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

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Member Since: June 28, 2006 Posts: 25 Comments: 8516
1603. twhcracker
 Quoting Jeff9641:To be honest I didn't think it would be this active in the Panhandle today. 1 tornado near Enterprise and now one near Tallahassee. I was expecting scattered thunderstorms nothing severe like this. My hurricane prediction is the same as Feb. of 17 8 5. The whole state of Florida could be in trouble this year and maybe as far west as New Orleans. I hope they have those Levee's ready. By the way I wasn't in a cave I was busy at work today.omg my house is south of dothan i better check the weather at home.
Member Since: July 30, 2007 Posts: 6 Comments: 1448
1602. weathermanwannabe
 Afternoon from Tallahassee......Been tied up at work all day (no windows where I was) but finally out and looking out the windows.....Also surprised about a few tornadoes spinning up (one NW of my house in Northern Leon County per my Wife) in our parts. The squall line is very narrow and about to pass through Tallahassee, and the local skies have that grey "nader" look with fast moving clouds but will have to see what happens over next hour or so.
1601. lilElla
 #1584Tell me it's not so!!!!!! Spring has been so peaceful................
 Quoting presslord:...he's Amy's boyfriend...LMAO!!!!
Member Since: June 28, 2006 Posts: 25 Comments: 8516
1599. NRAamy
 JFV/Cane2010....don't send me emails calling me "woman"......it doesn't matter what name you come back with...you always out yourself, bud......
Member Since: January 24, 2007 Posts: 319 Comments: 31956
1598. presslord
 ...he's Amy's boyfriend......or...maybe not...
Member Since: August 13, 2007 Posts: 0 Comments: 10538
1594. WaterWitch11
 Quoting Jeff9641:Your boy is BACK! HOWDY TWHCRACKERR!!there was some people missing you. weren't you in a cave or something.
1593. Michfan
 Quoting TankHead93:is it possible that we may experience a hyperactive atlantic hurricane season?The ingredients are shaping up to lean that way so far. The most unpredictable feature is going to be the wind shear but the models are showing that it is going to be somewhat low.
1591. Levi32
 Quoting Cane2010:Levi, do you have a month-by-month ridge forecast for the upcoming cane season?Lol, no, month by month will be done during the season. It's nearly impossible to know what the pattern will be in each separate month this early.
Member Since: November 24, 2005 Posts: 635 Comments: 26780
1589. Bordonaro
 NY and PA are UNDER THE GUN!!MESOSCALE DISCUSSION 0292 NWS STORM PREDICTION CENTER NORMAN OK 0157 PM CDT THU APR 08 2010 AREAS AFFECTED...NY THROUGH NRN AND CNTRL PA CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE VALID 081857Z - 082000Z STORMS ARE EXPECTED TO INTENSIFY DURING THE NEXT HOUR OR TWO ACROSS WRN PA AND WRN NY AND CONTINUE EWD. BOWING LINE SEGMENTS AND SUPERCELLS WITH DAMAGING WIND WILL BE THE MAIN THREATS. HOWEVER...A COUPLE OF ISOLATED TORNADOES AND SOME HAIL WILL ALSO BE POSSIBLE. TRENDS ARE BEING MONITORED FOR A WW. THIS AFTERNOON A CONVECTIVE OUTFLOW BOUNDARY EXTENDS FROM WRN NY SWD THROUGH WRN PA. A WARM FRONT EXTENDS FROM SRN NEW ENGLAND WWD THROUGH NRN NY. DIABATIC WARMING HAS BOOSTED TEMPERATURES INTO THE UPPER 70S F TO AROUND 80F IN WARM SECTOR. HOWEVER...THE MOIST LAYER IS APPARENTLY NOT VERY DEEP AND DEWPOINTS ARE MIXING DOWN INTO THE UPPER 40S SOUTH OF THE WARM FRONT WHICH WILL LIMIT MLCAPE TO AOB 500 J/KG. STORMS DEVELOPING ALONG AND JUST AHEAD OF THE CONVECTIVE OUTFLOW BOUNDARY WILL LIKELY INTENSIFY AS THE BOUNDARY LAYER DESTABILIZES. STRONG MID-UPPER FLOW WILL PERSIST IN WARM SECTOR AND RESULT IN 40-50 KT DEEP LAYER SHEAR SUPPORTING THE POTENTIAL FOR BOWING SEGMENTS AND SUPERCELLS. THE RELATIVELY DRY BOUNDARY LAYER...WHILE A LIMITING FACTOR FOR MORE ROBUST INSTABILITY...MAY SERVE TO ENHANCE DOWNDRAFT POTENTIAL. ISOLATED TORNADOES CANNOT BE RULED OUT MAINLY WITH ANY STORM DEVELOPING ALONG OR INTERACTING WITH WARM FRONT WHERE LESS MIXING WILL MAINTAIN HIGHER DEWPOINTS AND WHERE BACKED NEAR SURFACE FLOW WILL CONTRIBUTE TO LARGER 0-1 KM HODOGRAPHS. ..DIAL.. 04/08/2010
1588. NRAamy
 press.....you can't keep a JFV down....
Member Since: January 24, 2007 Posts: 319 Comments: 31956
1587. FloridaTigers
 Quoting Hurricanes101:That is a great question FloridaTigersI mean Provenza was forced out of the NHC for his "controversial" effort at trying to force a QuickScat replacement. What exactly happened? Why was he ignored/not deemed as a big deal?
1585. Bordonaro
 Well 2 Tornado reports so far, as of 2PM CDT!!
1584. presslord
 ....iiitttt'sss baaaaack.....
Member Since: August 13, 2007 Posts: 0 Comments: 10538
1582. NRAamy
 if it quacks like a JFV....;)
Member Since: January 24, 2007 Posts: 319 Comments: 31956
1581. jeffs713
 Quoting FloridaTigers:So why was Provenza ignored about the QuickScat when he was director of the NHC? The QuickScat would make life easier had it still been up and running, or a replacement was up thereProvenza made lots of political enemies, IIRC.
1579. twhcracker
 i will make my season prediction in a jeffstradamas manner, as follows:and around the soltice there shall arise and swarm forth from the hispanic one by name of kuba a greathowling wind that shall roar for twenty days and twenty nights seeking the birthplace of the one named crisp who shall rule with a limp wrist
Member Since: July 30, 2007 Posts: 6 Comments: 1448
Member Since: June 28, 2006 Posts: 25 Comments: 8516
1577. twhcracker
 Quoting Jeff9641:Your boy is BACK! HOWDY TWHCRACKERR!!well did you write some new quatrains for us? lets hear it. how is this front moving thru gonna be for us here in the nations armpit part of the GOM
Member Since: July 30, 2007 Posts: 6 Comments: 1448
 is it possible that we may experience a hyperactive atlantic hurricane season?
1575. saintsfan06
 NRAamy. So True!
 Quoting NRAamy:I was just kidding with you, my friend! Evidencial science is very difficult to ignore. On a serious note, though, everything points towards a very dangerous to come, huh?that sounds JFV-ish to me....yuppppppQuoting Michfan:Just had my first tornado warning of the year out of that line. Was a fun hour!sounds like it!
Member Since: June 28, 2006 Posts: 25 Comments: 8516
1571. NRAamy
 I was just kidding with you, my friend! Evidencial science is very difficult to ignore. On a serious note, though, everything points towards a very dangerous to come, huh?that sounds JFV-ish to me....
Member Since: January 24, 2007 Posts: 319 Comments: 31956
1569. Hurricanes101
 Quoting FloridaTigers:So why was Provenza ignored about the QuickScat when he was director of the NHC? The QuickScat would make life easier had it still been up and running, or a replacement was up thereThat is a great question FloridaTigers
 URGENT - IMMEDIATE BROADCAST REQUESTED TORNADO WATCH NUMBER 65 NWS STORM PREDICTION CENTER NORMAN OK 200 PM EDT THU APR 8 2010 THE NWS STORM PREDICTION CENTER HAS ISSUED A TORNADO WATCH FOR PORTIONS OF EXTREME SOUTHEAST ALABAMA THE FLORIDA PANHANDLE SOUTHWEST GEORGIA COASTAL WATERS EFFECTIVE THIS THURSDAY AFTERNOON AND EVENING FROM 200 PM UNTIL 700 PM EDT. TORNADOES...HAIL TO 0.5 INCH IN DIAMETER...THUNDERSTORM WIND GUSTS TO 70 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS. THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 70 STATUTE MILES EAST AND WEST OF A LINE FROM 30 MILES NORTHEAST OF ALBANY GEORGIA TO 25 MILES SOUTH SOUTHWEST OF PANAMA CITY FLORIDA. FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU5). REMEMBER...A TORNADO WATCH MEANS CONDITIONS ARE FAVORABLE FOR TORNADOES AND SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS AND POSSIBLE WARNINGS. DISCUSSION...DISCRETE WARM SECTOR STORM DEVELOPMENT SHOULD PERSIST THROUGH THE AFTERNOON ALONG THE MOIST AXIS AND IN ADVANCE OF A SURFACE COLD FRONT. LOW-LEVEL AND DEEP-LAYER SHEAR ARE SUFFICIENT FOR SUPERCELLS IN AN ENVIRONMENT OF WEAK-MODERATE INSTABILITY. GIVEN EFFECTIVE SRH AROUND 150-200 M2/S2 AND BOUNDARY LAYER DEWPOINTS IN THE MID-UPPER 60S...A COUPLE OF TORNADOES WILL BE POSSIBLE. AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT TO 0.5 INCH. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 450. MEAN STORM MOTION VECTOR 25025. ...THOMPSON
Member Since: June 28, 2006 Posts: 25 Comments: 8516
1567. FloridaTigers
 Quoting stoormfury:now we can no longer depend on the QuickScat for early detection of tropical activity, the onus is now left on ASCAT and the satelite imagery. with the seasonal activity pedicted to be high the lack of the QuickScat will make life a little difficultSo why was Provenza ignored about the QuickScat when he was director of the NHC? The QuickScat would make life easier had it still been up and running, or a replacement was up there
1566. Levi32
 Quoting Cane2010:I was just kidding with you, my friend! Evidencial science is very difficult to ignore. On a serious note, though, everything points towards a very dangerous to come, huh?It certainly looks that way.
Member Since: November 24, 2005 Posts: 635 Comments: 26780
1564. JRRP
 Quoting Levi32:Looking back at last year, the ECMWF model really nailed the 2009 hurricane season. This was its sea-level pressure forecast issued in March for the July-August-September period of last year, forecasting the high pressures and very limited convergence over the Atlantic which did indeed occur last season.The same forecast period for precipitation showed the ECMWF forecasting a very dry hurricane season overall in the tropical Atlantic and Caribbean, which verified nearly perfectly.And this is this year's March forecast for the same time period, showing the complete opposite of what the model was forecasting last year.MSLP:Precipitation:lol exactly the opposite
1561. twhcracker
 2005 (katrina) was the mnost ever, even went past the end to start alpha beta etc:Hurricane Wilma formed on October 17 in the western Caribbean southwest of Jamaica and rapidly strengthened. On October 19 it became the strongest tropical cyclone on record in the Atlantic basin, with 185 mph (295 km/h) winds and a central pressure of 882 mbar (hPa). The hurricane moved slowly and struck Quintana Roo on October 22 as a Category 4 hurricane, causing very heavy damage to Cancún and Cozumel. After emerging into the Gulf of Mexico, Wilma sharply changed directions and passed north of Cuba before striking southern Florida on the 24th as a Category 3 storm, then moving into the Atlantic Ocean and becoming extratropical. Wilma is directly credited with 23 deaths; total damages are estimated at around \$29 billion, mostly in the United States, Mexico, and Cuba.[40]Tropical Storm Alpha formed in the eastern Caribbean on October 22 and crossed Hispaniola, causing major flooding before merging with Wilma. A total of 42 people are reported dead from the storm in Haiti and the Dominican Republic.[41]Hurricane Beta formed in the southern Caribbean on October 26 and strengthened into a Category 3 hurricane before making landfall in the Colombian islands of San Andrés & Providencia and in Nicaragua on the 30th. As of 2008, damage and fatality reports have not yet been released to the public.[42] November, December, and January Hurricane Epsilon viewed from the International Space StationTropical activity declined only very slowly as the season wound down. Tropical Storm Gamma initially formed on November 15 in the central Caribbean, and degenerated into a tropical wave before reforming. Although the storm dissipated on November 20 after having made landfall in northern Honduras, rainfall from Gamma caused 41 deaths in Honduras and Belize.[43]Tropical Storm Delta formed in the eastern Atlantic on November 23; it approached but never attained hurricane strength. Delta became extratropical on the 28th shortly before striking the Canary Islands at full force, causing seven deaths and toppling El Dedo de Dios, a famous land formation on Gran Canaria.[44]Hurricane Epsilon formed as a tropical storm on November 29 in a hostile environment in the middle of the Atlantic. It reached hurricane strength on December 2 and defied forecasting by persisting for over a week before dissipating.[45]Tropical Storm Zeta became the final storm of the season when it formed on December 30, six hours short of tying the record of Hurricane Alice of 1954 as the latest-forming named storm in a season. Zeta dissipated on January 6, 2006, having become the longest-lived January tropical cyclone in Atlantic basin history
Member Since: July 30, 2007 Posts: 6 Comments: 1448
1560. Levi32
 Quoting Cane2010:G'afternoon, all! Levi, do you have any encouraging news regarding our upcoming hurricane season? LOL, :).I'll keep looking for some....lol.
Member Since: November 24, 2005 Posts: 635 Comments: 26780
1559. StormChaser81
 Quoting Cane2010:G'afternoon, all! Levi, do you have any encouraging news regarding our upcoming hurricane season? LOL, :).It hasn't started yet, there some really good news.
1558. twhcracker
 the 1995 season got us up to the name Tanya
Member Since: July 30, 2007 Posts: 6 Comments: 1448
1556. Levi32
 Quoting CyclonicVoyage:It's almost a no brainer to forecast an active season. Even JBastardi out in La La Land has fuel for his extreme season possibility.Which he came up with before most of the other big guns had issued their forecasts.....and he was the first to downplay last season. Honestly if you guys ever actually read anything he said you'd know he doesn't predict 2005s every year. He had his forecast all the way down to 8 named storms for last year by the time May came along.
Member Since: November 24, 2005 Posts: 635 Comments: 26780
1555. CyclonicVoyage
 It's almost a no brainer to forecast an active season. Even JBastardi out in La La Land has fuel for his extreme season possibility.

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Dr. Masters (r) co-founded wunderground in 1995. He flew with the NOAA Hurricane Hunters 1986-1990. Co-blogging with him: Bob Henson, @bhensonweather

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