Exam 12: The Ocean and the Atmosphere

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One of the most important natural influences on climate is the oceanic thermohaline circulation.For example,as mentioned earlier,the Gulf Stream current - the segment of the thermohaline circulation that returns warm water to the North Atlantic - is largely responsible for the moderate climate in coastal regions of eastern North America and western Europe.Because the ocean's conveyor belt circulation redistributes heat from the tropics to the poles,any weakening of this circulation would be expected to have a dramatic effect on the temperature distribution.For example,during the last Ice Age,the polar ice caps may have cut off the thermohaline circulation in the North Atlantic,which likely increased the length and severity of the glaciation.

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Some water was present from the beginning,trapped inside the planet along with other volatile elements among the materials from which Earth was formed.In the first few hundred million years after the planet formed,water was released in the form of steam from volcanoes.Early in Earth history,though,the surface of the planet was too hot for liquid water to persist.Additional water may have been added to Earth's chemical mix by comets coming in from the outer regions of the solar system,after the planet had already formed.As the surface slowly cooled,liquid water began to be retained in low-lying basins.