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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1655. Floodman
 Quoting twhcracker:on our local weather they said the forecast for this year is for more hurricanes to impact Florida on the EAST coast. so i guess that lets us off the hook here in the GOM?The only problem with that is once the storm passes over FL and enters the GOM, Now you got a problem.I'm amazed that anyone would be forecasting any increased liklihood for a specific area this early...but then again, there are a lot of TV mets that get their forecasts from Dr. Bunson Honeydew
1653. CybrTeddy
 Quoting Stormchaser2007:Not moving much at all... Strange, i wonder if the csu and the el nino advisory looked at this.
Member Since: July 8, 2005 Posts: 259 Comments: 25513
1652. WaterWitch11
 Quoting CycloneOz:I think the most distressing thing I feel about being swept away by a Cat 5 hurricane is that my personal epirb would be useless until the storm abated enough that a rescue mission could be launched.I've read many accounts of people who were swept away by major cat storms.None of those stories were a fun read.oh my god you guys enough with the pens & SSN number. oz you seem like a very smart guy, would you really try to be so close in a cat5 storm? don't you have family that is going to be upset and scared if you do this? i'm sorry it's really none of my business but i just had to comment.
1651. CybrTeddy
 Trying out the iPad again. I'm able to run models and watch some loops, i have to post pics the old traditonal way however but no real bother
Member Since: July 8, 2005 Posts: 259 Comments: 25513
1649. StormChaser81
 Quoting twhcracker:on our local weather they said the forecast for this year is for more hurricanes to impact Florida on the EAST coast. so i guess that lets us off the hook here in the GOM?The only problem with that is once the storm passes over FL and enters the GOM, Now you got a problem.
Member Since: August 11, 2008 Posts: 0 Comments: 2315
1648. Stormchaser2007
 Not moving much at all...
Member Since: June 9, 2007 Posts: 4 Comments: 16088
1647. weathermanwannabe
 Quoting StormChaser81:Be careful what you wish for, we could get a really big one and have solar winter for a couple of years.I know.... :).....Not "that" big of an eruption; just enough for some pretty sunsets and a few degrees cooler over the MDR.
1646. StormChaser81
 Quoting weathermanwannabe:At this rate, we might need a volcanic eruption somewhere, with lots of ash (preferably in a non-populated region of the world), to cool things down in the Atlantic come the Summer months.Be careful what you wish for, we could get a really big one and have solar winter for a couple of years.
Member Since: August 11, 2008 Posts: 0 Comments: 2315
1645. NttyGrtty
 1620. LOL! Everyone on here contributes information. One man's gem is another man's junk and I wouldn't assume anyone here knows the thinking of 95% of the blog. The regular posters are a very small percentage of the total blog. When someone gets banned, it's not the "reportados" on the blog that gets admin's attention, it's the 200 lurkers that flagged it...
1644. Levi32
 Quoting twhcracker:on our local weather they said the forecast for this year is for more hurricanes to impact Florida on the EAST coast. so i guess that lets us off the hook here in the GOM?We still have some things to figure out before we'll know which areas of the U.S. coastline may be at most risk. At this point I don't think I can say that any part of the coast may be off the hook this year though.Not to say anyone is ever off the hook in any year...
Member Since: November 24, 2005 Posts: 635 Comments: 26780
1643. TampaTom
 Quoting Patrap:Be sure to include your SSN on your Arm with a Magic Marker too.Arms and legs tend to get ripped off in debris fields. Back in 2004, we were telling folks to put the SSN on their torsos....Just sayin'...
1642. Levi32
 Quoting CybrTeddy:Afternoon drak, Levi, oz, Jeff and everyone else!Hey Teddy :)
Member Since: November 24, 2005 Posts: 635 Comments: 26780
1641. twhcracker
 on our local weather they said the forecast for this year is for more hurricanes to impact Florida on the EAST coast. so i guess that lets us off the hook here in the GOM?
Member Since: July 30, 2007 Posts: 6 Comments: 1448
1640. Levi32
 Quoting Drakoen:Or I have not been stalking it as well as you have Levi (tongue in cheek)Lol, well, being in Alaska I end up checking the websites later than you do on any given day.
Member Since: November 24, 2005 Posts: 635 Comments: 26780
1639. weathermanwannabe
 At this rate, we might need a volcanic eruption somewhere, with lots of ash (preferably in a non-populated region of the world), to cool things down in the Atlantic come the Summer months.
1638. Floodman
 Quoting Patrap:Be sure to include your SSN on your Arm with a Magic Marker too.Yep, that's the consensus...use a good permanent marker, as salt water tends to erode regular magic markers
1637. 47n91w
 Current webcam view in the backyard of OSNW3 in Oshkosh, WI.
1636. Drakoen
 Or I have not been stalking it as well as you have Levi (tongue in cheek)
1635. CybrTeddy
 Afternoon drak, Levi, oz, Jeff and everyone else!
Member Since: July 8, 2005 Posts: 259 Comments: 25513
1634. Patrap
 Be sure to include your SSN on your Arm with a Magic Marker too.
Member Since: July 3, 2005 Posts: 449 Comments: 139973
1632. Levi32
 Quoting Drakoen:I checked yesterday and it was not up.Well...Quoting Levi32 8:21 AM AKDT on April 07, 2010:The new UKMET Seasonal forecast is out for March. This forecast is overall more scary than their February forecast in terms of how things set up in the beginning of the Atlantic hurricane season.I believe they don't want their maps posted anywhere else, but you can go to their site and register to view the maps.What I can tell you is that the general trend is the same on the model, forecasting lower-than-normal surface pressures in the Caribbean and Gulf of Mexico in June-July-August, but stronger negative anomalies than last month's forecast. The rainfall forecast is downright scary for the Caribbean, with a wide swath of very high precipitation anomalies aimed out of the MDR right through the Caribbean and into Central America.The 500mb forecast continues to show a generally negative NAO look, with blocking over SE Canada. This is not a good pattern for the United States. I also took great interest to the fact that their temperature forecast is far warmer for the eastern CONUS than their February forecast. They do keep cooler-than-normal temperatures over the GOM and Florida during the JJA period, but they seem to be catching on more to the warm summer for most of the CONUS this year.Another thing I noticed is that the UKMET seems to be leaning towards a very southern-focused season affecting the Caribbean more than anywhere else, based on the MSLP and precipitation anomaly forecasts. Their forecasts only go out to the JJA period, which is just the beginning of the season, so we may see that change, but it is an interesting trend to follow on the model.I guess it just likes me more lol.
Member Since: November 24, 2005 Posts: 635 Comments: 26780
1630. Drakoen
 Quoting Levi32:You're a day late lol :)Yup the GloSea is fairly in line with the European on the pressures, SSTs, and precipitation. Both models' March forecasts look worse than their previous February forecasts.I checked yesterday and it was not up.
1628. Levi32
 Quoting Drakoen:The Glosea climate model finally updated its projections today. Things do not look good on this climate model. The first thing to mention is the Glosea showing 500mb anomalously higher heights over eastern Canada and then below average heights along the Pacific coast. This suggest a positive EPO western trough and a negative NAO eastern ridge regime, a dangerous setup to increase the risk of land-falling storms. The next thing to note is the forecast for June-July-August for temperatures in the MDR to be anywhere from 1C-2C above average. This is combined with the model showing below average sea level pressure -1mb to -2mb departures and well above average precipitation in the majority of the MDR suggesting a strong and consistent MJO.You're a day late lol :)Yup the GloSea is fairly in line with the European on the pressures, SSTs, and precipitation. Both models' March forecasts look worse than their previous February forecasts.
Member Since: November 24, 2005 Posts: 635 Comments: 26780
1626. Drakoen
 The model also shows us going into ENSO neutral conditions in May and then possibly going into a weak La Nina.
1624. jeffs713
 Quoting Drakoen:The Glosea climate model finally updated its projections today. Things do not look good on this climate model. The first thing to mention is the Glosea showing 500mb anomalously higher over eastern Canada and then below average heights along the Pacific coast. This suggest a positive EPO trough and a negative NAO eastern ridge regime, a dangerous setup to increase the risk of land-falling storms. The next thing to note is the forecast for June-July-August for temperatures in the MDR to be anywhere from 1C-2C above average. This is combined with the model showing below average sea level pressure and well above average precipitation in the majority of the MDR suggest a strong and consistent MJO.What does one around here have to do to get good news for this season?All I hear is "the CONUS and Caribbean are doomed", "the CONUS and Caribbean are doomed", and "the CONUS and Caribbean are doomed". Of course, based on all the model suites' forecasts, the CONUS and Caribbean are doomed.
Member Since: August 3, 2008 Posts: 16 Comments: 5958
1622. Bordonaro
 MESOSCALE DISCUSSION 0293 NWS STORM PREDICTION CENTER NORMAN OK 0300 PM CDT THU APR 08 2010 AREAS AFFECTED...CNTRL AND ERN GA THROUGH WRN SC CONCERNING...SEVERE POTENTIAL...WATCH LIKELY VALID 082000Z - 082200Z STORMS ARE EXPECTED TO DEVELOP NEWD THROUGH CNTRL AND ERN GA AND EVENTUALLY INTO WRN SC THIS AFTERNOON. THE PRIMARY THREATS WILL BE ISOLATED DAMAGING WIND AS WELL AS ISOLATED TORNADOES. WW WILL LIKELY BE NEEDED SOON. A COLD FRONT EXTENDS FROM THE SRN APPALACHIANS SWWD THROUGH NRN GA INTO SERN AL. SURFACE DEWPOINTS IN THE LOW 60S HAVE ADVECTED NEWD THROUGH THE PRE-FRONTAL WARM SECTOR...BUT WIDESPREAD CLOUDS AND MODEST LAPSE RATES ARE LIMITING MLCAPE TO UNDER 1000 J/KG. STORMS WILL LIKELY CONTINUE DEVELOPING ALONG FRONT AND PRE-FRONTAL WARM CONVEYOR BELT THIS AFTERNOON INTO THE EVENING. STRONG MID-UPPER FLOW WILL PERSIST DOWNSTREAM FROM UPPER TROUGH...AND HODOGRAPHS IN WARM SECTOR WILL BE MAXIMIZED ALONG NEWD MIGRATING LOW LEVEL JET. ORGANIZED STORMS INCLUDING LINEAR BOWING SEGMENTS AND SUPERCELLS WILL REMAIN POSSIBLE. THE THERMODYNAMIC ENVIRONMENT IS NOT OPTIMAL...BUT WILL REMAIN SUFFICIENT FOR A THREAT OF ISOLATED DAMAGING WIND AND ISOLATED TORNADOES GIVEN FAVORABLE VERTICAL SHEAR. ..DIAL.. 04/08/2010
Member Since: August 25, 2009 Posts: 20 Comments: 6785
1621. Drakoen
 The Glosea climate model finally updated its projections today. Things do not look good on this climate model. The first thing to mention is the Glosea showing 500mb anomalously higher heights over eastern Canada and then below average heights along the Pacific coast. This suggest a positive EPO western trough and a negative NAO eastern ridge regime, a dangerous setup to increase the risk of land-falling storms. The model shows anomalously higher 2m air temperatures over the eastern third of the country.The next thing to note is the forecast for June-July-August for temperatures in the MDR to be anywhere from 1C-2C above average. This is combined with the model showing below average sea level pressure -1mb to -2mb departures and well above average precipitation in the majority of the MDR suggesting a strong and consistent MJO.
1620. jeffs713
 1614. I fail to see what is reportable on that.CycloneOz actually contributes information to the blog. Other people whom I won't mention on here but are readily apparent to 95% of the readers of the blog... do not.
Member Since: August 3, 2008 Posts: 16 Comments: 5958
 Quoting CycloneOz:Oh geez, I even recognized "Your Song" right away. ;)
1615. NRAamy
 CycloneOz....you rock, dude!!!!!:)
Member Since: January 24, 2007 Posts: 320 Comments: 31970
1612. Patrap
Member Since: July 3, 2005 Posts: 449 Comments: 139973
1611. WPBHurricane05
 I wonder if JFV and STORMTOP are related. I imagine Levi saw Joe Bastardi's Hurricane Update on the Pro site. He certainly did nail last years forecast.
1610. jeffs713
 Quoting CycloneOz:It's a little bit funny, when you get bannedHow you get back in, we do not understandI'm not a WU admin, but if I wasI'd IP you out so hard, your head would buzzI've tried to ignore you, but you defeat me againNow I'm ready to stab myself in the head with a penYou're back one more time and I feel myself heaveNo matter what you call yourself now, you're still JFVAnd you can tell everybody, it's really not youSome may believe, but I'm not a foolI know it's you, manI know it's you, man...we sniff you out like a dogHow wonderful life is, when you're not on the blogAnd a + for you!
Member Since: August 3, 2008 Posts: 16 Comments: 5958
1608. 47n91w
 Quoting tornadodude:Quite a surprise overnight and this morning in Green Bay:PRELIMINARY LOCAL STORM REPORTNATIONAL WEATHER SERVICE GREEN BAY WI104 PM CDT THU APR 08 20101257 PM 04/08/2010 GREEN BAY, BROWN COUNTY44.51N 88.00W SNOW M5.8 INCH STORM TOTAL. WATER EQUIVALENT 0.56 INCHES.They were expecting a light dusting... ended up with quite a bit more. Up here in far northern Wisconsin, I had 31 degrees this morning with eleven snowflakes. Sunny at 14:45 and 37 degrees (which is nine degrees below the average high for the date).

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