A combination of strong climate action and regional interventions will almost certainly be required to halt the decline in coral health on the Great Barrier Reef (GBR). However, uncertainties in climate projections, ecological responses and efficacy of interventions will be ongoing and therefore need to be explicitly integrated into decision-making processes. Quantitative risk assessment can provide rigorous treatment of uncertainty by building on the strengths of ensemble climate and reef ecosystem modelling. I will demonstrate the power of this approach in estimating and communicating risk trajectories for coral loss on the GBR under proposed intervention strategies. Combining traditional risk assessment with ensemble climate modelling eliminates the need for independent estimates of exposure, sensitivity, and likelihood of impacts, all of which are dynamically integrated within the ensemble model. The approach can also provide quantitative estimates of the urgency of climate action and, if necessary, the point where we effectively lose control.