Uncertainty is intrinsic to science, to knowledge acquisition and risk assessment. When communicating about climate change, however, uncertainty can be used and understood as 'not knowing', that is, as ignorance. In this article we aim to understand how 'uncertainty' is used in a specific cultural and media context at two important periods in time. Using a corpus linguistic approach, we examine how 'uncertainty' was used in the context of UK press coverage of climate change in 2010 (following 'Climategate') and in 2014-15, after the latest IPCC report had been published. We find that after Climategate and the (failed) Copenhagen summit, 'uncertainty' was used to question the authority and credibility of climate science; after the latest IPCC report and in the run-up to the (more successful) Paris summit, discussions focused on uncertainties inherent in various climate change mitigation activities and associated with the economy, environment and politics more generally.