Albedo Calculator

Albedo is the dimensionless fraction of incident shortwave radiation that a surface reflects, computed here as reflected divided by incoming irradiance in W/m2. Field measurement uses paired pyranometers, one facing upward and one facing downward, mounted roughly 1 to 2 metres above the surface. Typical values span nearly the whole range: fresh dry snow 0.80 to 0.90, aged or melting snow 0.40 to 0.70, bare glacier ice 0.20 to 0.40, desert sand 0.30 to 0.40, grassland 0.15 to 0.25, conifer forest 0.08 to 0.15, and calm open ocean about 0.06 at high sun angles. Earth's global mean planetary albedo is close to 0.30, with clouds responsible for roughly half of all reflection. The equilibrium temperature output applies the Stefan-Boltzmann law using the solar constant of about 1361 W/m2: temperature equals the fourth root of the quantity S times one minus albedo, divided by four times sigma, where sigma is 5.670e-8 W/m2/K4. At an albedo of 0.30 this yields about 255 K, roughly 33 K below Earth's observed mean surface temperature near 288 K, the gap being the greenhouse effect. Several caveats limit interpretation. Albedo varies strongly with solar zenith angle, so a single midday reading is not a daily mean. Broadband and spectral albedo differ sharply, since vegetation is dark in visible wavelengths because of chlorophyll absorption yet bright in the near infrared. And the equilibrium formula treats the body as a uniform blackbody with no atmosphere, so it describes a reference case rather than a real surface temperature.

The word albedo, Latin for whiteness, entered optics through Johann Heinrich Lambert's Photometria of 1760, the same work that established the cosine law of diffuse reflection. Nineteenth-century astronomers applied the concept to planetary surfaces, and the Bond albedo, defined as the fraction of incident light reflected in all directions, is named for the American astronomer George Phillips Bond, who worked at the Harvard College Observatory in the mid-1800s. Distinguishing Bond albedo from geometric albedo, which is measured at zero phase angle, remains standard practice in planetary science today. Quantitative measurement of terrestrial albedo followed the development of reliable pyranometers in the early twentieth century. Anders Angstrom's work in the 1910s and 1920s on solar radiation and snow reflectance was foundational, and Andre Danjon measured earthshine from the 1920s onward to estimate the reflectivity of Earth itself. In 1969 Mikhail Budyko and William Sellers independently published energy-balance climate models that made ice-albedo feedback an explicit and central mechanism, showing how a modest cooling could cascade through expanding ice cover. Satellites then replaced inference with direct observation: the Earth Radiation Budget instruments on Nimbus-7 from 1978 and ERBE from 1984, followed by MODIS on Terra in 1999 and the CERES instruments, produced the continuous global albedo records now used to validate climate models.