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Human Activities Are Boosting Ocean Temperatures in Areas Where Hurricanes Form, New Study Finds

September 11, 2006

BOULDER—Rising ocean temperatures in key hurricane breeding grounds of the Atlantic and Pacific oceans are due primarily to human-caused increases in greenhouse gas concentrations, according to a study published online in the September 11 issue of the Proceedings of the National Academy of Sciences (PNAS).

Using 22 different computer models of the climate system, Benjamin Santer and six other atmospheric scientists from the Lawrence Livermore National Laboratory, together with Tom Wigley, Gerald Meehl, and Warren Washington from the Boulder-based National Center for Atmospheric Research (NCAR) and scientists from eight other research centers, have shown that the warming sea surface temperatures (SSTs) of the tropical Atlantic and Pacific oceans over the last century are linked to human activities.

ioke
Hurricane Ioke passes by the Hawaiian Islands on August 21, 2006, with 132-mile per hour winds in this satellite image. The storm, renamed Typhoon Ioke as it moved west across the International Date Line, later intensified to become the most powerful central Pacific storm on record. Click here or on the image to enlarge. (Image produced by Hal Pierce, SSAI/NASA GSFC.)

NCAR's primary sponsor is the National Science Foundation. Support was also received from the U.S. Department of Energy, which sponsors Lawrence Livermore.

"We've used virtually all the world's climate models to study the causes of SST changes in hurricane formation regions," Santer says.

Research published during the past year has uncovered evidence of a link between rising ocean temperatures and increases in hurricane intensity. This has raised concerns about the causes of the rising temperatures, particularly in parts of the Atlantic and Pacific where hurricanes and other tropical cyclones form.

Previous efforts to understand the causes of changes in SSTs have focused on temperature changes averaged over very large ocean areas, such as the entire Atlantic or Pacific basins. The new research specifically targets SST changes in much smaller hurricane formation regions.

For the period 1906-2005, the researchers found an 84 percent probability that human-induced factors—primarily an increase in greenhouse gas emissions—account for most of the observed rise in SSTs in the Atlantic and Pacific hurricane formation regions.

"The important conclusion is that the observed SST increases in these hurricane breeding grounds cannot be explained by natural processes alone," says Wigley. "The best explanation for these changes has to include a large human influence."

Hurricanes are complex phenomena that are influenced by a variety of physical factors, such as SSTs, wind shear, water vapor, and atmospheric stability. The increasing SSTs in the Atlantic and Pacific hurricane formation regions are not the sole determinant of hurricane intensity, but they are likely to be one of the most significant influences.

"It is important to note that we expect global temperatures and SSTs to increase even more rapidly over the next century," Wigley says.

According to Santer, "In a post-Katrina world, we need to do the best job we possibly can to understand the complex influences on hurricane intensity, and how our actions are changing those influences."

Other institutions contributing to the study include the University of California, Merced; Lawrence Berkeley National Laboratory; Scripps Institution of Oceanography; the University of Hamburg; the University of East Anglia; Manchester Metropolitan University; NASA's Goddard Institute for Space Studies; and NOAA's National Climatic Data Center.

Related sites on the World Wide Web 

Tip Sheet: Explaining Hurricane Behavior, Impacts, and Possible Links to Global Warming

Backgrounder: Hurricanes, Typhoons, and Cyclones

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