Global warming and the frequency of intense Atlantic hurricanes: model results
Could global warming increase wind shear over the Atlantic, potentially leading to a decrease in the frequency of Atlantic hurricanes? There is a growing consensus among hurricane scientists that this is indeed quite possible. Two recent studies, by Zhao et al. (2009), "Simulations of Global Hurricane Climatology, Interannual Variability, and Response to Global Warming Using a 50-km Resolution GCM", and by Knutson et al. (2008), "Simulated reduction in Atlantic hurricane frequency under twenty-first-century warming conditions", found that global warming might increase wind shear over the Atlantic by the end of the century, resulting in a decrease in the number of Atlantic hurricanes. For example, the second study took 18 relatively coarse (>60 km grid size) models used to formulate the 2007 IPCC climate report, and "downscaled" them using a higher-resolution (18 km grid size) model called ZETAC that was able to successfully simulate the frequencies of hurricanes over the past 50 years. When the 18 km ZETAC model was driven using the climate conditions we expect in 2100, as output by the 18 IPCC models, the authors found that a reduction of Atlantic tropical storms by 27% and hurricanes by 18% by the end of the century resulted. An important reason that their model predicted a decrease in the frequency of Atlantic hurricanes was due to a predicted increase in wind shear. As I explain in my wind shear tutorial, a large change of wind speed with height over a hurricane creates a shearing force that tends to tear the storm apart. The amount of wind shear is critical in determining whether a hurricane can form or survive.
Figure 1. Top: predicted change by 2100 in wind shear (in meters per second per degree C of warming--multiply by two to get mph) as predicted by summing the predictions of 18 climate models. Bottom: The number of models that predict the effect shown in the top image. The dots show the locations where tropical storms formed between 1981-2005. The box indicates a region of frequent hurricane formation where wind shear is not predicted to change much. Image credit: Geophysical Research Letters, "Increased Tropical Atlantic Wind Shear in Model Projections of Global Warming", by Vecchi and Soden, 2007.
Since the Knutson et al. study using the 18 km resolution ZETAC model was not detailed enough to look at what might happen to major Category 3 and stronger hurricanes, a new study using a higher resolution model was needed. This was done by a team of modelers led by Dr. Morris Bender of NOAA's GFDL laboratory, who published their results in Science in February. The authors used the GFDL hurricane model--the model that has been our best-performing operation hurricane track forecasting model over the past five years--to perform their study. The GFDL hurricane model runs at a resolution of 9 km, which is detailed enough to make accurate simulations of major hurricanes. The researchers did a double downscaling study, where they first took the forecast atmospheric and oceanic conditions at generated by the coarse (>60 km grid) IPCC models, used these data to initialize the finer resolution 18 km ZETAC model, then used the output from the ZETAC model to initialize the high-resolution GFDL hurricane model. The final results of this "double downscaling" study suggest that although the total number of hurricanes is expected to decrease by the end of the century, we should expect an increase of 81% in the number of Category 4 and 5 storms in the Atlantic. This trend should not be clearly detectable until about 60 years from now, given a scenario in which CO2 doubles by 2100. The authors say that their model predicts that there should already have been a 20% increase in the number of Category 4 and 5 storms since the 1940s, given the approximate 0.5°C warming of the tropical Atlantic during that period. This trend is too small to be detectable, given the high natural variability and the difficulty we've had accurately measuring the exact strength of intense hurricanes before the 1980s.The region of the Atlantic expected to see the greatest increase in Category 4 and 5 storms by the year 2100 is over the Bahama Islands (Figure 2), since wind shear is not expected to increase in this region, and sea surface temperatures and atmospheric instability are expected to increase there.
The net effect of a decrease in total number of hurricanes but an increase in the strongest hurricanes should cause an increase in U.S. hurricane damages of about 30% by the end of the century, the authors compute, assuming that hurricane damages behave as they did during the past century. Over the past century, Category 4 and 5 hurricanes made up only 6% of all U.S. landfalls, but accounted for 48% of all U.S. damage (if normalized to account for increases in U.S. population and wealth, Pielke et al., 2008.)
Figure 2. Expected change in Atlantic Category 4 and 5 hurricane per decade expected by the year 2100, accord to the Science paper by Bender et al. (2010).
Commentary
These results seem reasonable, since the models in question have been successfully been able to simulate the behavior of hurricanes over the past 50 years. However, the uncertainties are high and lot more research needs to be done before we can be confident of the results. Not all of the IPCC models predict an increase in wind shear over the tropical Atlantic by 2100, so the increase in Category 4 and 5 hurricanes could be much greater. Also, the GFDL model was observed to under-predict the strength of intense hurricanes in the current climate, so it may not be creating enough Category 4 and 5 hurricanes in the future climate of 2100. On the other hand, IPCC models such as the UKMO-HadCM3 predict a very large increase in wind shear, leading to a drastic reduction in all hurricanes in the Atlantic by 2100, including Category 4 and 5 storms. So Category 4 and 5 hurricane frequency could easily be much greater or much less than the 81% increase by 2100 found by Bender et al.
The estimates of a 30% increase in hurricane damages by 2100 may be considerably too low, since this estimate assumes that sea level rise will continue at the same pace as was observed in the 20th century. Sea level rise has accelerated since the 1990s, and it is likely that this century we will see much more than than the 7 inches of global sea level rise that was observed last century. Higher sea level rise rates will sharply increase the damages due to storm surge, which account for a large amount of the damage from intense Category 4 and 5 hurricanes.
Keep in mind that while a 30% in hurricane damage by the end of the century is significant, this will not be the main reason hurricane damages will increase this century. Hurricane damages are currently doubling every ten years, according to Pielke et al., 2008. This is primarily due to the increasing population along the coast and increased wealth of the population. The authors theorize that the Great Miami Hurricane of 1926, a Category 4 monster that made a direct hit on Miami Beach, would have caused about $150 billion in damage had it hit in 2005. By 2015, the authors expect the same hurricane would do $300 billion in damage. This number would increase to $600 billion by 2025 (though I think it is likely that the recent recession may delay this damage total a few years into the future.) It is essential that we limit coastal development in vulnerable coastal areas, particularly along barrier islands, to reduce some of the astronomical price tags hurricanes are going to be causing. Adoption and enforcement of strict building standards is also a must.
The authors of the GFDL hurricane model study have put together a nice web page with links to the paper and some detailed non-technical explanations of the paper.
References
Bender et al., 2010, "Modeled Impact of Anthropogenic Warming on the Frequency of Intense Atlantic Hurricanes", Science, 22 January 2010: Vol. 327. no. 5964, pp. 454 - 458 DOI: 10.1126/science.1180568.
Vecchi, G.A., B.J. Soden, A.T. Wittenberg, I.M. Held, A. Leetmaa, and M.J. Harrison, 2006, "Weakening of tropical Pacific atmospheric circulation due to anthropogenic forcing", Nature, 441(7089), 73-76.
Vecchi, G.A., and B.J. Soden, 2007, "Increased Tropical Atlantic Wind Shear in Model Projections of Global Warming", Geophysical Research Letters, 34, L08702, doi:10.1029/2006GL028905, 2007.
Jeff Masters
Reader Comments
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"In 3 Minutes it went From the Ground to the Roof"
Sorry about that!!!
dragginjeans.com (1 complete pair of those...price 'em, too!)
bladerunner.tv (1 complete pair of those...price'em, too!)
Plus...catcher's chest, kevlar neck guard, gloves, and steel-soled fireman's boots, catcher's shin guards, cup, waterproof socks, lacrosse arm pads, hockey shoulder pads, helmet, safety glasses, safety goggles underneath, and a backpack that carries the emergency lighting battery that powers the live web cam and my cell phone set to auto answer.
It takes me 90 minutes to gear up for a major Cat storm. I've timed myself.
Wasn't it Dan Rather who tied himself to a tree somewhere on the TX coast and reported live as a hurricane came in sometime in the 60's
I've watched that clip a dozen times and everytime I think about the guy in NOLA who didn't leave...he was being interviewed sometime after the storm...
"When the water started coming into the first floor I wasn't worried; I grabbed my wife and the roofing hatchet and we went upstairs. I told my wife not to worry, that the water wouldn't make into the second floor, it just wouldn't. About twenty minutes later, it was knee deep on the second floor and we went into the attic. 10 minutes later it was ankle deep in the attic and I thought 'I may have miscalculated'
I heard that interview the first time and I laughed for a good ten minutes...I may have miscalculated...
If you are in a very bad hurricane, and you are not prepared to lash yourself down, you have made a potentially life-threatening mistake in your preparation.
And the word "God",Lucky and "Never again", about 2 million times the following weeks too.
Well, I'm deadly serious, OZ; let a couple of us get with you and talk through all of your prep if you're looking at intercepting anything over a 3; as presslord is wont to say, more brains are better...you're our crazy, daredevil cousin here at WU and I think I speak for everyone when I say we want you to be in here next winter talking #$%^ and regaling us with stories of cars and trees spinning past you...
Okay, kids, got to bounce! BBL
AGREED!
Yeah man, we all think we're indestructible until we get about 10 seconds away from dying. I can tell you this: when I wo0ke up Sunday morning and the storm was now a CAT5 and it hadn't turned east, I scooped up my wife and stepdaughter and I RAN
Happy storm-chasing.
You folks should know what I've brought, but more importantly, where I plan on basing my operations.
You're right about more brains on that task. If I'm missing something, perhaps one of you guys can catch it before the mistake is made.
In a Cat 5, you can name it and it will kill you. Glass, aluminum sheds, cars, floods, nails, boards with nails, boards with other boards still attached to them...etc.etc...
That's why you have to know the best place to position yourself. It's all about location.
with or without jock!
;)
I think he's aware of that. I'm not concerned about the surge getting him, he's aware of the topography to the extent that surge shouldnt be the issue. My biggest concern is debris. Cat 5 winds are incredibly strong, add in vorticies higher than that even ... and I dont care if you're wearing steel plate, a 2x4 travelling at 200mph + ... if nothing else the concussive blow can be deadly, even if the steel isn't penetrated or the integrity sacrificed in anyway...
I disagree. Cat5 winds can penetrate further inland than where the surge reaches.
This is the same Neighborhood in St Bernard,Just east of NOLA by 8 Miles.
Note the Elder Vacarella talking about Betsy in 65 in the beginning.
Cat 3 Winds at Height,Cat 5 Surge
Rest of the series is available at my Photos section.
what really gets me and makes me cry when i think about it was watching it develop, cross florida and go into the gulf and the watching it grow. i can still see all the satellite images in my head. knowing with out a doubt that it was going to be horrific and many people would suffer and be gone AND NOT BEING ABLE TO DO A DAMN THING ABOUT IT.
Except a tornado only has cat 5 winds for about a mile and a cat 5 hurricane has a much larger wind field
dude....you need a jock strap next time!!!!!! seriously!!!!!!!!!
;)
It's too bad they don't deploy a "hurricane intercepter", a set of instruments like some of the "Tornado storm chasers" use to determine the strength of a tornado. That would be alot safer!
I'm sorry, did I say that a tornado had the same size wind field as a hurricane? I think I said that documentind winds of that speed would be no great feat. But since you mentioned it, yes, the windfield in a hurricane is much larger therefore making it even easier to document and even less of an accomplishment.
They don't do it because documenting Cat 5 wind speeds is no big deal. the surge is the killer and no intercept vehicle would be safe in the surge. Too much focus is placed on the winds in a hurricane, hence why this year, there will be a fundamental change in hurricane forecasting. Surge is the killer, not the wind.
No it isn't. Hurricane Andrew was Category 5 conditions well inland around the eyewall. Surge isn't the only thing in a storm.
I'm all about documenting a Cat 5 storm surge. But to do so "safely" has to take into account dozens of critical factors, base location being of prime importance.
Back to Katrina as an example. Had I intercepted that storm, I would have known that the Waveland, Pass Christian, and Bay St. Louis areas would be the worst place to be as far as location goes, because of the lack of seawall and lack of structures that could be used as a shelter.
I would've been in Biloxi, which was just far enough away from the inner eyewall to "not count." (Although the guys in that parking garage did get some amazing footage of storm surge.)
Yet, we did not see the worst of it, and Katrina's "most devastating surge" was not documented, because there was no one there to do it...as it should have been.
But lets, for the sake of the argument, say that Katrina moved further east at landfall...making Biloxi the bullseye.
I would have been in Biloxi. There are places there where a survival strategy could have been formed.
So let's see how this year plays out.
But rest assured, I will not be on some deserted beach that a Cat 5 has bullseyed.
That would be just plain stupid for me to do something like that.
Yeah...and these need to first sweep low about 30 feet above the wave action of the eye, then go in the eyewall "for the kill." Strong transmission for how long? 2 minutes at most?
Still...worthy.
Which is a shame because Max Mayfield is probably the best director the NHC has had and saved a ton of lives
I want to chase hurricanes from their development to landfall using submarines and "disposable" surface craft.
But no one thought that was a good idea last year when I proposed it.
And there it is in a nutshell. Exactly right.
Still, I believe it can be done using the right equipment and strategy, with location being of utmost and prime importance.
So it comes down to timing, location, personal will, and alot of luck...
They plan to test the Coyote UAS in a cyclone this year.
NOAA's utilization of Coyote unmanned aircraft systems for tropical cyclone research
It is launched like a dropsonde and then unfolds it's wings. Battery power with an estimated flight time of 1 hour. Sort of like a flying dropsonde.
you could use cyclonebuster's tunnels.....
;)
Why rip out the screens? Would the hurricane tear it apart anyways? My house was built shortly before Andrew, and was in West Kendall so the damage was no where near as bad as say Cutler Ridge or Countrywalk.
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