New Zealander Kevin E. Trenberth has been a lead author in the last three climate assessments produced by the Intergovernmental Panel on Climate Change (IPCC), and he shared in the 2007 Nobel Prize awarded to the IPCC. He is head of the climate analysis section at the National Center for Atmospheric Research in Boulder, Colo. IEEE Spectrum Contributing Editor William Sweet interviewed Trenberth about the impact of the theft last year of climate scientists’ e-mails from the University of East Anglia and proposals for reforming the IPCC.
IEEE Spectrum: You were a lead coauthor with Phil Jones of East Anglia of a key chapter in the latest IPCC assessment, and messages of yours were among the hacked e-mails that aroused such consternation.
Kevin E. Trenberth: One cherry-picked message saying we can’t account for current global warming and that this is a travesty went viral and got more than 100 000 hits online. But it was quite clear from the context that I was not questioning the link between anthropogenic greenhouse-gas emissions and warming, or even suggesting that recent temperatures are unusual in terms of short-term variability.
Spectrum: It seems to me the most damaging thing about the disclosed e-mails was not the issue of fraud or scientific misconduct but the perception of a bunker mentality among climate scientists. If they really know what they’re doing, why do they seem so defensive?
Trenberth: What looks like defensiveness to the uninitiated can just be part of the normal process of doing science and scientific interaction, and properly stating caveats. Scientists almost always have to address problems in their data, exercising judgment about what might be defective and best disregarded. When they talk about error bars, referring to uncertainty limits, it sounds to the general public like they’re just talking about errors.
Spectrum: You have been involved in the IPCC’s work going all the way back to 1990. Can you describe in a nutshell its working procedures?
Trenberth: There are three working groups—on the science of climate change, impacts and adaptation, and options for greenhouse-gas mitigation. The third group involves mainly social scientists. Each report runs to about a thousand pages, with a dozen or so chapters, each organized by one or two lead authors. About 70 people in an initial scoping meeting determine what the chapters and subsections of each report will be. A single chapter might have as many as 50 or 60 contributing authors, though 20 is more typical. About 700 scientists can be involved in producing a single assessment report, and when a draft chapter goes out for expert review, it might get 1400 to 1600 comments. Every comment goes into a huge Excel spreadsheet, and every comment is explicitly addressed. All chapters also go out for governmental reviews, with similar mechanisms for feedback.
Spectrum: Last August, a blue-ribbon panel chaired by former Princeton University president Harold T. Shapiro suggested that the peer review procedures might be too cumbersome and that perhaps comments should be dealt with in a more discriminating way. It called for the creation of an IPCC executive director who could deal with crises like Climategate in real time, and for more rotation among contributing scientists.
Trenberth: Well, in the last assessment, three-quarters of the contributors to the science working group were new. And, of course, there’s a lot to be said for having some veterans involved who understand the procedures and can help bring new participants up to speed. But the recommended changes in governance and management seem desirable to me, though some suggestions refer to procedures that already were supposed to be in place but had not always been properly implemented.
In some respects, the recommendations for reform do not go as far as they might. For example, I don’t see anything about the desirability of enhanced real-time climate services, an idea that the third World Climate Conference strongly endorsed last year. The urgent need for such services was exemplified by extensive wildfires in Russia last summer, which sent world grain prices soaring, and by the catastrophic flooding in Pakistan, which displaced a quarter of the country’s population. What is the probability of such events recurring in the near future? What can be done to prepare for them and mitigate their effects?
Spectrum: When the Shapiro report was released, a lot of press comment, especially in Britain, sought to find hidden messages about the incumbent chairman of the IPCC, R.K. Pachauri—whether it was giving him a quiet vote of confidence or calling for his replacement at first opportunity. Without getting into that, what’s the role of the IPCC chairman?
Trenberth: The chairman exercises influence and authority mainly in the initial selection of the lead contributors for each of the three reports, and then, when the drafts are completed, in negotiating the exact wording of the policy-oriented executive summary, which is adopted in a final meeting of IPCC member states.
Spectrum: The Shapiro panel was slightly critical of the way the IPCC has formulated issues of scientific uncertainty, but there also were complaints when the fourth assessment came out three years ago that some findings were excessively qualified.
Trenberth: The whole IPCC process is intrinsically conservative. And when the meeting of member governments takes place, you can assume that some will do their level best to take the bite out of every important finding. In the second and third assessments, Kuwait and Saudi Arabia tried to weaken every strong statement about climate. Last time around, in the fourth assessment, it was China playing that role, followed by Saudi Arabia. The United States largely stayed on the sidelines, though its representatives had played a strong role in forging consensus in the earlier assessments.
Basically, the scientists have veto power if statements are scientifically incorrect. Scientists determine what is said, but governments determine how it is said.
Spectrum: One constructive critic of the Shapiro report has said that the IPCC, instead of producing three assessments every few years, should do just two: one on science and one on policy.
Trenberth: Bear in mind that the fifth assessment is already organized and well under way. So, many of the reforms under discussion would have to wait for the sixth assessment. Consolidating the exercise into two reports might be advantageous if it brought closer together those working on basic science and those looking at impacts and adaptation. But it would be unfortunate if it led to still greater separation between physical and social scientists, with economists dominating the discussion of policy options even more than now.
Spectrum: I see that besides being a modeler, you do a good deal of basic physical science yourself. Among other things, you lay claim to having measured the mass of Earth’s atmosphere. Isn’t that something a lot of people have been doing for a long time?
Trenberth: There was some attention to this as early as the 18th century, notably in Germany, but there actually wasn’t much work in modern times until the International Geophysical Year was launched in 1957. Before IGY, we didn’t have the comprehensive surface-pressure measurements that you need to estimate the atmosphere’s mass. But yes, actually, I’ve published more on this than any other scientist.
This story was corrected on 1 November. Due to an editing error the word "massage" was included in one of Trenberth's answers. Trenberth never used that word in the interview.