How is model bias dealt with in UKCP09?

UKCP09 deals with model bias by providing projections of climate change, and by using these together with an observed climate dataset to estimate projections of absolute future climate.

In detail

Model bias is the term used to describe systematic errors in model results, used here specifically to refer to differences between modelled and observed climate for a baseline period.

In UKCP09, projected changes in climate are provided which helps to ameliorate the effect of model bias. The projected change is calculated by subtracting the modelled baseline climate from the modelled future climate, meaning that model bias is effectively cancelled out. Obviously this cannot account for any errors in the projected climate response, which are taken into account using the probabilistic approach in UKCP09 (whilst recognising that errors common to all models cannot be allowed for by any technique).