane damage will continue to increase, in part, due to greenhouse warming," Elsner said. "This research is important to the field of hurricane science by moving the debate away from trend analyses of hurricane counts and toward a physical mechanism that can account for the various observations."

Data questioned

Nevertheless, while Elsner's findings lend support to the contention that warmer temperatures will produce stronger hurricanes, they will not settle long-standing concerns among some scientists.

While several studies published since early 2005 have linked recent climate warming to the increasing occurrence and strength of hurricanes over the past thirty years, the research has proved controversial since some scientists say the system for tracking storms is flawed. They argue that storm data from 20 years ago is not nearly as accurate as current hurricane data making it nearly impossible to accurately compare storm frequency and strength over the period.

"Before aircraft and satellite monitoring were available, the Atlantic hurricane data are likely woefully underestimated - except where a hurricane ran directly over a ship or coastal community and there were meteorological observations of pressures and/or winds recorded," Chris Landsea, a scientist as the NOAA National Hurricane Center, told mongabay.com. "Given that ship captains did their best to NOT sail into the eye of hurricanes, there is a very large underreporting bias in our databases during the late 19th and early 20th Centuries, except for hurricanes at landfall along populated coastlines. Disentangling trends due to bias in the hurricane dataset and possible global warming induced changes is then very problematic."

The new paper fails to steer around this controversy since it compares average global near-surface air temperature and Atlantic sea surface temperature with "hurricane intensities" from the National Oceanic and Atmospheric Administration's Atlantic basin hurricane database (HURDAT) over the past 50 years. Climate researchers are currently working to re-analyze existing tropical cyclone databases to address these concerns.

"What data we do have - and there certainly are biases in HURDAT that need to be addressed storm by storm - suggest that the middle of the 20th Century was about as busy as the last active 11 years have been (1995 to 2005)," Landsea added. "Disentangling trends due to bias in the hurricane dataset and possible global warming induced changes is then very problematic."

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CITATION:
mongabay.com (August 15, 2006).

Hurricane intensity linked to global warming.

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