Does UKCP09 provide information about changes in extremes?

Yes, UKCP09 provides information about changes in extremes through both the probabilistic climate projections and through the Weather Generator.

In detail

The UKCP09 probabilistic climate projections provide information about projected changes in monthly, seasonal and annual conditions, and are therefore not well suited to extremes. However, changes in some annual extremes are reported in probabilistic terms e.g. changes in the hottest day of summer, coldest day of winter and wettest day of winter.

The UKCP09 Weather Generator has been introduced in UKCP09 in order to give users an idea of the implications of climate change on daily climate. It can be used to provide information on some extremes through generation of a long stationary series of future data representative of the statistics of daily climate, providing a large statistical sample from which to investigate extremes. There are important limitations of using this approach to investigate daily extremes. The Weather Generator has been trained on a period of only 30 years of climate observations, meaning that it may not simulate long return period events in the future. For instance, if an event was not represented in the observed climate then it is unlikely to be represented in the future climate. However, the Weather Generator may simulate changes in the type of extreme events observed in the baseline climate.