Currents are like rivers of water within the ocean. They are driven by several factors, including winds, precipitation, evaporation, and heating and cooling of the ocean. They can flow for thousands of miles, and they greatly impact the climate on different parts of the earth.
There are two ways that a rise in sea temperature could affect ocean currents.
The first involves wind. Generally, wind is created when warm air – which is lighter than cool air – rises and then cool air moves in to replace the warm air. When the surface temperature of the ocean becomes warmer, winds also change. Since wind is one of the factors that influence ocean currents, the currents change too.
Scientists expect that a warmer ocean will cause a slight shift in the jet streams, fast-flowing currents in the air. The jet streams will become a bit stronger and move toward the poles slightly. That will alter – just by a little – the strength of the wind-driven ocean currents. The change would be so slight that captains of ships wouldn’t even notice a difference.
Melting ice could also affect ocean currents. Glaciers, which consist of frozen fresh water, melt when the planet warms, and those parts of the ocean become a bit less salty. Scientists have debated for many years whether increased fresh water in the north Atlantic would slow down the thermohaline circulation, the conveyor belt of currents that carry heat from the tropics to the North Atlantic region. This circulation helps keep Europe’s climate moderate.
The film “The Day After Tomorrow” shows a wildly exaggerated scenario in which the conveyor belt halts and spurs an ice age in a matter of days. No models predict such a dramatic shut down, but some have shown that a slowdown of the conveyer belt could occur over a long period of time.
– Lynne Talley, research oceanographer and professor, Climate, Atmospheric Science, and Physical Oceanography division