Studies Rekindle Hurricane-Climate Change Debate
Another hurricane season has swung into gear, bringing with it more discussion about the possible human influence on nature's most powerful storms. The scientific and political rhetoric on this subject that erupted in the wake of the devastating hurricane seasons of 2004 and 2005 has weakened considerably from an initial Category Five monster debate, but every once in a while a new scientific study or weather event emerges that raises the specter of man-made, and not just man-named, storms.
Two new studies on the subject, combined with three named Atlantic tropical storms or hurricanes in the past week alone, have brought the topic to the fore once again in the mainstream media and the blogosphere. The main question continues to be whether greenhouse gas emissions are causing hurricanes to become more frequent and/or powerful. The answer continues to be blurry.
Keep reading for more on these new studies...
Much of what has been said about the new studies has been misleading or difficult to decipher, and it's time to set the spin aside and sift through the research in order to put the work into the broader context of the state of knowledge on this topic.
The new studies by two different research teams both examine the historical record of tropical cyclone (tropical storms and hurricanes) frequency and duration, and together they help answer the question of whether these severe storms are in fact occurring more frequently in recent years, or if scientists are just getting better at observing them.
The verdict? Possibly both.
I know that is not exactly the kind of resolution you were hoping for, and believe me, I'm right there with you, but science rarely if ever offers an open and shut case. That's part of what makes it so fascinating. Here's a brief breakdown of the studies and their conclusions, and what some of the key outstanding questions are at this point.
One of the studies, by a group of four scientists led by Michael E. Mann of Penn State University and published in the journal Nature, examined annual storm counts in the Atlantic basin during the past 1,500 years. Since there were no satellites to keep tabs on storms in say, the 18th Century, the researchers relied on so-called "proxy data," such as sediment records in coastal locations that can reveal evidence of storm surges from land falling hurricanes. They also used statistical techniques to estimate hurricane activity based upon "key large-scale climate factors" related to hurricane frequency, such as sea surface temperatures and El Nino.
Their conclusions: that recent tropical cyclone activity has been abnormally high, but that there was a past period of similarly high activity during medieval times around 1,000 AD. The researchers proposed several factors that might have contributed to the medieval peak, including relatively warm sea surface temperatures in the North Atlantic. Although the study itself did not address the question of whether human activities are behind the recent spike in hurricane activity, it's clear that Mann thinks that may be the case, since the study found a close relationship between sea surface temperatures and storm frequency.
Mann stated the following in a press release from Penn State: "It seems that the paleodata support the contention that greenhouse warming may increase the frequency of Atlantic tropical storms."
"It may not be just that the storms are stronger, but that there are there may be more of them as well," he stated.
The other study [PDF], published in the Journal of Climate, by Christopher S. Landsea of the National Hurricane Center in Miami and three other researchers, questions whether the upswing in hurricane activity in the late 20th Century reflects changing ways of observing storms rather than a real increase in storm activity. Rather than examining proxy data, these scientists took a look at the record of hurricane observations from ship reports, satellite tracking and other methods.
Their conclusions: that scientists are becoming more adept at catching the short-lived, typically weaker tropical cyclones, and that these are boosting annual storm counts. They found that once this and other factors in the record were accounted for, the upward trend in storm counts was greatly reduced.
Although neither study answers what to me are the most intriguing questions in this field, such as whether the strongest hurricanes will occur more frequently and get even stronger from warming seas as climate change progresses, they both offer interesting insight into an area of climate science that has captured the public's attention ever since a hurricane named Katrina tore into the Gulf Coast. One thing is for sure; neither study is going to be the last word on this topic.
Stay tuned to the Capital Weather Gang for continuing coverage of the 2009 Hurricane Season.
| August 18, 2009; 10:30 AM ET
Categories: Climate Change, Freedman, Media, Science
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