Pearce and Hollin reply —

Scientific information about climate change has proved to be a relatively poor motivator for meaningful public action1,2. That Jacobs et al.3 critique our recent Letter4 about public meanings attached to abstract scientific knowledge by using even more abstract scientific knowledge reaffirms this central point: that some in the climate science community fail to understand that scientific knowledge alone, no matter how certain, is poorly equipped to meaningfully communicate climate change.5.

Continuing this misplaced focus on certainty, much of the Jacobs et al. correspondence gives supporting scientific evidence for the claims of certainty made by speakers during the press conference for the Working Group 1 contribution to the Fifth Assessment Report of the IPCC. However, such evidence is superfluous, as we do not argue in our Letter that short-term events such as 'the pause' undermine any well-established certainty. Rather, we examine, first, the attempts of press conference speakers to make well-established certainty meaningful and, second, the resulting confusion among journalists as to what constitutes valid scientific evidence. This confusion seems to leave Jacobs et al. untroubled, as they ignore it in their Correspondence.

Instead, we highlight that the '30-year rule' is used flexibly during the press conference. Emphasizing the past decade, as IPCC speakers do, may well help to make anthropogenic global warming meaningful and potentially motivational for action6. However, this emphasis on the decadal scale also seems to makes journalists' questions about 'the pause' both reasonable (because it is also decadal in scale) and meaningful (for it might seem to demotivate action). If asking about the decade-long pause is an “ill-posed scientific question”, as asserted by Michel Jarraud during the press conference, then using the past decade of heat and extremes to emphasize the meaningfulness of anthropogenic global warming is not scientifically appropriate. It is the resulting confusion among journalists, caused by the flexible application of the '30-year rule', that illuminates the tension between certainty and meaning faced by climate communicators.

We also disagree that we misrepresent particular quotes in our Letter. First, a quote from former IPCC chair Rajendra Pachauri is said by Jacobs et al. to require contextualization. This particular portion of the press conference transcript was selected because it is illustrative of references to the warmest decade made by all three speakers. Second, Jacobs et al. suggest that we present a quote as concerning 'the pause' when it does not. This is not the case. The quote appears within a general discussion of technical uncertainty7,8 (within Supplementary Data C of our Letter4) that does not refer exclusively to the pause.

We hope that through restating our central argument this response has assisted in clarifying our original analysis. Excellent examples do exist of making climate change publicly meaningful through the acceptance and accommodation of uncertainties in science9,10,11,12. Sadly, the press conference in question was not such an example.