by Judith Curry

The consensus on anthropogenic climate change provided by the IPCC is the source of much controversy. Central to the controversy is the meaning and implications of “consensus,” in both scientific and sociological contexts.

Some important insights on this issue are provided by this paper on The authority of the IPCC and the manufacture of consensus by Jean Goodwin at Iowa State University. Some excerpts are provided below:

Through a series of (up to now) four reports starting in 1990, the IPCC has managed to establish as a political “given” that the earth is warming, and that human activity is a significant cause. The fourth report was the occasion for the Bush II administration’s shift from statements like this:

We do not know how much effect natural fluctuations in climate may have had on warming. We do not know how much our climate could, or will change in the future. We do not know how fast change will occur, or even how some of our actions could impact it.

in 2001, with it’s typical assertions of “uncertainty” as a reason for inaction, to statements like

[The IPCC report] reflects the sizeable and robust body of knowledge regarding the physical science of climate change, including the finding that the Earth is warming and that human activities have very likely caused most of the warming of the last 50 years.

in 2007. How did the IPCC manage this feat? In opposition to those who would create an appearance of doubt, the IPCC has made evident a broad and deep agreement among scientists—they have “manufactured consensus.”

As far as I can tell, the word “consensus” is absent in the WGI section of the FAR–in particular, it is absent from the initial “Policymakers’ Summary” Where it first turns up is in the earliest representation of the FAR: a statement defining for public audiences what the FAR is and how it should be taken. John Houghton, the UK’s Chief Meteorologist and chair of WGI, wrote the following in his “Foreword” to the report:

“In preparation of the main Assessment most of the active scientists working in the field have been involved. One hundred and seventy scientists from 25 countries have contributed to it, either through participation in the twelve international workshops organised specially for the purpose or through written contributions. A further 200 scientists have been involved in the peer review of the draft report. Although, as in any developing scientific topic, there is a minority of opinions which we have not been able to accommodate, the peer review has helped to ensure a high degree of consensus among authors and reviewers regarding the results presented.”

JC comment: It appears from this argument that John Houghton was responsible for the initial decision to use consensus as key element of the IPCC’s rhetoric, in the context of selling the FAR to the public.

What is being done by this complex of features?—this rhetorical form, which I will call a “consensus claim”? One place to begin is by realizing its oddity. After all, we teach our students to recognize and reject ad populum or “bandwagon” appeals. I suspect that it would be hard to find scientists claiming to each other that such & such ought to be believed, because a “consensus of scientists” thus quantified backed it. In fact, the WGI report itself did not frame its statements “socially,” with information about how many scientists of what type and nationality were speaking. Instead, it framed its statements “epistemically,” presenting in the Summary for Policymakers what “we are certain of…calculate with confidence…predict” as well as what “uncertainties” remain, and detailing in a series of chapters some of the evidence backing these claims. If scientists tend to offer each other epistemic as opposed to social grounds, it is no surprise that there seem to be no mechanisms within science for establishing that a scientific consensus exists.

JC comment: The wikipedia article on scientific consensus is worth reading. It states “Scientific consensus is not by itself a scientific argument, and it is not part of the scientific method.” It is “intended to communicate a summary of the science from the “inside” to the “outside” of the scientific community.”

The consensus claim thus seems to be primarily aimed at non-scientists, and in particular (I assert, somewhat speculatively) constitutes an appeal to authority. In this representation of the FAR, audiences are being invited to credit the assessment not because of its epistemic grounding, but because of the social fact of who wrote it. . . Whereas non-experts almost by definition are unable to assess an expert’s reasoning, they may be well capable of judging social facts, such as whether some procedures were inclusive. To adapt a phrase of Collins & Pinch, where we might find it impossible to assess scientists on scientific grounds, we can instead assess them on the same everyday, pragmatic grounds we trust plumbers.

JC comment: Climategate was about the social aspects of the consensus. Whereas scientists rightly claimed that climategate changed nothing epistemically with regards to climate science, the public saw substantial problems with the procedures upon which the consensus was built.

The consensus claim, furthermore, appears to be an elaboration of the appeal to authority specifically designed to heighten its force. “Credit what I say, because I say so” is the minimalist version of the appeal to authority. I have argued elsewhere that the force of this appeal is based in a kind of “blackmail”: it puts the audience in a position such that they will appear imprudent if they conspicuously go against the view of someone who obviously knows more. The minimalist appeal, however, is relatively easy for audiences to evade. For example, the audience can shop around for a second opinion, and then excuse their non-compliance with the appeal on the grounds that the experts themselves seem to be divided. If, however, all the experts say the same thing, the layperson’s “plausible excusability” is restricted.

JC comment: this strategy is clearly reflected in the arguments of Oreskes and Anderegg et al.

To make a consensus claim is thus to do as the Foreword says: to make an “authoritative statement.” It’s worth noting that there is some evidence that some participants in the IPCC process aimed it to achieve just such authority. Bert Bolin, the overall chairman of the IPCC itself, recalls that he “repeatedly pointed out to the working groups that the goal was not necessarily always to reach an agreement, but rather to point out different views when necessary and to clarify the reasons for disagreements when possible.” He goes on: “But this was still seldom tried”. In line with this, Houghton himself was quoted as saying (upon the establishment of the IPCC in 1988), “we must arrive at a general consensus”.

JC comment: is this aiming that makes this a manufactured consensus. It is illuminating to see that the idea of a consensus was pushed for by Hougton, with some resistance by Bolin.

Scientists involved in the first IPCC assessment process represented the final report as the result of a “consensus of scientists”; as far as I can tell, however, this was not the official position of the IPCC itself. This situation changed, however, in the course of the later IPCC process. Whatever its beginnings the consensus claim seems to have become one of the ways the IPCC represented itself to its audiences. For example, a flyer for the Third Assessment Report represented it as “an authoritative, international consensus of scientific opinion”.

The emphasis on consensus also became codified in the IPCC’s internal procedures, as they became increasingly settled after the first (and quite rushed) assessment process. As early as 1991, a rule was adopted stating that “in taking decisions, drawing conclusions, and adopting reports, the IPCC Plenary and Working Groups shall use all best endeavours to reach consensus”.

Meanwhile, however, the IPCC endured close to twenty years where its authority was undermined by objections which were legitimate under its own announced standards. By committing the IPCC to quantitative inclusiveness, those representing its work as a “consensus” created grounds for controversy.

JC comment: I agree that the claim of consensus is ultimate source of controversy surrounding the IPCC. As I’ve argued in my previous post no consensus on consensus, a consensus on this topic is neither necessary or desirable.

The IPCC and its defenders therefore were obliged to undertake a second task: the “boundary work” necessary to distinguish those qualified to contribute to a scientific consensus on global climate change, from those who were not. This work is evident in some of the press reporting above, where the “minority” was characterized not only as quantitatively small, but as “extreme” and “scientifically suspect.” Unfortunately, the need for boundary work also likely created temptations to make illegitimate attacks on the scientific credibility of opponents whose views did not fit with the consensus. Even when successful and legitimate, boundary-drawing created additional problems. If indeed every scientist within the consensus agreed that policy action was urgent, and every scientist outside thought otherwise, a strong appearance of politicization was created—i.e., that the boundary between “insiders” and “outsiders” was based on political views, not scientific relevance.

JC comment: This is an astute insight, on how the scientists have become politicized on this issue.

Finally, the consensus claim created opportunities for opponents to object that the IPCC’s emphasis on consensus was distorting the science itself. Once the consensus claim was made, scientists involved in the ongoing IPCC process had reasons not just to consider the scientific evidence, but to consider the possible effect of their statements on their ability to defend the consensus claim.

JC comments: I have argued previously that the IPCC is torquing (and even corrupting) climate science, and this article clarifies that the source of this corruption is the consensus building process.

“Consensus” is a strong claim, and it opens a wide argument space; that is what I have been trying to suggest in the above sketch. By representing their work as a “consensus,” the scientists of the IPCC essentially legitimated the objections of those commonly labeled as “denialists,” and committed themselves to a twenty year process of replying to them.

Let me close this section with a call that “more research is needed!” into the report as a rhetorical strategy—a subject that, as far as I can tell, has been almost entirely unexplored. It could be that we would find that the “report strategy” does not aim to construct an appeal to expert authority enforcing its conclusions, but attempts to seriously engage a lay audience with the modes of expert reasoning used to reach those conclusions. In the terms I suggested above, a “report strategy” would be taking an “epistemic,” as opposed to “social,” approach to communicating science. . . And it seems likely that pursuing a “report strategy” would require from its authors commitments different from, and much less than, the strategy of making a consensus claim.

JC comment: Goodwin hits the nail on the head in terms of the need to seriously engage the lay audience with the modes of expert reasoning used to reach those conclusions. In the absence of transparency on the IPCC’s reasoning and uncertainty assessments, I suspect that there is a substantial amount of fallacious reasoning (particularly circular reasoning) that underlies many of the IPCC’s conclusions and likelihood statements.

JC conclusion: Lets return for a moment to the previous post on agnoiology and this statement by Lehrer:

We shall argue that consensus among a reference group of experts thus concerned is relevant only if agreement is not sought. If a consensus arises unsought in the search for truth and the avoidance of error, such consensus provides grounds which, though they may be overridden, suffice for concluding that conformity is reasonable and dissent is not. If, however, consensus is aimed at by the members of the reference group and arrived at by intent, it becomes conspiratorial and irrelevant to our intellectual concern.

Goodwin makes a strong argument that the IPCC is a manufactured consensus that has been reached by intent. As such, Lehrer argued in 1975 that such a consensus is conspiratorial and irrelevant to our intellectual concern.

The IPCC needs to lose the emphasis on consensus and pay far more attention to understanding uncertainty and to actual reasoning. I’ll close with this statement by Oppenheimer et al. (2007)

The establishment of consensus by the IPCC is no longer as important to governments as a full exploration of uncertainty.