What emission scenario should be used?

The IPCC states that probabilities cannot currently be assigned to different emissions scenarios. Therefore users should consider projections across all three of the emissions scenarios provided in UKCP09 unless there is a specific justifiable reason to focus on only one.

In detail

There is a commentary in Annex 1 of the Climate change projections report on emissions scenarios. This describes relevant work that has taken place since the SRES scenarios were published. It also provides information as to what emissions scenario we are currently tracking based on a paper by Raupach et al (2007) and the caveats that go along with this research.