Mathematical models are useful whenever we admit we cannot predict precisely what is going to happen, for example in weather forecasting, insurance, nuclear safety, natural disasters, the effect of new medical interventions and, more controversially, in climate change and finance. Such models get so complex that multiple simulations of 'possible futures' may be necessary, which allow us to quantify chances of future events, which then need to be communicated to the public and policy-makers. But how good are these 'chances'? I shall look at the ways forecasts are provided and evaluated, and how we might try to communicate deeper uncertainties.

This talk is part of the UK Launch of Mathematics of Planet Earth 2013. More info @ www.newton.ac.uk/events/2013/mpe/