June 16, 2005
Consensus on Hurricanes and Global Warming
Posted to Author: Pielke Jr., R. | Climate Change
"[T]here is no sound theoretical basis for drawing any conclusions about how anthropogenic change affects hurricane numbers or tracks, and thus how many hit land." K. Trenberth, Science, 17 June 2005
Last winter, Chris Landsea caused a flap when he resigned from the IPCC claiming that Kevin Trenberth, the lead author of the IPCC chapter that he was contributing to, had made unfounded statements about hurricanes and global warming in a press conference organized by Harvard to allege a connection between the U.S. hurricane damages of 2004 and human-caused climate change. (Disclaimer: As most regular readers know, Landsea is a long-time collaborator of mine.) In this week's Science, Trenberth has an essay on hurricanes and climate change that should put this issue to rest. Trenberth's essay clearly vindicates Landsea's actions, and, in my opinion, it would not be inappropriate for IPCC officials who failed to support Landsea (Rajedra Pachauri and Susan Solomon) to issue him a public apology. But don't hold your breath.
Let's take a quick look at Trenberth's essay and explain why it vindicates Landsea.
Trenberth confirms in his Science essay what Landsea has claimed, that -- based on what is known today -- "there is no sound theoretical basis for drawing any conclusions about how anthropogenic change affects hurricane numbers or tracks, and thus how many hit land." None. There is no basis for claiming as Trenberth did that the hurricanes of 2004, much less their damages, could be attributed to human emissions of greenhouse gases/global warming. Earlier this year, Trenberth said that his participation in the Harvard press conference was "to correct misleading impressions that global warming had played no role at all in last year's hurricane season." It is good to see this claim corrected.
Trenberth confuses the issue by calling into question the role of hypothesis testing in science (one wonders what this apparently new found perspective on hypothesis testing means for the rest of climate science, but I digress), and some discussion of variables that clearly have some effects on hurricanes (i.e., ENSO), but in the end he concludes "it is not yet possible to say how El Nino and other factors affecting hurricane formation may change as the world warms."
A more comprehensive review of current understandings of hurricanes and global warming can be found in this peer-reviewed paper, forthcoming in the Bulletin of the American Meteorological Society:
Pielke, Jr., R. A., C. Landsea, K. Emanuel, M. Mayfield, J. Laver and R. Pasch, in press. Hurricanes and global warming, Bulletin of the American Meteorological Society. (PDF)
Bottom line: Landsea and Trenberth are scientifically on the same page, and the perspectives now being espoused by Trenberth are (in my interpretation) entirely consistent with what Landsea argued at the time he stepped down from the IPCC. Because of Trenberth's change in perspective, Landsea should feel completely vindicated. The IPCC should be big enough to note this and invite Landsea back into the fold.
A final note, NCAR's press release and those who approved it apparently learned little from the controversy as the press release irresponsibly muddies the issue by making it look like there is in fact a clear global warming-hurricane connection and that there is new information in the Trenberth paper. If the Trenberth paper is cited in the media as supporting a hurricane-global warming connection (and we'd welcome any links to media coverage), then I place full responsibility on the unnecessarily obfuscatory NCAR press release which sets the stage for a further mischaracterization of this issue, on which scientists who once differed, now agree. That is the real story.Posted on June 16, 2005 03:13 PM
Roger-- Not sure Trenberth's paper implies what you think. While he clearly states you can't link hurricane tracks/frequency with warming, he links intensity with warming. And I think that's what he was doing when made the remarks about the '04 Florida hurricanes. If I'm interpreting/remembering his press conference comments correctly, he was saying that one could not rule out the fact warming had some influence on the storms that formed. By this, I think he meant that human induced warming may have had some role in contributing to a favorable background environment (e.g. elevated SSTs) which, at least theoretically, could influence intensity (i.e. rain/wind).
And in no way does he back down from that line of reasoning in the Science paper.
Posted by: OnTheInside at June 16, 2005 04:12 PM
Om The Imside-
Thanks for your comment. Everything that you write is completely consistent with our BAMS paper. Thanks!
Posted by: From Far Away at June 18, 2005 08:52 AM
I don't see how the Trenberth paper is relevant to whether Landsea's actions were justified. It seemed to me that Chris's actions were based on his view that "the part of the IPCC to which (his) expertise is relevant (had) become politicized." I don't see how the Trenberth publication changes that. Either the process is still politicized or it wasn't then. To me, the threat was that the writing of the relevant portions of the AR IV would be influenced by that politicization. To me, that led to two choices of actions for Chris:
1) Resign because he didn't want to participate in the process, risking that the politicization would change the content of the document.
2) Continue to participate and, if the lead authors of the chapter changed the meaning of Chris's contribution, raise a ruckus.
Chris chose 1. I don't think I agree with that strategy, but I respect the decision. My preference would be to go through the roof if the editorial process tried to change the text. I participated in the TAR on the severe thunderstorm/tornado part and was concerned that my "we can't tell if anything's happened and have no basis to tell if anything will" tone would get changed. It didn't. I don't know if I'll end up getting asked to contribute anything this time, but I intend to follow the same path as I did last time.
Posted by: Harold Brooks at June 20, 2005 07:54 AM
Your assumption here seems to be that Trenberth is the one who is completely responsible for any misunderstanding that occurred between him and Landsea. Perhaps this is understandable given, as you note, that Landsea is a close collaborator of yours. However, you really haven't provided the evidence here to support this claim.
If any sort of apology is in order, it seems like it ought to be a mutual one by all parties. And, as for inviting Landsea back in the IPCC fold, I don't think the IPCC ever kicked him out or even implied that he was not welcome. It was his decision to resign from the IPCC and I assume that they would be just tickled to have him back if he chooses to come back.
Posted by: Joel Shore at June 24, 2005 09:54 PM
Joel, out of curiousity, how did Trenberth's give offense?
Posted by: Eli Rabett at June 29, 2005 11:31 PM