Here we demonstrate that speakers at the press conference for the publication of the IPCC’s Assessment Report 5 (Working Group 1) attempted to make the documented broad certainty of anthropogenic global warming (AGW) more meaningful to the public. Speakers sought such meaning through reference to short-term temperature increases. However, when journalists inquired about the similarly short-lengthed ‘pause’ in global temperature increase, the speakers dismissed the relevance of such timescales, thus becoming incoherent as to ‘what counts’ as scientific evidence for AGW. We call this the ‘IPCC’s certainty trap’. Speakers’ incoherence led to confusion within the press conference and subsequent condemnation in the media. While the speakers were well intentioned in their attempts to communicate the public implications of the report, these attempts threatened to erode their scientific credibility. In this instance, the certainty trap was the result of the speakers’ failure to acknowledge the tensions between scientific and public meanings. Avoiding the certainty trap in the future will require a nuanced accommodation of ongoing uncertainties and a recognition that rightful demands for scientific credibility need to be balanced with public and political dialogue about the things we value and the actions we take to protect those things.