Climate Change and the Oceans

The Basics


The Role of the Oceans in the Radiation Balance


The oceans play an important role in storing and redistributing heat absorbed from incoming solar radiation. Most of the solar radiation is aborbed near the equator, where the radiation is most intense. Currents then redistribute this heat throughout the oceans in what is known as the Thermohaline Circulation, also known as the "Global Ocean Conveyor Belt".

This very simplistic diagram of thermohaline circulation (below) depicts a cross-section through a bowl-shaped ocean basin with the polar regions at left and right.

Robin Muench (ESR)

Cooling and formation of sea ice in the polar regions makes the surface ocean water denser than the underlying water, so that the surface water sinks and moves towards the equator (light blue arrows). In the central basin a variety of processes including vertical mixing move the dense bottom water upwards toward the surface, where it is warmed by the intense equatorial solar radiation. The warmed water then moves poleward to take the place of the sinking dense water, thereby completing thermohaline circulation.


The previous "simple" diagram evolves into something like this when applied to the real oceans:



The currents are controlled by complex factors including the shape of the seafloor and the earth’s rotation, and the picture presented here is still oversimplified. Nonetheless, the basic mechanisms shown above can be seen at work. The North Atlantic Ocean and southern Weddell Sea (black circles) are both sites where intense cooling creates dense, sinking water. The equatorial Atlantic, Pacific and Indian oceans (red circles) are all sites where the water has upwelled from great depths to the surface and is warmed by incoming radiation ("insolation").


Relevance to climate change?

Because the ocean circulation depends so strongly on sinking of dense water at high latitudes, it is very sensitive to changes in precipitation. Increased precipitation at high latitudes will lower the density of the surface water and inhibit sinking of dense water, thereby slowing the thermohaline circulation. In the extreme case, thermohaline circulation is shut down.