110 Modellingthe climate
information in integrated assessment models (see box in Chapter 9,
page 237).
As the power of computers increases it becomes more possi-
ble to investigate the sensitivity of models by running a variety of
ensembles that include different initial conditions, model parameteri-
sations and formulations. A particularly interesting project^25 involves
thousands of computer users around the world in running state-of-the-
art climate prediction models on their home, school or work computers.
By collating data from thousands of models it will generate the world’s
largest climate modelling prediction experiment.
A great deal remains to be done to narrow the uncertainty of model
predictions. The first priorities must be to improve the modelling of
clouds and the description in the models of the ocean–atmosphere inter-
action. Larger and faster computers are required to tackle this problem,
especially to enable the resolution of the model grid to be increased, as
well as more sophisticated model physics and dynamics. Much more
thorough observations of all components of the climate system are also
necessary, so that more accurate validation of the model formulations can
be achieved. Further, regional climate modelling techniques will develop
rapidly as they are applied to a wide variety of situations. Very substan-
tial national and international programmes are underway to address all
these issues.Questions
1 Make an estimate of the speed in operations per second of Richardson’s
‘people’ computer. Do you agree with the estimate in Figure 5.1?
2 If the spacing between the grid points in a model is 100 km and there are
twenty levels in the vertical, what is the total number of grid points in a
global model? If the distance between grid points in the horizontal is halved,
how much longer will a given forecast take to run on the computer?
3 Take your local weather forecasts over a week and describe their accuracy
for twelve, twenty-four and forty-eight hours ahead.
4 Estimate the average energy received from the Sun over a square region
of the ocean surface, one side of the square being a line between northern
Europe and Iceland. Compare with the average transport of energy into the
region by the North Atlantic Ocean (Figure 5.16).
5 Take a hypothetical situation in which a completely absorbing planetary
surface at a temperature of 280 K is covered by a non-absorbing and
non-emitting atmosphere. If a cloud which is non-absorbing in the vis-
ible part of the spectrum but completely absorbing in the thermal infrared
is present above the surface, show that its equilibrium temperature will be
235K(= 280 / 20.^25 K).^26 Show also that if the cloud reflects fifty per cent of