90 Modelling theclimateFigure 5.13Schematic of
the climate system.
Since we live in the atmosphere the variables commonly used to
describe climate are mainly concerned with the atmosphere. But cli-
mate cannot be described in terms of atmosphere alone. Atmospheric
processes are strongly coupled to the oceans (see above); they are also
coupled to the land surface. There is also strong coupling to those parts
of the Earth covered with ice (the cryosphere) and to the vegetation and
other living systems on the land and in the ocean (the biosphere). These
five components – atmosphere, ocean, land, ice and biosphere – together
make up the climate system (Figure 5.13).Feedbacks in the climate system
Chapter 2 considered the rise in global average temperature which would
result from the doubling of the concentration of atmospheric carbon
dioxide assuming that no other changes occurred apart from the increased
temperature at the surface and in the lower atmosphere. The rise in
temperature was found to be 1.2◦C. However, it was also established that,
because of feedbacks (which may be positive or negative) associated with
the temperature increase, the actual rise in global average temperature
was likely to be approximately doubled to about 2.5◦C. This section lists
the most important of these feedbacks.