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May 01, 2006

Klotzbach on Trends in Global Tropical Cyclone Intensity 1986-2005

Posted to Author: Pielke Jr., R. | Climate Change | Disasters

Here (in PDF) is a very interesting paper by Phil Klotzbach, a student of Bill Gray’s at Colorado State University, accepted for publication by Geophysical Research Letters, and apparently in press for later this month (according to this page). The paper challenges the findings of recent high-profile studies on trends in hurricane intensities.

In the paper Klotzbach replicates the methodology of Webster et al. (2005) (PDF) and a very similar approach to Emanuel (2005) (PDF) to explore trends in tropical cyclone intensity over the period 1986-2005, which is a subset of the period used by Webster et al. and Emanuel, and apparently the period during which there is the most agreement on the quality of the observational data. What he finds is pretty interesting. Here are a few of Klotzbach’s talking points (PDF) that he prepared to accompany the paper:

3) If the increases in TC activity found by Emanuel [2005] over the past 30 years (based on data from 1975-2004) and Webster et al. [2005] over the past 35 years (based on data from 1970-2004) are robust, one would expect to see similar trends over the shorter time span evaluated in this paper (1986-2005), especially since SST increases have accelerated in the past twenty years.

7) With regards to ACE [Ed.- A measure of intensity, similar to Emanuel’s PDI], there has been a large increase in ACE in the North Atlantic basin since 1986. There has been a large decrease in ACE in the Northeast Pacific basin since 1986. All other basins show small upward or downward trends. Globally, there has been a slight increasing trend from 1986-2005; however, if only the past sixteen years are evaluated (1990-2005), there has actually been a slight decreasing trend.

8) With regards to the number of Category 4-5 hurricanes, there has been a large increase in North Atlantic storms but also a large decrease in Northeast Pacific storms. When these two regions are summed together, there has been virtually no increase in Category 4-5 hurricanes (i.e., 47 Cat. 4-5 hurricanes from 1986-1995 and 48 Cat. 4-5 hurricanes from 1996-2005). For the globe, there has been an approximate 10% increase in Category 4-5 storms from 1986-1995 to 1996-2005; however, most of this increase occurred from the late 1980s to the early part of the 1990s in the Southern Hemisphere where some data quality issues may have still been present. There has been very little change in the number of Category 4- 5 hurricanes since 1990, which is an agreement with Figure 4, panel A from Webster et al. [2005].

10) These findings indicate that there has been very little trend in global tropical cyclone activity over the past twenty years, and therefore, that a large portion of the dramatic increasing trend found by Webster et al. [2005] and Emanuel [2005] is likely due to the diminished quality of the datasets before the middle 1980s. One would expect that if the results of Webster et al. and Emanuel were accurate reflections of what is going on in the climate system, than a similar trend would be found over the past twenty years, especially since SSTs have warmed considerably (about 0.2°C – 0.4°C) during this time period.

Interestingly, from Table 2 of Klotzbach’s paper, he shows that the number of category 4-5 storms increased from 164 in 1986-1995 to 180 during 1996-2005. Between the same two periods the number of Category 4-5 storms in the Atlantic basin increased from 10 to 25 storms, meaning that setting the Atlantic aside, the rest of the globe saw and increase from 154 in 1986-1995 to 155 during 1996-2005, or no trend at all. However, a close look at the basins around the world shows lots of variability. Consequently, this paper is quite useful to my research because it means that in regions outside the Atlantic basin that damage trends related to storm intensity since 1986 must be due to factors other than changes in storm intensity.

More generally how this peer-reviewed paper, which challenges much of the received wisdom on hurricanes of late, is handled by the scientific community, the blogoshpere, and the media will say a lot about the current state of the debate over climate change.

Posted on May 1, 2006 02:22 PM


It is worth adding here that the period 1991-1994 in the Atlantic was the least active such period on record:

Landsea, C.W., N. Nicholls, W.M. Gray, and L.A. Avila, 1996: Downward trends in the frequency of intense Atlantic hurricanes during the past five decades. Geo. Res. Letters, 23, 1697-1700.

Posted by: Roger Pielke, Jr. at May 1, 2006 03:37 PM


This paper is apt to receive less coverage than the Emanuel and Webster papers for one very simple reason: it is not appearing in Science or Nature, which have far more well-oiled publicity machines, complete with embargoed access to articles for journalists who agree to abide by the restrictions.


Posted by: Eric Berger at May 1, 2006 10:44 PM

I think an interesting case for discussion of the politicization of science by scientists would be Gray's paper (
issued in advance of the 2006 27th Conference on Hurricanes and Tropical Meteorology.

Note the quotes from Sen. Inhofe (R,OK, from my home state!) about global warming being a hoax and the association of Petroleum Geologists quote about Chrichton's State of Fear.

There's an interesting thread on realclimate about this (from which I lifted the above), although its mainly focused on Gray's science claims.

I'm surprised since you are so quick to post on cases of scientists politicizing science that you haven't jumped all over this one yet.

DISCLAIMER: This post is not intended in ANY WAY to invalidate Gray's or Klotzbach's science. I intend this as a suggestion for a wholly different post/thread for discussion

Posted by: Sean D at May 2, 2006 12:11 PM

"...[the Gray paper] is not appearing in Science or Nature, which have far more well-oiled publicity machines, complete with embargoed access to articles for journalists who agree to abide by the restrictions."

Yeah, too bad he didn't submit it to FF, CO2Sci, make a Regenery or some other wingnut welfare media outlet pitch. It'd sure get more play there, youbetcha.


Sean D: good point. I like your stuff more and more.





Posted by: Dano at May 2, 2006 12:45 PM

Sean D.-

Thanks. We discussed Gray's perspectives here:

Posted by: Roger Pielke Jr. at May 2, 2006 02:23 PM

For the record, I tried to convince Dr. Gray to remove both the quotes from Inhofe and the Petroleum Geologists before submitting his AMS pre-print. I wholeheartedly agree that politics and science should be kept as separate as possible.

Posted by: Phil Klotzbach at May 2, 2006 02:41 PM

If we followed Phil Koltzbach's advice this blog and the institute it is associated with would close.

Posted by: Rabett at May 2, 2006 08:44 PM


That Gray post doesn't cut it.
If Judith Curry had submitted a paper to the AMS conference with an Al Gore quote about hurricanes and GW in it, you would have (rightly so) prominently displayed it on this blog and torn it apart. My point is, by not featuring this blatant politicizing of science by a prominent scientist in the field, you give people like me the impression that you are only concenerned with bringing to light the politicization of science by certain scientists and not others. I personally don't want to believe that this it your intention, but nevertheless it does give one the impression...

Posted by: Sean D at May 3, 2006 11:43 AM

Hi Sean-

I appreciate your perspective, but to be frank, you have no idea what I'd do with a non-peer reviewed Curry pre-print. My guess is nothing. In fact, just yesterday Curry had an interesting quote in a news story that I did not (and won't) discuss. A reader once emailed asking me to comment on Gray's interview and I did. You may have said someting different, and that is fine.

With this blog I try to focus on significant areas of science policy that may not be discussed anywhere else, but also, on issues that are important to me. A non-peer reviewed AMS pre-print full of scientific gobbldygook with nothing new in it from a science policy perspective doesn't cut it for me -- especially when it has already been discussed to death at RealClimate by the time it was mentioned as a topic here.

Do we focus on some people (scientists) more than others here? Certainly. Jim Hansen gets more than his fair share of airtime, as have Rajendra Pachauri, Leon Kass, Kerry Emanuel, Chris Landsea, Dan Sarewitz, and Kevin Trenberth. Kerry, Dan, and Chris because they are collaborators.

Of course, in trying to focus on "significant" issues I don't always (or often, depending on your views!;-) succeed, my focus is of course parochial to my own areas of interest/expertise/what I am reading at the moment, my definition of "significant" may not be your or anyone elses, and it is certainly colored by my values and politics -- but welcome to the blogosphere.

Eventually we hope to make Prometheus more of a group effort with different voices regularly represented. But until then, it seems that you are (mostly) stuck with my idiosyncracies. So I welcome suggestions for topics, but I'll pick and choose.

So -- yes, Gray was coloring his paper with a dark political hue. Had he asked me I would have suggested not doing so. He wouldn't have listened, I am sure;-)

Posted by: Roger Pielke, Jr. at May 3, 2006 12:12 PM

"It is worth adding here that the period 1991-1994 in the Atlantic was the least active such period on record:"

Wasn't this an anomalous climate period because of the global effects of the Mt. Pinatubo eruption?

Posted by: Ron Taylor at May 4, 2006 07:02 AM

At the National Hurricane Conference last month, I was fortunate enought to have a brief discussion with Dr. Neil Frank, ex-Director of the National Hurricane Center. We spoke mostly about Curry's presentation and the faulty assumptions she made about hurricane data sets; specifically, treating historical records as if they were as accurate as modern day records and then claiming to have found trends.

We briefly touched on Bill Gray and his use of satire in making a presentation.

Dr. Frank claimed that Bill Gray has been like that since he first met him almost 50 years ago, meaning he is a guy that always tells you what he thinks, regardless of the political fallout that could result. Many of us have found Gray's honesty refreshing and his annual presentations at the Hurricane Conference are always considered one of the highlights.

Unfortunatly, his politically incorrect presentations have given his opponents the green light to dismiss him outright, as we have seen above.

It is good to see that Phil Klotzbach is more sensative to how the game is played, if only to force those who disagree with him to deal directly with the science. I have little doubt that if Gray was the lead author on the Klotzback paper, and it said the exact same thing, it would be treated much differently.

As it is, it is awfully difficult to disagree with the science Phil presents, which makes Emmanuel's argument considerably weaker in my view.

Posted by: Jim Clarke at May 4, 2006 11:52 AM

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