Hurricanes and Climate Change: Huge Dangers, Huge Unknowns

By: Dr. Jeff Masters , 9:57 AM GMT on August 05, 2013

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Hurricane Sandy's enormous $65 billion price tag put that great storm in third place for the most expensive weather-related disaster in U.S. (and world) history, and six of the ten most expensive U.S. weather-related disasters since 1980 have been hurricanes. Thus, how the strongest hurricanes may be affected due a changing climate is a topic of critical concern. Since hurricanes are heat engines that extract heat energy from the oceans to power themselves, hurricane scientists are confident that the very strongest storms will get stronger by the end of the century, when Earth's land and ocean temperatures are expected to warm 2 - 3°C, to levels unmatched since the Eemian Era, 115,000 years ago. Computer modeling work consistently indicates that greenhouse warming will cause the globally averaged intensity of tropical cyclones to shift towards stronger storms, with intensity increases of 2–11% by 2100. But hurricanes are fussy creations, and are sensitive to wind shear and dry air. Although the strongest storms should get stronger when "perfect storm" conditions are present, these "perfect storm" conditions may become less frequent in the future, due to the presence of higher wind shear, altered atmospheric circulation patterns, or more dry air at mid levels of the atmosphere. Indeed, the climate models used to formulate the 2007 IPCC report suggested that we might see the strongest hurricanes getting stronger, but a decrease in the total number of hurricanes in the Atlantic (and worldwide) later this century. However, the latest set of models used to formulate the 2013 IPCC report left open the possibility that we might see in increase in the total number of hurricanes, and and increase in their intensity. Given the conflicting model results, we really don't know how global warming will affect the number of hurricanes and their intensity, but we run the risk of making one of humanity's greatest scourges worse.


Figure 1. The list of most expensive U.S. weather-related disasters since 1980 is dominated by hurricanes.

Climate models and hurricane frequency
The database we have on historical hurricanes does not extend far enough into the past and is not of high enough quality to make many judgements on how human-caused climate change may be affecting these great storms. A landmark 2010 review paper, "Tropical Cyclones and Climate Change", authored by ten top hurricane scientists concluded that the U.S. has not seen any long-term increase in landfalling tropical storms and hurricanes, and that "it remains uncertain whether past changes in tropical cyclone activity have exceeded the variability expected from natural causes" (tropical cyclone is the generic term which encompasses tropical depressions, tropical storms, hurricanes, and typhoons.) Based in part on modeling studies using climate models run for the 2007 IPCC report, the scientists concluded that "it is likely that global mean tropical cyclone frequency will either decrease or remain unchanged owing to greenhouse warming." For example, one of the modeling studies the review paper quoted, Knutson et al. (2008), "Simulated reduction in Atlantic hurricane frequency under twenty-first-century warming conditions", projected a decrease in Atlantic tropical storms by 27% and hurricanes by 18% by the end of the century. An important reason that their model predicted these decreases 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.

But a July 2013 study by MIT's Dr. Kerry Emanuel, "Downscaling CMIP5 climate models shows increased tropical cyclone activity over the 21st century", challenged this result. Dr. Emanuel argued that tropical cyclones are likely to become both stronger and more frequent as the climate continues to warm. This increase is most likely to occur in Western North Pacific, with smaller increases in the Atlantic. Dr. Emanuel took output from six newer higher-resolution climate models used to formulate the 2013 IPCC report, and used the output to drive a high-resolution hurricane model. The simulations found that the global frequency of tropical cyclones would increase by 11% to 40% by 2100, with intensity increases as well. The combined effects produced a global increase in Category 3 and stronger hurricanes of 40%. The behavior of these strongest hurricanes is critical, since they do most of the damage we observe. Over the past century, Category 3 - 5 hurricanes accounted for 85% of US hurricane damage, despite representing only 24% of U.S. landfalling storms. 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, see Pielke et al., 2008.)


Figure 2. Projected changes in tropical cyclone track density during the 2006-2100 period compared to the 1950-2005 period, using output from six climate models included in the 2013 IPCC report. The global frequency of tropical cyclones is predicted to increase by 11% to 40%, with the largest changes occurring in the Northwest Pacific off the coast of Japan. Smaller increases are predicted for the Atlantic and near Australia. Image credit: Kerry Emanuel, "Downscaling CMIP5 climate models shows increased tropical cyclone activity over the 21st century", Proceedings of the National Academy of Sciences, July 8, 2013, doi: 10.1073/pnas.1301293110.

However, a study by Knutson et al. (2013), using the same latest-generation climate models as used by Emanuel (2013), but using the output from the models to drive a different high-resolution hurricane model, found a 20% decrease in Atlantic tropical storms and hurricanes by 2100. Two other 2013 studies by Villarini et al. and Camargo, also using output from the 2013 IPCC models, found essentially no change in Atlantic tropical cyclones. The reason for the differences, lies, in part, with how much global warming is assumed in the studies. Dr. Emanuel's study, which found an increase in tropical cyclone activity, assumed a worst-case warming situation (RCP 8.5), following the "business as usual" emissions path humanity is currently on. The Knutson et al. study, which found a decrease of 20% in Atlantic tropical cyclones, used a scenario (RCP 4.5) where it was assumed humans will wise up and cause about half of the worst-case greenhouse warming. The study found found "marginally significant" increases in Atlantic Category 4 and 5 hurricanes of 39% - 45% by 2100. These dramatically different results give credence to Dr. Emanuel statement at the end of his paper, "the response of tropical cyclones to projected climate change will remain uncertain for some time to come." The 2013 IPCC report also emphasized the high amount of uncertainty in how climate change might affect hurricanes, stating that there was "low confidence" that we have observed any increases in intense tropical cyclones due to human causes. However, since the 1970s, it is virtually certain (99 - 100% chance) that the frequency and intensity of hurricanes and tropical storms in the North Atlantic has increased, and there is medium confidence that a reduction in small air pollution particles (aerosols) over the North Atlantic caused part of this effect. The report's forecast for the future stated that it is "more likely than not" (50 - 100% chance) that human-caused climate change will cause a substantial increase in intense tropical cyclones in some ocean basins by 2100, with the Western North Pacific and Atlantic being at particular risk. Also, there will likely (66 - 100% chance) be an increase in both global mean tropical cyclone maximum wind speed and rain rates by 2100, and more likely than not (50 - 100% chance) that the increase in the most intense tropical cyclones will be larger than 10% in some basins.


Figure 3. Expected change in Atlantic Category 4 and 5 hurricanes per decade expected by the year 2100, according to Knutson et al. (2013), "Dynamical Downscaling Projections of 21st Century Atlantic Hurricane Activity: CMIP3 and CMIP5 Model-based Scenarios." This research used the latest generation of climate models from the 2013 IPCC report, and found "marginally significant" increases in Atlantic Category 4 and 5 hurricanes of 39% - 45% by 2100.

Commentary
Hurricane damages are currently doubling every ten years without the effect of climate change, 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. Thus, by 2015, the same hurricane would do $300 billion in damage, and $600 billion by 2025. This is without considering the impact that accelerating sea level rise will have on storm surge damages. Global sea level rise over the past decade has been about double what it was in the 20th century, and the rate of sea level rise is expected to increase further in the coming decades. Storm surge does the majority of damage in major hurricanes, and storm surges riding on top of higher sea levels are going to do a lot more damage in the coming decades. If we toss in the (controversial) increases in Category 3 and stronger storms like Dr. Emanuel suggests may occur, the hurricane damage math gets very impressive. We can also add onto that the relatively non-controversial increase in tropical cyclone rainfall of 20% expected by 2100, which will sharply increase damages due to fresh water river flooding. It is controversial whether or not we are already be seeing an increase in heavy precipitation events associated with tropical cyclones in the U.S., though. The total number of daily rainfall events exceeding 2" associated with tropical cyclones in the Southeast U.S. on a century time scale has not changed significantly, according to Groisman et al., 2004. But a 2010 study by Kunkel et al., "Recent increases in U.S. heavy precipitation associated with tropical cyclones", found that the number of Southeast U.S. tropical cyclone heavy precipitation events, defined as 1-in-5-year events, more than doubled between 1994 - 2008, compared to the long-term average from 1895 - 2008.


Figure 4. Time series of the 15-year running average (plotted at the end point of the 15-yr blocks) of a Tropical Cyclone Heavy Precipitation Index (red) and 15-year running average of U.S. landfalling hurricanes (blue). Note that there has been no long-term increase in U.S. landfalling hurricanes, but there has been a sharp increase in extreme rainfall events associated with landfalling tropical cyclones--the kind of rainfall events most likely to cause damaging flooding. Image credit: Kunkel et al. (2010), "Recent increases in U.S. heavy precipitation associated with tropical cyclones", Geophysical Research Letters.

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 in the future. Adoption and enforcement of strict building standards is also a must, as well as more reforms to the government's National Flood Insurance Program (NFIP), which subsidizes development in high-risk coastal regions that private insurers won't touch. NFIP is now $25 - 30 billion in the red, thanks to Hurricane Katrina and Hurricane Sandy. Reform of NFIP is already underway. In 2012, before Sandy hit, Congress passed the Biggert-Waters Flood Insurance Reform Act, which requires people with NFIP policies to pay large premium increases of about 25% per year over the next five years. Naturally, this move has caused major controversy.

References
Camargo, S., (2013), "Global and regional aspects of tropical cyclone activity in the CMIP5 models," J. Climate.

Emanuel, K.A., 2013, "Downscaling CMIP5 climate models shows increased tropical cyclone activity over the 21st century", PNAS, July 8, 2013, doi: 10.1073/pnas.1301293110

Groisman, Pavel Ya, et al., "Contemporary changes of the hydrological cycle over the contiguous United States: Trends derived from in situ observations," Journal of Hydrometeorology 5.1 (2004): 64-85.

Knutson et al., 2010, "Tropical Cyclones and Climate Change", Nature Geoscience 3, 157 - 163, Published online: 21 February 2010 | doi:10.1038/ngeo779

Knutson et al., 2013, Dynamical Downscaling Projections of 21st Century Atlantic Hurricane Activity: CMIP3 and CMIP5 Model-based Scenarios, Journal of Climate 2013 ; e-View
doi: http://dx.doi.org/10.1175/JCLI-D-12-00539.1

Pielke, R.A, et al., 2008, "Normalized Hurricane Damage in the United States: 1900 - 2005," Natural Hazards Review, DOI:10.1061/ASCE1527-6988(2008)9:1(29)

Villarini, G, and G.A. Vecchi, 2012, "Twenty-first-century projections of North Atlantic tropical storms from CMIP5 models," Nature Clim. Change 2:604–607.

Related posts
Global warming and the frequency of intense Atlantic hurricanes: model results, my 2010 blog post.

Climate Central's analysis of the new 2013 Kerry Emanuel paper.

Goodbye, Miami: Jeff Goodell's sobering 2013 article in Rolling Stone on the challenges Miami faces due to sea level rise and hurricanes.


What the official climate assessments say about climate change and hurricanes
The 2013 IPCC report gives “low confidence”--a 20% chance--that we have observed a human-caused increase in intense hurricanes in some parts of the world. This is a reduction in odds from the 2007 report, which said that it was more likely than not (greater than 50% chance.) The IPCC likely took note of a landmark 2010 review paper, "Tropical Cyclones and Climate Change", authored by ten top hurricane scientists, which concluded that the U.S. had not seen any long-term increase in landfalling tropical storms and hurricanes, and that "it remains uncertain whether past changes in tropical cyclone activity have exceeded the variability expected from natural causes." The 2013 IPCC report predicts that there is a greater than 50% chance (more likely than not) that we will see a human-caused increase in intense hurricanes by 2100 in some regions; this is also a reduction from the 2007 report, which said this would be likely (66% chance or higher.)

The May 2014 United States National Climate Assessment found that “The intensity, frequency, and duration of North Atlantic hurricanes, as well as the frequency of the strongest (Category 4 and 5) hurricanes, have all increased since the early 1980s. The relative contributions of human and natural causes to these increases are still uncertain. Hurricane-associated storm intensity and rainfall rates are projected to increase as the climate continues to warm.”

Jeff Masters

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Quoting 317. VR46L:


Na a low end Tropical storm...



Nah. 1006 mb is a TS.
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317. VR46L
Quoting 313. wunderweatherman123:
is that a hurricane off the florida coast?


Na a low end Tropical storm...

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Slowly but surely coming around, need to get rid of the SAL and then its off to the races:

Member Since: June 30, 2013 Posts: 12 Comments: 8774
Good afternoon, weathergeeks! ;)


Quiet, for now. Still not liking the high setup. Have a nice Monday afternoon, all.


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The Scientists Monitoring Climate Change in Greenland

Member Since: July 3, 2005 Posts: 428 Comments: 129903
Quoting 304. VR46L:
Posting for drama entertainment purposes only ... CFS has really decided things are going to ramp up...

is that a hurricane off the florida coast?
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A new project aims to create the world’s “smartest lake” by installing smart water technology in New York’s Lake George.

Read about it: http://bit.ly/16oN2gT

I have no doubt that the lake will be smarter than some of the people I am seeing quoted here today....

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Here is my update hurricane numbers this year 7 more tropical storm 3 hurricane 1 major hurricane!!
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Quoting 307. hurricanes2018:
nice tropical wave here.

wow!! Maybe it starting early this storm
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Quoting 307. hurricanes2018:
nice tropical wave here.

The wave train! Choo-choo!
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nice tropical wave here.
Member Since: March 12, 2013 Posts: 113 Comments: 106789
There have been 370,000 people killed by climate change fueled weather events in the last decade. A couple weeks ago Climate Progress published a very troubling infographic that expose how deeply the fossil fuel industry is intertwined with members of Congress. More that 51 million, this year, has come in campaign contributions from big oil and gas. As part of this quid pro quo deal, many members of congress are responsible for opposing any legislation that would in any way curb greenhouse gas emissions. While we are hopelessly divided and keep these crooks in office; they are not beholden to us. They are bought and paid for to do the biddings of corporations. When I read reports on climate change, I always like to read the comments too. Between 80-90% of the comments are always that GW isn't happening and it's all wrong. The science and what the populace believe is light years apart. Combine that with a House and Congress that is corporate corrupt to do everything in their power to stop needed legislation to curb greenhouse gas emissions, and you get what your going to get. We will reap this harvest and the sowers are we the people. Wait for the methane releases to combine with the CO2. While many here get it and know the truth, the vast majority don't at all. When the truth is suppressed, bad things happen, and evil, greed, and corruption are allowed to reign. The car's already screaming towards the drop-off, now our "Leaders" are doing everything they can to remove the guardrail too.
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Quoting 280. KEEPEROFTHEGATE:
afternoon blog just checking in for the day

thanks for early morning update doc seems you were up with the birds this am
Thank you KEEPER...I respect your green "MOD"....Breaking out in an Aretha Franklin song...
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304. VR46L
Posting for drama entertainment purposes only ... CFS has really decided things are going to ramp up...

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Quoting 272. TampaSpin:
MLB suspensions will be released at 3pm today....now that is for sure Weather Related as Hail will be flying.


lol
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The ITCZ is starting to assume it climatologist place for August now when vigorous TW comes off the coast they will be greeted by a stream of moisture its only a matter of time before one start to take advantage a good looking wave over Africa lets see if it can hold as it will emerge by Wednesday/Thursday.



Wave over Central Africa:

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Quoting 291. Camille33:
No storm coming next 3 weeks!!
we got 14 days enjoy em
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Quoting 291. Camille33:
No storm coming next 3 weeks!!


Oh yeah Camille, just like how Dorian was going to become a 60 kt TS Right? Sorry, but no one is going to believe anything out of your mouth anymore.
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Quoting 293. SouthernIllinois:
Okay so the GFS for the 12Z run just gave me something TOTALLY huge to smile about. And I'm sure you all now why too. :-]


Looks like the east coast of Florida will be getting a break from the seabreeze thunderstorms for a while according to this
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Quoting 292. Camille33:

what going on here
Marvin Gaye
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Miami, FL WFO - Visible Loop
Member Since: July 3, 2005 Posts: 428 Comments: 129903
Quoting 293. SouthernIllinois:
Okay so the GFS for the 12Z run just gave me something TOTALLY huge to smile about. And I'm sure you all now why too. :-]


I am smiling too!
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Quoting 290. VR46L:
I have searched the models far and wide ...


what going on here
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No storm coming next 3 weeks!!
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290. VR46L
I have searched the models far and wide ...

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No suprise that hurricanes are at or near the top of the most expensive weather related disasters?

For my information I wanted to know where hurricanes stacked up against all natural disasters. Here's a site I found that has the top 100 natural disasters.

http://www.disastercenter.com/disaster/TOP100C.htm l
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Well, from what i see, development (and lots of it) is waiting around the corner.
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Quoting 272. TampaSpin:
MLB suspensions will be released at 3pm today....now that is for sure Weather Related as Hail will be flying.
You cheat.......You should be fired......The rule I grew up with since Kindergarten....No exceptions
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this map is update!! u see the tropical wave much better on here
Member Since: March 12, 2013 Posts: 113 Comments: 106789

Quoting 283. Hurricanes305:
Good Afternoon, the Atlantic is slowly starting to moisten up



There is still some SAL that might try to blow into the Atlantic but the Wave train may slow it down. By suspect by the end of this week we may have some potential areas for development.

12z GFS initialization shows pressures are already starting to lower which would explain the ITCZ becomes active again.



By Thursday, the ITCZ is looking ripe where some wave may become dominant and develop as they track into the Caribbean

Ooo, look at the 1005mb low over Oklahoma!
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Quoting 282. TampaSpin:


I don't think so....see the High rebuilding off the EAst Coast....that high should build in fast and close the gap.
Need to watch for same situation as Dorian where the high build on top of it. Also happened with Andrew and others I'm sure.
Member Since: August 2, 2011 Posts: 0 Comments: 2109
Good Afternoon, the Atlantic is slowly starting to moisten up



There is still some SAL that might try to blow into the Atlantic but the Wave train may slow it down. By suspect by the end of this week we may have some potential areas for development.

12z GFS initialization shows pressures are already starting to lower which would explain the ITCZ becomes active again.



By Thursday, the ITCZ is looking ripe where some wave may become dominant and develop as they track into the Caribbean

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Quoting 281. unknowncomic:
Looks like recurve if that gets strong, no.


I don't think so....see the High rebuilding off the EAst Coast....that high should build in fast and close the gap.
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Quoting 277. hurricanes2018:
Looks like recurve if that gets strong, no.
Member Since: August 2, 2011 Posts: 0 Comments: 2109
afternoon blog just checking in for the day

thanks for early morning update doc seems you were up with the birds this am
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Saturated South Florida brings wildlife concerns

Link
Member Since: August 2, 2011 Posts: 0 Comments: 2109
Quoting 231. LargoFl:


The cut-off from the trough off shore of Florida looks interesting. No chance of development however.
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180 hours out!
Member Since: March 12, 2013 Posts: 113 Comments: 106789
Quoting 269. MisterPerfect:
looks like a bulldozer in the atlantic is clearing the SAL away..
itcz working on it won't be long now
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Member Since: July 3, 2005 Posts: 428 Comments: 129903
Quoting 257. Tropicsweatherpr:
This wave is the one to watch down the road if it gets favorable conditions after it emerges Africa.

that tropical wave got a good spin to it.
Member Since: March 12, 2013 Posts: 113 Comments: 106789
Dorian is still alive. I predict that he will cross the North Atlantic then circle back past England and Spain before resuming his course back to the GOM.
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MLB suspensions will be released at 3pm today....now that is for sure Weather Related as Hail will be flying.
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Member Since: August 2, 2011 Posts: 0 Comments: 2109
Quoting 264. washingtonian115:
Do the models develop it?.We have to see how it does once it emerges of Afirca over the water it could fizzle.


"Some" of the models show something happening in about 120-140 hours
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looks like a bulldozer in the atlantic is clearing the SAL away..
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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.

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