SCIENCE OBSERVER
Storm Watch
David Schneider
In late January, Christopher W. Landsea, a hurricane specialist with
the National Oceanic and Atmospheric Administration in Miami,
publicly announced that he would end his participation in the
Intergovernmental Panel on Climate Change (IPCC), a group that comes
together periodically under the auspices of the United Nations to
report the latest advances in scientific understanding. Landsea's
withdrawal was sparked by a press briefing that followed the busy
2004 hurricane season in Florida. That event was promoted by a
Harvard University press release headlined "Experts to warn
global warming likely to continue spurring more outbreaks of intense
hurricane activity." One of these experts was Kevin E.
Trenberth of the National Center for Atmospheric Research in
Boulder—the person who had invited Landsea to contribute to
the IPCC's upcoming fourth assessment report.
Although Trenberth didn't explicitly state that the 2004 Florida
hurricanes were caused by global warming, some of the comments he
made at the briefing could easily be misconstrued. For example:
Referring to the heightened hurricane activity in 2004, Trenberth
said, "...in the Atlantic there's no guarantee that this is
going to continue, because in the Atlantic there is large, natural
decade-to-decade variability in hurricane activity...." So far
so good. But he then added: "...now superimposed on that
natural variability is also this longer-term trend that we associate
with global warming." A listener could easily reach the
conclusion that climatologists had at least some evidence of a
warming-induced upward trend in hurricane activity.
Although one can find theoretical support for the proposition that
hurricanes may indeed get worse—from a consideration of
general principles (hurricanes are fueled by the heat from tropical
seas, which will likely warm somewhat over the coming decades) and
from certain computer models (one 2004 study suggests that hurricane
winds might increase by 5 percent or so over roughly the next 80
years)—the historical record does not show any obvious trend.
In an open letter to the climate-science community, Landsea wrote:
...Given Dr. Trenberth's role as the IPCC's Lead Author
responsible for preparing the text on hurricanes, his public
statements so far outside of current scientific understanding led
[to my] concern that it would be very difficult for the IPCC process
to proceed objectively.... My view is that when people identify
themselves as being associated with the IPCC and then make
pronouncements far outside current scientific understandings[,] this
will harm the credibility of climate change science and will in the
longer term diminish our role in public policy.
Trenberth now says that "it was clear I was not speaking for
the IPCC." Yet the moderator for the briefing had introduced
Trenberth as "convening lead author of the 2007
Intergovernmental Panel on Climate Change report." And in his
opening remarks Trenberth volunteered, "I was a lead author on
the 2001 IPCC report for Working Group One, which deals with the
science of climate change, and in fact I was involved in developing
some of the information that is in that report dealing with hurricanes."
Commenting on Trenberth's controversial statements to the press,
Hans von Storch, a climatologist at the Institute for Coastal
Research in Geesthacht, Germany, says "It's a demonstration of
how highly politicized the IPCC process has become." Von Storch
should know, having lately been in the thick of some rather heated
climate debates himself. One erupted two years ago, forcing him to
resign his position as editor of Climate Research in
protest when he was prevented from publishing an editorial critical
of an article that had appeared in that journal, one that called the
uniqueness of recent global warming into question. (It's clear that
here von Storch was acting on principle, not campaigning to defend
the notion that the recent warming is extraordinary. Indeed, his own
work points in the other direction: Last year von Storch and five
coauthors published a paper in Science suggesting that
ancient swings in climate might well have been a lot larger than
many experts, including those on the IPCC, estimate.)
Although tropical hurricanes are not his specialty, von Storch has
studied the evolution of storminess elsewhere. Lars Bärring of
Lund University in Sweden and von Storch published a paper last year
(in Geophysical Research Letters) that uses measurements of
barometric pressure to gauge the degree of storminess in Scandinavia
since Napoleonic times. Their conclusion: Although there have been
oscillations up and down over the decades, there is no overall trend
during this interval. That article is an outgrowth of work that
began in the early 1990s, at time when, according to von Storch,
European newspapers were full of stories about increasing storm
activity, which was described as an early signal of global warming.
A more careful analysis by von Storch's group, however, found that
the level of storminess in Europe in 1995 was, in fact, similar to
the level existing in 1900.
Landsea suspects something similar will happen when Americans look
back at the busy hurricane season of 2004: "If I had to make a
guess for the next 20 years, I'd say it's going to be a lot like the
last 10 years." That is not to say that Landsea discounts any
influence of a warming planet. "No one should pooh-pooh the
possibility that global warming might do bad things," he says.
But he stresses that the increase in hurricane wind strength being
suggested on the basis of computer modeling is "pretty
tiny." And he points out that the monitoring of hurricane winds
today has a coarseness of about 5 miles per hour. So the influence
of global warming on hurricanes now, if it exists at all, is in the
noise. "Even in 2080," he says, "you might not be
able to measure it."—David Schneider
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