Albedo and reflective propertis of various types of snow and water
Snow acts as a reflective blanket over Arctic land and ice surfaces. It has two important effects. It reflects away the sun's heat, cooling the overlying air. And it insulates the ground in winter, preventing upper soil layers in some areas from freezing solid and protecting underlying vegetation from damage by severe frost. Snow reflects more of the sun's energy because it is white and more 'reflective' than the darker ground surface beneath.
In fact, snow is the most reflective natural surface on Earth. By reducing the amount of energy that reaches the ground, snow cover reduces the temperature in the lower atmosphere, because much of the heat near the surface is derived from the warmth of the ground. The onset of snow cover in the Arctic in autumn is associated with an abrupt drop of up to 10 centigrades in surface air temperatures. At least half of this sudden temperature change is due to the reflective effect of the snow.
In spring and early summer, when the Arctic is warming and snow melts, the opposite happens. The soil, rock and vegetation beneath the snow are darker and absorb more of the sun's energy. The ground warms quickly once the snow has gone, warming the air above, which in turn causes more snow to melt, and so on until the snow has gone.
A major implication of decreasing snow cover across the whole Arctic is to increase the rate of warming, especially in spring. It has been estimated that the reduced duration of Arctic snow cover seen between 1970 and 2000 has created an increased warming effect equivalent to around 5% of the warming caused by human-induced carbon dioxide emissions each year.