Albedo is the fraction of incoming solar radiation that a surface reflects back to space, expressed as a number between 0 (perfect absorber — no reflection) and 1 (perfect reflector — all light bounced back). Earth's mean albedo is approximately 0.30, meaning 30 % of incoming sunlight is reflected. The remaining 70 % is absorbed and converted to heat, driving weather, ocean currents, and life.
Different surfaces have vastly different albedos: fresh snow (0.80–0.90), thick cloud (0.60–0.90), desert sand (0.30–0.40), grassland (0.15–0.25), forest (0.10–0.20), ocean (0.06–0.10 at low sun angles, but virtually 0 at high sun). This variation creates important feedback loops: if snow or ice melts, the darker surface beneath absorbs more radiation, warming the area further and melting more ice — the snow-albedo feedback, one of the most powerful amplifiers of climate change in polar regions.
Albedo plays a central role in climate science and meteorology. Cloud albedo is one of the largest uncertainties in climate models — low stratocumulus clouds cool the planet by reflecting sunlight, while thin cirrus clouds warm it by trapping outgoing infrared. Urban areas (albedo 0.10–0.20) absorb significantly more heat than surrounding countryside, contributing to the urban heat island effect. Proposed geoengineering schemes to combat global warming include increasing Earth's albedo by injecting aerosols into the stratosphere or painting roofs white — though such approaches remain controversial.