Central estimate

The UKCP09 probabilistic climate projections are reported as a central estimate when referring to a projected change that has equal probability of being exceeded and not being exceeded.

In detail

The UKCP09 probabilistic climate projections are reported as a central estimate when referring to changes that have 50% probability of being greater than (or less than) a given value (also called the 50% probability level).

In a PDF, this is where a vertical line would divide the area under the graph into two equal parts (not necessarily the peak of the graph). In a CDF it is where the cumulative probabilities on each side of the result are both 50%. For sea level rise it is where half of the climate model results simulate a change that is lower, and half a change that is higher.

• The UKCP09 Maps & key findings and published material report cumulative probabilities at the 10% (very unlikely to be less than), 50% (central estimate), and 90% (very unlikely to be greater than) probability levels.

• 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 in Section 3.2.12 and discussion about the interpretation of UKCP09 probabilistic projections in Section 3.3.

• A discussion of sources of uncertainty in the UKCP09 probabilistic projections is available in Annex 2.4.