After my post on ABC’s coverage of the threat of global warming, I read through some interesting bits of the evidence on issues I raised. Several commenters pointed me to an interesting blog, Real Climate, which seemed to be a reasonable treatment of issues written by those who generally accept the orthodox view of man-made global warming. [In the comments, Bruce McCullough points me to a blog that disagrees with the prevailing orthodoxy, Climate Audit.]
Real Climate pointed to an interesting scholarly article on the hurricane debate: Curry, Webster, & Holland, "Mixing Politics and Science in Testing the Hypothesis That Greenhouse Warming Is Causing a Global Increase in Hurricane Intensity" in the current Bulletin of the American Meteorological Society (BAMS). Although I found the paper mostly persuasive that there had been a very large increase in category 4 hurricanes since 1970 (with drops or no change in the other categories of hurricanes), I see three problems with the paper.
Starting at 1970. First, the paper dismisses concerns that the choice of 1970 as a starting point may give a misleading account because of the evidence that there was global cooling from 1940 to 1970. They [combine] treat this legitimate concern as [with] a logical fallacy [and attack that fallacy], but they never explain [deal adequately with the implications of] coherently what’s fallacious about potentially choosing start or cut-off dates that are unrepresentative of larger trends or that give misleading measurements of the strength of any overall trend. [The authors justify their choice of 1970 because of the pooorer data quality before that date, which is fine, but they do not fully recognize the possible implications of that choice for the generalizability of their results.]
Double Counting 1994 Hurricanes? Second, if the authors actually did what they report having done with their data, then the BAMS paper should never have been published. In two charts showing the main hurricane trends, they report the data in five year periods, except for 1994, which is included in two periods, 1990-94 and the six-year period 1994-99. This may be just a typographical error, but they make this error three times in the paper (in most of the most important charts). And exactly the same error appears in another paper they published in Science in 2005 using related data, so it may well not be a typo. If these are not merely typographical errors, and they did what the article reports that they did (i.e., double counted 1994 hurricanes), then the paper should never have been published. [Just to be crystal clear, if I had to bet, I'd bet that the authors just made repeated typographical errors. And even if the error is substantive, obviously it wouldn't have been intentional.]
False Statements to the Public About Category-5 Hurricanes. Third, although the article ended with a substantial discussion of responsible argumentation over the issue of hurricanes and global warming in the mainstream press, as an apparent model they pointed to their own public commentary:
In our AAAS press release . . ., given the recent devastation associated with Hurricane Katrina, the main public message that we wanted to communicate was
The key inference from our study [in Science released along with the press release] of relevance here is that storms like Katrina should not be regarded as a “once-in-a-lifetime” event in the coming decades, but may become more frequent. This suggests that risk assessment is needed for all coastal cities in the southern and southeastern U.S. . . . The southeastern U.S needs to begin planning to match the increased risk of category-5 hurricanes.
Just to remind people: Katrina was a category-5 hurricane at its peak, but it was a category-3 hurricane when it hit the Gulf Coast, and it was only a category-1 hurricane at New Orleans (95 mph), though it was just below the threshold for a category-2 hurricane. The damage at New Orleans probably occurred, not because it was such an unusual hurricane but because the levees were in appalling condition (whether you fully buy Wizbang’s provocative account or not).
But the data presented in the BAMS paper show what looks to be a very small and statistically insignificant rise in category-5 hurricanes from 1970 through 2005 (these data include some Pacific as well as some Atlantic hurricanes). The big increase shown in the BAMS paper is almost a tripling of category-4 hurricanes; other classes of hurricanes seem to show significant drops or no significant changes.
A 2005 Science article co-authored by the same group as the BAMS paper--Webster, Holland, Curry, & Chang, "Changes in Tropical Cyclone Number, Duration, and Intensity in a Warming Environment"--does look at Northern Atlantic hurricanes 1970-2004 separately from Pacific ones, but lumps category-4 and category-5 storms together, showing an increase for the combination, not reporting anything on category-5 hurricanes alone. I went to the data source cited in the 2005 Science paper and this is what I found for 1960-2004 hurricanes (the Science study covered 1970-2004, excluding the first two rows below and the 4 category-5 hurricanes that occurred after the period of their data, in 2005):
Category 5 Hurricanes in the North Atlantic:
1960-64 . . 4
1965-69 . . 2
1970-74 . . 1
1975-79 . . 2
1980-84 . . 1
1985-89 . . 2
1990-94 . . 1
1995-99 . . 1
2000-04 . . 2
As you can see, in the data they claimed to have used in their Science article (as I counted the events), there is absolutely no trend in category-5 hurricanes in the period of their study: 1970-2004. Indeed, the 1990s showed insignificantly fewer hurricanes than either the 1970s or 1980s. Thus, all of the increase in the North Atlantic category 4-5 storms reported in the 2005 Science article must be due to an increase category-4, not category-5 storms.
Neither paper reports any data that would show a statistically significant increase in category-5 storms that would form the scientific basis for their public claim, made along with their release of the 2005 Science article: “The southeastern U.S needs to begin planning to match the increased risk of category-5 hurricanes.”
What increased risk?
If they have the data to support that claim, they should make it public. Anyone reading that claim would think that their Science paper showed such a significant increase. But it didn’t. Even after I added the 2005 data on category-5 hurricanes, which they did not use because the season wasn’t over yet, the quick regressions I ran didn't show any statistically significant increase in category-5 storms.
Did they just fabricate this claim of "increased risk" of category-5 storms?
If they don’t have such data—-and it appears that they don’t—-then it’s irresponsible for a scientist to imply a scientific basis for such a fear-inducing claim released along with a scientific paper. And it’s particularly odd that the authors of the 2006 BAMS paper actually discuss and criticize the mainstream press for poor environmental reporting that gives too much weight to critics of the environmental orthodoxy. The authors tell us that their scrupulousness put themselves at a disadvantage in public debate because they restricted themselves to making claims that were supported by peer-reviewed articles and data. Yet their own peer-reviewed data would seem to me to show that they had no scientific basis for saying that “The southeastern U.S needs to begin planning to match the increased risk of category-5 hurricanes.”
Bottom line:
1. The new BAMS article shows persuasive evidence of a huge jump in category-4 hurricanes 1970-2004, but declines or flat trends in the numbers of stronger and weaker hurricanes.
2. The BAMS article does not deal adequately with whether its choice of a relative cool period (1970) as a starting time influenced the results.
3. In both their 2005 Science article and their 2006 BAMS article, the authors appear to double count data from 1994, but it may just be the result of repeated typographical errors in both journals.
4. In the BAMS article, the authors criticize others for irresponsible public statements on global warming and praise their own caution, yet the press release they quote asserts an “increased risk” of category-5 hurricanes threatening the southeastern U.S., but neither their own two articles, nor the data they claim to have used, show any such statistically significant trend.
5. If the quality of peer review and editing in this field is only as careful as it seems to be on the BAMS paper, then I think it prudent for educated lay people to continue to be skeptical about the research and public assertions of climate experts, especially those who tell you to just trust them or who insist that they are just relying on what their data show. Wouldn’t expert reviewers of the BAMS paper already know that there had been no increase in category-5 hurricanes in the North Atlantic, and thus that the public statements that the authors proudly trumpet were irresponsible? Certainly, this brief foray into the literature leads me to be less confident of the conclusions of climate researchers, no matter how fervently they are asserted.
UPDATE: I emailed Judith Curry, the first author on the BAMS paper, pointing out the double listing of 1994 and requesting her 1970-2005 data by year by basin by hurricane category, which should allow me to resolve some oustanding questions.
There is a lot of back-and-forth discussion in the comments, particularly here, here, and here.
2d UPDATE: Judith Curry responded at RealClimate here and here. I have submitted a response, which has yet to appear there.
Overall, my criticisms seem to be pretty well confirmed. After thanking Judith Curry for her prompt response, I review where the exchange stands.
1. I am happy that you have confirmed the “1994” errors I found in your two papers, and I am also happy that they are typographical, rather than substantive.
2. You justify your choice of 1970 as the starting date for your study. My criticism was not whether the starting date was the best one (it probably was), but rather how choosing a relative minimum as the start date should affect the interpretation and generalizability of your results. I think we have both said our piece on this issue; I doubt that further discussion will resolve things any further.
3. I was pleased that you acknowledged that, as I had pointed out, the data on cat-5 hurricanes shows no significant trend, an observation that was the main focus of my comments (at realClimate.org post #212). On this point, you wrote:
With regard to category 5 storms, there is no point to trying to identify a trend only in the category 5 storms, owing to the small numbers and the uncertainties in classifying storms with the strongest windspeeds.
Of course, statistical significance is determined not only by sample size, but by the strength of any relationship and the variability in the data. From eyeballing your data, it appears that, if the relationship for cat-5 storms worldwide had been as strong as the powerful relationship that you nicely established for cat-4 storms, then the sample size of cat-5 storms was probably large enough to show statistically significant results. So the fact that there is no significant trend in cat-5 storms is due to the absence of a strong relationship in the data, as much or more than to the relatively small sample sizes.
As for my criticizing your assertion of an increase in the risk of cat-5 storms, which you now acknowledge that your data do not show, you wrote:
I did not rummage through your group’s responses to the press to unearth something your co-authors said in dealing with the press back in 2005. In your 2006 BAMS article, which I was commenting on, you purported to quote just three sentences from your group’s 2005 dealings with the press. These were the sentences that your new 2006 paper chose to emphasize. These were the three sentences that I quoted, taking issue with the last sentence:In terms of our statements in the press release issued in sept 2005, specifically the Q&A from Science, we had NO IDEA that anyone would even pay much attention this, particularly a year later. We never anticipated this paper and subject to become such a big deal. We were as careful as we could be (given our inexperience with press releases and media in general, and specifically were very careful not to overplay the global warming issue). . . .
The key statement of contention was in our Q&A with Science, which was made in response to the following direct question:
It is not a statement that we made in our Science paper, nor in the news release issued from Georgia Tech. Rather, it was a statement made on a short time fuse at a request from Science, to respond to policy makers and to the catatstrophe [sic] in New Orleans. In hindsight, I don't thing we would change a word that was said. What is said by a scientist in peer reviewed publications in done in a very different context from interacting with the media. Scientists are expected to respond to questions outside of their field that they are ill prepared to deal with, and do not directly follow from their scientific research. This is the so-called value gap between scientists and policy makers that was addressed in the BAMS article.Given that increased intensity, what are the possible ramifications for policy-makers, generally? Would your research have any bearing, at least potentially, on decisions regarding the rebuilding of New Orleans and Gulf Coast?
Since, as you now kindly acknowledge, your data show no increased incidence of cat-5 hurricanes--indeed, you argue that “there is no point to trying to identify a trend only in the category 5 storms”--I objected to your group’s use of the phrase “the increased risk of category 5 hurricanes.”“The southeastern U.S. needs to begin planning to manage the increased risk of category 5 hurricanes.”
My criticism thus seems eminently sound, with one strange, but important caveat.
Judith, you write that the passage I criticize was said in response to a question posed by Science about precautions for hurricanes and you quote those questions. But the phrase that I objected to--“the increased risk of category 5 hurricanes” --does not appear in the interview you referenced. Webster referred instead to “the risk of category 5 hurricanes.” In the interview, Webster later refers to “this increased risk,” but in context he appears to be referring to a range of risks from cat-3 through cat-5 that the public needs to address, so there is nothing objectionable about such a reference.
Judith, can you point me to any place where Webster or anyone in your group actually uttered or wrote the words that you quote in your 2006 BAMS article?
Or did someone (mistakenly) rewrite Webster’s answer to add a scientific assertion that is not supported by the data you present (i.e., “the increased risk of category 5 hurricanes”)?
You write: “In hindsight, I don't thing [sic] we would change a word that was said.” But if you just pointed us to the right source for the text you quoted, it appears that someone (mistakenly) did “change a word that was said”--and changed it to something unwarranted by the scientific data your group presents.
Is there any way to correct the online version of the 2006 BAMS paper so that the charts are labeled correctly and so that you don’t make a claim of an “increased risk of category 5 hurricanes” if Webster didn’t actually say that in the passage you purport to quote.
The main reason the paper has relevance is because weather is a chaotic non-linear dynamical system. Therefore, while climatologists may talk about global climate statistics (avg. global temperature, albedo, etc), climate will vary on local geographical scales. In fact, while weather will be dependent on climate in adjacent and other geographical regions, it will usually be very different from the weather of an appropriately sized adjacent zone. There are actually some simple 1-dimensional EBM codes (there are probably some available at GISS' site [which is a great group that posts tons of info for the public]) which demonstrate that and What's the relevance of the numerb of one type of hurricanes in just one part of one ocean? I don't see how that's a helpful metric at all.
The main reason the paper has relevance is because weather is a chaotic non-linear dynamical system. Therefore, while climatologists may talk about global climate statistics (avg. global temperature, albedo, etc), climate will vary on local geographical scales. In fact, while weather will be dependent on climate in adjacent and other geographical regions, it will usually be very different from the weather of an appropriately sized adjacent zone. There are actually some simple 1-dimensional EBM codes (there are probably some available at GISS' site [which is a great group that posts tons of info for the public]) which demonstrate that and which you can probably launch either from windows or in the respective webpages. So as a consequence, curry, et al. are justified in such a narrow analysis because the particular regions they're looking at have a characteristic set of climate/weather patterns and a consistent and directioned variability would likely point to more global changes.
also, an interesting bit of news about the upcoming ipcc report news about ipcc report
by the way prof. lindgren--it seems youre getting interested in the subject so if you have some free time you should really give some thought to getting a book called 'a climate modelling primer' by henderson-sellers and mcguffie
its very user friendly and not very long and is incredibly well regarded by many climatologists
here's the link to the book i was mentioning climate modelling primer
most climatologists agree that after a read of this book you'll generally be prepared to tackle any paper in the subject, particularly those regarding some of the models used in climate simulations
If you like Real Climate (which is actually run by
a bunch of so-called "climate scientists" who
don't know statistics) you'll love
www.climateaudit.org
whose purpose is to correct the nonsense on realclimate
Anyone who knows the rudiments of multivariate analysis
can easily see that the so-called "hockey stick" graph
is, at best, the result of gross incompetence. (You
can feed a constant series into that algorithm, and
it will produce a hockey stick.)
Regards,
Bruce
One other thought, and I simply don't have time this week to read this report - but how do they address the increase in funds towards the study of hurricanes and satellite and aeronautic instruments over the last 10 to 15 years which have enabled us to identify many more storms as hurricanes which only a couple of decades ago may have gone unnoticed or been misclassified?
It seems to me that they have to factor in the huge increase in attention to hurricanes and advancements in reporting technology otherwise their data sets are fundamentally flawed and otherwise worthless.
Is it proof? No. But we are not talking about "absolute proof". We are talking about what is prudent.
Suppose you are a golfer. You know that the more of your first strokes stop on the green, the greater your chances of getting a hole in one. On average, however, only 1 out of 1000 shots that stop on the green are a hole-in-one. On average, however, 50 out of 100 shots stop on the green. Now let's suppose you switch to a new club, and after 500 shots you notice that the percentage of shots that stop on the green have gone from 50% to 75%.
Is it reasonable to infer that your chances of getting a hole in one have increased? Probably. Is it proof? No.
Note that I'm not claiming that in this particular case, what they did was reasonable. I'm just saying that claiming an increased probability of cat-5 hurricanes only on the observed increased probability of cat-4 hurricanes is not clearly a mistake.
i don't live in Florida either but I do own property there - on the beach - and spend a significant amount of time at another house in Georgia and can't really say I've seen any increase in hurricanes let alone an 10 degree increase in the average temperature. Increased news coverage with the 24 hour cable channels, yes. But not actual increases in hurricanes or anything approaching the temperature change you allege.
That would work as an explanation, except that they didn't do that for any of the other data points. They labelled the "pentads" as: 70/74, 75/79, 80/84, 85/89, 90/94, 94/99, and 00/04.
++++++++++++++++++
Kate1999 wrote:
OK, so that's a good reason why they shouldn't be able to claim that there is an increased risk of cat-5 hurricanes in the SE U.S.
+++++++++++++
AnonPerson:
Neither their statistical analysis nor mine is based on land-reaching hurricanes. No recent hurricanes have been cat-5 when they landed, so they DEFINITELY are not making that claim.
+++++++++++++
Volokh Groupie,
Thanks.
Where in Florida are summer temps 10 degrees higher in the apst four years? I checked data from several weather stations in Orlando, such as here and saw no significant increase in temperatures. What part of Florida are you talking about? You can get data from weather stations in Florida here.
The data I found was located by clicking on Average Maximum under the Monthly Temperature Listings menu on the sidebar.
Climateaudit is simply a closed minded denier site, though. For example, its analysis of the Hansen projections used a single year baseline (like Jim has criticized here), rather than the rolling average that is customarily used. It has a singleminded "anti" purpose, which is valuable but not to be trusted without independent checking.
Maybe her central airconditioning broke 5 years ago, so her house in summer has been 10 deg hotter the past four.
We must agree with her, don't you think, that if more hurricanes hit Florida, then there are more hurricanes everywhere in the world hitting everywhere else?
With some understanding about the underlying distributions and mechanisms producing the events, it's not unreasonable to infer the probability of very rare events from the observed probability of the less rare events.
Again, nice try, but the author of the paper, Judith Curry argues:
So, your golf analogy is pretty clever, but it doesn't apply to hurricanes in the North Atlantic, according to the author of the article I am criticizing.
Face it, they just scewed up.
Thanks for the info on Climate Audit. At the moment, I'm trying not to trust anybody too much on these things.
Jim
Not sure what you mean here. They are not rebutting your statistical analysis of cooling. According to the paper, the criticism is that US landfalling hurricanes have a minima in 1970, therefore, 1970 is a bad start date. They rebutting by saying that the percentage of US landfalling hurricanes is such a small percentage of the total global hurricanes, that it cannot be used to infer the trend for global hurricanes.
In other words, the criticism that they are dismissing as a logical fallacy is not your criticism, but rather a different one. That is why it makes no sense as a rebuttal to your criticism. It is a rebuttal to a different (but perhaps related) one.
So, I'm just trying to say that they did seem to do a reasonable job of rebutting the chosen criticism. Whether or not it was the right criticism to rebut is an entirely different matter. They seem to have mostly ignored your critism.
Thanks a lot. That makes sense.
Jim
Well, no. If they had said, "The number of cat-4 hurricanes in the world has no correlation to the number of cat-5 hurricanes in the world", then it would be clear evidence that they screwed up.
Instead, they are saying that US landfall data is not well correlated to NATL data. This is a lack of spatial correlation, not a lack of correlation across hurricane sizes.
It would more accurately be described as antichaotic, since large changes in initial conditions always result in no net change in later conditions.
Climate has been around for a long, long time. If there were any net trend, we wouldn't be here.
frankcross contrasts thusly:
Except that the Wegman Report - submitted to the U.S. House Energy and Commerce Committee in July, and headed by GMU stats prof and chairman fo the National Academy of Sciences Aplied Stats Section, Edward Wegman - was unable to replicate the realclimate.org icons Mann, Bradley, and Hughes (1998, 1999) Hockey Stick papers, but was able to replicate climateaudit.org's "amatuer" critiques of MBH by McIntyre and McKitrick (2003, 2005). What does THIS say about these respective authorities? Bona fide "climatologists" versus non-climatologists? Mann said of the Wegman Report, it “simply uncritically parrots claims by two Canadians.”
Who is engaged in constuctive criticism and who is dodging the effort to establish legitimacy for thie claims? Given that MBH have resisted and remain to yet release all their data for several years, research which was federally funded that makes them obliged to do so - isn't one conclusion obvious?
The Report reads in part:
"The debate over Dr. Mann’s principal components methodology [employed by MBH] has been going on for nearly three years. When we got involved, there was no evidence that a single issue was resolved or even nearing resolution. Dr. Mann’s RealClimate.org website said that all of the Mr. McIntyre and Dr. McKitrick claims had been ‘discredited’. UCAR had issued a news release saying that all their claims were ‘unfounded’. Mr. McIntyre replied on the ClimateAudit.org website. The climate science community seemed unable to either refute McIntyre’s claims or accept them. The situation was ripe for a third-party review of the types that we and Dr. North’s NRC panel have done."
Furthermore, McIntyre updated the summer's news the situation last month in Canada's National Post by noting that "an earlier report in June by a National Academy of Sciences panel chaired by Gerald North of Texas A&M, which also endorsed specific criticisms of Mann’s methodology and which concluded that no statistical confidence could be placed in his claims that temperatures in the 1990s exceeded those in the medieval warm period."
Since MBH constitutes the only evidence for Anthropogenic Climate Warming (ACW) not dependent upon recent instrumentation or climate modeling, one would think that good science would had taken care of this problem instead of smearing its investigators and obscurring its resolution. But you put $6.5 billion (just current FY) in front of a trailer park of scientists, and you're likely to get not just whores for ACW, but pimps too.
I was responding to your golfing analogy, which implied that if you could not observe something rare (a hole in one), you could still observe changes in something that is not rare, such as hitting the green, and make educated guesses about the likelihood of the thing you hadn't yet observed, a hole in one.
I assumed that you were referring to something that rarely happened, a North Atlantic cat-5 hurricane that later hit land in the SE US, causing major damage. But if you were just referring to the number of cat-5 hurricanes worldwide, we have that data. We have a huge increase in cat-4 hurricanes and a trivial and insignificant increase in cat-5 hurricanes.
Our observations suggest that your speculation about increased risk of a cat-5 hurricanes is not true. Certainly, there is no scientific evidence that would justify the claim made by the Curry group as if it were established in their Science article.
Jim
A few comments:
1) I'd bet that the "94-99" error is just a typo. Things like that are very easy to miss for both the author and the referee(s?). If it's not a typo, there's presumably a good explanation and its likely accounted for in the other plots. Those are both much more likely explanations than such a basic and stupid error in the analysis.
2) Katrina was category 3 at landfall, but it had the storm surge of a category 5 hurricane in some places.
3) The press is stupid, and press releases are written only to draw the press to the work. I also think that the statement that category 5 storms is somewhat justified for a press release - given the increased risk of category 4 storms, its reasonable to speculate that the risk of category 5 storms is also higher, even though the number of category 5 storms itself is too insignificant to used as evidence in either direction.
4) The link between hurricane intensity and global warming is interesting and makes intuitive sense. Although some poor grad student may wind up digging through old records to improve data, there will always be problems with comparing the present day to 50 years ago. I don't see the problem with starting at 1970 in a single paper, particularly if the older data is either less accessible or accurate. Choosing 1970 makes sense to me for a single paper.
The authors also compare the number of US hurricanes between 1945-55 and 1995-2005. I think this comparison suggests that they'd like to do what you suggest (look at earlier periods as rigorously as 1970-2005), but are unable or uncomfortable with doing that for some reason.
Other papers have/will look at the older data. The public may find this frustrating, but that's how science often is done. No paper is perfect or complete. The magnitude of the hurricane/global warming link needs substantial work before its proven, but work such as what you linked to is part of the big picture.
Again, this is crappy binning of the data. You should not just look at the trend in a particular bin, especially a bin as far out along the tail as category five. A better thing to do is to fit each year to a distribution and examine the trend in the fit parameters. Assuming you have a good model for the single year distribution, it is perfectly legit to make predictions about the future of category five storms. (Not that I'm saying that this is what they did -- I haven't read the paper.)
Anyways, I really wish that when people found something they did not understand in a paper, they would phrase their response as a question rather than assuming that an entire field of scientific research is full of idiots. Mr. Ockham probably wouldn't like that hypothesis.
(As for the other comments, do we really have to talk about MBH again? The result isn't not the sole bit of evidence for anthropogenic global warming and it has been independently reproduced. Life goes on.)
I'm not really sure the 1994 thing changes anything. Neither 1993 nor 1994 had anything above a Category 2 storm. Sloppiness, yes. Does it matter? No.
Yes, it's probably a typo, but it's made in 2 papers. I did not argue that the error was driving their results, but it may be.
You are looking at the Atlantic data, but their articles look at Pacific data as well. According to Wikipedia, "1994 Pacific hurricane season": "Of note in this season is an unusual spree of very intense storms."
So, does it matter? If it's not a typo, perhaps Yes.
You also may want to not selectively choose quotes that support your argument, while ignoring the entirety of the report.
Climate has been around for a long, long time. If there were any net trend, we wouldn't be here.
I'm afraid this is profoundly wrong.
Nothing in chaos theory demands that large changes in initial conditions lead to no "net change in later conditions".
What chaos theory describes is usually misinterpreted, but is that nonlinear systems are stable, until they change and find a new equilibrium. Butterflys in China and all are cool, and there is reason to think about that, but unless you're interested and well versed in the topic, there's good reason to try to be, ah, conservative, in your claims about how chaos theory works. One of the key points is that chaotic systems are stable*.
Defining your terms might be interesting. Changes in what, exactly?
Beyond that, you're displaying a nonuseful mishmash of math terms and selected research. You clearly don't understand chaos, or dynamic systems*.
I hate to say this, but this is a product of a hack. I think Jim's better than that.
*That's really dumbing things down.
*For the record, people who study them don't, either. I don't. They're complicated, and not understood. But we do know certain things about how they behave in certain contexts.
All of the quotes you attack were not written by me, but rather by Harry Eager.
On his math, the Wegman Report destroyed Mann. Period.
I congratulate the Volokh blog for finding the inconsistencies in Curry's paper. Here's another: Her four year binned chart shows a noticable trend. An annual chart has a trend that is barely noticable, with a big spike in 2005. An autocorrelation of the time series shows a periodicity of... four years!
frankcross - Dude. There is no "unorthodox" view of gravity. It works always and everywhere according to the established equations (a couple of guys known as Ike Newton and Al Einstein figured it out - without any consensus!) Geesh - you make this GW stuff sound like a religion. "Unorthodox?"
I grew up in Boston, Massachusetts and during the 1950s and early 1960s we had a major hurricane pass through my neighborhood about every three-four years. In the next 25 years two hurricanes got that far north and neither caused much damage.
This is not true. See, e.g., this article.
One superb resource on the public policy of climate change is the University of Colorado’s Center for Science and Technology Policy Research at Boulder, CO. — directed by Roger Pielke, Jr. Pielke recently offered some good advice to environmental activists on this issue of hyping a warming-hurricane connection.
A good example of their work is summarized in my post on Pielke's recent testimony before the House Committee on Government Reform: Climate change: policy analysis, mitigation and management. E.g., here's a summary of Roger's eight "take home points":
1. Human-caused climate change is real and requires attention by policy makers to both mitigation and adaptation – but there is no quick fix; the issue will be with us for decades and longer.
2. Any conceivable emissions reductions policies, even if successful, cannot have a perceptible impact on the climate for many decades.
3. Consequently, costs (whatever they may be) are borne in the near term and benefits related to influencing the climate system are achieved in the distant future.
4. However, many policies that result in a reduction in emissions also provide benefits in the short term unrelated to climate change.
5. Similarly adaptation policies can provide immediate benefits.
6. But climate policy, particularly international climate policy under the Framework Convention on Climate Change, has been structured to keep policy related to long-term climate change distinct from policies related to shorter-term issues of energy policy and adaptation.
7. Following the political organization of international climate change policy, research agendas have emphasized the long-term, meaning that relatively very little attention is paid to developing specific policy options or near-term technologies that might be put into place with both short-term and long-term benefits.
8. The climate debate may have begun to slowly reflect these realities, but the research and development community has not yet focused much attention on developing policy and technological options that might be politically viable, cost effective, and practically feasible.
Run this query for some 64 climate change/science policy posts summarizing Pielke's research at CIRES.
The link goes to an insurance company site and there is an interesting story behind that. The time period from 1970 to 1994 had a historically below average number of hurrricances. During this time the coast of Florida experienced a surge in development and population growth, so an increase in hurricane intensity or frequency is of great interest and concern to insurance companies, at least if they want to remain financially solvent.
I also found a more technical analysis of hurricane frequency
here. This paper, which was published in the Journal of Climate, has a much more narrow focus but it does analyze the aforementioned frequency oscillations in detail, including citiations of data sources and statistical time series analysis of the data.
The strong impression that I got from briefly going through these papers is that Jim Lindgren is absolutely correct in his concern over the Curry et al. paper starting the data analysis with 1970. Given the known history of hurricane frequencies, one would expect the number of hurricanes to rise after that quiescent period, global warming or no global warming. Hope that people find the information in these links helpful.
But also the limitations. In his congressional testimony, he said that he believed the evidence showed that manmade global warming was in fact occurring. I'm sure the climateaudit crowd that praises him generally will abandon his veracity on this point.
Frankcross, you should try reading what climate audit says instead of making things up.
So someone who publishes primarily in law reviews is criticizing the quality of peer review and editing in another field?
If very, very small changes are alleged to be driving climate today, then it is absurd to claim that very, very large changes would not have also in the past. Obviously, they didn't. Unlike Venus or Mars, Earth'[s climate is not in equilibrium. It is dynamically stable.
I am saying that climate is not mathematically chaotic, so your objection is not only pointless but opposite to my point.
Lorenz himself was becomingly modest about whether even weather is chaotic. See his Danz Lectures.
Average Joe: That Atlantic hurricanes were fewer doesn't mean that the number of hurricanes worldwide were fewer.
As a leader of the law reform movement in the early 1990s, I have been one of the chief critics of law review editing (including the lack of peer review), though as I get more exposure to peer review journals, I see a bit more of the advantages of law reviews than I used to see.
I think peer review is generally better, though one error in the BAMS article that I didn't bother to note in my post--the press release that the BAMS article quotes does not match the text quoted from that release in the article--would surely have been caught. I expect that the typo or double counting of 1994 would probably have been flagged as well, though I'm less certain of that.
But mainly, law professors do not usually tell people that anyone who disagrees with their scholarship is like a holocaust denier. The historian Michael Bellesiles tried this when an entire set of records that he claimed to have studied had been destroyed in the 1906 San Francisco earthquake. And he had to resign in disgrace.
You statement
Is just wrong for the reasons I've stated.
For others, the number of hurricanes is a red herring. The question is relative intensity. The claim is that this shows a strong correlation with sea surface temperature.
Sallie Baliunas and Willie Soon are two astronomers who claim that global warming is not manmade, but caused by solar forcing. Baliunas oftens says things like:
Certainly, solar forcing is an interesting topic. So what, exactly, does her research say? Check out Figure 4 here.
Turns out, their own models show that greenhouse forcing is the dominant cause of climate change in the last 50 years. Yet skeptics cling to her public statements, despite that her models don't support her public claims, and despite that they are unable to physically explain the mechanism by which solar activity would produce as much warming as their models suggest (by contrast, the physical mechanism behind greenhouse forcing is very well understood, and physical models explain the amount of warming).
Whenever I've looked into the work of other skeptics, I find the same type of dishonesty.
I'll stick with my post yesterday that I think about 99% of this GW "research" and its "conclusions" are driven by politics and green-religion and only about 1% by legitimate scientific inquiry.
Well, no. First of all, one data point means nothing. Second of all, there have been so few hurricanes this season that, if there aren't many more for the rest of the season, the statistical weight of that data point is very low.
It is not even certain whether there has been ANY increase in greenhouse gases. There has been an increase in carbon dioxide, but for all you know, it has been overmatched by a decrease in the dominant greenhouse gas, water vapor.
I'm not sure exactly what you are saying, because it's not written clearly. But I think you are promoting a Gaia-type theory, that the Earth always manages to adjust and everything always evens out.
Snowball Earth destroys that idea - it did warm eventually, but for a while Earth would've been a terrible place for any complex organism to fluorish. Earth has been in a rather nice state for a while, but that doesn't mean other states aren't possible - they are, and they have happened.
It is not even certain whether there has been ANY increase in greenhouse gases. There has been an increase in carbon dioxide, but for all you know, it has been overmatched by a decrease in the dominant greenhouse gas, water vapor.
That's just stupid. I'm not going to get drawn into a scientific debate in a lawyer-based forum like this one, but if you are going to question the evidence of "the other side", you may want to actually provide some evidence yourself. But feel free to continue to spew idle lay speculation.
Logic is as logic does! If this years hurricane events hold out for the remainder of the season then it will certainly be fair and logical to draw the conclusion that we are entering a period of global cooling. N'est pas?
I should have added a smiley face at the end of that sentence, but I thought "N'est pas" would do it. No, the logic doesn't hold anymore than the logic that a marginal increase in Hurricane intensity is evidence of global warming.
It's always best to be able to demonstrate a direct causal relationship, but you can't always get what you want. Sometimes all you can manage are models and correlations. Can you say that definitely, absolutely global warming is causing more intense hurricanes? Of course not. But you can say that there is evidence for that statement.
Well, according to the article under discussion not much. Since they are using 1970 as the starting point it is hardly enough time to say "I see a long term trend". We were just beginning to be able to measure hurricane strength in the 70's much less to identify them. Satellites &Hurricane hunter airplanes were just coming into use. IMOP we just don't have enough historical data over A LONG ENOUGH PERIOD to even begin to know if there is a long term trend. 36 years is yesterday in climatoligical trends, and yet we have young scientists trying to guage the future of the Earth with insufficent data. A good way to make a living I guess since they can never be "proven" wrong, so they go on collecting their grant money. Global warming? Probably. Global warming = big hurricanes? Give me a break.
- Webster et al (2005) examined a *global* data set, not just the North Atlantic (which has only 11% of global tropical cyclone activity, BTW). A global analysis going back farther is literally not possible since satellites were needed to get accurate counts in a number of the basins.
- The Curry et al comment that Katrina should be seen as a wake-up call is shared by all hurricane scientists. Even those who believe there will never be a detectable global warming signal in hurricanes agree that the state of existing planning for hurricanes along the vulnerable U.S. coastlines is very poor indeed.
--------------------------
A brief deconstruction of your summary points:
1. The new BAMS article shows persuasive evidence of a huge jump in category-4 hurricanes 1970-2004, but declines or flat trends in the numbers of stronger and weaker hurricanes.
Reply: OK.
2. The BAMS article does not deal adequately with whether its choice of a relative cool period (1970) as a starting time influenced the results.
Reply: The BAMS article shouldn't (and couldn't) have recapitulated the entire contents of it references. Webster et al (2005), which you say you read, addresses the issue thoroughly:
"We deliberately limited this study to the satellite era because of the known biases before this period (28), which means that a comprehensive analysis of longer-period oscillations and trends has not been attempted. There is evidence of a minimum of intense cyclones occurring in the 1970s (11), which could indicate that our observed trend toward more intense cyclones is a reflection of a long-period oscillation. However, the sustained increase over a period of 30 years in the proportion of category 4 and 5 hurricanes indicates that the related oscillation would have to be on a period substantially longer than that observed in previous studies."
3. In both their 2005 Science article and their 2006 BAMS article, the authors appear to double count data from 1994, but it may just be the result of repeated typographical errors in both journals.
Reply: You could have easily confirmed that it was a typo by comparing the graph with the table immediately following it in Webster et al (2005). The total number of 1990-2004 cat 4-5s in the table matches the number shown in the graph for the three five-year periods from 1990-2004.
4. In the BAMS article, the authors criticize others for irresponsible public statements on global warming and praise their own caution, yet the press release they quote asserts an "increased risk" of category-5 hurricanes threatening the southeastern U.S., but neither their own two articles, nor the data they claim to have used, show any such statistically significant trend.
Reply: This amounts to an argument that land use and disaster planners in hurricane-vulnerable areas should plan only for an increase at cat 4s since an increase in cat 5s was not found over the limited period of the study. That would be extremely bad advice. There is no scientific basis for thinking that an increasing storm strength trend would limit itself permanently to cat 4s, and as noted below a good basis for thinking otherwise. As well, bear in mind that extensive areas of the U.S. were vulnerable to cat 4s/5s before this increasing trend was discovered.
Here is the quoted passage in its full context (from a AAAS interview with Peter Webster):
"Q. Given that increased intensity, what are the possible ramifications for policy-makers, generally? Would your research have any bearing, at least potentially, on decisions regarding the rebuilding of New Orleans and Gulf Coast?
"A. The key inference from our study of relevance here is that storms like Katrina should not be regarded as a "once-in-a-lifetime" event in the coming decades, but may become more frequent. This suggests that risk assessment is needed for all coastal cities in the southern and southeastern U.S. for category 5 storms, and for the more northern cities (e.g. New York City) probably for category 3 storms (note the categorical risk for coastal cities at higher latitudes needs to be assessed using typhoon data from the Pacific). The southeastern U.S. needs to begin planning to manage the risk of category 5 hurricanes. There is an additional issue of communicating this increased risk to the public. Past strategies for "weathering the storm" will not work in the face of increased hurricane intensity."
So Webster was not implying that Katrina was a cat 5, but rather was using it as an example of the type of disaster that could occur elsewhere. Note also that the vulnerability of New Orleans to strong hurricanes is not that unusual for a populated area. New York City, Chesapeake Bay and Houston are very vulnerable to similar events where the bulk of the damage results from storm surge. As well, Andrew and the somewhat weaker Rita showed that more ordinary stretches of shoreline can host major disasters.
"Q. More generally, what sort of hurricane activity should the Gulf Coast and the East Coast of the United States expect in the years ahead?
"A. Besides the overall global trend of increasing hurricane intensity, the key issue of concern raised by our study is that the hurricane intensities in the North Atlantic for the last decade have been lower than elsewhere on the globe. It is likely that the differences among the different ocean basins is associated with natural variability. This implies that at some point within the next decade, there is the risk that the intensity of North Atlantic hurricanes could increase rapidly to the global average (with possibly a concurrent decrease in another ocean basin). The variation of Atlantic hurricanes relative to hurricanes in other basins in the context of known cycles of natural variability needs further investigation."
5. If the quality of peer review and editing in this field is only as careful as it seems to be on the BAMS paper, then I think it prudent for educated lay people to continue to be skeptical about the research and public assertions of climate experts, especially those who tell you to just trust them or who insist that they are just relying on what their data show. Wouldn't expert reviewers of the BAMS paper already know that there had been no increase in category-5 hurricanes in the North Atlantic, and thus that the public statements that the authors proudly trumpet were irresponsible? Certainly, this brief foray into the literature leads me to be less confident of the conclusions of climate researchers, no matter how fervently they are asserted.
Reply: I think this is where you started.
And because the standards of construction were far too low for a coastal community. As a coastal Florida resident who experienced Charlie (Cat 4) and other storms, I learned the importance of construction standards. Homes situated side-by-side, exposed to the same wind and blown debris, suffered either a total loss or mere superficial damage solely due to construction standards. Low-cost details like ring shank nails instead of staples, heavier shingles with six nails per tab, and low cost window coverings make all the difference in the world.
The period of 1970-1990 lulled everyone into forgetting that these storms will occur. The local experience during Charlie demonstrated that the post Andrew state-wide construction standards work during hurricanes, even major ones.
However, to determine trends of vulnerability in this region ALL that matters is studying trends for hurricanes that made landfall in that region.
Of course not. People use proxies with better statistics all the time.
What would those be?
Let me say what I understand you to be saying here. You are saying that the vulnerability of the US East Coast to hurricanes is validly studied by examining the "cyclone" history of China/Phillipines/Japan/Guametc., The Mexican Riviera, the open water Pacific, and Northern Australia?
Much earlier you said:
The Official US Hurricane Season starts June 1 and ends November 30.
If you can establish that they're valid proxies, sure. I don't know what's been established in this field -- I'm just commenting that these sweeping prounouncements people have been making aboust statistics are just wrong.
The Official US Hurricane Season starts June 1 and ends November 30.
Yes, and I can think of at least one storm that lasted into January (last year, in fact).
It seems to me the unofficial Atlantic "season" starts when it starts so far as hurricanes are concerned, as early as April, and ends when it ends. The only relevance of June to that is the official season, ending in November, which presumably encompasses when most hurricanes take place. Whatever the "season" is, is irrelevant to the calendar year for accounting purposes, which seemed to me to be the contrary of what you were saying.
Do you wish to revise and extend your remarks to clarify what you meant?
Thanks for coming over here from Real Climate and reposting your response to me here as well as there. My reply here reflects your text as you posted it at Real Climate.
For VC readers who may not have seen it, in response to Bloom's post and mine at Real Climate, Graham Dungworth wrote:
Thanks, Graham, for your extravagant praise.
Steve Bloom had a different view. He wrote what he calls “A brief deconstruction” of my summary points.
First, it appears that Steve and I agree on what I view as the main accomplishment of the BAMS paper:
Next, Steve takes issue with my argument about the possible implications of the 1970 starting date.
My second point :
My Reply: I had read the passage that Steve quotes before I posted, and it seems to confirm my point, since it tends to emphasize what the authors wrote in the BAMS article about a cooling period ending in 1970. I did not accuse the authors of the BAMS paper of bias; I did not say that they should have chosen a different period. I said that “the paper dismisses concerns that the choice of 1970 as a starting point may give a misleading account because of the evidence that there was global cooling from 1940 to 1970,” and that they do “not deal adequately [with] whether [their] choice of a relative cool period (1970) as a starting time influenced the results.”
The authors admit that 1970 is near a minimum. They argue that the world cooled from 1940 to 1970. So it would seem that Steve has pointed to the precise language to support my prior concern over start or cut-off dates that might be “unrepresentative of larger trends or that give misleading measurements of the strength of any overall trend.”
I don’t know how extensive Steve’s statistical training is, but if it is extensive, then he must recognize the potential problems I raised: using 1970 as a start date may give a misleading picture of the larger trend or it may give a misleading measure of the strength of that trend. These are hardly contentious observations (and do not involve a suggestion that the authors made a mistake in starting at 1970 because of the poor quality of data before 1970). In any event, thanks, Steve, for quoting language from the Science article that so clearly supports my point.
My third point:
My Reply: Steve, are you serious in this argument? The authors’ repeated claims that they included 1994 in two different periods (1990-94 and 1994-99) are clearly errors, and there is no way to tell whether they are just typos or something more serious from just looking at the two papers.
First, the graph immediately preceding the table does not have any data labels, so one can’t compare and confirm whether the authors double counted 1994 or instead made 4 typos in two different papers (as you are certain they did). All one can do is eyeball the data in the chart, which is not at all clear whether it matches the data table. Indeed, from my eyeballing of the data, I would have estimated more than 270 cat-4 and cat-5 hurricanes 1990-2004 in the chart you point to, not fewer than 270, as the data table you point to shows.
Second, even if the chart were drawn in such a way that one could tell whether it exactly matched the data table (which it most definitely isn’t), one still couldn’t know whether they double counted 1994 or instead made 4 typos. If the authors mistakenly counted 1994 hurricanes in two of the three groups of years comprising the 1990-2004 period--and summed their three groups to get the total for 1990-2004--then the chart and the table would match exactly and the data would still be wrong because they double counted 1994. You may have some other basis for knowing that the errors are just typos, but the basis that you give would not persuade any sophisticated, fair-minded reader.
My fourth point:
My Reply:
Steve, you write: “Here is the quoted passage in its full context.”
This is false.
You claim to show the passage that I quoted “in its full context,” but you don’t include the sentence that I quoted (and criticized), which was taken directly from the 2006 BAMS paper. I quoted ALL of the indented quotation that appeared in the BAMS paper. Here is the exact wording of the BAMS paper that I quoted. (The ellipsis is in the BAMS paper itself; I added the bracketed phrase):
I took issue with the last sentence, pointing out that there was no evidence in either the 2005 Science paper or the 2006 BAMS paper of an “increased risk of category-5 hurricanes.” Steve, you claim to present this quoted excerpt in its full context, but you do not include the sentence that I challenged.
You also claim that my comment “amounts to an argument that land use and disaster planners in hurricane-vulnerable areas should plan only for an increase at cat 4s since an increase in cat 5s was not found over the limited period of the study.”
I said nothing of the kind.
My goodness, New Orleans was so badly protected that it couldn’t withstand a category-1 hurricane, which is what Katrina was when it hit New Orleans. It may have been fortunate that Katrina had been a cat-5 hurricane at some point, because the New Orleans levees may not have been able to withstand the next cat-2 hurricane, which might not have been scary enough to lead to as extensive an evacuation as happened with Katrina. I wasn’t at all objecting to the advice, which seems eminently sound; I was objecting to the idea that the authors’ data showed a significantly “increased risk of category-5 hurricanes.” It doesn’t. Remember that in the 2006 BAMS article, the authors claimed that they were only making arguments that were supported by good scientific data. But in the one indented passage that they quoted they made an argument that was not supported by their data, which presumably is the best available.
This brings us to your next argument: “There is no scientific basis for thinking that an increasing storm strength trend would limit itself permanently to cat 4s, and as noted below a good basis for thinking otherwise.”
Steve, your speculation is an entirely plausible one (and it occurred to me before I posted)--but it’s just that, speculation.
So far the data reported by the authors of the BAMS and Science studies do not show significant support for your view. If a tripling in cat-4 hurricanes does not lead to any significant increase in cat-5 storms, it’s hard to imagine what kind of a dramatic increase in cat-4 hurricanes could lead to a significant effect on cat-5 storms. Your belief is a matter of faith, not evidence.
Steve’s Reply continues, quoting a 2005 interview of Webster:
My Reply:
Steve, since Webster’s data shows no statistically significant worldwide increase in cat-5 storms, to the extent that this claim is supported by evidence Webster is arguing that a worldwide increase in cat-4 hurricanes may lead to an increase in cat-4 storms in the North Atlantic. They have no data showing a significant increase in cat-5 storms either worldwide or in the North Atlantic, so this statement that you quote does not bear on my claims at all. It deals with the distribution of cat-4 storms to different basins, not to the risk that cat-4 storms will turn into cat-5 hurricanes. really, you have to be more careful in your argumentation.
Conclusion:
Steve, it would be hard to imagine a less successful “deconstruction” of my comments than yours.
As I said at the beginning, the BAMS article shows very good evidence of a big rise in cat-4 hurricanes in the 1970-2004 period.
Why do you also have to pretend that the limitations and clear errors I point to are not limitations and errors? This is academics. No one is perfect. Everyone makes mistakes; we can all learn from each other if we have an open mind for both the merits and demerits of new research.
James Lindgren
Northwestern University
guest wrote: "You also may want to not selectively choose quotes that support your argument, while ignoring the entirety of the report."
Wegman states that that M&M's critique is replicable and valid and that MBH is neither: “While the work of Michael Mann and colleagues presents what appears to be compelling evidence of global temperature change, the criticisms of McIntyre and McKitrick, as well as those of other authors mentioned are indeed valid.” “Overall, our committee believes that Mann’s assessments that the decade of the 1990s was the hottest decade of the millennium and that 1998 was the hottest year of the millennium cannot be supported by his analysis.” Now exactly what did I get wrong?
As for his actual testimony under questioning before Congress, frankcross is correct: Wegman believes ACW is occurring. He is entitled to his opinion, of course - that's not what a statistician's expertise is in, but it is one of my graduate fields at the University of London where my instructors think solar variability may account for as much as half of all recently observed warming. If true, why is it our urgent responsibility to reduce CO2?
During this summer's Congressional Committee testimony, Tom Karl of NCAR endorsed the reliability of GCMs, which purport to demonstrate a challenging degree of planetary warming is imminent (albeit with wide variance between models, and without any ability to resolve albedo fundamentals like cloud distribution), while John Christy noted that the detailed temperature records in California spanning 150 years show no statistically significant warming in the lower state with the greatest longitudinal range. But who is getting most of the federal research funding? Not people at Imperial College London - not data-driven climatologists like Christy. Nor is the famous hurricane prediction expert William Gray at Colorado State University.
Gray specifically blames the politically generated Gold Rush into ACW research during the 1990s for curtailing his obviously more life saving research into understanding the variables of hurricane prediction. Now even he has joined the ACW-skeptics crowd, a field especially populated with senior scientists instead of young bucks striving to "make a name" for themselves, like Michael Mann, leader of the Hockey Team.
Why do I mention all this sociology and division within the scientific ranks? Because mega-billions (yes-we're over $50 billion in the US down this scandalous rat-hole since 1990), are obviously driving the research output in politicized directions - not the science directing the research. This may not bother you, but it does Roger Pielke, Jr, at the University of Colorado at Boulder, an atmospheric scientist and policy researcher who is not unsympathetic to ACW. (Just Google prometheus and Pielke to find his blog.)
Indeed, when the IPCC lied about a leading hurricane experts work, Chris Landsea at NOAA, in an effort to pimp the hurricane data for ACW-"Truth," he quit last year. When Roger Revelle, who Al Gore claims as his scientific mentor, was shown to have harbored doubts about the significance of ACW, Gore sued to silence the publicity. When New Scientist magazine dropped Steven McIntyre as a source in a story about the Hockey Stick debate, all it took was Mann (et al) to convey the lie from Environmental Defense that McIntyre was paid by corporate oil money. It’s a rigged and dirty game if you challenge Big Science, funded by government’s Black Boot. As Pielke, Jr., blankly observed in April 2005, “If scientific debate equals political debate, then we will find that science has simply become another political battleground, and we will lose much of the positive contributions of science in policy.”
Also last year, when the head of the IPCC was reported in Mother Jones to have said: “…we have about a ten-year window to make very, very deep cuts in our carbon fuel use, if, quote, ‘humanity is to survive,’” Pielke, Jr., replied: “I am less troubled by the fact that Dr. [Rajendra] Pauchuri made these remarks…than I am about the overall silence about the way that IPCC science has become transformed into issue advocacy among the rank and file in the broader community of IPCC scientists.” Our scientific institutions are thus rendered unreliable prostitutes grubbing for political agendas.
Which brings us back to Lindgren's hurricane paper above. Three points follow.
First, as Gray argues, a long running multi-decadal cycle of increased hurricane activity followed by decline is apparent from the historical record; its causes are unknown causes, but it predates human impact. Given this, how much weight ought we give to any "mostly persuasive" scientific paper? Some? A lot? Or uncertain? Given the propensity for Big Science to generate fads, this publishing cycle beginning with last year's work by MIT's Kerry Emanuel in Nature (implying that the Curry, et al paper is a follow-on), I'd say not much.
Second, there is an "angels dancing on the head of pin" quality to any ACW debate that turns on arcana like distinguishing Cat-4 from Cat-5 hurricanes in a data set of varying quality. Why? Because the history of modern instrumentation in data gathering of extreme weather events always shows an up-tick in numbers whenever observational networks improve. Take the best documented example, tornados and radar. Each expansion of instrumentation and every technological leap forward in electronic imaging resulted in a magnitude increase in reported numbers of US tornados. Small and brief ones – the smallest ever measured was a scant seven feet! - formerly remote or too transient, are now detected and compiled into the historic record. But arbitrarily truncating this data for analytical convenience amounts to scientific malpractice.
Similarly with hurricane records, only with reverse observational consequences. In 1975, only daylight hurricane imagery was available from two satellites parked in geostationary orbit. By contrast, the technology of the 1990s permits round the clock observational data from eight satellites. Today we know that hurricane intensity can vacillate from one Cat to the next and back again in a single day - and that such changes are not uncommon - something unknown in the 1970s, and not yet well-documented until the 1990s. Therefore, given the coincidence of improved data gathering with cyclical change, that some category over a recent three decades span might yield an apparent increase sould not be surprising. In fact, the surprise would be if there were none.
More importantly for grasping global significance, even if hurricane activity in the North Atlantic is up over the past two decades, what are we to make of ACW in light of the fact that it is down in the Pacific basin (as Philip Klotzbach documented in Geophysical Research Letters this spring)?
Finally, consider the sheer arbitrariness of the Saffir-Simpson categories based on maximum sustained winds. Last year’s Katrina came ashore as a Cat-3 event, delivering winds to New Orleans that were barely Cat-2, yet with cloud cover and atmospheric pressure (and consequent storm surge) more typical of a Cat-5 hurricane. Thus, the reduction of multidimensional storms to a single number reveals our considerable ignorance about the complex natural phenomenon from which we are supposed to derive a small ACW signal. Honestly, aren’t we simply expecting too much significance from too little data? In short, underlying complexities may be obscured by conventions imposed upon continuously variable phenomena.
By contrast, the significance of the Wegman Report for the ACW debate is simple: we are pushed back to a data-driven versus model-idolatry controversy - where the next salient question is: "are these 'idols' worthy of our golden calf-like worship, or not?" - which was the "state of the art" in climatology before 1998 when MBH first appeared.