Hurricane expert reconsiders global warming's impact

[vbhoutex]

April 11, 2008, 12:19PM
Hurricane expert reconsiders global warming's impact


By ERIC BERGER
Copyright 2008 Houston Chronicle

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One of the most influential scientists behind the theory that global warming has intensified recent hurricane activity says he will reconsider his stand.

The hurricane expert, Kerry Emanuel of the Massachusetts Institute of Technology, this week unveiled a novel technique for predicting hurricane activity. The new work suggests that, even in a dramatically warming world, hurricane frequency and intensity may not substantially rise during the next two centuries.

The research, appearing in the March issue of Bulletin of the American Meteorological Society, is all the more remarkable coming from Emanuel, a highly visible leader in his field and long an ardent proponent of a link between global warming and much stronger hurricanes.

His changing views could influence other scientists.

"The results surprised me," Emanuel said of his work, adding that global warming may still play a role in raising the intensity of hurricanes but what that role is remains far from certain.

Emanuel's work uses a new method of computer modeling that did a reasonable job of simulating past hurricane fluctuations. He, therefore, believes the models may have predictive value for future activity.

During and after the 2004 and 2005 hurricane seasons, which were replete with mega storms and U.S. landfalls, scientists dived into the question of whether rising ocean temperatures, attributed primarily to global warming, were causing stronger storms.

Among the first to publish was Emanuel, who, just three weeks before Hurricane Katrina's landfall, published a paper in Nature that concluded a key measurement of the power dissipated by a storm during its lifetime had risen dramatically since the mid-1970s.

In the future, he argued, incredibly active hurricane years such as 2005 would become the norm rather than flukes.

This view, amplified by environmentalists and others concerned about global warming, helped establish in the public's mind that "super" hurricanes were one of climate change's most critical threats. A satellite image of a hurricane emanating from a smokestack featured prominently in promotions for Al Gore's An Inconvenient Truth.

"Kerry (Emanuel) had the good fortune, or maybe the bad fortune, to publish when the world's attention was focused on hurricanes in 2005," said Roger Pielke Jr., who studies science and policy at the University of Colorado. "Kerry's work was seized upon in the debate."

After the 2005 hurricane season, a series of other papers were published that appeared to show, among other things, that the most intense hurricanes were becoming more frequent.

What has not been as broadly disseminated, say Pielke and some hurricane scientists, is that other research papers have emerged that suggest global warming has yet to leave an imprint on hurricane activity. One of them, published late last year in Nature, found that warming seas may not increase hurricane intensity.

That paper's co-author, Gabriel Vecchi, a research scientist with the National Oceanic and Atmospheric Administration, said Emanuel's new work highlights the great uncertainty that remains in the field of hurricane science.

"While his results don't rule out the possibility that global warming has contributed to the recent increase in activity in the Atlantic, they suggest that other factors — possibly in addition to global warming — are likely to have been substantial contributors to the observed increase in activity," Vecchi said.

Scientists wrangling with the hurricane-global warming question have faced two primary difficulties. The first is that the hurricane record before 1970 is not entirely reliable, making it nearly impossible to assess with precision whether hurricane activity has increased during the last century.

The second problem comes through the use of computer models to predict future hurricane activity. Most climate models, which simulate global atmospheric conditions for centuries to come, are not sensitive enough to detect individual tropical systems.

Emanuel's new research attempts to get around that by inserting "seeds" of tropical systems throughout the climate models and seeing which develop into tropical storms and hurricanes. The "seeds," bits of computer code, tend to develop when simulated atmospheric conditions, such as low wind shear, are ripe for hurricane formation.

In the new paper, Emanuel and his co-authors project activity nearly two centuries hence, finding an overall drop in the number of hurricanes around the world, while the intensity of storms in some regions does rise.

For example, with Atlantic hurricanes, two of the seven model simulations Emanuel ran suggested that the overall intensity of storms would decline. Five models suggested a modest increase.

"The take-home message is that we've got a lot of work to do," Emanuel said. "There's still a lot of uncertainty in this problem. The bulk of the evidence is that hurricane power will go up, but in some places it will go down."

The issue probably will not be resolved until better computer models are developed, said Judith Curry, of the Georgia Institute of Technology, a leading hurricane and climate scholar.

By publishing his new paper, and by the virtue of his high profile, Emanuel could be a catalyst for further agreement in the field of hurricanes and global warming, Curry said.

The generally emerging view, she said, seems to be that global warming may cause some increase in intensity, that this increase will develop slowly over time, and that it likely will lead to a few more Category 4 and Category 5 storms. How many? When? No one yet knows.

eric.berger@chron.com


http://www.chron.com/disp/story.mpl/front/5693436.html

[Tampa Bay Hurricane]

That is very interesting - thank you for posting that.
Global warming may not mean massive increases in hurricane
intensity, and more research needs to be done. Thank you
for that perspective.

[HURAKAN]

The new work suggests that, even in a dramatically warming world, hurricane frequency and intensity may not substantially rise during the next two centuries.

To me it's nothing new. I have always believed that GW would have little effect on the global hurricane activity. The scientists saying that there has been a dramatic increase in hurricane activity over the past century have been using false information.

If you just look at the numbers, it looks like hurricanes have been increasing over the past 50 to 100 years, but when you take into account the new technologies and undertanding that we have today and was lacked before the 1960s, you come into realization that there hasn't been much of an increase or anything like that for that fact.

[Tampa Bay Hurricane]

Yup Hurakan I agree! If we had satellites and technology before
the 50s we would have seen at least 3-6 more storms each year.

[drezee]

To me it is simple, kinetic energy is the key. Warmer atmosphere means that more molecules have to move. This indirectly means more windshear, because more air is traveling in all directions up/down and side to side. What this also means is that if you have an exisiting tropical system, it has the ability to evacuate more air. The problem is this, with the increase in temperature there will be years like 2004 and 2005. In these years, there were a ton of existing systems and therefore the global warming was a plus.

The fundamental flaw in most hurricane reasearchers is that are they fact that they are hurricane researchers. They look at the effects of global warming as to how it effect hurricanes, when the only thing we really know for certain is that more air will move around and more moisture can be held in the atmosphere at any given time. They are making a leap to make blanket statements, when it will be a year to year variation on what events take advantage of the things that we know can happen.

[Category 5]

Yup Hurakan I agree! If we had satellites and technology before
the 50s we would have seen at least 3-6 more storms each year.

Absolutely, especially in the 30s and 40s during that active period. Which at times seemed worse then this one.

[MiamiensisWx]

I think several subtropical storms were detected, but they were not classified in the '60s, '70s, and '80s. Storms like Delta 2005 and Chantal 2007 were essentially "missed" even in recent years. Gross underestimation of several older tropical cyclones' intensities has also contributed to the false perception that the 2000s have contained more intense Atlantic hurricanes than previous decades. When the reanalysis project is finished, we well see a cleaner database, with the numerous overestimated storms downgraded and an overall increase in average intensities because of extensive reanalysis.

[Ptarmigan]

I think several subtropical storms were detected, but they were not classified in the '60s, '70s, and '80s. Storms like Delta 2005 and Chantal 2007 were essentially "missed" even in recent years. Gross underestimation of several older tropical cyclones' intensities has also contributed to the false perception that the 2000s have contained more intense Atlantic hurricanes than previous decades. When the reanalysis project is finished, we well see a cleaner database, with the numerous overestimated storms downgraded and an overall increase in average intensities because of extensive reanalysis.

I think every season has multiple subtropical storms. 1914, which recorded only one storm, likely had more.

[Category 5]

I think several subtropical storms were detected, but they were not classified in the '60s, '70s, and '80s. Storms like Delta 2005 and Chantal 2007 were essentially "missed" even in recent years. Gross underestimation of several older tropical cyclones' intensities has also contributed to the false perception that the 2000s have contained more intense Atlantic hurricanes than previous decades. When the reanalysis project is finished, we well see a cleaner database, with the numerous overestimated storms downgraded and an overall increase in average intensities because of extensive reanalysis.

Important to note we've likely made gross overestimations as well.

*cough* Ethel *cough*

[btangy]

This study shows that any future projections of frequency and especially intensity are highly uncertain. I don't think it refutes the possibility that global warming is causing hurricanes to become more intense. It's an interesting read. If anything, look at figures 8 and 9 and read the summary (ftp://texmex.mit.edu/pub/emanuel/PAPERS ... l_2008.pdf).

One must be mindful of changes in rainfall and surge (caused by any sea level rise) that would potentially be far more devastating than any increase in wind. Additionally, even if the climatology of hurricanes stayed the same in every aspect, we are still building up high rise condos and other very vulnerable infrastructure right along the coast. The cost of hurricanes will continue to exponentially grow, and that I think is something everybody can predict and agree on.

[btangy]

Yup Hurakan I agree! If we had satellites and technology before
the 50s we would have seen at least 3-6 more storms each year.

An interesting problem to pose is that 20 years from now if some new novel technology comes around that allows us to really pinpoint the wind field of a hurricane, do we then throw out all the data we have now since it would be inferior? I feel like we're chasing the carrot on the stick. Past data will always be deficient in some regard relative to what's currently available. Take the SFMR for instance that was introduced recently allowing much better estimates of surface wind speed. The only way scientists will solve this problem is to figure out what the role of hurricanes are in the climate system and how that role will change in the future. Not just in the Atlantic but globally. That's a completely open question right now.

[Tampa Bay Hurricane]

We must keep all data but add some storms to correct for it. Take X number of
data tracked storms, add about 4-6 and you get a better estimate (to years before satillites), IMO.