Albedo

For other uses, see Albedo (disambiguation).

Albedo change in Greenland: the map shows the difference between the amount of sunlight Greenland reflected in the summer of 2011 versus the average percent it reflected between 2000 and 2006. Some areas reflect close to 20 percent less light than a decade ago.[1]

Albedo (/ælˈbiːdoʊ/ al-BEE-doh; from Latin albedo 'whiteness') is the fraction of sunlight that is diffusely reflected by a body. It is measured on a scale from 0 (corresponding to a black body that absorbs all incident radiation) to 1 (corresponding to a body that reflects all incident radiation). Surface albedo is defined as the ratio of radiosity Je to the irradiance Ee (flux per unit area) received by a surface.[2] The proportion reflected is not only determined by properties of the surface itself, but also by the spectral and angular distribution of solar radiation reaching the Earth's surface.[3] These factors vary with atmospheric composition, geographic location, and time (see position of the Sun).

While directional-hemispherical reflectance factor is calculated for a single angle of incidence (i.e., for a given position of the Sun), albedo is the directional integration of reflectance over all solar angles in a given period. The temporal resolution may range from seconds (as obtained from flux measurements) to daily, monthly, or annual averages.

Unless given for a specific wavelength (spectral albedo), albedo refers to the entire spectrum of solar radiation.[4] Due to measurement constraints, it is often given for the spectrum in which most solar energy reaches the surface (between 0.3 and 3 μm). This spectrum includes visible light (0.4–0.7 μm), which explains why surfaces with a low albedo appear dark (e.g., trees absorb most radiation), whereas surfaces with a high albedo appear bright (e.g., snow reflects most radiation).

Ice–albedo feedback is a positive feedback climate process where a change in the area of ice caps, glaciers, and sea ice alters the albedo and surface temperature of a planet. Ice is very reflective, therefore it reflects far more solar energy back to space than the other types of land area or open water. Ice–albedo feedback plays an important role in global climate change.[5] Albedo is an important concept in climate science.

  1. ^ "Greenland's Ice Is Growing Darker". NASA. 2011. Retrieved 6 July 2023.
  2. ^ Pharr; Humphreys. "Fundamentals of Rendering - Radiometry / Photometry" (PDF). Web.cse.ohio-state.edu. Archived (PDF) from the original on 9 October 2022. Retrieved 2 March 2022.
  3. ^ Coakley, J. A. (2003). "Reflectance and albedo, surface" (PDF). In J. R. Holton; J. A. Curry (eds.). Encyclopedia of the Atmosphere. Academic Press. pp. 1914–1923. Archived (PDF) from the original on 9 October 2022.
  4. ^ Henderson-Sellers, A.; Wilson, M. F. (1983). "The Study of the Ocean and the Land Surface from Satellites". Philosophical Transactions of the Royal Society of London A. 309 (1508): 285–294. Bibcode:1983RSPTA.309..285H. doi:10.1098/rsta.1983.0042. JSTOR 37357. S2CID 122094064. Albedo observations of the Earth's surface for climate research
  5. ^ Budyko, M. I. (1 January 1969). "The effect of solar radiation variations on the climate of the Earth". Tellus. 21 (5): 611–619. Bibcode:1969Tell...21..611B. doi:10.3402/tellusa.v21i5.10109. ISSN 0040-2826.