Global Climate

The sun’s rays strike the polar regions at a more grazing angle than over equatorial regions, where the rays strike at a more direct angle. The sun's angle is the primary reason why the polar regions are cold and the equatorial regions are warm.

Sea ice is white, so nearly all of the sunlight that hits the sea ice surface is reflected back into space; thus, it has a high albedo. High albedo helps keep the polar regions cold, because the sunlight reflected back into space does not warm the surface. When the climate changes enough to warm the Arctic and to melt sea ice, the polar regions have less of a reflective surface. More heat is absorbed, which causes more melting, which amplifies the warming. This cycle is known as a positive feedback loop that ultimately alters the circulation of the atmosphere.

Atmosphere and Ocean Circulation

The atmosphere and ocean act as “heat engines,” always trying to restore a temperature balance by transporting heat toward the poles. Our weather is a manifestation of this phenomenon. Low-pressure systems, such as storms, which can be especially strong in winter, are one of nature’s best ways of transporting heat poleward by atmospheric circulation. The oceans, by contrast, tend to transport heat in a slower and less violent fashion. Changes in the amount of sea ice alter how cold the poles are, which could affect atmospheric and ocean circulation.

Ocean currents transport heat from the equator to the poles through a heat- and saline-driven process called thermohaline circulation. Warm water moves from the equator northward along the ocean surface and eventually cools. As it cools, it becomes dense and heavy and sinks. This cold water then moves south along the lower part of the ocean and rises near the equator to complete the cycle. Like the atmospheric heat transport discussed earlier, this is a natural process that contributes to a proper temperature balance across the earth. It also explains why Europe is relatively warm, because as northward flowing surface water in the Atlantic Ocean cools, heat is released to the atmosphere.