Global warming and the frequency of intense Atlantic hurricanes: model results

By: Dr. Jeff Masters , 1:37 PM GMT on April 05, 2010

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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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Member Since: July 3, 2005 Posts: 426 Comments: 128698
Quoting hydrus:
Last night you said some mountains near you were dusted with snow, where ya at?


northern california
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Link

Cool stuff, basically debates about icecaps will be based on a lot more reliable data once this satellite gets its gears on. Of course we will need to be patient and wait a few years to confirm trends, but should prove interesting to follow! I hope this time the launch is successful (due to launch on thursday).
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Quoting WaterWitch11:


good morning hydrus
Last night you said some mountains near you were dusted with snow, where ya at?
Member Since: September 27, 2007 Posts: 1 Comments: 21429
Quoting hydrus:
WaterWitch- Read post-513.


good morning hydrus
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WaterWitch- Read post-513.
Member Since: September 27, 2007 Posts: 1 Comments: 21429
Quoting StormW:
Trouble.



trouble = reading further
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Quoting Skyepony:
Levi~ Your 1998 neg NAO reference isn't reassuring me that FL has escaped it's post El Nino drought & burning.. Too many years the El Nino wet winter with many freezes ends in some part of the state on fire come summer. Summer of 1998 was pretty memerable..like when they told the tourists to leave the state & evacuated Volusia county. You couldn't leave town without checking on the fires & road closures for months..
Florida definitely has had some bad fire years. 1985 was one of them.
Member Since: September 27, 2007 Posts: 1 Comments: 21429
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Member Since: July 3, 2005 Posts: 426 Comments: 128698
Quoting indianrivguy:


But it is going to have to stick around for more than a season for it to anything but an aberration. I'm thinking that I read that the most important ice is the older stuff and that the amount of second third and fourth year ice has declined along with the outer edges. It would suit me just fine to see a reversal, colder is better for Florida, sea level rise is not Florida's friend. :)


True enough..but imagine what some folks like (AG for example) would be saying if it was at a 10 year low for this date.
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There is lot's of hype going on because most of the seasoned pro forcasters are predicting an active season.....There will probably be plenty of storms to track this year and the best advice I can give to newer members of the blog is to not get caught up in the hype, study the books so to speak, and pay attention to Dr. Master's posts and some of the real experienced Bloggers on here as the season progresses....You will learn a lot if you stay out of the petty fights and occasional spats ( I know more than you) once things ramp up in a few months.....There are some really good amateur mets on here, like Storm, and they welcome good questions which increases your knowledge base in this area.
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Quoting hurricane23:


From my previous post earlier this morning...

It's still to early to discern the exact position of the Bermuda High this year and what impact it will have on the upcoming hurricane season but if you dont mind i can briefly explain how it works for those that dont know the mechanics behind it.Imagine the Bermuda High as an enormous blocking wall. Tropical cyclones will move along the southern side of this high pressure system until it finds the western side. This turn to the northeast usually occurs somewhere in the Caribbean. For example the position of the Bermuda High in the 2007 season was farther south and west which, along with the building ridges that extended down into the GOM that year, carried the storms over Central America before the turn to the north took place.

Here's a picture i like to use from nasa to go along with what I'm trying to explain..



How far north the Bermuda High moves will be one of the more significant factors in determining what type of hurricane season Florida will experience. As you can see from the graphic of the BH i posted above, just a slight movement of the BH to the south and your turn to the north will be delayed so to speak, and landfall would be displaced to the west of Florida. The same goes if the BH in that image was more to the north. Your turn to the north and eventually to the northeast would be sooner, and Florida would have more of a heightened chance of being impacted. Of course, other steering patterns play a role in a tropical systems track.Tropical systems follow the least path of resistance, so even if the BH were to signify a panhandle landfall, you could have a building ridge that blocks northern movement and the system ends up moving westward towards Texas or Mexico. Using the same scenario of a building ridge, you could have a cut off low build up over Florida behind the ridge, creating a weakness that would draw the system northward towards Florida.
Good post. And then we have to factor in any troughs that might weaken the western periphery of the Bermuda high. That is if there are any troughs at all . If a zonal flow in prevalent, the troughs are to weak to pull storms north and re curve them.
Member Since: September 27, 2007 Posts: 1 Comments: 21429
543. Skyepony (Mod)
Levi~ Your 1998 neg NAO reference isn't reassuring me that FL has escaped it's post El Nino drought & burning.. Too many years the El Nino wet winter with many freezes ends in some part of the state on fire come summer. Summer of 1998 was pretty memerable..like when they told the tourists to leave the state & evacuated Volusia county. You couldn't leave town without checking on the fires & road closures for months..
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Just hope we dont see paths like Katrina, Rita, Gustav, Ike
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Quoting stoormfury:
with the official start of the 2010 hurricane season only seven weeks away, the hype on the blog is on the increase. after a relatively quiet 2009 season the pundits are already seeing anomalies that could signal an active season. with the CSU april forecast a few hours away and the likelihood of the numbers increasing from the december forecast as a result of what is happening in the MDR.
One thing I have noticed in 2010 is everyone seems to believe this year will have a above average number of storms. I have not seen or heard anything to the contrary from one single person or source. this is rather curious considering the knowledge most of these people and administrations have on the subject.
Member Since: September 27, 2007 Posts: 1 Comments: 21429
Quoting msgambler:
Wouldn't a weaker A/B High cause more storms to curve StormW or just still continue as a regular A/B High causing a more Westerly track


From my previous post earlier this morning...

It's still to early to discern the exact position of the Bermuda High this year and what impact it will have on the upcoming hurricane season but if you dont mind i can briefly explain how it works for those that dont know the mechanics behind it.Imagine the Bermuda High as an enormous blocking wall. Tropical cyclones will move along the southern side of this high pressure system until it finds the western side. This turn to the northeast usually occurs somewhere in the Caribbean. For example the position of the Bermuda High in the 2007 season was farther south and west which, along with the building ridges that extended down into the GOM that year, carried the storms over Central America before the turn to the north took place.

Here's a picture i like to use from nasa to go along with what I'm trying to explain..



How far north the Bermuda High moves will be one of the more significant factors in determining what type of hurricane season Florida will experience. As you can see from the graphic of the BH i posted above, just a slight movement of the BH to the south and your turn to the north will be delayed so to speak, and landfall would be displaced to the west of Florida. The same goes if the BH in that image was more to the north. Your turn to the north and eventually to the northeast would be sooner, and Florida would have more of a heightened chance of being impacted. Of course, other steering patterns play a role in a tropical systems track.Tropical systems follow the least path of resistance, so even if the BH were to signify a panhandle landfall, you could have a building ridge that blocks northern movement and the system ends up moving westward towards Texas or Mexico. Using the same scenario of a building ridge, you could have a cut off low build up over Florida behind the ridge, creating a weakness that would draw the system northward towards Florida.
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Quoting hydrus:
Thanks, I am not familiar with that term. Kinda like holy rock bottom.

Yep, basically.

The NWS office here uses the term "cratering" or "craters" in much the same way. A sharp decline, followed by a steady state at low levels.
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Quoting jeffs713:

By tanking, he means "going way down" or "cratering". In this case... *bad*.
Thanks, I am not familiar with that term. Kinda like holy rock bottom.
Member Since: September 27, 2007 Posts: 1 Comments: 21429
with the official start of the 2010 hurricane season only seven weeks away, the hype on the blog is on the increase. after a relatively quiet 2009 season the pundits are already seeing anomalies that could signal an active season. with the CSU april forecast a few hours away and the likelihood of the numbers increasing from the december forecast as a result of what is happening in the MDR.
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Quoting StormW:


That depends on the position...wha you have to understand with a negative NAO, is that it also affects the stregnth of the Icelandic low, which would be weaker. This in turn also weakens that familiar trof we see hanging out in the western Atlantic that recurves storms, and keeps it a little farther north. Not saying that we can't see recurvature totally, however the recurve tends to be more subtle.

I've been researching as well, the correlation with the negative NAO and track, so far (I have more research to do), it appears more U.S. Strikes occur when the NAO comes from a moderate to strong negative, and transitions to a brief, weak positive...the period of transition seems to have more U.S. landfalls.
This is well written and easy to understand.
Member Since: September 27, 2007 Posts: 1 Comments: 21429
Quoting hydrus:
I understand everything except(tanks) does that mean the same as maxed out?

By tanking, he means "going way down" or "cratering". In this case... *bad*.
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Quoting StormW:


A negative NAO implies a weaker A/B High. In turn, weaker trades, especially if it tanks as forecast...weaker trades, less shear; less upwelling...less upwelling, warmer SST's and more build up of heat...shall I stop here?
I understand everything except(tanks) does that mean the same as maxed out?
Member Since: September 27, 2007 Posts: 1 Comments: 21429
Quoting Levi32:
1998 had a negative NAO all season long, and that year did see a batch of storms recurve in the eastern Atlantic due to a weakness there, but the position of the Bermuda High farther to the west directed most of the storms towards the United States and the Caribbean, resulting in 7 U.S. landfalls that year.


Why do I get the feeling that we (speaking of all of us that are impacted by Atlantic hurricanes) are looking down a tunnel, and we are all seeing a bright white light.

Yes, it could be the other side of the tunnel, but most likely, it is a train.
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dashboard cow man!!!!

:)
Member Since: January 24, 2007 Posts: 317 Comments: 31946
Hope everyone has a wonderful day. I have to get back to work. Seems like I can't get anyone else to do it for me
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1998 had a negative NAO all season long, and that year did see a batch of storms recurve in the eastern Atlantic due to a weakness there, but the position of the Bermuda High farther to the west directed most of the storms towards the United States and the Caribbean, resulting in 7 U.S. landfalls that year.

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In this neck of the woods, we've got a nice fat storm approaching, too. Wind and mountain snow before the weekend. http://www.ssd.noaa.gov/goes/west/nepac/loop-avn.html
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all i know is there is a certain little sweet spot for the bermuda high where it causes drought and unbearable unrelentless heat in the fla panhandle and honestly i would rather have mild hurricanes and tropical storms just training over me than that horrible drought and 110 degree humid heat all freakin summer long. its just too oppressive.
Member Since: July 30, 2007 Posts: 6 Comments: 1448
Thank you StormW I think I understand
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525. JRRP
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Quoting hydrus:
I agree, upper level winds are blowing E-NE, Tropically nothing can happen. It should be interesting to watch though with the lower level winds heading toward the west.


True! But the lower-level winds are the constant Trades, so they do that regardless!
I would not go as far as to say that 'nothing can happen' though.
Heavy rain is worse than wind (and more frequent) in the Islands because of the geography. Rain takes more life overall than wind.
Anyway, as you say, interesting that the model has latched on to something like that, so early in the year.
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Quoting Skyepony:


You keep saying that.. I'm seeing a cooler spring, lower power bill, lettuce bolting later & an extended growing season for most the warm season veggies here in central & south FL...well til 'cane season when their chances of being defoliated by a hurricane should be higher usual..

Ok, I laughed at the last part.

(I'm hoping to get some spinach here before it gets too hot)
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Quoting StormW:


A negative NAO implies a weaker A/B High. In turn, weaker trades, especially if it tanks as forecast...weaker trades, less shear; less upwelling...less upwelling, warmer SST's and more build up of heat...shall I stop here?


You know, I'm really beginning to not like you. ;)
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Quoting pottery:


I would need to see a big change in upper and mid level winds, for that "low" to end up where it is shown (Northern Islands).
You think it is possible? The model does. I am not convinced as yet.
(if that is indeed the "low" that they pick up)
I agree, upper level winds are blowing E-NE, Tropically nothing can happen. It should be interesting to watch though with the lower level winds heading toward the west.
Member Since: September 27, 2007 Posts: 1 Comments: 21429
A graph is never trouble..one can have a Hundred Named systems a season,but as of today,no one on the Planet can tell anyone,where one will strike.


Preparation is the ONLY key to being ready come May 15th.


I moved the Season Opening back 2 weeks.

Cuz I can..

LOL
Member Since: July 3, 2005 Posts: 426 Comments: 128698
Wouldn't a weaker A/B High cause more storms to curve StormW or just still continue as a regular A/B High causing a more Westerly track
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Good morning all.

Nino 3.4 has dropped below the moderate level now in the weekly values.

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CFS is forecasting the anomalies to decrease






From Monthly Ocean Briefing (PDF)
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Quoting hydrus:
I think I see the future low on that sat pic Chicklit. Right on the coast, N.E. Brazil.


I would need to see a big change in upper and mid level winds, for that "low" to end up where it is shown (Northern Islands).
You think it is possible? The model does. I am not convinced as yet.
(if that is indeed the "low" that they pick up)
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514. Skyepony (Mod)
Quoting StormW:
Trouble.



You keep saying that.. I'm seeing a cooler spring, lower power bill, lettuce bolting later & an extended growing season for most the warm season veggies here in central & south FL...well til 'cane season when their chances of being defoliated by a hurricane should be higher than usual..
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Quoting StormW:
Trouble.

Storm, when you say trouble I know something important is transpiring. What is it exactly that concerns you?
Member Since: September 27, 2007 Posts: 1 Comments: 21429
Quoting StormW:
Trouble.


Rut-roh
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508.

If it is such a waste of bandwidth, please press the little "X" in the top right corner of your browser window. This way, you aren't wasting any more bandwidth.
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Quoting msgambler:
Ok, who got me on a soap box this morning
You are blessed to have lived through such a disaster. I have lived through a few myself. I will never take a single for granted.:) P.S. Nothing wrong with sharing a couple of experiences on the soap box Gambler.
Member Since: September 27, 2007 Posts: 1 Comments: 21429
Patterning a model on nonexistent "global warming" while quoting the IPCC at the same time. What a waste of bandwidth.
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Ok, who got me on a soap box this morning
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I was young hydrus but do remember hiding under a table with my parents, sister, and 2 german shepards (that were going crazy). And the wind howling through a door that scared the holy crap out of my sister and myself for years ever time we heard it. My mom, after the storm, bought every book she could find documenting the storm. I did the same thing after Katrina so my children, who were in GA at the time will always remember what can happen and leave when told to do so. IMHO I think everyone who moves to the Coastline areas should be given one of these book documenting Katrina or Camille and a video of what happens during a storm so they don't sit there and say "I'll just ride it out"
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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.