Covering some 71% of the Earth and absorbing about twice as much of the Sun's radiation as the atmosphere or the land surface, the oceans are a major component of the climate system. With their huge heat capacity, the oceans not only moderate temperature fluctuations but also play a dynamic role in transporting heat. Ocean currents move vast amounts of heat across the planet—roughly the same amount as the atmosphere does. But in contrast to the atmosphere, the oceans are confined by landmasses, so that their heat transport is more localized and channeled into specific regions.