Global warming and the frequency of intense Atlantic hurricanes: model results

By: Dr. Jeff Masters , 1:37 PM GMT on April 05, 2010

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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 hurricanes per decade expected by the year 2100, according 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

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Man the Southern Plains all the way to the Upper Midwest is having a "Thunderstorm Party"!!
Member Since: August 25, 2009 Posts: 20 Comments: 6785
Quoting skepticall2:
Some people just don't understand cycles at all. If the Earth was supposed to be just one big average temperature sphere then they would find something else to complain about. Seriously the Earth has to go through cycles it is inevitable, to think it doesn't is just ignorant.

Doesn't this look like cycles? Also doesn't it look like the Earth has been much warmer than today? I know my SUV wasn't invented back then.

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You make a very good point and observation. Everything in nature on this planet goes through cycles, especially climate. We could very well be part of yet another rotation in the cycle.
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Wow! 845 is even more compelling...
Member Since: August 13, 2007 Posts: 0 Comments: 10479
844 well...the eloquence of the presentation, coupled with the uttelry unique graphic, convinces me...I'm sold...
Member Since: August 13, 2007 Posts: 0 Comments: 10479
Quoting GeoffreyWPB:
And what does that show Storm?

Hey Geoff. The map shows a Sea Surface Analysis, showing how much warmer or cooler the oceans are than normal.
Member Since: August 25, 2009 Posts: 20 Comments: 6785
And what does that show Storm?
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Quoting winter123:


Whoever wrote that is a great doomcaster. He should come to JM's blog.

Lemme try... The first hurricane of 2010 is forecasted to form in the carribean in two weeks. It will intensify to a cat 5, then hit New Orleans, turn back into the GOM then hit Miami, then reintensify to a cat 9 and hit NYC.


The scenario, and apparently it was postulated by Lovelock, is certainly possible. However I disagree with the idea that China will neccesarily need to enter Siberia, as there are areas in Gansu and Shaanxi that should remain desert-free and are still sparsely populated. The population crash scenario is also a bit unrealistic, and my estimate would be closer to about 3.5 billion people by 2100. Some effects are inevetable but can be further abated using carbon capture technology, most of which is still "in the works". Even with that "saling above the Niagara falls" analogy, a crash could possibly be prevented by grabbing some oars and moving as quickly as possible towards the shore--but don't try this at home! By the way, your predictions, though probably sarcastic, are about 100x more unrealistic than mine. EVEN more than the predictions on the Hurricanes Wikia!
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Nice graphic showing forecasted position and speed of the loop current.

Found this after following the link Patrap posted for spectral evolution. A bit mysterious that one.




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So easy a Caveman can understand it...or a Geico Lizard.

"Fancy a Crisp"..?
Member Since: July 3, 2005 Posts: 421 Comments: 127640
Quoting Jeff9641:


Thanks for the laughs on my behalf. I can't believe some lady on here gave me that name. Maybe she was in a bad mood today!


Jeff, this is an entertainment blog. Yes, posters give very good information...and some do not. Always rely on your local authorites when a storm approaches.
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Agreeing dosent make the Reality of a Warming climate,documented as fact go away.

But it does increase the Kum-bah-ya effect between those with similar views on the Subject.

And thats cool too.

But the data is the end all every time

And the Peer reviewed satellite derived data,surface and SST all show a warming Planet with the Co2 and other Forcing's as the predominate drivers.


We are changing the Atmosphere in a way that will..and is..not very good for man in the Short,nor long term.

Not many Squirrels and Whales driving 365/24/7 planet wide nor digging Coal and Burning it in Power Plants.




Member Since: July 3, 2005 Posts: 421 Comments: 127640
This is for Hydrus, for the threat of Severe Weather for tomorrow in TN :0)!!


Here is a portion of the Area Forecast Discussion out of Nashville, TN from earlier today:
.PREV DISCUSSION... /ISSUED 347 PM CDT TUE APR 6 2010/

SHORT TERM...ANOTHER VERY WARM AFTERNOON IN PROGRESS ACROSS THE
MID STATE, WITH 3 PM TEMPERATURES, ONCE AGAIN, BACK INTO THE LOWER
AND MIDDLE 80S. WINDS WERE STRONG AND GUSTY OUT OF THE SOUTHWEST...
SOMETIMES GUSTING TO AROUND 30 MPH. DUE TO THE LOW HUMIDITY AND
STRONG WINDS, ENHANCED FIRE POTENTIAL EXISTS FOR THE REST OF THE
AFTERNOON, AND SMOKERS SHOULD BE CERTAIN TO EXTINGUISH CIGARETTES
IN A PROPER MANNER AND NOT TOSS SMOLDERING BUTTS ONTO THE GROUND
OR OUT OF CAR WINDOWS.

STILL LOOKS LIKE A COLD FRONT WILL SWEEP INTO THE AREA WEDNESDAY
NIGHT AND EARLY THURSDAY, AND A FEW SHOWERS OR THUNDERSTORMS COULD
EVEN WORK THEIR WAY INTO OUR MOST NORTHWESTERN COUNTIES BY LATE
TOMORROW AFTERNOON.

WE SHOULD GET LOCALLY HEAVY RAINFALL FROM THE BAND OF SHOWERS AND
STORMS THAT MOVE THROUGH, WITH MOST AREAS RECEIVING BETWEEN THREE
QUARTERS AND ONE INCH, AND LOCALLY HIGHER AMOUNTS WHERE THE STRONGER
STORMS OCCUR.

THERE IS A POTENTIAL FOR ISOLATED SEVERE THUNDERSTORMS WITH THIS
COLD FRONT. ACCORDING TO SPC, THE PRIMARY CONVECTIVE MODE SHOULD
BE LINEAR WITH POTENTIAL FOR BOW/LEWP FORMATIONS...AND PERHAPS A
FEW EMBEDDED SUPERCELLS.

POST-FRONTAL SHOWERS AND CLOUDS WILL KEEP TEMPERATURES RELATIVELY
COOL ON THURSDAY, WITH HIGHS ONLY IN THE UPPER 50S TO MID 60S.

LONG TERM...WE COULD SEE SOME PATCHY FROST SATURDAY MORNING, AS COLD
HIGH PRESSURE SETTLES IN ACROSS THE AREA, AND THOSE WITH OUTDOOR
TENDER VEGETATION SHOULD PLAN ON TAKING APPROPRIATE PRECAUTIONS
SHOULD THE POSSIBILITY OF FROST BE ENTERED INTO THE FORECAST. BY
EARLY NEXT WEEK, A WARMING TREND COMMENCES, WITH HIGHS PUSHING
BACK INTO THE 70S AND MAYBE EVEN PUSHING BACK TO AROUND 80 AGAIN IN
THE LATTER PART OF THE PERIOD. EXTENDED PERIOD LOOKS DRY FOR SATURDAY
THROUGH WEDNESDAY.
Member Since: August 25, 2009 Posts: 20 Comments: 6785
Quoting Jeff9641:


Keep your head up brother because things will get better just stay strong.


I think you may have quoted the wrong post. lol
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Quoting Patrap:
So was Gravity for 300 years..

But Apollo 14 Solved dat one with a Hammer and a Feather.
I rememba dat one. That was won heavy fetha, or a really lite hammer. lol
Member Since: September 27, 2007 Posts: 1 Comments: 20539
Quoting Jeff9641:


Yeah, because I said a squall line and a strong one a that is going to move into TN. tomorrow.
yes, I remember that post this morning. It does look like there will be some strong to severe storms around. The mets said to stay tuned, its a tough one to pin down.
Member Since: September 27, 2007 Posts: 1 Comments: 20539
So was Gravity for 300 years..

But Apollo 14 Solved dat one with a Hammer and a Feather.
Member Since: July 3, 2005 Posts: 421 Comments: 127640
In reading back through the comments here, through all the media articles, and through scientific journals, its becoming more and more evident to me that nobody out there has anywhere near a true understanding about the Global Warming issue since its such a complex issue in nature. So much evidence exists to support so many positions regarding global warming and so many different either personal or political agendas that there will never be a consensus. So, at least in my opinion, nobody should attack anyone for their views on the subject since there's no definitive scientific law, since in my eyes, I view global warming as a scientific theory.
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Quoting AstroHurricane001:
Wow, a strong line of thunderstorms is moving northeast and it looks like we'll get some storms tomorrow. And what is that "thing" coming offshore from Rhode Island?



The remnants of today's thunderstorm activity that raced across MI, parts of ON, NY, and across New England. Some of those storms traveled at 50-60 MPH.
Member Since: August 25, 2009 Posts: 20 Comments: 6785
The great thing about empirical data and the scientific Method...is that

"It has no Dog in the fight over the Data".

It has no personal pre-conceived bias as well.

Its Empirical and above the din.


Cookies anyone?

Fresh Oatmeal Raisin?

C'mon,we all Like cookies on a Tuesday night?
Hmmm,Hmmm?



Member Since: July 3, 2005 Posts: 421 Comments: 127640
Quoting bappit:
Bad news in Rio De Janeiro. 95 dead from eleven inches of rain.

I wonder if the death tolls from landslides are included in the inland flooding stats for hurricanes? Seems like a separate category to me.
If the landslides are caused by the direct rainfall of a hurricane and kills people, they should be considered hurricane related fatalities. Someone dies from shoveling snow and they count that crap.
Member Since: September 27, 2007 Posts: 1 Comments: 20539
Levi, I still disagree with you interpretation of the IPCC graphics which in my take is only slightly more moist conditions but taking into consideration the northwest I simply cannot find anything dramatic enough. And the Sahel runs from east Africa to West Africa. We can agree to disagree if you wish.
Member Since: October 28, 2006 Posts: 57 Comments: 29928
Quoting hydrus:
what? I thought it was jeffradamas. JK...really..jk.


LOL...Just giving a 20th century updated name!
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Wow, a strong line of thunderstorms is moving northeast and it looks like we'll get some storms tomorrow. And what is that "thing" coming offshore from Rhode Island?

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Spectral Evolution

Tropical Storm Bill (06/2003)

Hurricane Lili (10/2002)

Tropical Storm Isidore (09/2002)
Member Since: July 3, 2005 Posts: 421 Comments: 127640
Bad news in Rio De Janeiro. 95 dead from eleven inches of rain.

I wonder if the death tolls from landslides are included in the inland flooding stats for hurricanes? Seems like a separate category to me.
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Quoting Jeff9641:


Yeah, Bastardi. I hope he's not right this year because if he is then Florida is some big trouble.

Jeff Mckown is my name not Edgar or Casey.
what? I thought it was jeffradamas. JK...really..jk.
Member Since: September 27, 2007 Posts: 1 Comments: 20539

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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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