Chapter 5
Modelling the climate
Chapter 2looked at the greenhouse effect in terms of a simple radiation
balance. That gave an estimate of the rise in the average temperature at
the surface of the Earth as greenhouse gases increase. But any change in
climate will not be distributed uniformly everywhere; the climate system
is much more complicated than that. More detail in climate change pre-
diction requires very much more elaborate calculations using computers.
The problem is so vast that the fastest and largest computers available
are needed. Butbefore computers can be set to work on the calculation,
a model of the climate must be set up for them to use.^1 A model of the
weather as used for weather forecasting will be used to explain what is
meant by a numerical model on a computer, followed by a description
of the increase in elaboration required to include all parts of the climate
system in the model.
Modelling the weather
An English mathematician, Lewis Fry Richardson, set up the first nu-
merical model of the weather. During his spare moments while working
for the Friends’ Ambulance Unit (he was a Quaker) in France during the
First World War he carried out the first numerical weather forecast. With
much painstaking calculation with his slide-rule, he solved the appropri-
ate equations and produced a six-hour forecast. It took him six months –
and then it was not a very good result. But his basic methods, described
in a book published in 1922,^2 were correct. To apply his methods to real
forecasts, Richardson imagined the possibility of a very large concert
hall filled with people, each person carrying out part of the calculation,
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