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
Reader Comments
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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.
Tropical Cyclone Advisory
TROPICAL CYCLONE ROBYN, CAT 2 (12U)
3:00 AM WST April 6 2010
=================================
At 18:00 PM UTC, Tropical Cyclone Robyn, Category 2 (985 hPa) located at 16.2S 92.2E has 10 minute sustained winds of 50 knots with gusts of 70 knots. The cyclone is reported as moving northeast at 1 knots.
Storm Force Winds
=================
25 NM from the center
Gale-Force Winds
==================
90 NM from the center in northern quadrant
120 NM from the center in southern quadrant
Dvorak Intensity: T3.5/3.5/W1.0/12HRS
Forecast and Intensity
===========================
12 HRS: 16.1S 91.7E - 45 knots (CAT 1)
24 HRS: 16.1S 90.9E - 45 knots (CAT 1)
48 HRS: 16.3S 88.6E - 35 knots (CAT 1)
72 HRS: 16.5S 84.6E - 30 knots (Tropical Low)
Additional Information
=========================
Tropical Cyclone Robyn has started to weaken as it enters an environment of stronger wind shear. UW-CIMMS at 1800 UTC indicated NW shear of about 15 knots. A Dvorak analysis yields a T-number of 3.5 based on a shear pattern with the low level centre located less than 1/3 of a degree into the strongest temperature gradient.
Motion has remained slow in the last 12 hours as a mid-level trough passes to the south. The cyclone should start taking a westerly track during Tuesday as a mid-level ridge develops in the wake of the trough. The extent of the westerly track is dependent upon weakening/shearing processes.
The cyclone is likely to remain over open waters and does not pose a risk to island or coastal communities.
when I click modify post the post I am trying to edit glitches..
If its below cat 3 wind wise, your gonna be fine inland, other than tree damage, a power pole or two, broken highrise windows( aint nobody gonna be around there) and without electricity.
If it's cat 3 or higher wind wise, you gotta problem and then the exact path is what you have to be watching.
Near Ocean and or bays less than 15 miles away:
Below cat 3 storm surge, still going to have flooding in some areas and overwash and beach erosion. House on stilts should be fine.
Cat 3 and higher storm surge:
Lucky if you have a house to return to.
Size
Surge
Sustained winds
Wind Gusts
Moisture content
Central Pressure
Velocity ect
there needs to be a scale that incorporates most if not all of these features
EDIT: I don't think I am having any issues with it.
I thought Galveston was the largest city in TX in 1900.
yellow fever drove off the citizens, then the hurricane cleaned the slate.
I don't understand why they need a rating system to begin with. Most people don't understand what it means anyway. Why not just say is will be a 130 MPH hurricane with a 15 foot storm surge that will travel 3 miles inland. Then the idiots might understand what they are dealing with. If you have to have categories I would go with something like:
Ho Hum
Hide the lawn furniture
Hide the kids
Get outta Dodge
Kiss your butt good bye
Some may understand that.
As sad as it is, it would work
Wind: Cat 2
Storm Surge: Cat 4
This is all the NHC has to do for hurricanes.
People inland expect this, people near the ocean and bays expect this.
Wind: Cat 5
Storm Surge: Cat3
Andrew Hitting Louisiana:
Wind: Cat 3
Storm surge: Cat 4
Hard to do that, since one storm can have very strong components of some, but not others. You could have a large storm pushing an incredible surge, but weaker winds (Ike). Or a small storm pushing a small surge, but incredible winds (Andrew). Or you could have a large storm, with high winds, but a very small radius of the hurricane force winds, and a very low pressure.
Oh, dear. Add to this the potential sea level rise, which is much more likely to impact the "barrier-island-like" Bahamas, and u are working on a worst case scenario right there.... by 2100 there wouldn't be much left.....
:(
URGENT - IMMEDIATE BROADCAST REQUESTED
TORNADO WATCH NUMBER 49
NWS STORM PREDICTION CENTER NORMAN OK
250 PM CDT MON APR 5 2010
THE NWS STORM PREDICTION CENTER HAS ISSUED A
TORNADO WATCH FOR PORTIONS OF
CENTRAL ILLINOIS
EAST CENTRAL MISSOURI
EFFECTIVE THIS MONDAY AFTERNOON AND EVENING FROM 250 PM UNTIL 900
PM CDT.
TORNADOES...HAIL TO 2.5 INCHES IN DIAMETER...THUNDERSTORM WIND
GUSTS TO 70 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE
AREAS.
THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 60 STATUTE
MILES NORTH AND SOUTH OF A LINE FROM 20 MILES NORTH NORTHWEST OF
SAINT LOUIS MISSOURI TO 40 MILES EAST OF MATTOON ILLINOIS. FOR A
COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH OUTLINE
UPDATE (WOUS64 KWNS WOU9).
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.
OTHER WATCH INFORMATION...CONTINUE...WW 48...
DISCUSSION...THUNDERSTORMS ARE INCREASING IN COVERAGE ACROSS CENTRAL
IL...IN VICINITY OF RETREATING SURFACE WARM FRONT. MODERATE
INSTABILITY AND RATHER WEAK CAP WILL PROMOTE FURTHER INTENSIFICATION
THROUGH THE AFTERNOON AND EARLY EVENING. FAVORABLE DEEP LAYER
VERTICAL SHEAR SUGGEST SUPERCELL STORM STRUCTURES ARE LIKELY...WITH
THE RISK OF LARGE HAIL AND DAMAGING WINDS. ISOLATED TORNADOES
CANNOT BE RULED OUT DUE TO PROXIMITY OF WARM FRONT AND MOISTENING
BOUNDARY LAYER.
AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL
SURFACE AND ALOFT TO 2.5 INCHES. EXTREME TURBULENCE AND SURFACE
WIND GUSTS TO 60 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO
500. MEAN STORM MOTION VECTOR 26030.
...HART
Is it that each CWA starts at number 1 for the first watch of each type and keeps going until the end of the year or something? I've always wanted to know that. I don't think I'm right, considering several watches span over several CWAs.
The Watch Numbers are in numerical order, starting at #1 in Jan 1st of each year.
I'm reminded of old-time attitudes towards alchemists, who reputedly were trying to turn lead to gold. Sure there were scoffers. It even turns out the scoffers were right. However, in the process, those old-time alchemists set our collective feet on the path of increased knowledge and understanding of the world around us and the properties of rocks and minerals which are more valuable than gold today.
Maybe what we should be learning from these studies has little or noting to do with global warming.
All the more reason for a scale like this. It doesn't have to be one number there could be a combined score telling people what to look for
There's no such thing as a certain category in terms of storm surge. Much of it has to do with bathymetry and size of the wind envelope. I've done a lot of work with a potential hurricane scale and so have many other people. If you're interested look into the Hurricane Hazard Index and the Hurricane Intensity Index by Kantha, or Integrated Kinetic Energy. The problem is even if you have one scale, so much damage is localized. Even down to your neighborhood. For example with Hurricane Andrew, the damage to houses at the end of an east to west culdesac was much greater than the other houses. It's hard to comprise that with one scale. There's so many factors to hurricane damage. Even if you have two scales, one for wind and one for storm surge, what about flooding? i.e. tropical storm Allison. The biggest problem is people don't understand storm surge and the other damaging components of a hurricane. 98% of the public won't know what a category 4 storm surge means. They just want to know if they need to evacuate or not and why.
WHERE DID SUMMER COME FROM
I'd say it's a possibility.
Yellowstone seismograph picked it up pretty well.
Link
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