Michelle Pham (University of Washington, Seattle)
Science skeptics often undermine expert scientific testimony by appealing to lack of consensus. Climate change deniers, for example, highlight lack of agreement among climate scientists regarding anthropogenic climate change (Oreskes and Conway 2010). A crucial, though implicit, assumption behind this strategy is that expert opinion is trustworthy only if it is nearly or completely unanimous. Let's call this the "unanimity criterion" for trustworthy scientific consensus, according to which one should be skeptical if there is dissent within the expert community. A piece from the Heritage Foundation, for example, states: “When the IPCC released its report in 2007, 400 climate experts disputed the findings; that number has since grown to more than 700 scientists, including several current and former IPCC scientists” (Loris 2010, p. 4). Here the skeptic appeals to dissent, supposedly by members of the same expert community, to undermine the IPCC’s consensus position.
One response to climate science skeptics is to corroborate the IPCC’s consensus position. Analyzing the abstracts of 928 relevant peer-reviewed publications between 1993 and 2003, Naomi Oreskes finds that “none of the papers disagreed with the [IPCC’s] consensus position" (2004, p. 1686). This result, Oreskes argues, legitimates the IPCC's position. Such a response effectively accepts the unanimity criterion.
Oreskes does not discuss, however, that many of the surveyed papers are jointly authored. The positions espoused in these papers are not typically a result of aggregating each individual author's beliefs. More often such papers display a jointly negotiated stance that I argue is amenable to Margaret Gilbert’s (1996) joint commitment model, where members of a group can agree to let a position stand as the group’s view even if they personally believe otherwise. I thus question the aggregative framework invoked by both climate change skeptics and Oreskes to assess expert scientific consensus on climate change. Instead, I offer an alternative conception of consensus based on the joint commitment model, which captures the collective nature of many jointly authored papers.
I also argue that the IPCC’s consensus position represents something much closer to a joint commitment. The reports from which the consensus position emerges are subject to multiple rounds of revision in response to expert reviewers. The report’s conclusion, rather than an aggregation of what individual participants believe about particular issues, represents an act of letting a position stand as the group’s view after a process of deliberation and negotiation about the scientific content. Understanding the IPCC’s consensus position as a joint commitment displays how unanimity is not a relevant marker for assessing trustworthiness of the group’s position. Rather, we should focus on the quality of deliberation, as well as the group’s response to criticism from the relevant experts.
