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

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

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

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

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454. aquak9
 hahaha...yeah that was a compliment...
453. msgambler
 Thank you I think Aquak9
452. aquak9
 Quoting msgambler:StormW, I need your help with something. I don't really understand why we need a new warning system. I know that if I have a Cat.1 coming then I really just sit around and watch the limbs blow around. A Cat.2 that just formed off Cuba and ran straight to AL Coast is a little worse but managable. Gonna be some work to do afterwards. Now a Cat.5 that has been brewing for days, slowly churning, then comes in as a Cat.3 is going to have Cat.3 winds with Cat.4-5 surge. So I do not understand if I am missing something on the reasoning for needing a new warning system.What you're missing, is that most people aren't as intelligent as you. :)
451. msgambler
 Ohh yeah and good morning to all. Hope all are doing well this beautiful am.
450. msgambler
 StormW, I need your help with something. I don't really understand why we need a new warning system. I know that if I have a Cat.1 coming then I really just sit around and watch the limbs blow around. A Cat.2 that just formed off Cuba and ran straight to AL Coast is a little worse but managable. Gonna be some work to do afterwards. Now a Cat.5 that has been brewing for days, slowly churning, then comes in as a Cat.3 is going to have Cat.3 winds with Cat.4-5 surge. So I do not understand if I am missing something on the reasoning for needing a new warning system.
447. aquak9
 But at what point does it stop being their fault and our responsibility?Excellent point to ponder, as some folks will always point fingers and say, "It's THEIR fault!" But responsibility starts at HOME. If one is so mindless as to always depend on others...then they will always be dependent on others.
446. weathermanwannabe
 Good Morning from North Florida. No stats here and things quiet across the SE right now....Just watching that t-storm complex headed towards the Great Lakes.
444. HurricaneSwirl
 It's HOT in Georgia, as usual I guess.Many places through out GA are supposed to hit 93 today, and 91-92 tomorrow. I've already hit 92 yesterday.Our all time highest temperature in the month of April ever recorded is only 94!
 Quoting juslivn:Hi tornadodude, saw that one coming for you, unfortunately. Springfield, Decatur, then Danville, IL area then out east by you right when the energy was pretty intense. (aren't I scientific) but glad you are ok. We had some walnut sized hail and this little thing to my west just east of Rockford had upper level rotation and had lower for a moment. It is too far north I think to come your way again. Tomorrow should be just as interesting though.yeah it has been a busy day for storms, and yeah tomorrow and wednesday should be interesting as well
Member Since: December 31, 1969 Posts: Comments:
441. juslivn
 Hi tornadodude, saw that one coming for you, unfortunately. Springfield, Decatur, then Danville, IL area then out east by you right when the energy was pretty intense. (aren't I scientific) but glad you are ok. We had some walnut sized hail and this little thing to my west just east of Rockford had upper level rotation and had lower for a moment. It is too far north I think to come your way again. Tomorrow should be just as interesting though.
 Quoting juslivn:Hey Bordornaro (and all)! Thanks for posting. Staying up till that one out west by Rockford gets by us here in North Eastern IL. It may go north...hey!had some rough ones in Indiana today, they were south of me, but a few tornado warnings and some tennis ball sized hail too
Member Since: December 31, 1969 Posts: Comments:
439. juslivn
 Hey Bordornaro (and all)! Thanks for posting. Staying up till that one out west by Rockford gets by us here in North Eastern IL. It may go north...
438. homelesswanderer
 Interesting discussion on hurricane warnings. Maybe one day they will come up with the perfect warning that will work with everybody. But as many mentioned all storms are not created equal. And there are probably a thousand stories for each storm that we never hear about. A lot more of SE TX was flooded after Ike than people know. A lot more of TX and Louisiana was damaged by Rita's winds than most people know. Not to mention Rita erased SW LA. So there are 2 examples of Cat 2 and Cat 3 damage that was not typical. And then there are the Cat 1's that are just a "nuisance" Well thats not always true either...example 1 Humberto. Other than all the other weird stuff he did this stat really surprised me...Very heavy rains associated with Humberto were noted in a small area of extreme southeastern Texas and southwestern Louisiana. The maximum storm total precipitation was 14.13 at East Bay Bayou, Texas, and a large surrounding area of 3-5 inches stretched northeastward into central Louisiana. And 10.71 inches at Mayhew Bayoy/Winnie Wetlands TX. Once again not typical of the category. And those are just some of the examples I know about. Like I said there are probably thousands more. It's obvious we need a better understanding of these storms across the board. And yes our officials definitely need to be educated so they can make the right calls. But at what point does it stop being their fault and our responsibility? Granted the call for Ike came too late. I left Orange County on the 11th. There were already impassable roads. And I believe by the time the "leave or face certain death" call was made it was too late. I don't know. Its a hard call. But it did surprise me that the people around here didn't take heed. There was still a lot of "It'll never happen to me." going on. And it was sad. :(
437. BDAwx
 Bermuda's Climate Report for March has come in headed as "Cooler and Wetter than Average"Air temp was 1.2C/2F below averageWater temp was 1C/1.8F below average Precipitation was 0.69" above average - not too bad.Temps have come up from January and February compared to average.JanuaryAir temp 1.9C/3.5F below avgWater temp 2.7C/4.9F below avgFebruaryAir temp 2C/3.7F below avg.Water temp 2.7C/4.7F below avgA quick calculation puts average wind speeds at:Januaryrecorded 30mph - WSW/W (257degrees)average 15mph - SW (225degrees)Februaryrecorded 32mph - WSW/W (257degrees)average 16mph - W (270degrees)Marchrecorded 26mph - SW/WSW (237degrees)average 17mph - W (270degrees Bermuda Climate
436. xcool
Member Since: December 31, 1969 Posts: Comments:
435. xcool
 :0
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434. Levi32
 Quoting gordydunnot:Please people I know the season is getting closer, but this play by play of all ocean and gulf temperatures is a little crazy. Its not that informative, so lets wait for the season to get a little closer. Imo shear rules the day and we are not close enough to the season to judge its value yet.No but we are close enough to start figuring out what it may be like, so we are going to explore the possibilities. Unless another major event is going on, people are going to post SST maps on a daily basis. That's not a bad thing...we're all just watching and waiting. It is unnerving for many to see the record SSTs day after day on the maps.
Member Since: December 31, 1969 Posts: Comments:
433. gordydunnot
 Please people I know the season is getting closer, but this play by play of all ocean and gulf temperatures is a little crazy. Its not that informative, so lets wait for the season to get a little closer. Imo shear rules the day and we are not close enough to the season to judge its value yet.
432. Bordonaro
Member Since: December 31, 1969 Posts: Comments:
431. Bordonaro
 SEVERE WEATHER STATEMENTNATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL1035 PM CDT MON APR 5 2010ILC031-043-089-097-111-060400-/O.CON.KLOT.SV.W.0005.000000T0000Z-100406T0400Z/MCHENRY IL-LAKE IL-COOK IL-KANE IL-DUPAGE IL-1035 PM CDT MON APR 5 2010...A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT FOR NORTHERNDUPAGE...NORTHEASTERN KANE...NORTHERN COOK...LAKE AND SOUTHEASTERNMCHENRY COUNTIES UNTIL 1100 PM CDT...AT 1031 PM CDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED ALINE OF SEVERE THUNDERSTORMS CAPABLE OF PRODUCING WALNUT SIZE HAIL...AND DESTRUCTIVE WINDS IN EXCESS OF 70 MPH. THESE STORMS WERE LOCATEDALONG A LINE EXTENDING FROM LAKE VILLA TO VILLA PARK...MOVING EAST AT45 MPH.1.5 INCH HAIL WAS WAS REPORTED IN STREAMWOOD WITH THESE STORMS.LOCATIONS IMPACTED INCLUDE... BUFFALO GROVE...GAGES LAKE...VERNON HILLS...LIBERTYVILLE...MOUNT PROSPECT...WHEELING...OHARE AIRPORT...DES PLAINES...LINCOLNSHIRE... GURNEE...FRANKLIN PARK...RIVERWOODS...ROSEMONT...PARK CITY... MAYWOOD...PARK RIDGE...DEERFIELD...LAKE FOREST...WAUKEGAN AND NORTH CHICAGO.PRECAUTIONARY/PREPAREDNESS ACTIONS...THIS STORM HAS A HISTORY OF PRODUCING DESTRUCTIVE WINDS AND LARGEDAMAGING HAIL. SEEK SHELTER NOW INSIDE A STURDY STRUCTURE AND STAYAWAY FROM WINDOWS!TO REPORT SEVERE WEATHER...CONTACT YOUR NEAREST LAW ENFORCEMENTAGENCY. THEY WILL RELAY YOUR REPORT TO THE NATIONAL WEATHER SERVICEIN CHICAGO.
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430. Levi32
 Quoting KEEPEROFTHEGATE:drak i believe the MDR is the warmest ever seen been checking back never seen this much heatNot only is it the warmest ever seen in the MDR (since 1982 when satellite SST measurements began), but it it is also the coldest ever seen this time of year between 30N and 40N. This is also a bad sign for the United States and Caribbean countries, as it really helps focus heat and surface convergence to the south over the deep tropics, and deters storms from recurving.
Member Since: December 31, 1969 Posts: Comments:
427. hydrus
 Quoting Jeff9641:Infact I was just speaking with some of my friends there earlier today and they said this heat has be relentless. There has also been quite a bit of rain in Puerto Rico as well this winter. I saw a few fronts this winter stalled out in there vicinity. That was probably a contributing factor. The rain is a blessing and a bad thing at the same time. They need water stores for drinking. But too much rain in that region (especially Haiti ) which is prone to landslides and is still ravaged from the Jan-12 earthquake . The news has stated that lives were lost from flooding since the earthquake took place. the rainy season is starting there already according to some.
Member Since: December 31, 1969 Posts: Comments:
426. Tropicsweatherpr
 Quoting Jeff9641:I have numerous friends in PR and they said this is the HOTTEST WINTER they ever seen there as temps most of the winter hoovered between 90 and 95 with high humidity.Yes,that is true as I live here in PR.Look at how many high temp records were broken in March alone.Link
424. Drakoen
 Quoting Jeff9641:I have numerous friends in PR and they said this is the HOTTEST WINTER they ever seen there as temps most of the winter hoovered between 90 and 95 with high humidity.Surface Air Temperature Anomalies:
423. hydrus
 Quoting WaterWitch11:89 degrees? it rained here all day yesterday and last week or so we had a light dusting of snow on our nearby mountains.i bet the water over there is amazing to swim in! The water is still chilly. But the water and the waterfalls are nothing short of awesome.
Member Since: December 31, 1969 Posts: Comments:
421. Patrap
Member Since: December 31, 1969 Posts: Comments:
417. Patrap
 The GOM will support a Major easily in Aug and Sept,every year..That is always a given.Preparation now,,is the Key to being ready for what may come.,,throughout the Atlantic BasinTake the Grace of time now,to be Ready when it counts.
Member Since: December 31, 1969 Posts: Comments:
415. KEEPEROFTHEGATE
 drak i believe the MDR is the warmest ever seen been checking back never seen this much heat
414. WaterWitch11
 89 degrees? it rained here all day yesterday and last week or so we had a light dusting of snow on our nearby mountains.i bet the water over there is amazing to swim in!
Member Since: December 31, 1969 Posts: Comments:
413. winter123
 Quoting Drakoen:In the GOM there may not be and that is because our winter was colder than 2005. Other areas are similar to if not warmer than 20052010:2005:Yeah, everywhere is warmer than 05 except the north and west GOM. But people keep telling me it'll warm up, so this could be a crazy year if the el nino lets up.
410. KEEPEROFTHEGATE
 Quoting weatherblog:The SST's in the Gulf of Mexico are relatively weak. That is good news because, while it still will warm up, I don't think we well have super, super hot temperatures from like 2005 or like a lot of the recent years. HOWEVER, a lot of the caribbean, central antlantic, Bahamas, and the East African coast is warming up at an extremely fast rate and some of it is a LOT above average. I don't know what exactly this will mean for this upcoming hurricane season but I would bet it would mean a lot of long trackers and when it reaches those hot waters near the Antilles, Caribbean, and the Bahamas region expect some storms to blow up.storms will blow up way before then expect the season to have a lot of quick spin ups due to warm sst's in MDR of central south North Atlantic as they ride in cooler coastal waters if thats the way it turns out will just aid in starting the weakening phase much sooner but as always things can and will change if rains and cloundiness dev over GOM SE gulf coasts then temps will take longer to response alot depends on how a lot of factors will play out over the next 60 days we wait watch and see
409. bappit
 Atmo:"That early surge was a Gulf shelf-traveling Kelvin wave that brought up water levels ahead of the actual surge."Very cool info. What set the wave off?
408. hydrus
 Quoting bappit:402Spring has sprung. I guess hail has sprung too. Someone said 2" diameter stones.
Member Since: December 31, 1969 Posts: Comments:
407. weatherblog
 The SST's in the Gulf of Mexico are relatively weak. That is good news because, while it still will warm up, I don't think we well have super, super hot temperatures from like 2005 or like a lot of the recent years. HOWEVER, a lot of the caribbean, central antlantic, Bahamas, and the East African coast is warming up at an extremely fast rate and some of it is a LOT above average. I don't know what exactly this will mean for this upcoming hurricane season but I would bet it would mean a lot of long trackers and when it reaches those hot waters near the Antilles, Caribbean, and the Bahamas region expect some storms to blow up.
406. Drakoen
 Quoting GeoffreyWPB:It seems there is no comparison to the SST's from 2005 against the current SST temps. Also, from maps that were posted earlier, the 2005 El Nino was pretty much gone as opposed to what remains of it today. As of this posting, I do not see '05 as an analog year.In the GOM there may not be and that is because our winter was colder than 2005. Other areas are similar to if not warmer than 20052010:2005:
405. bappit
 402Spring has sprung.

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