The Weekly Reader

Climate change may be fueling storms

Global warming is a probable cause of a dramatic upswing in the power of hurricanes, according to a new study.

By Martin Merzer
mmerzer@herald.com
http://www.miami.com/mld/miamiherald/news/12272807.htm

The accumulated power of Atlantic hurricanes has more than doubled in the past 30 years, with a particularly dramatic spike since 1995, and global warming likely is a major cause, according to a study to be published this week.

Follow up:

Though a connection between global warming and hurricane ferocity might seem logical, the report by a reputable climatologist at the Massachusetts Institute of Technology is the first to draw a statistical relationship between the two.

''The large upswing in the last decade is unprecedented and probably reflects the effect of global warming,'' scientist Kerry Emanuel wrote in a study that will appear in the Thursday edition of the journal Nature. Copies of the article were made available Sunday.

Importantly, his study did not shed any light on the effect, if any, of global warming on the number of storms.

But that is only of modest consolation.

One reason: Scientists at the National Oceanic and Atmospheric Administration's hurricane research division on Virginia Key have concluded that, due to long-term natural cycles, we are in the middle of a decades-long period of more frequent hurricane formation.

The current season, with a record seven named storms by July 23, provides unpleasant support for that conclusion.

Another source of concern: Most experts expect global warning to persist.

DESTRUCTIVE POWER

So, if both camps of scientists are correct, we could be facing stronger storms and more of them -- a potentially catastrophic collision of phenomena.

''My results suggest that future warming may lead to an upward trend in tropical cyclone destructive potential and -- taking into account an increasing coastal population -- a substantial increase in hurricane-related losses in the 21st century,'' Emanuel wrote.

He said his analysis of wind-speed reports by the National Hurricane Center and other sources show that the accumulated power of hurricanes in the Atlantic basin, which includes the Caribbean Sea and the Gulf of Mexico, has more than doubled since 1970.

A particularly steep increase began in 1995, according to the study.

''This large increase in power dissipation over the past 30 years or so may be because storms have become more intense, on the average, and/or have survived at high intensity for longer periods of time,'' he wrote.

Emanuel said the trend is closely linked to an increase of about one degree in the average ocean surface temperature, which might not seem significant but can be crucial.

''It sounds like a small amount, but we know that as waters get even a little bit warmer, the potential exists for hurricanes to get dramatically stronger,'' said Chris Landsea, an NOAA scientist on Virginia Key and one of the nation's leading hurricane researchers.

NOT CONVINCED

Still, he is not fully convinced by Emanuel's study.

Landsea said the 1995-04 spike in accumulated hurricane power correlated precisely with the beginning of the period of increased hurricane formation.

''It's very difficult to separate out what's caused by this natural cycle of activity versus man-made warming,'' Landsea said.

He also raised concerns about some statistical procedures employed by Emanuel, whom he described as ``a very respected researcher.''

''This is a serious study and it needs to be taken seriously,'' Landsea said. ``But when you take a close look at it, there's a lot of caveats. So, at this point, I'm not convinced he's found the smoking gun between global warming and hurricanes.''

In October 2004, Tom Knutson, a hurricane researcher at the government's Geophysical Fluid Dynamics Laboratory in Princeton, N.J., told The Herald he had noticed persistently high water temperatures in the main hurricane production zone of the Atlantic.

''The latest 10-year average is warmer than anything else in the record'' dating to 1870, he said. ``More research is needed to try to figure out how much of this is attributed to natural fluctuations and whether any of it is related to a broad-scale, global warming factor.''

Knutson, who did not participate in Emanuel's study, coauthored a report that was published in September 2004 and sparked new interest in the topic.

FUTURE OUTLOOK

It found that by the 2080s, global warming could cause the typical hurricane to produce 6 percent stronger winds and 18 percent more rain.

In some cases, those winds could raise the average storm a half-step on the five-category Saffir-Simpson scale of hurricane intensity.

''There's some uncertainty, but we're saying that environmental conditions will support stronger hurricanes,'' Knutson told The Herald.