Atmosphere-Ocean Climate Interactions
How Do the Oceans Affect Global Climate? Just like the oceans affect weather patterns, they play a major role in the Earth's climate system. The oceans have tremendous thermal and dynamical inertia, which can slow and dampen the rate of climate change. The upper ten feet (3 meters) of the ocean holds as much heat as the entire atmosphere. The moderating effect of ocean temperature reduces the daily and annual range of coastal temperatures, and results in a lag of the global summer and winter seasonal temperatures extremes by several weeks behind the annual track of the sun. For the considerably longer periods decades to millennia which are relevant for climate change, the significantly larger heat capacity of the deep ocean is important. Ocean currents and mixing by winds and waves can transport and redistribute heat to deeper ocean layers. It can reside in this deep reservoir for centuries, further stabilizing the Earths climate and slowing the effects of climate change.
The ocean stores and transports not only heat but also carbon dioxide (CO2), a potential major source of global warming. About half of the total CO2 added to the atmosphere during the past century by human activity mostly from the use of fossil fuels and deforestation has been absorbed by the ocean. Most of the CO2 emitted into the atmosphere will eventually be absorbed by the ocean. However, this process will take several decades to centuries. Phytoplankton also stores carbon dioxide from the upper layers of the ocean. Many species sequestered CO2 in their carbonate shells, which eventually sink to the ocean floor for burial, or long-term removal from the carbon cycle.
Why Are the Ocean Currents Important to Climate? Ocean currents transport and redistribute heat and salt. Both play an important role in driving the planetary climate engine. Of particular importance are the western boundary currents (e.g., Gulf Stream and Kuroshio Current) and eastern boundary undercurrents (e.g., California Undercurrent), which transport heat from the tropics toward the poles, effectively acting as the ocean's "great conveyor belt". Fluctuations in the transport of these currents alter the rate that heat is redistributed through the oceans. Sudden shifts in these currents are thought to have initiated past ice ages.
In addition to the horizontal transport of water and heat, vertical motions in the ocean are critical to the exchange of heat and gases such as CO2 between the surface layer and the deep ocean. One of the most common processes is upwelling. Interannual variations in upwelling at the coast create fluctuations in biological production in coastal ecosystems. Longer term trends in upwelling are thought to be related to global warming.