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Why global warming means killer storms worse than Katrina and Gustav, Part 1

By Joe Romm  

"Why global warming means killer storms worse than Katrina and Gustav, Part 1"


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Relative sizes of Typhoon Tip and Tropical Cyclone TracyHurricanes can get much, much bigger and stronger than we have so far seen in the Atlantic. The most intense Pacific storm on record was Super Typhoon Tip in 1979, which reached maximum sustained winds of 190 mph near the center. On its wide rim, gale-force winds (39 mph) extended over a diameter of an astonishing 1350 miles. It would have covered nearly half the continental United States.

“More than half the total hurricane damage in the U.S. (normalized for inflation and populations trends) was caused by just five events,” explained MIT hurricane expert Kerry Emanuel in an email. Storms that are Category 4 and 5 at landfall (or just before) are what destroy major cities like New Orleans and Galveston with devastating winds, rains, and storm surges.

In Part 2, we’ll look a little more in detail at Katrina (and Gustav), and why they weren’t (and probably won’t be) as strong and hence as devastating at landfall as they could have been.

But let’s first ask, How did Katrina turn into a powerful Category 5 hurricane ? The National Climatic Data Center 2006 report on Katrina begins its explanation by noting 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, and the warm temperatures extended to a considerable depth through the upper ocean layer.” The report continues, “Also, Katrina crossed the ‘loop current‘ (belt of even warmer water), during which time explosive intensification occurred. The temperature of the ocean surface is a critical element in the formation and strength of hurricanes.”

An important factor was that the ocean warming had penetrated to a considerable depth. One of the ways that hurricanes are weakened is the upwelling of colder, deeper water due to the hurricane’s own violent action. But if the deeper water is also warm, it doesn’t weaken the hurricane. In fact, it may continue to intensify. Global warming heats both the sea surface and the deep water, thus creating ideal conditions for a hurricane to survive and thrive in its long journey from tropical depression to Category Four or Five superstorm.

A 2005 study, “Penetration of Human-Induced Warming into the World’s Oceans,” led by Scripps Institution of Oceanography compared actual ocean temperature data from the surface down to hundreds of meters (in the Atlantic, Pacific, and Indian oceans) with climate models and concluded:

A warming signal has penetrated into the world’s oceans over the past 40 years. The signal is complex, with a vertical structure that varies widely by ocean; it cannot be explained by natural internal climate variability or solar and volcanic forcing, but is well simulated by two anthropogenically forced climate models. We conclude that it is of human origin, a conclusion robust to observational sampling and model differences.

This figure shows what they found:


Figure: Anthropogenic forcing signal strength (green hatched region) compared to that obtained from the observations (red dots). There is excellent agreement at most depths in all oceans. The hatched region shows the range of the signal strength estimates from five different realizations of identically forced simulation with the Parallel Climate Model, whereas the smaller green dots within the region are the individual realizations. Click to enlarge.

[And yes, the latest analysis shows "that ocean heat content has indeed been increasing in recent decades, just like the models said it should."]

Tropical cyclones are threshold events

Tropical cyclones are threshold events–if sea surface temperatures are below 80°F (26.5°C), they do not form. Some analysis even suggests there is a sea surface temperature “threshold [close to 83°F] necessary for the development of major hurricanes.” Global warming may actually cause some hurricanes and some major hurricanes to develop that otherwise would not have (by raising sea surface temperatures above the necessary threshold at the right place or time).

And the more warm, deep water that gets generated by global warming, the more super-intense hurricanes we will see. No wonder ABC News reported in 2006 that hurricane scientists are considering adding a Category 6, for hurricanes above 175 miles per hour. Ultimately, they may become common.

If we don’t reverse our emissions paths quickly, global temperatures will rise faster and faster through 2100 and beyond. This will translate into warmer oceans in all three dimensions: Warmth will spread over wider swaths of the ocean as well as deeper below the surface-we’ve already seen that in the first known tropical cyclone in the South Atlantic (2004) and the first known tropical cyclone to strike Spain (2005). That means we will probably see stronger hurricanes farther north along the East Coast in the coming decades.

More intense storms will be seen earlier and later in the season. The 2005 hurricane season was the most striking example of that trend, with Emily “the earliest-forming Category 5 hurricane on record in the Atlantic,” in July, and Zeta, the longest-lived tropical cyclone to form in December and cross over into the next year, where it became the longest-lived January tropical cyclone.

We have already seen a statistically significant increase in the length of the average hurricane season over the last several decades, according to a 2006 analysis. The data from the past century indicates that a 1°F increase in sea surface temperatures leads to an extra five tropical storms a year in the Atlantic–an ominous statistic in a world taking no actions to stop a projected 2°F increase in average sea surface temperatures by mid-century, and more than double that by century’s end.

And this is not a worst-case prediction, where global temperatures could rise more than 9°F this century (see “Is 450 ppm (or less) politically possible? Part 0: The alternative is humanity’s self-destruction“).

Part 2 will look a little more in detail at Katrina and Gustav, and why future Gulf storms are all but certain to be more devastating at landfall.

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21 Responses to Why global warming means killer storms worse than Katrina and Gustav, Part 1

  1. As with most things in the coupled atmosphere/ocean/land system, there are many complex interactions. What made Katrina so devastating was not the intensity per se, but rather the extraordinary size of the circulation. A recent conference presentation indicates this might have occurred as a result of an extra injection of vorticity (spin) from higher latitudes. This is still consistent with global warming, however, since heating of the atmosphere produces a more energetic system.

  2. Luddhunter says:

    [JR: Ludd -- we have certain rules that are well-established here. I don't reprint long-debunked disinformation (and that certainly includes anything the Competitive Enterprise Institute has ever written). And we certainly don't publish posts that are riddled with ad hominem attacks. I'm afraid that covers pretty much in 99% of your first post.]

    POST 1 excerpt: Your snake oil won’t replace real oil, Joe. You’ve lost credibility because you just couldn’t stick to science, and compete on that field, you had to go ahead and enter the policy arena without consensus from your peers. Who’s to believe your science posts are not biased by your mystical chanting about choking current technologies before new ones are market-competitive economically viable substitutes?

    You’re a Ludd, Joe, you are already killing growth by creating fear of investment in industry which is on it’s way to being overregulated and de facto nationalized. Ludds hurt our chances to survive as a species. Please do not breed anymore, Joe, we can’t afford more Ludds in the genepool.

    Curious, what underlies your Luddism? I’m guessing Technophobia (Turdeating), or Socialism (Statesucking).

    [JR: You really should go to A global warming denier site, or maybe Dot Earth, to post that.]

    POST 2 in its entirety:

    Cool! Did you spike me, Joe? Bad idea. Like OJ in the Bronco, baby.

    [JR: I guess you are comparing me to a murderer, but the comment is a bit too cryptic to be sure.]

    I’ll give you another day to post my comment, and I’ll even invite you on my podcast (equal time promised) to make your case that there is consensus on AGW causing hurricane power to increase.

    Don’t be a pussy, post my neanderthal comments and respond with class and don’t waste your time tell me how much science you know (wrong tack, i’m not arguing science, i’m arguing consensus), since YOU decided to come in the policy mudpen without consensus, not me.

    To not respond is to admit you’re dogmatic and overtaken by Pope Gore’s shaman spell and don’t listen to credible dissent form you peers (not me, the science I cited).

    [JR: Yeah, I'm the dogmatic one. Anyway, you apparently didn't bother to actually read my post or you'd realize how non-germane your comments were. Anyway, like I said, this isn't the website for trolls.]

  3. Ronald says:

    I saw a map of the US with the most dangerous places to live weather and earth quake wise and by far most of it was along the gulf coast and southern Atlantic coasts. Tornados in the midwest weren’t very bad at all.

    It might be time or past time for poeple to not live along these coasts at least in the low areas.

  4. Robert says:

    Realistically, what will happen is that we will continue to burn fossil fuels until they are depleted. Hurricanes will get much worse, but the workaround will be to abandon cities such as New Orleans. Once the ‘cane makes landfall it rapidly loses strength, so it is really only a coastal issue.

  5. John Hollenberg says:

    Joe, I think you showed remarkable restraint in publishing even excerpts of the LuddHunter diatribe/attack. Please don’t feel the need to allow any more of the garbage from this individual on climateprogress. This blog is remarkably free of junk like this, which is what makes it such a pleasure to read.

    Keep up the great work!

  6. David B. Benson says:

    What John Hollenberg just wrote.

    A Dr. Box, associated with the Byrd (Center?, Institute?), has written that from Greenland ice shee3t melt so far, he expects a rise in sea level of one to two meters by century’s end. That’ll really spoil the parade for the gulf coast and lotss of other places.

  7. Dano says:

    Shorter Luddhunter:

    I’m all hat, no cattle.

    Delete away, Joe.



  8. TomG says:

    Jerks like Luddhunter throwing nothing but fecal matter are not needed…

  9. hapa says:

    i wonder which NAMfan17 character will be the first to say “people should just get used to it and leave NYC.”

  10. Magnus says:

    Why do you chose a hurricane in 1979 and not the by far strongest, in the beginning of the 20th century?

    A curious “cherry pick”…

    The statistics:

    Hurricans and storms globally:

    From Science Magazine:

    US hurricanes strikes 1900-2004:

    Numbers of cyclones globally:

    Cyclone energy on the northern hemisphere:

    Intensity in tropical cyclones:

    I’ve got more graphs on hurricane activity with sloping curves, but this is enough here.

    [JR: I don't understand the thrust of your comment at all. But for the record, Tip is "largest and most intense tropical cyclone on record."]

  11. Magnus says:

    BTW: Kerry Emanuel changed his mind on stronger huricanes early this year.


    At least get facts right in this otherwise funny rhetorical blog.

    [JR: Again, not sure what the point of this comment is. You do not actually seem to have read this post.]

  12. Johnnyb says:

    I seem to recall in 2006 the Global Warmists came out and said that it was going to be the worst hurricane season ever, and not a single one hit the US and I believe that there were fewer storms formed than in previous years, below the longterm average. Then 2007 rolls around, and the Global Warmists come out and say that this will be the worst hurricane season ever, and the results were the same as 2006, no hurricanes hitting the US and fewer storms than normal.

    OK, so the Argos project confirms a recent cooling trend in the world oceans, and temperature monitors from arounf the globe confirm that 2008 is the coolest year that we have had at least since 2000. And joila, we get what appears to me to be an average hurricane season.

  13. David B. Benson says:

    Johnnyb — Is ten named storms by this date average?

  14. TomG says:

    Johnnyb terrible at recall.
    From Philip Klotzbach, William M. Gray and their associates at Colorado State University the average number of storms/season based on 1950-2000 stats: 9.6 tropical storms
    5.9 hurricanes
    2.3 major hurricanes
    They got their prediction for 2006 wrong (17, 9 and 5), but there still were:
    10 tropical storms
    5 hurricanes
    2 major hurricanes
    No hurricane hit the US
    The prediction for 2007 was much better (17, 9 and 5). There were:
    15 tropical storms
    6 hurricanes
    2 major hurricanes
    Humberto hit the US as a cat 1, Dean hit Yucatan as a cat 5
    and Felix hit Nicaragua also as a cat 5
    As for 2008….Sept 2 and we already have 10 storms?? This average?
    Use Google, not your recall.
    It took me all of 5 seconds to find all this information.

  15. TomG says:

    Bit of a follow-up…
    The original prediction for the 2007 season was issued in December 2006.
    It was 14 storms, 7 hurricanes and 3 major hurricanes.
    In April 2007 they changed the numbers to 17, 9 and 5.

  16. Luddhunter says:


    OK forget CEI. I noticed you didn’t mention my second source for cvlaiming Non-Consensus: the Geophysical Research Letters science that came out last year, so if you’ve debunked it, it’s not “long-debunked”, and I’d like to see the debunk. If you spike this one, I’ll know I’m on to something. I’ll take your debunk at face value and promise not to troll again (on this thread).


    Calling someone a Ludd and requesting they don’t breed more Ludds is not ad hominem. The former is a simple characterization of someone who advocates a ban/reg/tax without a viable replacement and without a strong case for safety impact. The latter is just good comedy. The Mating Curse is one of my staples for Ludds… like all good comedy, it’s half rational…if you were an ECONOMIC parasite on humanity, as are all able bodied individuals who willingly stifle growth for social/political gain, isn’t genetic de-selection advantage the species? Lighten up, Joe, it’s derision. You gotta be able to think on your feet in the polemic mud pen. You came in the mudpen when you started recommending policy, I’m not dumb enough to go in your science ivory tower and get my ass kicked.

    I know you’re not insecure enough to run an echo chamber, so please, debunk away.

    [JR: No need to debunk. That study is not germane to my post, if you were to actually read both!]

  17. John Hollenberg says:

    The LuddHunter is not a good advertisement for whatever position he is advocating. Impossible to tell what he is ranting about (or why). Please, please don’t feel obliged to allow this stuff in the comments. It contributes nothing to the discussion, and is a waste of everyones time.

  18. David B. Benson says:

    Correction — I think there are currently only nine named storms. No Josephine just yet.

  19. David B. Benson says:

    Now ten:


    August was ‘slightly above average’.

  20. I was looking for a group like this.