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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I have a few ideas, Oz, if you'd like to discuss them in WUMail, for example...you see, I'm not just the class clown (though it IS my favorite role)
1) if it's still standing after the hurricane has passed and
2)if it's taller tha 30 ft tall.
Oz, I'm no stormchaser - I've ridden out the relatively few storms we've had in Nassau in my sturdy concrete brick home - but I can't imagine anyone choosing to stand outside during a cat 5, anywhere. I could at least potentially see a parking deck scenario, but that itself would require specific preps that I'm sure u've thought about.
Also, I seriously doubt ur cell / wireless capabilities would last all the way to the arrival of cat 5 winds. If most wx equipment doesn't last much beyond 120 mph winds, I doubt wireless / cell towers will.
Hey Flood!!! With all this talk about Hurricanes and flagpoles, reminds me of a a ditty I remember from the army about......"then the monkey tied his tail around a flagpole.... I don't remember the rest.
Get the #$%#$% out LOL
But they didnt talk,nor describe the experience.
Dats all Im saying.
Or a top-end cat 4...Andrew was barely a cat 5...
lolz, I don't think there's too much of a difference between Top end 4's and low end 5's. It's just arbitrary numbers at that point. You're in deep **** regardless
so the crowd there...
could see his tail ____
1) He is CRAZY..... lol I mean he actually thinks hanging out in hurricanes is fun....
2) He is not ur average bear.... by that I mean he is actually thinking a LOT about strategies that will get him the most possible exposure with the least possible damage
3) Like a good friend of mine, he's going to do what he feels he has to do, no matter what.
My bigger concern is that other lesser prepared pple don't try to follow his example to their detriment or even, God forbid, their deaths. I do understand where u are coming from, though. There are some places and times where u just choose to let Mother Nature "do her thing", and u just get the H--- outa Dodge....
No, I don;t think I will...I'll be happy to help poke holes in any survival strategy you porpose though, because it will tend to help keep you alive. I've been through over a dozen tornados, literally hundreds of supercell thunderstorms, a CAT3 hurricane and a number of tropical storms and I will tell you this: I vowed to never be on the ground close to a CAT 4 and to be at least two states away from any landfalling CAT5s.
You're right; survivability is due primarily to location; Waveland and Pass Christian were non-survivable areas for a landfall; too low and topographically bad (back bay and body of water wise)...any coastline will be bad, in one or another but man...CAT5? I believe it was said in here earlier that the aftermath of a CAT5 on a city is incromprehensible; it's Haiti earthquake bad...people don't design for survivability of that sort of energy
And thats all Emg Mgt and Local First Responders need is more Media and Gawkers broadcasting and tweeting from the Beach.
'Merica,gotta Lub it.
LOL
I love Oz,..always have.
He has my Hurricane Prep PDF,or used to now..LOL
I just worry bout his one Life.
But We always enjoy his travels.
Been fun to see it grow too.
OTOH, I am not fool enough to think that I could do what u do. I hope others also know the difference....;o)
omg those katrina stories gave me nightmares. people in the attic trying to bust through the ceiling while water up to their chins.
hahahahaha
I am sure there is a way to record a CAT 5 and survive it. I remember Hurricane Andrew, had those "fabled hot towers" generated wind gusts of between 190-220MPH, which literally wiped Homestead, FL off the map in minutes. I don't know if a human can withstand a sustained wind over 120MPH, unless he is wearing a titanium suit, strapped to a concrete pillar, securely.
I wish you the best, be safe. It is nice to report on a major Hurricane, from the source, I don't want to see anything bad happen to you, remember, your only human.
“ Snow and blowing snow ending near noon then cloudy with 30 percent chance of rain showers. Snowfall amount 2 cm. Wind west 70 km/h gusting to 90. High plus 5.”
And for recreation one can always attend a pertinent seminar;
“TECHNICAL PRESENTATION: CANADIAN GEOTECHNICAL SOCIETY SPRING CROSS CANADA LECTURE TOUR
Presents: ICE ROAD TRUCKERS AND THE GEOTECHNICAL ENGINEER
Winter roads have a long history of use by provincial and territorial transportation departments to provide seasonal access to remote northern communities.”
Please let there be golf soon !!
I understand your passion Oz,..and I stayed when told to go,but was lucky in 05.
...many who were only a mile away werent so.
I support your work and offer you a place to hang here if ever the need comes.
Thats usually well,you know,Aug and Sept.
Gustav's first Outer Band approaching 08
what...no jock strap?
;)
;)
The dry season is the only time of year I like the weather in Florida-Late September through the first of June(typically)!
You're right about one thing here, Oz...no matter what, there will be those out there with you wearing a pair of cut offs with a cooler full of Old Milwaukee so that they can say they were in the hurricane...wasn't it Camille in mIssissippi where those fiolks had the infamous "Hurricane Party" and the only sirvivor was the kid who was lucky enough to find himself in a tree, hanging on for dear life? Just like most people have no idea iof a billion anything looks like, most people have no conception of what 115mph wind looks like; in Jeanne I "stood" in a dog walk in our hotel with 80+mph winds and I was standing at a 45degree angle to the ground cause otherwise I would have been thrown off the second story...I had a fair idea of what I was dealing with and took very few chances and I did fine, but I was there through a number of miscalculations, partly on the NHC and partly on me (remember Jeanne did that cool loop the loop thing before landfall)...I would certaily have left if I had the chance, but by the time I knew she was coming I didn't have a lot of choice
What you need is some type of "body armor" that is lightweight, that can protect you from flying objects in 155+MPH winds, and a safe, secure anchor system to keep you "planted, stationary in one place", away from the storm surge, away from "flying missiles".
Remember, a 120MPH wind can drive a drinking straw an inch into a palm tree. The highest wind gusts I have seen were 115MPH, during a severe thunderstorm in Arlington, TX, in 1989. That was terrifying to me. I don't quite have the "heart" you do.
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