albedo

The proportion of light that a surface reflects — its reflectivity, expressed as a number from 0 (absorbs all light) to 1 (reflects all light). Fresh snow has an albedo near 0.9; open ocean is around 0.06; a forest canopy around 0.15. Albedo determines how much solar energy a surface absorbs and is one of the key variables in climate: as Arctic ice melts, high-albedo white surfaces are replaced by low-albedo dark ocean, which absorbs more heat, which melts more ice. The feedback loop is as simple as it is relentless.