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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Also remember, IKE had 130 MPH winds just above the surface. JUST IMAGINE if they would have translated to the surface!
ZCZC MIATCDAT4 ALL
TTAA00 KNHC DDHHMM
HURRICANE IKE DISCUSSION NUMBER 48
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL092008
1100 PM EDT FRI SEP 12 2008
A PLETHORA OF DATA FROM NOAA DOPPLER WEATHER RADARS...NOAA AND AIR
FORCE RECONNAISSANCE AIRCRAFT...AND SATELLITE IMAGERY ALL INDICATE
THAT THE STRUCTURE OF IKE HAS IMPROVED MARKEDLY OVER THE PAST 6
HOURS...AND A 40 NMI DIAMETER EYE HAS BECOME PROMINENT. THE LOWEST
PRESSURE REPORTED BY RECON HAS BEEN 952 MB. DOPPLER RADAR
VELOCITIES IN THE NORTHERN EYEWALL AT 6500 FT HAVE BEEN AS HIGH AS
114 KT...AND A DROPSONDE IN THAT SAME AREA MEASURED A PEAK WIND
VALUE OF 116 KT. MAXIMUM FLIGHT-LEVEL WINDS AT 700 MB HAVE RANGED
FROM 103-105 KT...AND A RELIABLE SFMR SURFACE WIND SPEED OF 90 KT
WAS MEASURED IN THE SOUTHERN EYEWALL AROUND 0140Z. ALL OF THIS
INFORMATION CORRESPONDS TO A MAXIMUM SURFACE WIND SPEED ESTIMATE OF
95 KT.
THE LARGE EYE OF IKE HAS BEEN WOBBLING CONSIDERABLY OVER THE PAST 6
HOURS...BUT A GENERAL MOTION OF 315/10 SEEMS TO HAVE BEEN THE
PREFERRED DIRECTION OF TRAVEL. SHORT TERM EXTRAPOLATION WOULD PLACE
THE CENTER OF IKE ALONG GALVESTON ISLAND AND/OR THE UPPER-TEXAS
COAST SHORTLY BEFORE SUNRISE SATURDAY MORNING. AFTER LANDFALL...IKE
IS EXPECTED TO CONTINUE MOVING AROUND THE WESTERN PERIPHERY OF A
SUBTROPICAL RIDGE SITUATED EAST-WEST ALONG THE NORTHERN GULF COAST
AND TURN NORTHWARD IN ABOUT 12-18 HOURS...AND THEN RECURVE RAPIDLY
TO THE NORTHEAST BY 24 HOURS AHEAD OF A FAST APPROACHING FRONTAL
SYSTEM. BY 36-48 HOURS...IKE MAY BECOME ABSORBED BY THE FRONTAL
SYSTEM OVER THE UPPER MIDWEST. THE OFFICIAL FORECAST TRACK IS
ESSENTIALLY JUST AN UPDATE OF THE PREVIOUS TRACK...AND IS DOWN THE
MIDDLE OF THE TIGHTLY CLUSTERED NHC MODEL GUIDANCE.
IKE STILL HAS ABOUT A 6-HOUR WINDOW OF OPPORTUNITY TO STRENGTHEN
INTO A 100-KT MAJOR HURRICANE. EQUALLY IMPORTANT...HOWEVER...IS THE
EFFECT THAT STRONGER WINDS ALOFT WILL HAVE ON HIGH RISE BUILDINGS.
WIND DATA FROM LAND-BASED DOPPLER RADARS AND AIRCRAFT DROPSONDES
INDICATE THAT WINDS NEAR CATEGORY 4 STRENGTH...115 KT OR 130 MPH
...EXIST JUST A FEW HUNDRED FEET ABOVE THE SURFACE. THERE COULD BE A
REPEAT OF DAMAGE TO WINDOWS IN HIGH RISE STRUCTURES SIMILAR TO WHAT
OCCURRED DURING HURRICANE ALICIA IN 1983. THE PEAK WIND SPEED AND
VARIOUS WIND RADII WERE HELD HIGHER THAN OUR INLAND WIND DECAY
MODELS ARE PREDICTING DUE TO THE MUCH LARGER SIZE OF IKE.
it was a powerful storm, I dont think anyone is disagreeing there. Katrina caused more widespread damage and loss of life.
...if only stupidity were painful...
it is...to those of us who have to see it....
Katrina was a whole different storm than Ike, you really cant compare them at all.
It's like comparing a Chevy cobalt to a Corvette.
I'd love to see who had Hurricane force winds for 14 hours, how about a little proof? Like Rita said, the wind damage wasn't that bad.
FYI... The Levee's didn't break after the Hurricane was over with. They broke while the Hurricane was passing through. I know because I was here for it. lol
Oh, it is for those who do "stupid things" of any type, the consequences are usually very painful.
A favorite quote: Pain is inevitable; suffering is optional.
POOF
That is also a barge.
What proof? lol Sounds like you can't produce a station that recorded 14 straight hours of Hurricane Force winds in association to Ike.
Its the opposite. You just randomly sent me to stormpulse. Not an actual reporting station. lol The bottom line is that Ike was not a major Hurricane when it impacted the Texas Gulf Coast. It was a 110 mph Category 2 Hurricane with a 10-20ft storm surge. Sure it was a significant event but it was not an exceptionally powerful Hurricane.
that is funny!
What an awful idea
did you see the national geographic article about a year after andrew, where some japanese scientist had concluded andrew was unique with its "ripping winds" that approached tornado force and left swaths of bare earth for miles. cant remember details but it sorta explained why it was so devastating..
janice
Umm...
Ole lady Kat had a peak radius of TS-force winds of 200 nm and a 64 knot radius of 90 nm. (Though some of this is still debated...some of the Katrina records do not include what some deny is a double eyewall.)
Ike maxed out his radius of TS-force winds at 240 nm and a 64 knot radius of 110 nm.
And Ike's rains show a larger area of greater than 10 inches rainfall.
But, the single peak wind speed at landfall favors Katrina. And, of course, Katrina's act of setting so much water in motion before landfall.
Major. This is just a word...
The real consideration is vulnerable population. SE LA and the MS coast has the TX coast trumped in that regard. TX coast east of Galveston is mostly uninhabited. Bolivar to Port Arthur is bare. Cannot say that about anywhere between NOLA and Pensacola.
i think it's a good idea to have more detailed information on the hurricanes. i didn't see storm surge being a factor in the numbering system.
Then we start another debate, because a strong Cat 3 should blow shingles off...then people will start riding out a strong cat 3 because the shingles were still on during Ike. Then a small compact cat 3 comes along and then blows the roof off and everybody is wondering what the hell happened
After six weeks of nearly no change, this past week showed a little weakening (in region 3,4..where it is measured)
I don't expect this to be the beginning of a fast crash with more heat coming from the east & where we may see even more surface soon.
Andrew had eye wall mesovortices.. much like tornados. wiki say's;
Eyewall mesovortices
Eyewall mesovortices are small scale rotational features found in the eyewalls of intense tropical cyclones. They are similar, in principle, to small "suction vortices" often observed in multiple-vortex tornadoes. In these vortices, wind speed can be up to 10% higher than in the rest of the eyewall. Eyewall mesovortices are most common during periods of intensification in tropical cyclones.
Eyewall mesovortices often exhibit unusual behavior in tropical cyclones. They usually rotate around the low pressure center, but sometimes they remain stationary. Eyewall mesovortices have even been documented to cross the eye of a storm. These phenomena have been documented observationally,[15] experimentally,[16] and theoretically.[17]
Eyewall mesovortices are a significant factor in the formation of tornadoes after tropical cyclone landfall. Mesovortices can spawn rotation in individual thunderstorms (a mesocyclone), which leads to tornadic activity. At landfall, friction is generated between the circulation of the tropical cyclone and land. This can allow the mesovortices to descend to the surface, causing large outbreaks of tornadoes.
"Vortical swirls in hurricane eye clouds"
Plus, central, surface pressure in a hurricane is almost never actually measured. Dvorak and/or flight level-reduced.
Old St. Joe never recovered from the terrible (yellow fever) scourge. For two or three years the palatial homes, fine public buildings, and full warehouses, awaited their owners never to return. Only a few venturesome fishermen attracted by the stories of great treasures, dared to come near the city. In 1844 a great hurricane followed by a tidal wave, swept over the deserted homes. For three days and nights the fierce winds as if maddened by their lost prey raged through Old St. Joe. Brick and marble were swept miles inland or carried into the sea by the same receding tidal wave. At the end of the third day the storm abated, but only after there was no more damage it could do to Old St. Joe. Only a few scattered blocks of marble or a brick every now and then, and the graveyard, three miles inland, were left where lately stood the splendid homes and public buildings. Even today, there are no homes within miles of the old town which might have been the capital of Florida, which was the Queen City of the South.
I never said names. Don't assume I was talking about you. The word troll gets thrown alot liberally, I am the furthest thing from a troll. Scale was, Ike wasn't a major hurricane. But thats all. The damage was terrible, and the damage from the storm surge that left everything behind is consistent with a major hurricane. You can't look at the scale as an end all thing though.
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