Ocean currents

The oceans interact with climate, in many ways. One example is called the el Niño oscillation, a flip-flop between two self-reinforcing states, el Niño and la Niña (Fig. 7.7). During la Niña, the thermocline along the equator in the Pacific Ocean slopes upward toward the east, bringing cold waters to the sea surface. The temperature contrast between east and west drives winds which travel from east to west, maintaining the slope of the thermocline. The other state, el Niño, flattens the slope in the thermocline and collapses the wind. The coupled atmosphere/ocean system flips back and forth between these two climate states one cycle every 4-7 years. The state of la Niña affects climate to varying extents all around the world. There is a possibility that with global warming, the Pacific may tend to favor the la Niña state, but the model forecasts for this are not very reliable.

West

East

Atmosphere

Ocean Warm water

Cold water

Weak wind

Strong wind

East

Atmosphere Ocean

Strong wind

East

Atmosphere Ocean

Fig. 7.7 The configuration of the atmosphere and ocean along the equator in the Pacific Ocean during el Niño and la Niña phases of the el Niño climate oscillation. (a) la Niña: In the la Niña phase of the oscillation, the slope in the ocean temperature boundary, and the winds in the atmosphere, collapse. The climate oscillates back and forth between these two states every 4-7 years or so, affecting climate conditions around the rest of the world. (b) el Niño: During el Niño, the boundary between warm water and cold water in the ocean slopes up from west to east, exposing cold water to the atmosphere in the east near Peru. In addition to stimulating the Peruvian fisheries, the cold water drives a strong wind from east to west which tends to sustain the slope in the ocean temperature boundary.

Fig. 7.7 The configuration of the atmosphere and ocean along the equator in the Pacific Ocean during el Niño and la Niña phases of the el Niño climate oscillation. (a) la Niña: In the la Niña phase of the oscillation, the slope in the ocean temperature boundary, and the winds in the atmosphere, collapse. The climate oscillates back and forth between these two states every 4-7 years or so, affecting climate conditions around the rest of the world. (b) el Niño: During el Niño, the boundary between warm water and cold water in the ocean slopes up from west to east, exposing cold water to the atmosphere in the east near Peru. In addition to stimulating the Peruvian fisheries, the cold water drives a strong wind from east to west which tends to sustain the slope in the ocean temperature boundary.

Another potential feedback from the ocean to climate is in the North Atlantic Ocean. Warm water is carried to the North Atlantic in the Gulf Stream discovered by Benjamin Franklin. As the water cools, its density increases and it sinks to the deep Atlantic, making room for more warm water to carry more heat to the high northern latitudes. Our climatic and oceanographic reconstructions of the North Atlantic region from the last ice age point to an instability in this system. The climate record in the ice in Greenland shows huge temperature swings called Dansgaard-Oeschger events - temperature changes of 10°C at that location within a few years. Oceanographic reconstructions from sediment cores show that the overturning circulation in the North Atlantic starts and stops in synchrony with these temperature swings. One large climate shift, 8200 years ago, has been correlated with the catastrophic release of a Great Lake's worth of fresh water into the North Atlantic, as an ice dam holding the lake in finally burst. Fresh water is not as dense as salty water, so an input of fresh water could have stopped the overturning circulation.

The circulation in the North Atlantic may change in the coming century in response to rising temperature or precipitation. Warming is more intense in high latitudes than the global average because of the ice albedo feedback. Warming tends to increase rain and snowfall because there is more water vapor in warm air than cold air. Another potential source of new fresh water to the North Atlantic is by melting of the Greenland ice sheet if it were to melt quickly enough.

Was this article helpful?

0 0
Guide to Alternative Fuels

Guide to Alternative Fuels

Your Alternative Fuel Solution for Saving Money, Reducing Oil Dependency, and Helping the Planet. Ethanol is an alternative to gasoline. The use of ethanol has been demonstrated to reduce greenhouse emissions slightly as compared to gasoline. Through this ebook, you are going to learn what you will need to know why choosing an alternative fuel may benefit you and your future.

Get My Free Ebook


Post a comment