Global warming and the frequency of intense Atlantic hurricanes: model results
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 hurricane per decade expected by the year 2100, accord 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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Tell me it's not so!!!!!! Spring has been so peaceful................
omg my house is south of dothan i better check the weather at home.
SEVERE WEATHER STATEMENT
NATIONAL WEATHER SERVICE TALLAHASSEE FL
320 PM EDT THU APR 8 2010
GAC037-061-099-081930-
/O.CON.KTAE.TO.W.0014.000000T0000Z-100408T1930Z/
EARLY GA-CALHOUN GA-CLAY GA-
320 PM EDT THU APR 8 2010
...A TORNADO WARNING REMAINS IN EFFECT UNTIL 330 PM EDT FOR
SOUTHEASTERN CLAY...WESTERN CALHOUN AND NORTHEASTERN EARLY COUNTIES
IN SOUTHWEST GEORGIA...
AT 318 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR CONTINUED TO
INDICATE A TORNADO. THIS TORNADO WAS LOCATED NEAR COLOMOKEE...OR 6
MILES NORTHEAST OF BLAKELY...MOVING EAST AT 35 MPH.
OTHER LOCATIONS IN THE WARNING INCLUDE BUT ARE NOT LIMITED TO JEFF...
TURMAN...PARKSVILLE...NICHOLASVILLE...EDISON...COMMISSARY HILL AND
ARLINGTON
PRECAUTIONARY/PREPAREDNESS ACTIONS...
IN ADDITION TO THE TORNADO...THIS STORM IS CAPABLE OF PRODUCING
QUARTER SIZE HAIL AND DESTRUCTIVE STRAIGHT LINE WINDS.
THE SAFEST PLACE TO BE DURING A TORNADO IS IN A BASEMENT. GET UNDER A
WORKBENCH OR OTHER PIECE OF STURDY FURNITURE. IF NO BASEMENT IS
AVAILABLE...SEEK SHELTER ON THE LOWEST FLOOR OF THE BUILDING IN AN
INTERIOR HALLWAY OR ROOM SUCH AS A CLOSET. USE BLANKETS OR PILLOWS TO
COVER YOUR BODY AND ALWAYS STAY AWAY FROM WINDOWS.
IF IN MOBILE HOMES OR VEHICLES...EVACUATE THEM AND GET INSIDE A
SUBSTANTIAL SHELTER. IF NO SHELTER IS AVAILABLE...LIE FLAT IN THE
NEAREST DITCH OR OTHER LOW SPOT AND COVER YOUR HEAD WITH YOUR HANDS.
RELAY REPORTS OF SEVERE WEATHER TO THE NATIONAL WEATHER SERVICE IN
TALLAHASSEE AT (8 5 0) 9 4 2 8 8 3 3. OR...YOU MAY CONTACT THE
NEAREST LAW ENFORCEMENT AGENCY OR YOUR COUNTY EMERGENCY MANAGEMENT.
THEY WILL RELAY YOUR REPORT TO THE NATIONAL WEATHER SERVICE.
A TORNADO WATCH REMAINS IN EFFECT UNTIL 700 PM EDT THURSDAY EVENING
FOR SOUTHEAST ALABAMA AND CENTRAL FLORIDA AND SOUTHWESTERN GEORGIA.
&&
LAT...LON 3154 8495 3162 8470 3140 8463 3137 8491
TIME...MOT...LOC 1920Z 253DEG 31KT 3145 8485
$$
Quite a surprise overnight and this morning in Green Bay:
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREEN BAY WI
104 PM CDT THU APR 08 2010
1257 PM
04/08/2010
GREEN BAY, BROWN COUNTY
44.51N 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).
And a + for you!
I imagine Levi saw Joe Bastardi's Hurricane Update on the Pro site. He certainly did nail last years forecast.
:)
Oh geez, I even recognized "Your Song" right away. ;)
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.
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.
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
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.
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.
Well...
I guess it just likes me more lol.
Current webcam view in the backyard of OSNW3 in Oshkosh, WI.
Yep, that's the consensus...use a good permanent marker, as salt water tends to erode regular magic markers
Lol, well, being in Alaska I end up checking the websites later than you do on any given day.
Hey Teddy :)
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'...
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...
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.
The only problem with that is once the storm passes over FL and enters the GOM, Now you got a problem.
Viewing: 1601 - 1651
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