GREENHOUSE GASES EFFECTS 429
Heights of the 11 specified pressure surfaces
Short- and long-wave radiation fluxes
Cloud amount, height and liquid-water content
Precipitation/rain/snow
Atmospheric pressure at Earth’s surface
Land surface temperature
Soil moisture content
Snow cover and depth
Sea-ice cover and depth
Ice-surface temperature
Sea-surface temperatureare remarkably successful in simulating the main features
of the present global climate—the distribution of tempera-
ture rainfall, winds, etc. and their seasonal and regionalvariations. They do, however, contain systematic errors,
some different in different models, and some common to
most. Identification of these errors and biases by compari-
son with the observed climate is important since these must
be taken into account when evaluating predictions. These
may not appear to be too serious in making predictions of
the effects of a prescribed (e.g., man-made) perturbation
since these involve computation of the differences between
a perturbed and a control (unperturbed) simulation in
which the systematic errors may largely cancel. However
this linear reasoning may not necessarily be valid for such
complex non-linear systems even if the perturbations are
small, and the predictions will carry greater credibility if
the control runs realistically simulate the observed climate
and its variability.FIGURE 2 Simulation of the global mean surface pressure field for June, July and August
by the UKMO climate model compared with observation.C007_002_r03.indd 429C007_002_r03.indd 429 11/18/2005 10:27:58 AM11/18/2005 10:27:58 AM