Ice plays an important role in the regulation of the earth's climate in a number of ways:

Reflecting solar radiation

As solar radiation reaches the earth's atmosphere and surface, a certain percentage is reflected back out to space. The percentage of sunlight that is reflected, however, depends on the albedo (reflectivity or whiteness) of the surface. Ice and snow have a high albedo and hence reflect about 80% of incident sunlight. Thus, once formed, ice tends to be maintained. However, if ice cover were to decrease, less solar radiation would be reflected away from the surface of the earth, and as a result, the atmosphere would absorb more heat.

Insulating layer on top of the warm ocean waters

Each year, the Arctic and the Antarctic Oceans experience the formation and subsequent melting of vast amounts of sea ice floating on the sea surface. At the North Pole, an area of ice the size of Europe melts away every summer and then freezes again the following winter. The thickness of this sea ice plays a central role in polar climate as it moderates heat transport by insulating the ocean from the cold polar atmosphere.

Production of heavy, saline waters that drive the thermohaline circulation

The seasonal changes of polar sea ice have a significant effect on certain global ocean circulation patterns, known as thermohaline circulation. As ice melts, there is an influx of fresh water into the surrounding ocean; this decreases the salinity and consequently the density of the water. Conversely, as ice is formed, salinity and therefore the density of the water increases. The density increase causes the surface waters to sink and effectively act as a pump, driving deep ocean currents from the polar regions towards the equator, while at the surface warmer, less dense water masses flow from low to high latitudes. For more information see also: Gulf stream