What observed climate variables are used for weighting variants of the Met Office Hadley Centre models used in UKCP09?

A set of global metrics of observed climate are used, including measures of both the observed climate baseline (1961–1990) and trends through the twentieth century.

In detail

The observed climate metrics used to weight the variants of the Met Office Hadley Centre global climate model are:

• latitude-longitude fields of sea surface temperature
• land surface air temperature
• precipitation
• pressure at mean sea level
• shortwave and longwave radiation at the top of the atmosphere
• shortwave and longwave cloud radiative forcing
• total cloud amount
• surface fluxes of sensible and latent heat 
• latitude-height distributions of zonally averaged atmospheric relative humidity

In addition, we also include changes in large scale features of surface temperature patterns observed during the twentieth century as an additional constraint.

The sets of variables, whilst incomplete, constitute a large collection of variables covering a variety of physical climate characteristics. This should substantially reduce the risk of erroneously assigning a high weight to a location in parameter space which achieves a good fit to observations through a fortuitous compensation of errors.