April 18, 2007
Chris Landsea on New Hurricane Science
Posted to Author: Others | Climate Change | Disasters
Chris Landsea has submitted a guest post today on a recent paper on hurricanes and global warming. We share Chris' comments below, and welcome reactions and alternative perspectives.
Guest post by Chris Landsea, NOAA
Today a new paper by Gabe Vecchi and Brian Soden has been published:
Vecchi G. A., B. J. Soden (2007), Increased tropical Atlantic wind shear in model projections of global warming, Geophys. Res. Lett., 34, L08702, doi:10.1029/2006GL028905. (PDF)
My reading of the paper by Vecchi and Soden is that this is a very important contribution to the understanding of how global warming is affecting hurricane activity. The study thoroughly examines how the wind shear and other parameters that can alter the number and intensity of hurricanes because of manmade global warming. What they found - surprisingly - is that in the Atlantic that the wind shear should increase significantly over a large portion of where hurricanes occur - making it more difficult for hurricanes to form and grow. This was identified in all of the 18 global climate models they examined. (Perhaps it's not that surprising given that Knutson/Tuleya 2004 showed some of the same signal for the more reliable models back then. Now the signal is in ALL of the CGCMs.) Even the MPI changes in the Atlantic appear mixed, due to the smaller SST increases there (with more uniform upper trop temp changes) compared with the rest of the global tropics/subtropics.
One implication to me is that this further provides evidence that the busy period we've seen in the Atlantic hurricanes since 1995 is due to natural cycles, rather than manmade causes. We've seen a big reduction in wind shear in the last thirteen hurricane seasons, which is OPPOSITE to the signal that Vecchi and Soden have linked to manmade global warming changes. Another implication is that this paper reconfirms earlier work that suggests that global warming will cause very small changes to Atlantic hurricanes, even several decades from now.Posted on April 18, 2007 08:16 AM
I noticed in the most recent BAMS a report on a conference on hurricanes and climate change: http://ams.allenpress.com/archive/1520-0477/88/3/pdf/i1520-0477-88-3-389.pdf
I'd be interested to know what you felt came out of the conference, and whether you think there needs to be more cross-disciplinary work between meteorologists and climatologists to further our understanding of the processes involved and improve model outputs?
I'd also be interested to know if there are any recent findings on Pacific TC activity, as there does not seem to be too much about at the moment.
Posted by: fergus brown at April 18, 2007 09:45 AM
Yesterday, in a lecture at the Norwegian Academy of Sciences, Judith Curry said that hurricanes are becoming more frequent due to global warming. She said that the number of hurricanes has doubled since 1970 and is the highest ever since 1850. According to the newspaper article she did not express any hesitation with regard to the certainty of the link between more, stronger hurricanes and global warming.
Posted by: Anders Valland at April 18, 2007 10:29 AM
Fergus- Thanks for your comments, I'll ask Chris to weigh in as well. That was a very good meeting, in my view it was particularly notable for its discussion of catastrophe models (a subjected I've discussed frequently here).
As far as where the state of the science is, my sense is that the WMO consensus report remains current, and that our 2005 and 2006 BAMS articles stand up exceedingly well.
Posted by: Roger Pielke, Jr. at April 18, 2007 11:36 AM
As far as I am concerned, Chris's comments re: Vecchi and Soden are right on the mark. We have detailed similar thoughts in depth a bit more at our usual spot:
Apparently, the boys over at RC aren't so inclined:
Comment #29 (at http://www.realclimate.org/index.php/archives/2007/04/ocean-cooling-not/ ): Gavin, I know this is only tangential to this thread but do you have any comment on the new paper by Vecchi and Soden in GRL, which Chris Landsea is promoting as evidence both that the recent increase in Atlantic hurricane activity is due to the AMO, and that global warming should reduce activity (because it increases windshear)?
[Response: I have no knowledge of (or frankly, interest in) what Chris Landsea may be is saying about the paper, but I don't see this paper as changing the picture significantly. Two points are relevant here, (1) our modeling of future changes in TC remains an uncertain area of the science. Nonetheless, predictions of increased potential intensity due to rising SST which rest on fairly fundamental thermodynamic arguments, remain robust, and I would refer you back to our discussion of this previously. Climate model predictions of changes in ENSO and the Walker circulation, upon which the conclusions of this paper with regard to possible changes in wind sheer rest, remain far from robust for reasons we discussed here previously. In short, the Emanuel (2005) study continues to stand on its merit, and I don't see where this paper puts even a dent in it. We may have more to say about this paper in the near future. -mike]
I, for one, can't wait to hear what more thay may have to say about it!
Posted by: Chip Knappenberger at April 19, 2007 12:28 PM
Thanks Chip- I actually agree with Mike Mann that one paper does little to change the consensus view. That being said I am surprised at his trumpeting of Emanuel (2005) in the face of a broader consensus (in WMO and IPCC). In fact on that thread he completely misrepresents Emanuel (2005), I assume because he must believe his readers are rubes. Here is a comment I just left (we'll see if it appears;-):
You are simply incorrect when you assert: "Emanuel (2005) shows that the warming SSTs are behind the increased TC intensity in the Atlantic. No impartial reading of that paper could come to any other conclusion."
Here is what Emanuel actually says:
"Tropical cyclones do not respond directly to SST, however, and the appropriate measure of their thermodynamic environment is the potential intensity, which depends not only on surface temperature but on the whole temperature profile of the troposphere. . . The above discussion suggests that only part of the observed increase in tropical cyclone power dissipation is directly due to increased SSTs; the rest can only be explained by changes in other factors known to influence hurricane intensity, such as vertical wind shear."
Misrepresenting Emanuel is bad enough, but for a site that often underscores the importance of consensus, your favoring of one single study (on a thread about not favoring one single study) when consensus perspectives exist (WMO, IPCC) does a disservice to your readers.
Posted by: Roger Pielke, Jr. at April 19, 2007 06:09 PM
I would like to see discussion on hurricanes world-wide not just the Atlantic.
Posted by: pat neuman at April 20, 2007 03:04 PM
Do you see any inconsistency in widely promoting Lyman et al (recent cooling of world's oceans, now retracted to to problems with the Argus float data) as evidence that the climate models are unreliable...
And then turning around and promoting a study that relies entirely on modeling?
Posted by: Ike Solem at April 24, 2007 06:43 PM
RealClimate has an alternative take on this paper: www.realclimate.org
Posted by: Roger Pielke, Jr. at April 24, 2007 07:42 PM
Ike- Thanks for your comments. You may want to recheck authorship of this guest commentary and also whether in fact I've said anything about the merits of that ocean cooling paper;-) Thanks!
Posted by: Roger Pielke, Jr. at April 24, 2007 07:59 PM
A few replies to comments here. As to Fergus Brown's question about the conference at Lamont-Doherty, that was a very good meeting where some ground-breaking new work was presented. The hurricane-climate field, however, is evolving so quickly that there have been even more research that has been undertaken (like the Vecchi and Soden paper) as a result of the controversy in the field.
As to Curry reported comments in Norway as provided by Anders Vallant, Curry's suggesting that we've had more hurricanes recently than at any point back to 1850 makes me scratch my head as to why someone would think that we can homogeneously compare hurricane activity now versus 150 (or even 100) years ago. We've got some amazing detection tools available now (aircraft, geostationary satellite, polar orbiting satellites like AMSU and QuikSCAT, buoys, radars, and a lot more shipping traffic) that we simply didn't have back then. If indeed she said this (though i do not know if it is true), then Curry's being incredibly naive about what the hurricane record can tell us.
As for Ike Solem's comments about me promoting the Lyman et al. study: i've not read nor commented on the paper in question.
Finally, with regards to Michael Mann's quoted comments: I would agree with him that modeling of the future is very uncertain and that it is quite possible that all 18 of these coupled climate models have it wrong. However, if one wants to make attribution now of what the cause of the increased hurricane activity we've seen in the Atlantic since 1995, the Vecchi and Soden study is pretty clear: it can't be global warming because both the dynamics AND thermodynamics don't support it, if these models are to be believed.
Posted by: Chris Landsea at April 28, 2007 03:54 PM