Chris Rapley, Professor of Climate Science, University College London, gives the final lecture in the Uncertainty series. This talk will cover the complexity of the Earth systems, and the nature and magnitude of the challenge of exploring and understanding how it functions. Key outcomes of the research effort will be summarised, as will the approaches used to predict the future trajectory of the system and the consequences for humanity. A key uncertainty is the extent to which humans will take measures to mitigate anthropogenic influences on climate, and so I will address the phenomenon of 'climate delusion' and its consequences. Creative Commons Attribution-Non-Commercial-Share Alike 2.0 UK: England & Wales; http://creativecommons.org/licenses/by-nc-sa/2.0/uk/