Albedo
Albedo is the fraction of light that is reflected by a body or surface. When the sun’s rays hit the white, reflective surfaces of ice, much of the radiation is reflected back to space, thus causing a net cooling effect of the atmosphere.

The Earth's albedo influences global warming: As the ice and snow cover over land and sea is reduced, the albedo of the area is reduced as well. Darker surfaces underneath are revealed, and since a dark surface can absorb more heat, the result is a feed-back process which causes increased heating.