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Probabilistic climate projection

UKCP09 provides what are known as 'probabilistic' climate projections. These are projections of future absolute climate that assign a probability level to different climate outcomes. This projection provides an absolute value for the future climate (as opposed to giving values that are relative to a baseline period).

In detail

The Met Office Hadley Centre have developed a methodology to provide probabilistic climate projections to describe the future climate for the each 25 x 25 km grid square in the UKCP09 25 km grid and for certain pre-defined Aggregated area.

A probabilistic climate projection is a measure of strength of evidence in different future climate change outcomes. This measure is dependent on the method used, is based on the current available evidence and encapsulates some, but not all, of the uncertainty associated with projecting future climate.

Find out more


  • Section 1.1.1 of the UKCP09 Climate Change Projections report explains what is meant by probability in UKCP09. We also recommended that users read the 'Before you start using UKCP09...' page.
  • An overview of how probabilistic projections are created and presented in UKCP09 is described in Box 3 of the UKCP09 Briefing Report.
  • More details are provided in Chapter 3 of the UKCP09 Climate Change Projections report, including an overview of the methodology and a discussion about the interpretation of UKCP09 probabilistic projections.
  • Some case studies have been developed that using use dummy outputs to examine how the UKCP09 probabilistic climate change projections might be used.
  • There are some variables for which probabilistic projections could not be produced for UKCP09. These are summarised in the UKCP09 Briefing Report with further detail in the UKCP09 Climate Change Projections report.
  • A discussion of sources of uncertainty in the UKCP09 probabilistic projections is available in Annex 2.4 of the Climate change projections report.
  • The UKCP09 User Interface allows the UKCP09 probabilistic projections to be provided as either future absolute climate or as change from the 1961-1990 baseline climate.
  • Sexton, D.M.H., Murphy, J., Collins, M. & Webb, M. 2011. Multivariate probabilistic projections using imperfect climate models Part I: Outline of methodology. Climate Dynamics. Doi: 10.1007/s00382-011-1208-9
  • Sexton, D.M.H. & Murphy, J. 2011. Multivariate prediction using imperfect climate models part II: Robustness of methodological choices and consequences for climate sensitivity. Climate Dynamics. Doi: 10.1007/s00382-011-1209-8