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Statistical Analysis Bolsters Theory Linking Warmer Oceans to Stronger Hurricanes

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Posted by lkgeo1 on April 1, 2006, 10:32 pm

Statistical Analysis Bolsters Theory Linking Warmer Oceans to Stronger

 Image: NASA

Since the 1970s, ocean surface temperatures around the globe have been
on the rise--from one half to one degree Fahrenheit, depending on the
region. Last summer, two studies linked this temperature rise to
stronger and more frequent hurricanes. Skeptics called other factors
into account, such as natural variability, but a new statistical
analysis shows that only this sea surface temperature increase explains
this trend.
Climate researcher Judith Curry and her colleagues at the Georgia
Institute of Technology looked at the hurricane records for storms
between 1970 and 2004 in all of the world's ocean basins, yielding a
total sample of 210 seasons over the six regions. They subjected the
records to a mathematical test derived from information
theory--so-called mutual information, which measures the amount of
information two variables share, so that if they do not overlap at all
this measure would be zero.

The researchers then looked at sea surface temperature, specific
humidity, wind shear and wind variation over longitude to see what, if
anything, these variables shared with the increasing number of strong
storms the world over. According to the analysis appearing online today
in Science, this trend only depends on sea surface temperature. "If you
examine the intensification of a single storm, or even the statistics
on intensification for a particular season, factors like wind shear can
play an important role," Curry says. "However, there is no global trend
in wind shear or the other factors over the 35-year period."

The link between rising ocean temperatures and overall climate change
remains murky because of the overlap between natural cycles and any
global warming. "But if you buy the argument that global warming is
causing the increase in sea surface temperatures--and everybody seems
to be buying this--then it's a pretty small leap to say global warming
is causing this increase [in hurricane frequency]," Curry says. Her
team will now focus on clarifying the mechanisms at work in the North
Atlantic by separating out the 75-year natural cycle and climate
change. "The last peak was in 1950, the next is in 2025," she adds.
"We're only halfway up [the cycle] and we're already 50 percent worse
[in terms of storms]. To me, that's a compelling issue that needs to be
confronted." --David Biello