The Intersection

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In my previous post, I went into some detail about the intense argument between Greg Holland and Peter Webster on the one hand (PDF), and Chris Landsea on the other (PDF), over whether the total number of Atlantic storms is increasing. And I concluded, somewhat unsatisfyingly, that there may be limits placed upon the extent to which we can determine who’s right and wrong in this debate. After all, we will never know for certain how many storms were missed in previous eras.

However, that doesn’t mean that we can’t draw any conclusions about the current debate–it’s just that they may not be purely scientific conclusions. Here are some broad takeaway points that I’d like to stress:

1. The hurricane-climate debate is broadening and changing focus. That’s a good thing (for science, at least). Back in 2005, the central issue about the relationship between hurricanes and global warming was whether the average hurricane had intensified–globally. But now a new debate has begun over Atlantic storm numbers and how climate change may be affecting those. Expect both debates to rage even as scientists start studying variability in other hurricane attributes as well: Size, regional distribution and tracks, season length, etc. The hurricane-climate relationship has become a hot topic in science, and because it’s very complex, it offers many possible angles of attack. As a result, new researchers are diving in and looking at the issue through a variety of different lenses and with a variety of different methodological approaches.

This is good for science in the long run. But in the short run, it may lead to a lot of contradictory results, studies, and headlines. As the Times‘ Andrew Revkin pointed out in comments on the previous post, that’s precisely what we’d expect from a relatively young field of science.

2. The best hurricane data are in the Atlantic, so that’s where the rubber hits the road. In the prior phase of the hurricane-climate argument, skeptics like Landsea and Bill Gray had similarly argued that global hurricane intensity data become much less reliable as one goes further back in time due to changes in the nature of our observing system (which, of course, has greatly improved over the past several decades). The skeptics further noted that across global hurricane basins, observational methodologies have also varied and, in fact, continue to differ very substantially. For example, the Atlantic is the only basin where there has been regular aircraft reconnaissance of hurricanes for the past 50 years–and airplane reconnaissance is the best way of finding out how intense a hurricane is.

The new debate over what’s going on in the Atlantic–rather than over what’s happening globally–signals a recognition both that we may see different responses in different hurricane basins as a result of global warming, but also that the Atlantic is where the data are most reliable. Now to be sure, those data are not infinitely reliable, as the current debate over missed storms clearly shows. But still, the Atlantic data are much better than the data for the rest of the world. So if scientists can’t achieve consensus about what’s going on in the Atlantic, they probably won’t achieve it for the rest of the world either.

3. More years = more data; but from a societal perspective, we can’t wait. We’ll never know exactly how many Atlantic storms were missed in 1933–and, therefore, whether it might truly have been a rival to the record 2005 hurricane season. With the exception of a few storms that might be rediscovered here and there thanks to laborious historical or archival research, most missed storms in the past will probably always be missed.

However, it’s a safe bet that in 2007, there won’t be any significant missed Atlantic storms whatsoever–our observing system has literally gotten that good. In fact, with each succeeding year, we will get more reliable data, and the trend in storm numbers (and intensity) will either become increasingly robust or vanish. So we will have a definitive answer, eventually, about whether the Atlantic is indeed changing in an alarming way.

However, I would strongly advise against simply assuming that Chris Landsea wins this debate and that, therefore, we don’t have to worry about an increase in storm numbers. From a policy perspective, the proper question to ask is, what if Holland and Webster are right? Because if they are, we may not even have seen the worst yet in the Atlantic. As Holland Webster write: “If we project past increases forward, then an increased SST over the next 50 years of, say, 1-2 C could lead to an average of 20-25 cyclones and 10-15 hurricanes per year. ” Jesus. 2005 would become the new normal. This is a nightmare scenario, and while it may not be realized, it is bad enough we ought to think of it as a kind of hypothetical worst case and tailor our precautionary plans accordingly.

At minimum, that would involve factoring in potential global warming-induced changes to hurricanes, of the sort Holland and Webster are talking about, into any forward looking agenda for the protection of cities like New Orleans. With the second anniversary of Hurricane Katrina coming up, that’s a sobering thought indeed.


  1. #1 Fred Bortz
    July 31, 2007

    This is a nightmare scenario, and while it may not be realized, it is bad enough we ought to think of it as a kind of hypothetical worst case scenario and tailor our precautionary plans accordingly.

    This raises I question I was thinking of discussing in my blog (click my name), but have held off. Perhaps it is better discussed here.

    In the current issue of New Scientist, Jim Hansen writes about the difficulty of getting people to pay attention to extreme scenarios, like the nightmare 5-meter sea-level rise that he thinks will result from a “business as usual” approach.

    Not only do people resist such scenarios, but apparently the researchers who mention them lose funding. So says Hansen at the following link:–unless-we-act-now.html

    I have two reactions. First, I wonder if it is time to stop citing “business as usual” scenarios, because it is becoming increasingly clear that even the U.S. will look for some ways to respond to AGW. I’d rather read about scenarios of what would happen to CO2 levels if we take certain minimal steps but not others, and what impact that would have on worst-case sea level rise, for example.

    Second, how do policy makers know what to do with nightmare scenarios unless they have some way to judge their likelihood. Hansen, who has an outstanding 20-year record of projecting problems, needs to be heard. But even he would not be able to say whether his 5-meter rise nightmare is 0.1, 1, 5, 10, 20, 50, or 90 percent certain based on a given policy regime.

    I’m all for making sure the realistic nightmare scenarios are out there, but I don’t have the slightest idea how to factor them into policy decisions.

  2. #2 Andy Revkin
    July 31, 2007

    Steve Schneider at Stanford has thought long and hard about the importance of paying attention to worse-case tail of the curve of possible impacts from greenhouse buildup. His analogy, at least to my understanding, is that climate policy — for that reason — is more like buying fire insurance than rushing to put out a fire. You don’t buy fire insurance for the little stovetop fizzle. You buy it against the catastrophe.
    I quoted Schneider on this here recently:
    There are still huge problems of course — particularly in a world where different countries face different risks with different resources. How are they going to agree on a common hazard insurance policy? Stay tuned.

  3. #3 Fred Bortz
    July 31, 2007

    I think the insurance model is incomplete.

    I would put it more like this:

    You carry major medical insurance to enable you to weather a catastrophe, but you also carry basic health insurance to make your health costs more predictable. A good basic health insurance policy encourages the insured to get preventative care.

    We need to be thinking about this from the perspective of the insurance company rather than the insured. What policies should we offer?

  4. #4 alvinwriter
    August 1, 2007

    I’m writing in from TheScienceDesk at TheNewsRoom and I believe these arguments about the frequency of hurricanes over the Atlantic will subside in a couple of years or so when people finally get to experience firsthand if hurricanes do occur more often and with more intensity than in previous decades.

    I live in Southeast Asia and the opposite seems to be happening. It’s supposed to be typhoon season but there’s actually a drought and water supplies are obviously in danger of running out, affecting crops, power supply, and overall availability of water.

    Here’s a link to TheNewsRoom about the problems than can be caused by drought in the Philippines:

    You can find and use more great news, pictures, and video on global warming in TheNewsRoom. If you’re interested, you can email for the details. TheNewsRoom welcomes you.

  5. #5 Lance
    August 2, 2007

    ” ‘If we project past increases forward, then an increased SST over the next 50 years of, say, 1-2 C could lead to an average of 20-25 cyclones and 10-15 hurricanes per year. ‘ Jesus. 2005 would become the new normal.”

    Yeah, and if I “project forward” the current growth of my 6 month old niece she’ll be 12 feet tall by the time she is 10. This is the same disingenous game that global warming scaremongers have been playing for years.

    I’m glad none of you are running my insurance company.

  6. #6 Fred Bortz
    August 2, 2007

    This is the same disingenous game that global warming scaremongers have been playing for years.

    In quoting Chris, you left out the rest of the paragraph, which included this:

    This is a nightmare scenario, and while it may not be realized, it is bad enough we ought to think of it as a kind of hypothetical worst case and tailor our precautionary plans accordingly.

    So while Lance might prefer that his insurance company ignore the worst case scenario, I would prefer that mine consider all possibilities in setting their rates so they have the money to cover my catastrophic losses if I happen to have such losses in an unusually bad year for the insurer.

    In fact, it is just such considerations that have led some insurance companies to raise rates or even stop insuring properties in high-risk areas like flood plains. That action leads to changes in behavior of potential policyholders, like deciding not to develop flood-prone tracts of land.

    It is not scaremongering to lay out scenarios supported by the scientific consensus, nor is it scaremongering to consider worst-case scenarios with appropriate caveats as to their probability.

    That gives policymakers the information they need to develop appropriate government responses. A carbon tax, cap-and-trade schemes, public information campaigns, and business as usual all are possible policy responses. Choosing the appropriate response requires the best available information, including both sweet-dream and nightmare scenarios.

    An extreme but affordable example is choosing to continue to search for near-earth asteroids and to invest government resources to develop technologies to divert them if they are on a collision course. It may be a once in 10,000 year event that a city-destroying bolide hits Earth (the Tunguska event in 1908 would have wiped out a city if it had hit elsewhere), but we would be foolish not to work out scenarios and contingency plans for such an event.

    (I wrote a kids’ book called Collision Course! Cosmic Impacts and Life on Earth in 2001. Click my name for details.)

  7. #7 Steve Bloom
    August 5, 2007

    I just spotted a new paper (abstract pasted below) on North Atlantic hurricane counts. These authors also did a ship-track analysis, but came to conclusions that are consistent with H+W.

    Also, Chris, it’s important to mention that a major reason why Kerry Emanuel and Kevin Trenberth back the H+W results is the consistency with Emanuel’s proposal that TCs are a major mechanism for heat transport from the tropics to the poles and that we should expect more TC activity as the planet warms. See this discussion of Matt Huber’s recent Nature paper showing that the scale and pattern of this heat transport neatly explain why the tropics haven’t been much hotter when the planet has been warmer.

    GEOPHYSICAL RESEARCH LETTERS, VOL. 34, L14801, doi:10.1029/2007GL030169, 2007

    Is the number of North Atlantic tropical cyclones significantly underestimated prior to the availability of satellite observations?

    Edmund K. M. Chang and Yanjuan Guo

    Institute for Terrestrial and Planetary Atmospheres, Marine Sciences Research Center, Stony Brook University, Stony Brook, New York, USA

    Abstract: The number of North Atlantic tropical cyclones that may have been undetected before satellite observations are available is estimated by passing the cyclone tracks taken from 1976 to 2005 through ship observations from 1900 to 1965. The probability of detection is equated to the probability that the ships would have made wind observations of 18 m/s or higher had the tropical cyclones been present during the earlier years, based on the probability computed from actual wind observations around tropical cyclones during the satellite era. It is estimated that the number of tropical cyclones not making landfall over any continent or the Caribbeans may have been underestimated by up to 2.1 per year during 1904-1913, with this number decreasing to 1.0 per year or less during the 1920s and later decades. Our results suggest that the characteristics of North Atlantic tropical cyclone track statistics might have changed during the 20th century.

    Received 27 March 2007; accepted 15 June 2007; published 17 July 2007.

  8. #8 alvinwriter
    August 30, 2007

    The research on hurricane frequency is based largely on historical statistical data, which might not be enough to establish a trend. But in my experience here in Southeast Asia, there have been times when typhoons are frequent and times when they are scarce. It’s September, and I count only a handful of typhoons, causing water-shortage problems in the Philippines and other parts of the continent. It’s strange that on the other side of the globe, hurricanes are said to come more frequently.

    Hurricane frequency, climate change linked:

    Global warming’s impact on hurricanes more complex than thought:

    – Alvin from TheScienceDesk at

  9. #9 vano
    February 26, 2008

    Very good

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