While the rate of warming of the Earth’s surface has slowed since 1999, ocean temperatures have continued to increase, especially at depth.
The results of a recent study from the University of Washington described here and published in the journal Science, has shown that a slow-moving current in the Atlantic, which carries heat between the two poles, sped up earlier this century to draw heat down almost a mile (1,500 meters) into the ocean.
This current oscillates between warming and cooling periods. During the warming period, faster currents bring more tropical water to to the North Atlantic, warming both the surface and the deep water. The warmer surface water melts ice, slowly decreasing the density of the water. Since salty water is more dense, it sinks and acts as a driver for the current. With less saline water at the surface, the circulation slows and a 30-year cooling phase begins. The current began to draw heat deeper into the ocean around 2000, counteracting human-caused warming at the surface.