Online climate change projections report 3 Construction of projections
The Met Office Hadley Centre has designed a methodology to provide probabilistic projections for UKCP09 which reflect major known uncertainties in relevant climate system processes. The method uses large ensembles of climate model projections, which are processed using advanced statistical methods to generate thousands of plausible climate outcomes, which are then weighted using historical observations.
This chapter provides a comprehensive review of the methodology used to construct the UKCP09 probabilistic projections, for readers requiring a more complete scientific insight into their basis. It is necessarily written assuming a higher level of scientific understanding than other chapters, although it does not seek to document each aspect of the method to the level of technical detail that would appear in a specialist journal paper. Published papers (cited below where relevant) are already available for some components of the method, and will be provided for remaining components in due course. A technical note will also be supplied after the launch of the projections (by October 2009, contingent on the demand for post-launch scientific advice from users), giving a mathematical description of the methodology to supplement the qualitative description given in this Chapter.
Section 3.2 describes the elements of the method, and Section 3.3 provides a discussion of the nature, credibility and interpretation of the projections. A short, less technical summary of this material can also be found in Chapter 2, Section 2.2.