Planetary Albedo Calculator

Bond albedo is the fraction of incident stellar power a body reflects, integrated over all wavelengths and all directions, and it is the quantity that belongs in an equilibrium temperature calculation of the form T_eq equals the fourth root of S(1-A) divided by 4 sigma. Earth Bond albedo sits close to 0.30, split roughly two thirds from clouds and one third from the surface plus atmospheric scattering and aerosols. Surface values span a wide range: fresh snow 0.80 to 0.90, sea ice 0.50 to 0.70, desert sand 0.30 to 0.40, bare soil 0.15 to 0.25, closed-canopy forest 0.10 to 0.15, and open ocean near 0.06 under a high Sun. Geometric albedo, which compares brightness at zero phase angle against an ideal Lambertian disk, is a different number and should not be substituted here; for Earth it is roughly 0.43. Because temperature scales with the fourth root of absorbed flux, albedo changes act more gently than they first appear: dropping Earth albedo from 0.30 to 0.20 raises equilibrium temperature by roughly 9 K rather than by any proportional amount. The real leverage comes from feedback, since retreating snow and sea ice expose surfaces four to ten times darker and reinforce the warming that removed them, a principal reason the Arctic has warmed several times faster than the global mean. Across the solar system the NASA fact-sheet Bond albedos are 0.088 for Mercury, 0.77 for Venus, 0.306 for Earth, 0.25 for Mars, and about 0.50 for Jupiter. Venus shows why albedo alone settles nothing: it reflects roughly three quarters of the sunlight reaching it and still holds a surface near 735 K, because its greenhouse effect governs the outgoing side of the balance.

The word entered science through Johann Heinrich Lambert, whose Photometria of 1760 established the quantitative treatment of reflected light and used the Latin albedo, meaning whiteness. The Bond albedo is named for George Phillips Bond, director of the Harvard College Observatory, who in the 1860s made careful photometric comparisons of the brightness of the Moon, Jupiter, and the Sun. Henry Norris Russell formalized the distinction between the total reflected fraction and the opposition brightness in a pair of papers on the albedo of planets and satellites published in 1916, establishing the definitions still in use. Measuring Earth own albedo proved harder than measuring that of other planets, because the observer sits inside the system being measured. Andre Danjon addressed this in the 1920s and 1930s through photometry of earthshine, the faint glow on the lunar night side lit by reflected Earthlight, a technique revived at Big Bear Solar Observatory by Philip Goode and colleagues from 1998. Spaceborne broadband radiometry began with the instrument built by Verner Suomi for Explorer 7 in 1959 and matured through the Nimbus satellites, the Earth Radiation Budget Experiment from 1984, and the CERES instruments from the late 1990s onward. Since 2015 the EPIC camera aboard DSCOVR has watched the entire sunlit disk continuously from the L1 Lagrange point, a vantage unavailable to satellites in low Earth orbit.