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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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.
1554. 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:
Member Since: December 31, 1969 Posts: Comments:
1553. 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 difficult
1552. NttyGrtty
 Quoting PcolaDan:I was watching it and hoping, then it just fizzled out. Pulled itself north, slid by, then dropped back down some. Just scattered stuff right now, and light. I've got blue sky...
1551. Skyepony (Mod)
 The Chinese government is so worried about the drought that it has embarked on a massive rain-making operation, involving firing thousands of shells and rockets into the sky to seed clouds.Until last summer, Damoguzhen was home to a lake that stretched across a mile-wide expanse of water in Yunnan, a southern Chinese province famed for its mighty rivers, moist climate and beautiful views.Today, it joins 310 reservoirs, 580 rivers and 3,600 pools that have been baked dry by a once-in-a-century drought that is evaporating drinking supplies, devastating crops and stirring up political tensions over dam construction, monoculture plantations and cross-border water management in south-east Asia. Linking specific weather events to human-caused climate change is impossible, but the drought is consistent with what climate scientists expect to see more of in future.
1550. stillwaiting
 tampa tom SSW at around 15mph down here in srq,should cloud up overnight with scattered showers and t-storms tomorrow as the front pushes thru the region,maybe a isolated severe report tomorrow as well in our area!!
 Quoting NttyGrtty: It absolutely poured just east of you...for about 15 secondsI was watching it and hoping, then it just fizzled out. Pulled itself north, slid by, then dropped back down some. Just scattered stuff right now, and light.
1547. NttyGrtty
 Quoting PcolaDan:Most of the rain just skipped right by us. :( It absolutely poured just east of you...for about 15 seconds
 Quoting TampaTom:Wind's coming in rather briskly from the east at the Memorial Causeway in downtown Clearwater...I guess it's coming in advance of the front?Most of the rain just skipped right by us. :(
1545. Skyepony (Mod)
 Levi~ Thanks.. Neat graph, you can see the volcano eruptions. I think the stratosphere temp drop to 1995 was partially ozone hole related.
1544. watchingnva
 Quoting CycloneOz:Tiger Woods is all wet.And soon, he'll be rained on, as well.pointless...cant wait for the rain to get to us this evening....really hope for a few decent storms..
1542. Bordonaro
 NW Florida radar our of NWS Tallahassee, FL:
1541. TampaTom
 Wind's coming in rather briskly from the east at the Memorial Causeway in downtown Clearwater...I guess it's coming in advance of the front?
1539. Bordonaro
 5.3Mw Aftershock from the N Mexico quake, link below. Initially reported as a 5.5 Mw, but was reviewed and downgraded by USGS seismologist:Link
1538. Levi32
 Man check out these temperature anomalies for the last 5-day period. Pretty incredible.
Member Since: December 31, 1969 Posts: Comments:
1537. RTLSNK
 Little boomers on the way, be back later. :)Edit: let me try this again:
1536. Tropicsweatherpr
 CPC monthly update says Neutral by summer.Link
1535. Levi32
 Quoting Skyepony:Levi~ That's March average.. & is that for the mesosphere only?.. this was a cold April morning & all it has to be is cold enough to freeze water.. if you check the state of the climate I haven't seen a stratosphere less than 10 coldest in the last 5 years. Usually it's 1 0r 2 especially when the surface is running this hot but I suspect we are seeing 7th & 8th Feb as El Nino vents. Everytime El Nino dies a little, stratosphere warms a little from top 2 coldest.. There are several pics on WU as the shuttle is leaving the atmosphere a vapor cloud surrounds..that then condensed into the very bright white/blue NCL seed cloud..that is in the beginning of the gif I posted..it was completely dark... NASA did another study they launched in VA right after dark just to study NLC formation from launches. It was more toward summer & VA was selected as it is higher & latitude so more likely to be a success..Yeah I know....just pointing out it hasn't been that cold up there recently, though probably cold enough. That is the lower stratospheric temperatures....not the mesosphere.Besides, global stratospheric temps haven't gone anywhere since 1995. I could only find a graph up until 2008 though.The blue line is lower tropospheric temperature and the green line is the stratospheric temperature.But yeah....that was a really cool slideshow you put together :)
Member Since: December 31, 1969 Posts: Comments:
1534. Skyepony (Mod)
 Levi~ That's March average.. & is that for the mesosphere only?.. this was a cold April morning & all it has to be is cold enough to freeze water.. if you check the state of the climate I haven't seen a stratosphere less than 10 coldest in the last 5 years. Usually it's 1 0r 2 especially when the surface is running this hot but I suspect we are seeing 7th & 8th Feb as El Nino vents. Everytime El Nino dies a little, stratosphere warms a little from top 2 coldest.. There are several pics on WU as the shuttle is leaving the atmosphere a vapor cloud surrounds..that then condensed into the very bright white/blue NCL seed cloud..that is in the beginning of the gif I posted..it was completely dark... NASA did another study they launched in VA right after dark just to study NLC formation from launches. It was more toward summer & VA was selected as it is higher & latitude so more likely to be a success..
1533. Bordonaro
 MESOSCALE DISCUSSION 0291 NWS STORM PREDICTION CENTER NORMAN OK 1124 AM CDT THU APR 08 2010 AREAS AFFECTED...SE AL...SW GA...FL PANHANDLE CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE VALID 081624Z - 081730Z A FEW SUPERCELLS WILL REMAIN POSSIBLE THE NEXT FEW HOURS...BUT THE NEED FOR A WATCH IS UNCLEAR BASED ON A RATHER MODEST INSTABILITY/ SHEAR ENVIRONMENT. SMALL DISCRETE STORMS HAVE BEEN DEVELOPING ALONG THE MOIST AXIS... IN ADVANCE OF THE COLD FRONT ACROSS AL AND A MIDLEVEL SHORTWAVE TROUGH PROGRESSING EWD FROM MS. LOCAL VWP/S AND SHORT-TERM FORECAST SOUNDINGS SHOW A MODEST VERTICAL SHEAR ENVIRONMENT WITH EFFECTIVE BULK SHEAR OF 40-50 KT...AND EFFECTIVE SRH OF 100-200 M2/S2. SURFACE TEMPERATURES OF 75-80 F AND BOUNDARY LAYER DEWPOINTS OF 64-68 F ARE SUPPORTING MLCAPE VALUES OF 500-1000 J/KG...AND THIS COMBINATION OF VERTICAL SHEAR AND INSTABILITY IS SUFFICIENT FOR ROTATING STORMS. THE TENDENCY INTO EARLY AFTERNOON WILL BE FOR CONTINUED DESTABILIZATION WITH MOISTURE ADVECTION AND SURFACE HEATING...BUT VERTICAL SHEAR IS NOT EXPECTED TO INCREASE THROUGH THE AFTERNOON. THE STRONGEST STORMS IN THIS AREA WILL BE CAPABLE OF PRODUCING STRONG WIND GUSTS...AND POSSIBLY A BRIEF/WEAK TORNADO...BUT THE OVERALL SEVERE THREAT STILL APPEARS SOMEWHAT MARGINAL FOR A WATCH ISSUANCE. ..THOMPSON.. 04/08/2010
1532. Bordonaro
 Quoting ycd0108:Speaking of record numbers:1013 earthquakes on this maphttp://earthquake.usgs.gov/earthquakes/recenteqsww/Maps/10/245_35.phpThere are quite a few earthquakes on that map. The 7.2Mw quake in N Mexico was on a plate zone that normally produces many small quakes on a regular basis. The number appears to be high, but that is "normal". What concerns me is there were almost no aftershocks on the 7.7Mw quake in Indonesia, plus the "USGS map" appears to be fairly quiet, at least for now. I have noticed when the USGS map gets quiet, there appears to be a fairly large quake occurs within a few days. Please note, that is only my opinion. The USGS people say seismic activity worldwide is "perfectly normal".
1531. Levi32
 Quoting Skyepony:Oss~ Those photos are good but I don't agree with the guy saying they aren't Noctilucent clouds. NASA has done studies in launch, including Shuttle plumes. They are 97% water & a bit gets injected into the upper reaches were it freezes for these clouds to form. NASA classified them as NLC & have tracked the moisture to the Arctic where it created the classic version, though we've seen the more classic looking version after launch here.. At's certainly a physical sign that the most outer parts of our atmosphere has cooled. There were no NLC pre 1885 & none in the lower latitudes even launching the perfect time of day til a few years ago.Well it hasn't been cooler than normal up there recently above Florida.
Member Since: December 31, 1969 Posts: Comments:
1530. Skyepony (Mod)
 Oss~ Those photos are good but I don't agree with the guy saying they aren't Noctilucent clouds. NASA has done studies in launch, including Shuttle plumes. They are 97% water & a bit gets injected into the upper reaches were it freezes for these clouds to form. NASA classified them as NLC & have tracked the moisture to the Arctic where it created the classic version, though we've seen the more classic looking version after launch here.. At's certainly a physical sign that the most outer parts of our atmosphere has cooled. There were no NLC pre 1885 & none in the lower latitudes even launching the perfect time of day til a few years ago.Thanks Flood, Pat, Indainriverguy..
1529. ycd0108
 Speaking of record numbers:1013 earthquakes on this maphttp://earthquake.usgs.gov/earthquakes/recenteqsww/Maps/10/245_35.php
1528. Patrap
 The Daily Downpour Join meteorologists Shaun and Tim on The Weather Show today. Please join us as we will discuss a variety of topics.We will also be taking your phone calls!Here is the schedule for today:All times are in Eastern4:00-4:10: National Forecast4:10-4:20: Dr. Jeff Masters Blog Recap4:20-4:30: Learning Corner4:30-5:00: The Weather Show with Shaun and Tim.Please join us. We promise you will learn something!
1527. indianrivguy
 Nice slide show Skye, thanks for sharing!
1523. Patrap
 Skye is our resident NASA ,KSC Launch photographer.If one hasnt witnessed a Launch Live,a Shuttle Launch,...I highly recommend attending one of the last 3..
1520. AussieStorm
 Quoting skepticall2:Or U and Q?They don't do those names because how many people you know with QUXYZ names? They would run out real quick.and probably cause its rare to make it that many named storms in a season
1518. Floodman
 Skye, that's a seriously cool slideshow...
1517. Patrap
 I feel a new entry coming...soon.O da drama,..the excitement,..its palatable.
1515. Skyepony (Mod)
 Here's a slide show I put together of the Shuttle Discovery created Noclilucent Cloud the other day.
1514. Floodman
 Quoting Bordonaro:They're actually been picking on "Jeff9461", not Jeff Masters, our "blog chief". OK, bring on the "mystery blog" please.Hey Bord! Do you still have my number? If you do, call me, huh?
1512. Ossqss
 Pretty cool site, and has some great shots of the recent Shuttle (STS131) related clouds :) Atmospheric Optics
1511. Levi32
 The NAEFS is forecasting above-normal temperatures to continue over the eastern US for the next 1-2 weeks. The only reason it's showing below-normal temperatures over the Gulf of Mexico is simply because the water is colder than normal and moderating the temps. As the SSTs recover due to the surrounding warm air this forecast will become warmer as well.
Member Since: December 31, 1969 Posts: Comments:
1510. AussieStorm
 Quoting Stormchaser2007:I feel like Igor is gonna give us trouble this year. Its always those pesky Russian namesAlexBonnieColinDanielleEarlFionaGastonHermineIgorJuliaKarlLisaMatthewNicoleOttoPaulaRichardSharyTomasVirginieWalterX?Y?Z?Has there ever been an X, Y or Z name in a season???
1509. hydrus
 Quoting AussieStorm:The GOM has warmed up a fair bit in 5 days. not a good sign.Yeah, the Gulf will be like a bowl of soup by the end of May. A meal High in energy for storms.
Member Since: December 31, 1969 Posts: Comments:
1508. Levi32
 Quoting AussieStorm:The GOM has warmed up a fair bit in 5 days. not a good sign.Like we've said it won't take very long at all to warm the gulf back up to normal. As soon as those arctic shots left the area it started skyrocketing.
Member Since: December 31, 1969 Posts: Comments:
1507. AussieStorm
 Quoting Levi32:March 31st:April 5th:5-day SST Change:The GOM has warmed up a fair bit in 5 days. not a good sign.
1506. Stormchaser2007
 I feel like Igor is gonna give us trouble this year. Its always those pesky Russian names
1505. Patrap
 O,..then "nevermind"LOL

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