I can't get over these numbers?

"I can't get over these numbers: The 1980s saw three official Category 5 hurricanes. The 1990s saw two. The 2000s, so far, have seen eight..." says Chris Mooney.

But what are these numbers supposed to mean?

Well, Chris doesn't say what they mean, but since he talks about paradigm shifts (!?!) I'm sure we're supposed to be relating these numbers to global warming in some way. And his co-bloggers comments clarify that these numbers *are* supposed to be linked to GW.

But in what way? The world hasn't suddenly got warmer since 2003 (indeed 1998 was warmer than 2003). And (as Chris says) there were 6 cat5 in the 60s, which was cooler still. Perhaps the relevant areas of sea have got warmer? Possible, but in that case I'm pretty sure people would have noticed and written it up (looking a bit harder, there is this, from RC (scroll down to fig 2) which shows a sharp increase recently in trop atl SSTs. But still doesn't explain the large number of cat 5's in the 60s).

If you want to know if its got warmer, then hurricanes are clearly a poor indicator - the record is too noisy. And we have a far better record: that of the temperature. If you want to know, conversely, if GW is going to lead to more or deeper or scarier hurricanes, then counting numbers by decade isn't a good idea either.

More like this

With a storm like Felix out there, I've been spreading it around in terms of my blogging. I've just posted about the storm at both The Daily Green and The Huffington Post. Here's the gist from the latter post: To be sure, it might be the case that there's a natural up-and-down cycle in the Atlantic…
The kerfuffle over my intemperate denunciation of Chris Mooney refers. Check the comments. As CM observes, "There have now been eight Category 5 Atlantic hurricanes in the past five years (Isabel, Ivan, Emily, Katrina, Rita, Wilma, Dean, Felix); There have been two Atlantic Category 5s so far this…
There are inevitably plenty of typos, but after the jump I've pasted in the transcript of my Science Friday conversation with NPR's Ira Flatow about hurricanes and global warming. Callers raised several interesting questions. Enjoy. National Public Radio (NPR) August 24, 2007 Friday SHOW: Talk Of…
In order to get a tropical cyclone spinning, a lot of things have to go right (or wrong, depending upon your perspective). First, you need a location that's warm but also a certain distance north or south of the equator. In places too close to latitude zero, winds won't swirl inwards towards an…

Hi William,

I don't know exactly what the numbers mean, and I pretty clearly said that in the post. In fact, I noted that reclassifying a few storms from the 1960s would mean there were just as many Cat 5s in that decade. So I tried to include the requisite caveats.

And of course, going by decade is a crude way of doing it. But still, don't you find the numbers a bit striking?

The way these numbers are presumably "linked" (what a vague word) to global warming is this: While no storm in itself proves anything, we have widely accepted theoretical predictions of storm intensification--and we have a lot of intense hurricanes.

[I still think the post is dubious. Yes you put in caveats, but you're clearly trying to lead people to... what? I don't think you know, and I can't work it out. Some kind of link to GW. But whatever the link is, its far too nuanced for this approach. If its GW, then the 60s were a fluke. But if the 60s were a fluke, why aren't the 0's? You're pretty close to the level of "another flood; another storm; oh its not proof of GW but its pretty striking, know wot I mean?" -W]

we have a far better record: that of the temperature.

Which temperature record would that be, William? The surface one with all the manual adjustments, and with insufficient documentation to independently reproduce them? Adjustments made with codes Gavin Schmidt argues should never be released to the public?

Do you trust that record? Why?

Would you trust scientists from another field if they insisted you accept measurements on face-value while refusing to give you enough information to reproduce their results?

[I'm talking about SSTs.

Meanwhile, your email address is faked. Please provide a valid address in future or your comments will be deleted -W]

mugwump, Lex and company have the data. Why do you suppose they're twisting in the wind so much trying to avoid independently reproducing their own analysis? (Note that there's nothing "independent" about copying the steps GISS took.) If they were scientists they'd have no problem with that concept.

By Steve Bloom (not verified) on 03 Sep 2007 #permalink

I am tempted to forecast that within about 5 years or so, the relatively low numbers of cat 5s between 1970 and 1994 will be shown to be connected to one or both of two factors: (a) the modest peak in cooling-related aerosols over the N Atlantic (as has already been shown for TC counts) or (b) the severe deforestation of N Africa's coastal regions, resulting in significantly more African dust. But cat 5s are rare in the Atlantic (yes, even in the last 10 years they represent only 9 storms out of 145, ~6%), and with such a small sample size, and such a doubtful history of measurements, attributing trends in frequency of cat 5s will continue be a hard problem for a long time. Nonetheless, they make up a significant portion of cat 4+ hurricane counts, major hurricane counts, and of metrics like PDI and ACE, all of which have been associated with AGW in the Atlantic (though the evidence for an association in the rest of the world remains ambiguous). It would be surprising if AGW caused increases in cat 4+ counts, PDI, and ACE, but not cat 5 counts.

There's another factor, which must affect the writing of someone from NOLA (as Chris is) : an enormous amount of housing and infrastructure has been and (despite the 2004 & 2005 hurricanes seasons) continues to be built on tropical coastlines. It's quite reasonably an ocean away for your (William) concerns, but America's economy was hit hard by the hurricane seasons of 2004 & 2005. Although most category 5s do not make landfall at that strength, most do make landfall at major hurricane strength. Thus, more cat 5s imply more major hurricane landfalls (unless the cause is solely changes in measurement methods). In that sense, whether trends in cat 5s are primarily due to AGW or tropical mode variations (forget the AMO as a driver of TC activity), they show that the risk of living on tropical coastlines is much higher than previously believed, and thus, the modern rush to tropical coastlines is quite dangerous. In this sense, more cat 5s than expected represent the fact that many of America's style of living choices are incognizant of environmental issues that affect their lives.

The cat5 numbers are Poisson distributed at best, and probably a bit overdispersed Poisson. Before trying to link them anywhere, it makes sense to check out that they are statisticaly different enough. The counts are so low that I don't think they are.

(Disclaimer: I'm not a denialist of any kind, quite the opposite.)

By Janne Sinkkonen (not verified) on 03 Sep 2007 #permalink

>"If you want to know if its got warmer, then hurricanes are clearly a poor indicator - the record is too noisy. And we have a far better record: that of the temperature."

That seems a bit wild. Yes global warming is in the title but the post is mainly about hurricanes and why are there higher numbers of Cat5s recently.

[Is the post about why there are more cat 5s? It doesn't say so. What explanations does it put forward? Is there any useful discussion in it? -W]

>"If you want to know, conversely, if GW is going to lead to more or deeper or scarier hurricanes, then counting numbers by decade isn't a good idea either."

It might be helpful if you explained why it isn't a good idea rather than just stating it.

[Oh, I thought that was obvious: because the statistics aren't stable. There is a comments to CM's post saying so -W]

Also are you jumping to conclusions with inferring this is the purpose of the post. Wouldn't it be more appropriate to assume a more basic and general purpose of trying to understand the patterns in hurricne and cat5 numbers and what the potential explanations are eg asking is global warming the best explanation or are there other causes?

[I'm complaining that the purpose of the post isn't clear. IF CM was trying to explore possible explanations, then... why didn't he? -W]

In this context llewelly's post is very useful. Your post just complains and does nothing good other than prompting llewelly's post while Chris Mooney's post has done something in prompting debate.

[Errr... my post appears to have prompted debate -W]

The first task would seem to gather all the possible explanations together. AMO has been suggested in which case numbers are only a little higher than the 60s and the pattern doesn't appear much to worry about. However from what I gather the evidence for this does not seem very good - the GW evidence seems better.

It would appear far too early to suggest the best explanation for the pattern I have seen so far is a mixture of GW plus llewelly suggestions. I would want to see other causes suggested and their abilities to explain the trends compared.

[Yes indeed, and so we come back round to the first point: why is CM just putting up a suggestive trend in numbers rather than actually exploring these questions? -W]


I have to say I find all of this more than a little unfair. First, you're taking a brief quote from something I've written on Huffington Post. The full item is here

Did you read it? In it I explain the basic caveats, data problems, etc. I ought to know them, I wrote an entire book on hurricanes and global warming, which has been widely pronounced scientifically accurate, including by Real Climate

Anyways, there are still more nuances and caveats in the Huffington Post piece, like this one: "Granted, the decadal comparison presented in the final bullet point comes with some caveats. I'm sure we missed some Category 5 storms in earlier decades due to deficiencies in our observing systems; and the borderline between Category 4 and 5 is hazy to begin with. Still, I don't think anyone could deny that we're seeing a shocking number of Category 5 hurricanes lately."

And I don't think anyone could deny that it is fully appropriate to discuss global warming, and what scientists say we ought to expect, in the context of dramatic weather like this. It is also appropriate to discuss the extremes/records we're seeing and how well they mesh or don't mesh with theoretical expectations, and what nuances need to be brought into the discussion as we engage in that exercise because of gaps in our data, past busy periods, etc.

Radio shows that I've been on have been doing all of this regularly. Will you denounce them too? Is all mention of global warming simply verboten unless we can prove each connection to a statistical test that satisfies all experts?

[I think you're being a bit touchy here, going down the "denounce" and "verboten" line is overkill. You're entitled to post as you will; I'm entitled to criticise it. I hadn't read your Huff post piece. Having now read it, my opinion is unaltered. TDG is a bit better, because you almost commit yourself to something there, but you don't quite. You're still very vague. You think there is some connection between these storms and GW. This is entirely possible. But is it possible to read anything meaningful into these statistics? I rather doubt it. Should people in the 60's have said "oh dear, 6 cat 5's this decade, and it will be warmer in the next few decades, there will be lots more in the 80's and 90's!" - clearly not. I shall do another post on this -W]

Well, here is another number: 2 category 5 Atlantic landfalls in one year. There's no prior record of more than one cat 5 Atlantic landfall in a year. But how statistics alone can tease anything out of something so rare (only 13 recorded in the last 100 years), with records so inhomogenus, I can't imagine.

Although the numbers of category 5 storms per decade are a crude measure, I was curious to find out whether one can infer anything of them statistically. One can look for the posterior probability of decreased hurricane intensity, under a vague gamma prior, with these lines of R code:

nsim = 100000
pps = function (s) {rgamma(nsim, .001+sum(s), .001+length(s))}

That is, the previous four decades are tested against this decade, and the fact that we have only had about 7.5 seasons so far has been taken into account.

The result is p=0.011, which is indeed approaching significant.

This assumes Poisson distribution. If there is any kind of clustering tendency in the appearance of the storms, as there probably is (SST varies etc.), the test becomes overconfident.

One could also test for the past five years, but that would not be honest anymore, for we have seen the yearly data.

[Thanks for the comment. I don't speak R, but I do think this is the sort of thing people ought to be doing. I'm pretty sure that this is the sort of thing the hurricane folk should be able to do, or find someone to help them do. Maybe they do and I haven't read it -W]

By Janne Sinkkonen (not verified) on 04 Sep 2007 #permalink

As a longtime reader, what I'd hope to see from science writers -- always -- is a paragraph that starts off asking the question William and Janne both ask above (William's words):

"... some connection ... is entirely possible. But is it possible to read anything meaningful into these statistics?"

There are many science writers, and more science bloggers, opining than doing the math. This is regrettable.

Statistics isn't easy, and isn't certain, at best.

I recently heard about a survey of student satisfaction with courses at Berkeley --- the course "Physics for Future Presidents" got high marks for opening kids' minds up to ways of thinking they hadn't imagined needing to understand.

Muller, who teaches the course, wrote this some years ago:

----excerpt follows -----
My own reading of the literature and study of paleoclimate suggests strongly that carbon dioxide from burning of fossil fuels will prove to be the greatest pollutant of human history. It is likely to have severe and detrimental effects on global climate. I would love to believe that the results of Mann et al. are correct, and that the last few years have been the warmest in a millennium.

Love to believe? My own words make me shudder. They trigger my scientist's instinct for caution. When a conclusion is attractive, I am tempted to lower my standards, to do shoddy work. But that is not the way to truth. When the conclusions are attractive, we must be extra cautious.

The public debate does not make that easy....
----- end excerpt -----

By Hank Roberts (not verified) on 04 Sep 2007 #permalink

My pre take on this was there was a lot of energy in the seas between SA and FL, and if a hurricane got in there it would explode. To me, the most interesting statistic was how fast Felix went from Cat 1 to Cat 5. I think we want to look at how fast the ssts recover from the cooling effect of the storm.

Eli, Dean and Felix especially were both small and fast-moving - both attributes that result in less heat being taken out of the water. Further more, the 26C thermocline is quite deep throughout the Caribbean. Recall that in 2005 Emily crossed a portion of Dennis' track were Dennis had been intense, but because the warm water was so deep there, Dennis left a warm wake, and Emily continued to intensify while crossing the track of Dennis. We may not see significant cooling in the wake of Felix.

For all those who would blithely follow the climatologists over the proverbial cliff, this from McIntyre's latest post:

As noted, Praha Dec 1986 is missing from one version and is 1.4 deg C in another version. Hansen then estimates the missing value at -3.6 deg C, a value of no less than 5 deg C lower than the actual value. There are 48 months in common, so he then concludes that the average bias is -0.1 deg C and adjusts all early Praha values down by 0.1 deg C. It sounds pretty absurd when written down. The methodology is not reported in the publications that NASA spokesman Gavin Schmidt has said to contain a comprehensive description of calculations.

Shenanigans like this would discredit a scientist in any other field (or land you in gaol if you worked at a drug company).