Climate change has mutated from being a physical phenomenon to be studied to an idea to be contested. The sites of adjudication between competing truth claims have therefore moved from the secluded academy and scientific peer review to the vociferous agora and the extended peer community. This move is illustrated here using the case of the shrinking glaciers of Mt Kilimanjaro. Both the British engineer Guy Callendar, in 1944, and the American campaigner Al Gore, in 2006, claimed that the primary cause of this glacial recession was rising world temperature. Both were passionate believers in the reality of human-induced global warming, but they had very different resources at their disposal to advance these beliefs. While Callendar’s claim was revealed only to the editor of the science journal Nature, Gore’s claims were visible to millions through his film An Inconvenient Truth. While the force of Callendar’s claim was weighed and adjudicated by one peer reviewer, the validity of Gore’s claim was tested very publicly in the British courts. Both claims about the cause of Kilimanjaro’s retreating glaciers were found wanting. The paper argues that this simple, but powerful, comparison between identical claims-making drawn from two different eras of science, yet with contrasting processes of truth-adjudication, illuminates the different ‘post-normal’ world of science climate change now inhabits. The case study is used to reflect on the role of the extended peer community in establishing and validating scientific knowledge about climate change: who participates, how trust is stabilised and whether science is thereby democratised.