Online climate change projections report 2 Why we need probabilistic projections
This chapter describes the uncertainties in projections of climate change and how they arise. It goes into some detail on how climate models are structured, and the reasons why different models give different projections of change. This provides the background to a simplified description of the methodology which has been developed to provide the probabilistic projections for UKCP09. Next, it outlines some of the limitations of these projections. Finally, it describes the three scenarios of future emissions which underlie the projections.