94 Modelling theclimate
Figure 5.16Estimates of transport of heat by the oceans. Units are terawatts
(10^12 W or million million watts). Note the linkages between the oceans and
that some of the heat transported by the north Atlantic originates in the Pacific.The oceans act on the climate in four important ways. Firstly, there are
close interactions between the ocean and the atmosphere; they behave
as a strongly coupled system. As we have already noted, evaporation
from the oceans provides the main source of atmospheric water vapour
which, through its latent heat of condensation in clouds, provides the
largest single heat source for the atmosphere. The atmosphere in its turn
acts through wind stress on the ocean surface as the main driver of the
ocean circulation.
Secondly, they possess a large heat capacity compared with the at-
mosphere, in other words a large quantity of heat is needed to raise the
temperature of the oceans only slightly. In comparison, the entire heat
capacity of the atmosphere is equivalent to less than three metres depth
of water. That means that in a world that is warming, the oceans warm
much more slowly than the atmosphere. We experience this effect of the
oceans as they tend to reduce the extremes of atmospheric temperature.
For instance, the range of temperature change both during the day and
seasonally is much less at places near the coast than at places far in-
land. The oceans therefore exert a dominant control on the rate at which
atmospheric changes occur.
Thirdly, through their internal circulation the oceans redistribute heat
throughout the climate system. The total amount of heat transported
from the equator to the polar regions by the oceans is similar to that