Changes in the concentration of greenhouse gases in our atmosphere affect the thermal-energy balance in Earth’s climate system. But thanks to its huge volume, deep basins, and large heat capacity, the global ocean has largely forestalled atmospheric warming by acting as a heat sink. Indeed, the ocean stores more than 90% of the excess heat Earth has accumulated since 1971. Compare that with the scant 1% stored in the atmosphere, as shown in figure 1.

The ocean also redistributes the absorbed energy around the planet. Colder and thus denser waters from high latitudes can sink from the surface and spread toward the equator beneath warmer, lighter waters at lower latitudes. In the northern North Atlantic Ocean and the Southern Ocean around Antarctica, water is cooled so much that it can sink to great depths, where it then spreads out to fill much of the rest of the deep ocean....

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