June 24, 2005

A Man on a Mission

Filed under: Climate Extremes, Hurricanes

Dr. Kevin Trenberth, head of the Climate Analysis Section at the National Center for Atmospheric Research, has been assigned the position of Lead Author of the “observations” chapter of the upcoming (due out in 2007) Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC). As such, he is responsible for heading the effort to gather together and summarize the current state of scientific understanding concerning observed climate variability and change. However, based upon some recent statements that have been attributed to him, it is not clear that he can be trusted to fulfill that role.

In the June 23rd issue of Nature magazine, Quirin Schiermeier wrote the following in his article “Trouble brews over contested trend in hurricanes”:

Trenberth counters that skeptics are ignoring the evidence. “I am trying to get people to think about things in a different fashion,” he says. “The point is that all meteorological events around the world are influenced in some way by global warming.”

This quote implies that Trenberth seems to think he knows the “truth” about global warming and that he is not swayed by people who won’t admit that (i.e. the skeptics). This is an unusual sentiment for a lead author if the IPCC to hold (or at least state publicly), as it indicates a certain unwillingness to accept scientific findings that run counter to Trenberth’s held notions. Surely this attitude cannot lead to an unbiased handling of the topics presented in the IPCC chapter for which he is responsible.

Consider who the skeptics are that Trenberth is referring to. This quote was supposedly in response to a group of scientists who contend that the link between global warming and hurricanes is thus far weak and undetectable. These “skeptics” lay out their case in a soon-to-be-published article in the Bulletin of the American Meteorological Society (BAMS) entitled “Hurricanes and global warming.” The “skeptics” who wrote the article are: Roger Pielke, Jr., a leading researcher on risk and loss association with severe storms and hurricanes; Christopher Landsea, a leading researcher on hurricanes and climate; Kerry Emanuel, a leading hurricane modeler; Max Mayfield, the head of the National Hurricane Center; Jim Laver, head of the Climate Prediction Center; and Richard Pasch, a hurricane specialist at the National Hurricane Center. According to Pielke Jr., the paper’s lead author, the purpose of the paper was “to provide a concise, largely non-technical, scientifically rigorous, globally inclusive, and interdisciplinary perspective on the state of current understandings of hurricanes and global warming that is explicitly discussed in the context of policy.”

The authors conclude:

To summarize, claims of linkages between global warming and hurricanes are misguided for three reasons. First, no connection has been established between greenhouse gas emissions and the observed behavior of hurricanes (IPCC 2001; Walsh 2004). Yet such a connection may be made in the future as metrics of tropical cyclone intensity and duration remain to be closely examined. Second, a scientific consensus exists that any future changes in hurricane intensities will likely be small in the context of observed variability (Knutson and Tuleya 2004, Henderson-Sellers et al 1998), while the scientific problem of tropical cyclogenesis is so far from being solved that little can be said about possible changes in frequency. And third, under the assumptions of the IPCC, expected future damages to society of its projected changes in the behavior of hurricanes are dwarfed by the influence of its own projections of growing wealth and population (Pielke at al. 2000). While future research or experience may yet overturn these conclusions, the state of knowledge today is such that while there are good reasons to expect that any connection between global warming and hurricanes is not going to be significant from the perspective of event risk, but particularly so from the perspective of outcome risk as measured by economic impacts.

Yet, claims of such connections persist (cf. Epstein and McCarthy 2004; Eilperin 2005), particularly in support of a political agenda focused on greenhouse gas emissions reduction (e.g., Harvard Medical School 2004). But a great irony here is that invoking the modulation of future hurricanes to justify energy policies to mitigate climate change may prove counterproductive. Not only does this provide a great opening for criticism of the underlying scientific reasoning, it leads to advocacy of policies that simply will not be effective with respect to addressing future hurricane impacts. There are much, much better ways to deal with the threat of hurricanes than with energy policies (e.g., Pielke and Pielke 1997). There are also much, much better ways to justify climate mitigation policies than with hurricanes (e.g., Rayner 2004).

As IPCC lead author, Trenberth would be hard put to find a more qualified group of scientists to contribute information about the past and present state of tropical cyclones to his “Observations” chapter. The problem is, is that by his remarks and attitude, Trenberth is alienating the world’s leading tropical cyclone experts.

For instance, about 6 months ago, Chris Landsea (one of the BAMS article authors) decided to formally withdraw from the writing process of the IPCC’s AR4 because of what he viewed as the IPCC’s tendency to lean away from the best scientific knowledge and instead embrace “preconceived agendas” toward global warming and its potential impacts on tropical cyclones. Landsea arrived at his conclusions after an exchange with the IPCC higher ups concerning statements made by Trenberth at a press conference last fall. Landsea was a bit taken aback by Trenberth’s remarks that not only was global warming currently impacting the intensity of tropical systems, but further, that it likely played a role in last year’s hurricane activity along the Florida coast. Landsea characterized Trenberth’s remarks as “far outside of current scientific understanding.” After several frustrating exchanges with Trenberth (both before and after the press conference) and other IPCC officials, Landsea came to the determination that “it would be very difficult for the IPCC process to proceed objectively with regards to the assessment on hurricane activity.” Not wanting to be associated with this perturbation of sound science, Landsea resigned from his accepted writing task (Landsea had been heavily involved in the writing of the tropical cyclone sections in previous IPCC reports).

Trenberth was unfazed by Landsea’s resignation and went as far to say (in the February 4th issue of the Economist, http://www.economist.com/agenda/displayStory.cfm?story_id=3630425) that “politics is very strong in what is going on, but it is all coming from Landsea and colleagues. He is linked to the sceptics.” In this case, Trenberth’s “link” to the “skeptics” was referring to an article that was written by World Climate Report’s Patrick Michaels to which Landsea was a co-author. The article, which has now been accepted and awaiting publication in the Journal of Climate commented on the findings of hurricane modelers Knutson and Tuleya (finding that underlie Trenberth’s position that global warming will lead to more intense hurricanes) that concluded that within 80 years, global warming will increase the peak wind speed of strong Atlantic hurricanes by about 6% and increase precipitation near the storm’s center by about 7%. Michaels (and Landsea) contended that the modeled relationship between sea surface temperatures (SSTs) and hurricane intensity was overly strong and that the modeled rate of SST warming was far greater than is being observed. Together, these findings suggested that the projections made by Knutson and Tuleya were too large and too fast (see here for further details). Apparently, Trenberths’s contention is that if you disagree with his views that global warming is leading to more intense hurricanes, even if it is done in the scientific literature, you are a skeptic.

The fact that Trenberth admits to be on a mission to try “to get people to think about things in a different fashion…[that] all meteorological events around the world are influenced in some way by global warming” is precisely the reason that Landsea quit the IPCC. Obviously Trenberth has an agenda, and it is one that lies outside of the current state of our best science.

It will be interesting to see how Trenberth’s new comments are viewed by the IPCC officials. Obviously they don’t sit well with one well-respected group of scientists, and outwardly they don’t give the appearance of being unbiased. Is the IPCC interested in representing the true state of scientific understanding, or rather, in advocating for climate change?

If it is the former, then the IPCC should act quickly to replace Trenberth in order to at least seem to be setting out to produce an unbiased report of the current state of scientific knowledge. If it the latter, expect to see Trenberth featured prominently in the upcoming AR4.


Knutson T. R., and R. E. Tuleya, 2004. Impact of CO2-Induced Warming on Simulated Hurricane Intensity and Precipitation: Sensitivity to the Choice of Climate Model and Convective Parameterization. Journal of Climate, 17, 3477-3495.

Michaels, P.J., Knappenberger, P.C., and C. Landsea, 2005. Comments on “Impacts of CO2-Induced Warming on Simulated Hurricane Intensity and Precipitation: Sensitivity to the Choice of Climate Model and Convective Scheme”. Journal of Climate, in press.

Pielke, Jr., R. A., C. Landsea, K. Emanuel, M. Mayfield, J. Laver and R. Pasch, 2005. Hurricanes and global warming, Bulletin of the American Meteorological Society, in press. (http://sciencepolicy.colorado.edu/admin/publication_files/resourse-1762-hurricanes%20and_global_warming.pdf)

Schiermeier, Q., 2005. Trouble brews over contested trend in hurricanes. Nature, 435, 1008-1009.

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