Overview

The oceans, after the atmosphere, form the second fluid of the climate system. Theircirculations are responsible for between 10 and 15 percent of the total energy transported from thetropics to the polar regions each year. Despite this relatively small proportion of the totalenergy transport, the influence of the oceans cannot be ignored because they act as the flywheelsof the climate system. The enormous mass of the major oceans mean that, once initiated, surfacecurrents and other planetary scale ocean circulations tend to persist and continue their transportof energy around their respective basins.

The oceans also have an enormous thermal capacity when compared to the atmosphere. The scaleof the different thermal capacities of the oceans and atmosphere can be gauged from the fact that,for each unit of area, the upper 3 metres of the ocean has the same thermal capacity as theatmosphere above. The overall mass of the oceans and their thermal capacity underscores that theoceans are a major energy reservoir and the flywheels of the climate system.

The enormous thermal capacity of the oceans ensures that apparently subtle changes to theircharacteristics can have a dramatic impact on the atmospheric circulation and regional climates.For example, El Ni o events, involving anomalous warming of the eastern equatorial Pacific Ocean,displace global weather patterns from their usual locations and cause regional droughts, floodrains and severe storms ^[85]. The changes in the circulation of the tropical Pacific Ocean that areassociated with El Ni o events, and the consequent variations to global sea surface temperaturepatterns, are a...