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Why future Katrinas and Gustavs will be MUCH worse at landfall, Part 2

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"Why future Katrinas and Gustavs will be MUCH worse at landfall, Part 2"

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Part 1 discussed why global warming means killer storms worse than Katrina and Gustav.  This post looks in more detail at Katrina and Gustav, and why they weren’t as strong and hence as devastating at landfall as they could have been.

My key point here is one that is rarely discussed in the literature dealing with global warming and hurricanes: All things being equal, if a storm taking the same track of Gustav (or Katrina) occurred in 2050, then, rather than weakening before making landfall, it would probably have strengthened considerably, creating far more havoc.

Let’s look at the region in 2050, assuming BAU (business-as-usual) warming, or no effort to reverse current emissions trends.

ornl-final.jpg2050-ornl-final.jpg

Now that is bad news for New Orleans, the Gulf Coast, and the South Atlantic. The average warming in the Gulf, Caribbean, and coastal Atlantic is 1°C to 2°C, but this model has an enormous body of very warm water 2°C to 3°C over much of the typical storm path for a hurricane like Katrina or Gustav. There are two relevant points to recall:

  1. The National Climatic Data Center 2006 report on Katrina notes that the surface temperatures (SSTs) in the Gulf of Mexico during the last week in August 2005 “were one to two degrees Celsius above normal.
  2. In the case of both Katrina and Gustav, they hit colder water before hitting the coast — a key reason they were far weaker at landfall than they might have been, as these pictures make clear:

Here are some plots of the Gulf’s sea surface temperature (SST) as Gustav would have seen it (from Jeff Masters’ WunderBlog):

Figure 1. Tropical Cyclone Heat Potential (TCHP) for August 28, 2008. Values of TCHP greater than 80 are commonly associated with rapid intensification of hurricanes. The forecast points from the NHC 5 am Saturday forecast are overlaid. Gustav is currently crossing over a portion of the Loop Current with extremely high value of TCHP of 120. However, Gustav will then cross over a cold eddy, and will miss crossing the warm Loop Current eddy that broke off in July.

Figure 2. Forecast track and sea surface temperature response to the passage of Gustav, as simulated by the GFDL model at 8 am EDT Saturday 8/30/08. Passage of Gustav over the relatively shallow depth of warm water near the coast will allow Gustav to upwell large amounts of cold water from the depths. This will chill the surface waters down by up to 5°C (9°F).

Now imagine we are in the year 2050 with the same storm track. We could easily be talking a Gustav2050 that is a Category Four or even Category Five at landfall, rather than just a strong Category 2.

What about Katrina? It did reach Category 5 status in the Gulf, but it made landfall only as a Category 3 [see "The Storm of the Century (so far)"]. Again, cold water played a role, as this University of Colorado graph reprinted in Wikipedia shows (where sea surface height is a proxy for SST, see here):

Image:Katrina vs sea surface height.JPG

Obviously, Katrina was able to ride the Gulf Loop Current and Eddy Vortex (!) closer to the coast than Gustav, but it still smashed into cold water. Again, in 2050, that weakening is going to be a lot less likely to occur.

What precisely would happen if a hurricane was ever able to ride warm Gulf water all the way to landfall? We have some idea because that appears to have happened once in the relatively recent past:

An example of how deep warm water, including the Loop Current, can allow a hurricane to strengthen, if other conditions are also favorable, is Hurricane Camille, which made landfall on the Mississippi Gulf Coast in August of 1969. Camille formed in the deep warm waters of the Caribbean, which enabled it to rapidly intensify into a Category 3 hurricane in one day. It rounded the western tip of Cuba, and its path took it directly over the Loop Current, all the way north towards the coast, during which time the rapid intensification continued. Camille became a Category 5 hurricane, with an intensity rarely seen, and extremely high winds that were maintained until landfall (190 mph / 305 km/h sustained winds were estimated to have occurred in a very small area to the right of the eye).

That of course was pure happenstance, pure bad luck. But by mid-century, the whole damn Gulf in the summer is going to be much, much warmer, thanks not to bad luck but to human emissions. So it seems a near certainty that the Gulf coast will see one or more Category 5′s make landfall in the coming decades. Indeed, as I wrote in my book:

At the same time, the inland United States will heat up at an even faster rate, so the Mississippi River will not be such as cool a stream of water pouring into the Gulf. As the sea level rises, the protective outer delta of the Mississippi River will continue to disappear and storm surges will penetrate deeper inland. Hurricanes weaken rapidly over land. Even one foot of shallow delta water can dramatically reduce this weakening effect, allowing hurricanes to reach deeper inland with their destructive force.

So not only will we see increased Category 4 and Category 5 hurricanes, but sooner or later–probably sooner–one of the hurricanes that enters the Gulf will ride a wide and deep mass of warm water straight to the shore, and rather than weakening as it approached the shore, like Katrina did, it will maintain its strength. Then a Category 5 super-hurricane will bring havoc back to New Orleans and the Gulf Coast.

Only one major issue remains, I think. Clearly global warming means warmer surface water and, as I discussed in Part 1, warmer deep water. All things being equal, that means future hurricanes that travel the same path are going to stay stronger longer and possibly even intensify where earlier hurricanes had weakened.

What we don’t know is if, in fact, all things will be equal. Perhaps global warming will create other conditions that might serve to weaken hurricanes or change their storm path. Some have suggested that climate change could lead to a permanent El Ni±o condition. That would be an unmitigated catastrophe for the planet, but would probably lead to fewer Atlantic hurricanes. Global warming could also lead to more wind shear, which tends to break up hurricanes.

That said, serious global warming has been going on for a few decades now, and just this decade we’ve had two major hurricanes ride straight up into the the New Orleans area, three if you count Rita. So I don’t think it makes much sense to hope or expect that future global warming means significantly fewer major hurricanes that end up on a path towards the Louisiana coast.

We are stuck with a fair amount of warming over the next few decades no matter what we do. But if we don’t reverse emissions trends soon, then Category 4 and 5 storms smashing into the Gulf coast seem likely to become a rather common in the second half of this century. And that will be a doubly untenable situation because by then we will be probably also be facing sea level rise of a few inches a decade or more.

Preserving the habitability of the Gulf and South Atlantic Coast post-2050 can only occur if we reverse U.S. and global emissions trends immediately.

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12 Responses to Why future Katrinas and Gustavs will be MUCH worse at landfall, Part 2

  1. David B. Benson says:

    By 2050 CE there will surely be a separate Category 6 classification.

    Preserve the habitability? How many moved back to New Orleans? How many have abandoned homes in the smaller fishing villages of the Gulf Coast? I t seems that the area is already less habitable than it was.

    Going to drown out the oil refineries as well, methinks.

  2. Gail says:

    “We are stuck with a fair amount of warming over the next few decades no matter what we do.”

    From what I’ve read, here and elsewhere, this is indubitably correct.

    The question is, how much warming, and how much more will be the contributions of the positive feedbacks that result from the inevitable “fair” amount of warming? How volatile will climate chaos be, from big fierce storms to the slowing of ocean currents, perhaps?

    Of course, I believe no matter what, we must persevere in efforts to mitigate, and seek technological solutions, demand governments mandate reductions in carbon emissions, insist that the worst emitters help the less fortunate in developing countries who are most vulnerable to the adverse consequences of climate change.

    But..but..but…I am interested in learning, just how much out-of-control warming are we already poised to endure? Should I dig a bunker and scrape together the money for a machine gun? Buy several year’s worth of freeze-dried food and bottled water? Beg my children to give up their higher education and take a crash course in basic agriculture?

    When even the experts, the scientists, seem overwhelmed by their own predictions, it’s hard for ordinary folks to know what to think.

  3. PeterW says:

    Hi Joe, Doesn’t this also make it more likely that the northern east coast will experience some of these massive storms? What happens when a category 4 or 5 storm hits Washington, New York or Boston at high tide? I’m guessing it wouldn’t be good.

    [JR: There is a scenario on the web -- I think it is the weather Channel -- of a Cat 3 hitting Manhattan in just the wrong way. It ain't pretty. Yes, I think this analysis also applies somewhat to the East Coast -- it is just that the Gulf of Mexico is largely closed off and ultimately going to get warmer and warmer over time.]

  4. Rick Covert says:

    Joe,

    What’s the prognosis for Houston by 2020 to 2030 under a 2º C increase in temperature by 2050?

  5. Rick Covert says:

    Joe,

    I should have quanfied that 2º C increase to average global temperature which I know is pretty optimistic but I just want to know the conditions for Houston from a starting point.

  6. JoelArmstrong says:

    The article says:
    “Global warming could also lead to more wind shear, which tends to break up hurricanes.”

    Not sure what he relies upon to come to that conclusion, but it makes you think more wind shear might be a good thing, but here is what Wikipedia says about wind shear:

    “Strong vertical wind shear within the troposphere also inhibits tropical cyclone development, but helps to organize individual thunderstorms into living longer life cycles which can then produce severe weather.”

    So it’s probably more of a bad thing overall. I think what we can expect overall is more weather inconsistency….everywhere. Which means more ruined crops, less food, more emergencies such as power outages, forest fires, etc. And then there are the positive feedback loops we still have so much to learn about. My intuition tells me the future will be very windy.

  7. Gail writes:

    When even the experts, the scientists, seem overwhelmed by their own predictions, it’s hard for ordinary folks to know what to think.

    This is the leadership problem in a nutshell. Gail, really well put. I would add that it probably makes the most sense for ordinary people to turn away from the problem entirely, even though they obviously know what’s going on and care. That’s what is happening right now, and in a democracy, we aren’t going to get anywhere unless that specific inertia is overcome.

  8. David B. Benson says:

    Gail — Strikes me as prudent for everybody to learn the basics of gardening.

  9. Gail says:

    David B. Benson, that would be better than lawns. Where I live people have acres of lawns and all the 3-stroke engine equipment needed to maintain them is terrible for the environment, much more polluting than cars even.

    I have been a gardener all my life but I never had to rely on producing my own food and the thought of being forced to do so is intimidating to say the least. I think it will be exceedingly difficult for people to transition to farming their own food. In some ways the inhabitants of poorer agrarian societies may fare better than modern city-dwellers and suburbanites. Unless they live near the ocean which, of course, most of them do.

  10. David B. Benson says:

    Gail — Live near the ocean? Why? Almost all fished out and with seas rising the shoreline shellfish will also suffer.

  11. paulm says:

    I think we are past the climate change misery threshold.

    Austrailia, Brazil, China, Caribbean, India & Bangladesh all in constant climate chaos and misery. North America and Europe will be following shortly.


    According to the Associated Press, some 2.3 million people ! were affected by Aila, many of them stranded in flooded villages. Storm surges in Bangladesh flooded agricultural areas with salty water. Home to roughly 25,000 residents, the coastal island Nijhum Dwip was reported to be completely submerged. As of May 27, 2009, many rural villages had not yet been reached by relief workers, and the death toll was expected to rise significantly as search and rescue efforts continued.

  12. David B. Benson says:

    paulm — Also, Southeast Asia.