Models for climateprediction 95transported by the atmosphere. However, the regional distribution of
that transport is very different (Figure 5.16). Even small changes in the
regional heat transport by the oceans could have large implications for
climate change. For instance, the amount of heat transported by the north
Atlantic Ocean is over 1000 terawatts (1 terawatt=1 million million
watts= 1012 watts). To give an idea of how large this is, we can note
that a large power station puts out about 1000 million (10^9 ) watts and the
total amount of commercial energy produced globally is about twelve
terawatts. To put it further in context, considering the region of the north
Atlantic Ocean between north west Europe and Iceland, the heat input
(Figure 5.16) carried by the ocean circulation is of similar magnitude to
that reaching the ocean surface there from the incident solar radiation.
Any accurate simulation of likely climate change, therefore, especially
of its regional variations, must include a description of ocean structure
and dynamics.
Ice-albedo feedback
An ice or snow surface is a powerful reflector of solar radiation (the
albedo is a measure of its reflectivity). As some ice melts, therefore, at
the warmer surface, solar radiation which had previously been reflected
back to space by the ice or snow is absorbed, leading to further increased
warming. This is another positive feedback which on its own would in-
crease the global average temperature rise due to doubled carbon dioxide
by about twenty per cent.
Four feedbacks have been identified, all of which play a large part
in the determination of climate, especially its regional distribution. It is
therefore necessary to introduce them into climate models. Because the
global models allow for regional variation and also include the important
non-linear processes in their formulation, they are able in principle to
provide a full description of the effect of these feedbacks. They are,
in fact, the only tools available with this potential capability. It is to a
description of climate prediction models that we now turn.
Models for climate prediction
For models to be successful they need to include an adequate description
of the feedbacks we have listed. The water vapour feedback and its
regional distribution depend on the detailed processes of evaporation,
condensation and advection (the transfer of heat by horizontal air flow) of
water vapour, and on the way in which convection processes (responsible