UKCP09 was based on the best science available at the time it was produced. But science does not stand still and there have been developments in climate modelling since its release. However, a recent study by the Met Office shows that UKCP09 continues to provide a valid assessment of the UK climate and can still be used for adaptation planning.
These conclusions were reached after comparing one of the core climate model ensembles that underpin UKCP09 (that is based on the Met Office HadCM3 model) with results from the latest international modelling assessment from the Climate Modelling Intercomparison Project (CMIP5). The conclusions from CMIP5 informed the Intergovernmental Panel on Climate Change's (IPCC's) fifth assessment report published in 2014.
The Met Office found that since the release of UKCP09 there have been improvements in the typical performance of climate models, mainly relating to some aspects of climate variability and extremes. But despite this, the performance of their HadCM3 model in simulating historical climate ensemble remains competitive with more recent CMIP5 models.
In addition, the ranges of future change in average climatological conditions across CMIP5 models were generally found to be consistent with the probabilistic projections from UKCP09. However, the study did find some differences for projections of UK summer rainfall. While UKCP09 and CMIP5 agree that average summer rainfall is more likely to reduce rather than increase in the future, CMIP5 suggests smaller reductions than UKCP09, and a somewhat larger chance that UK summer rainfall could remain similar or become wetter than it is today. The Met Office advises that CMIP5 results should be considered alongside UKCP09 in making decisions that are sensitive to future changes in summer rainfall.
A technical note providing more information on the Met Office assessment of UKCP09 compared to the CMIP5 findings will be available in spring 2015. Options to update UKCP09 are currently being explored by government.
For more information contact the UKCP09 technical Helpdesk.