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[[File:Albedo-e hg.svg|thumb|upright=1.3|The percentage of [[diffuse reflection|diffusely reflected]] [[sunlight]] relative to various surface conditions]]

'''Albedo''' ({{IPAc-en|æ|l|ˈ|b|iː|d|oʊ}}) ({{lang-la|albedo}}, meaning 'whiteness') is the measure of the [[diffuse reflection]] of [[sunlight|solar radiation]] out of the total [[solar radiation]] received by an [[astronomical body]] (e.g. a [[planet]] like [[Earth]]). It is [[dimensionless number|dimensionless]] and 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 (radiometry)|radiosity]] to the [[irradiance]] (flux per unit area) received by a surface.<ref>http://web.cse.ohio-state.edu/~parent.1/classes/782/Lectures/03_Radiometry.pdf</ref> 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.<ref>{{cite web |url=http://curry.eas.gatech.edu/Courses/6140/ency/Chapter9/Ency_Atmos/Reflectance_Albedo_Surface.pdf |title=Reflectance and albedo, surface |work=Encyclopedia of the Atmosphere |editors=J. R. Holton and J. A. Curry |last=Coakley |first=J. A. |publisher=Academic Press |year=2003|pages=1914–1923}}</ref> These factors vary with atmospheric composition, geographic location and time (see [[position of the Sun]]). While bi-hemispherical [[reflectance]] 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.<ref>{{cite journal |last=Henderson-Sellers |first=A. |last2=Wilson |first2=M. F.|year=1983 |quote=Albedo observations of the Earth's surface for climate research |jstor=37357 |journal=Philosophical Transactions of the Royal Society of London A |volume=309 |issue=1508 |title=The Study of the Ocean and the Land Surface from Satellites |pages=285–294 |bibcode=1983RSPTA.309..285H |doi=10.1098/rsta.1983.0042}}</ref> 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 spectrum|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).

Albedo is an important concept in [[climatology]], [[astronomy]], and environmental management (e.g., as part of the [[Leadership in Energy and Environmental Design]] (LEED) program for sustainable rating of buildings). The average albedo of the Earth from the upper atmosphere, its ''planetary albedo'', is 30–35% because of [[cloud cover]], but widely varies locally across the surface because of different geological and environmental features.<ref>{{cite book |title=Environmental Encyclopedia |url=https://archive.org/details/environmentalenc01cunn |url-access=registration |edition=3rd |publisher=Thompson Gale |year=2003 |isbn=978-0-7876-5486-3}}</ref>

The term albedo was introduced into optics by [[Johann Heinrich Lambert]] in his 1760 work ''[[Photometria]]''.

==Terrestrial albedo==
{| class="wikitable" style="float:right; margin:10px"
|+ Sample albedos
|-
! Surface
! Typical<br />albedo
|-
| Fresh asphalt || 0.04<ref name="heat island">{{cite web
 | last=Pon | first=Brian | date=30 June 1999
 | url=http://eetd.lbl.gov/HeatIsland/Pavements/Albedo/
 | title=Pavement Albedo | publisher=Heat Island Group
 | accessdate=27 August 2007
| archiveurl= https://web.archive.org/web/20070829153207/http://eetd.lbl.gov/HeatIsland/Pavements/Albedo/| archivedate= 29 August 2007<!--Added by DASHBot-->}}</ref>
|-
|Open ocean
|0.06<ref>{{Cite web|url=https://nsidc.org/cryosphere/seaice/processes/albedo.html|title=Thermodynamics {{!}} Thermodynamics: Albedo {{!}} National Snow and Ice Data Center|website=nsidc.org|access-date=14 August 2016}}</ref>
|-
| Worn asphalt || 0.12<ref name="heat island"/>
|-
| Conifer forest<br />(Summer) || 0.08<ref name="Betts 1">{{Cite journal
 | author=Alan K. Betts
 | author2=John H. Ball
 | title=Albedo over the boreal forest
 | journal=Journal of Geophysical Research
 | date=1997
 | volume=102
 | issue=D24
 | pages=28,901–28,910
 | url=http://www.agu.org/pubs/crossref/1997/96JD03876.shtml
 | accessdate=27 August 2007
 | doi=10.1029/96JD03876
|bibcode = 1997JGR...10228901B | archiveurl= https://web.archive.org/web/20070930184719/http://www.agu.org/pubs/crossref/1997/96JD03876.shtml| archivedate= 30 September 2007<!--Added by DASHBot-->}}</ref> 0.09 to 0.15<ref name="mmutrees"/>
|-
| [[Deciduous trees]] || 0.15 to 0.18<ref name="mmutrees"/>
|-
| Bare soil || 0.17<ref name="markvart">{{Cite book
  | author=Tom Markvart
  | author2=Luis CastaŁżer | date=2003
  | title=Practical Handbook of Photovoltaics: Fundamentals and Applications
  | publisher=Elsevier | isbn=978-1-85617-390-2 }}</ref>
|-
| Green grass || 0.25<ref name="markvart"/>
|-
| Desert sand || 0.40<ref name="Tetzlaff">{{Cite book
 | first=G. | last=Tetzlaff | date=1983
 | title=Albedo of the Sahara
 | work=Cologne University Satellite Measurement of Radiation Budget Parameters
 | pages=60–63 }}</ref>
|-
| New concrete || 0.55<ref name="markvart"/>
|-
| Ocean ice|| 0.50 to 0.70<ref name="markvart"/>
|-
| Fresh snow || 0.80<ref name="markvart"/>
|}
Any albedo in visible light falls within a range of about 0.9 for fresh snow to about 0.04 for charcoal, one of the darkest substances. Deeply shadowed cavities can achieve an effective albedo approaching the zero of a [[black body]]. When seen from a distance, the ocean surface has a low albedo, as do most forests, whereas desert areas have some of the highest albedos among landforms. Most land areas are in an albedo range of 0.1 to 0.4.<ref name="PhysicsWorld">{{cite web|url=http://scienceworld.wolfram.com/physics/Albedo.html |title=Albedo – from Eric Weisstein's World of Physics |publisher=Scienceworld.wolfram.com |accessdate=19 August 2011}}</ref> The average albedo of [[Earth]] is about 0.3.<ref name="Goode"/> This is far higher than for the ocean primarily because of the contribution of clouds.

[[File:Ceres 2003 2004 clear sky total sky albedo.png|thumb|upright=1.2|left|2003–2004 mean annual clear-sky and total-sky albedo]]
Earth's surface albedo is regularly estimated via [[Earth observation]] satellite sensors such as [[NASA]]'s [[MODIS]] instruments on board the [[Terra (satellite)|Terra]] and [[Aqua (satellite)|Aqua]] satellites, and the CERES instrument on the [[Suomi NPP]] and [[Joint Polar Satellite System|JPSS]]. As the amount of reflected radiation is only measured for a single direction by satellite, not all directions, a mathematical model is used to translate a sample set of satellite reflectance measurements into estimates of [[directional-hemispherical reflectance]] and bi-hemispherical reflectance (e.g.,<ref name="NASA"/>). These calculations are based on the [[bidirectional reflectance distribution function]] (BRDF), which describes how the reflectance of a given surface depends on the view angle of the observer and the solar angle. BDRF can facilitate translations of observations of reflectance into albedo.

Earth's average surface temperature due to its albedo and the [[greenhouse effect]] is currently about 15&nbsp;°C. If Earth were frozen entirely (and hence be more reflective), the average temperature of the planet would drop below −40&nbsp;°C.<ref name="washington" /> If only the continental land masses became covered by glaciers, the mean temperature of the planet would drop to about 0&nbsp;°C.<ref name="clim-past"/> In contrast, if the entire Earth was covered by water – a so-called [[ocean planet]] – the average temperature on the planet would rise to almost 27&nbsp;°C.<ref name="Smith Robin"/>

===White-sky, black-sky, and blue-sky albedo===
For land surfaces, it has been shown that the albedo at a particular [[solar zenith angle]] ''θ''<sub>''i''</sub> can be approximated by the proportionate sum of two terms:
* the [[directional-hemispherical reflectance]] at that solar zenith angle, <math>{\bar \alpha(\theta_i)}</math>, sometimes referred to as black-sky albedo, and
* the [[bi-hemispherical reflectance]], <math>\bar{ \bar \alpha}</math>, sometimes referred to as white-sky albedo.
with <math>{1-D}</math> being the proportion of direct radiation from a given solar angle, and <math>{D}</math> being the proportion of diffuse illumination, the actual albedo <math>{\alpha}</math> (also called blue-sky albedo) can then be given as:

:<math>{\alpha}= (1-D) \bar \alpha(\theta_i) + D \bar{ \bar \alpha}.</math>

This formula is important because it allows the albedo to be calculated for any given illumination conditions from a knowledge of the intrinsic properties of the surface.<ref name="BlueskyAlbedo"/>

== Astronomical albedo ==

The albedos of [[planet]]s, [[Natural satellite|satellites]] and [[minor planet]]s such as [[asteroid]]s can be used to infer much about their properties. The study of albedos, their dependence on wavelength, lighting angle ("phase angle"), and variation in time comprises a major part of the astronomical field of [[photometry (astronomy)|photometry]]. For small and far objects that cannot be resolved by telescopes, much of what we know comes from the study of their albedos. For example, the absolute albedo can indicate the surface ice content of outer [[Solar System]] objects, the variation of albedo with phase angle gives information about [[regolith]] properties, whereas unusually high radar albedo is indicative of high metal content in [[asteroid]]s.

[[Enceladus]], a moon of Saturn, has one of the highest known albedos of any body in the Solar System, with an albedo of 0.99. Another notable high-albedo body is [[Eris (dwarf planet)|Eris]], with an albedo of 0.96.<ref name="sicardy">
{{cite journal
| title = Size, density, albedo and atmosphere limit of dwarf planet Eris from a stellar occultation
| journal = European Planetary Science Congress Abstracts
| volume = 6
| date = 2011
| url = http://meetingorganizer.copernicus.org/EPSC-DPS2011/EPSC-DPS2011-137-8.pdf
| accessdate = 14 September 2011
| bibcode = 2011epsc.conf..137S
| last1 = Sicardy
| first1 = B.
| last2 = Ortiz
| first2 = J. L.
| last3 = Assafin
| first3 = M.
| last4 = Jehin
| first4 = E.
| last5 = Maury
| first5 = A.
| last6 = Lellouch
| first6 = E.
| last7 = Gil-Hutton
| first7 = R.
| last8 = Braga-Ribas
| first8 = F.
| last9 = Colas
| first9 = F.
| page = 137
| displayauthors=8
}}
</ref> Many small objects in the outer Solar System<ref name="tnoalbedo">{{cite web
  |date=17 September 2008
  |title=TNO/Centaur diameters and albedos
  |publisher=Johnston's Archive
  |author=Wm. Robert Johnston
  |url=http://www.johnstonsarchive.net/astro/tnodiam.html
  |accessdate=17 October 2008| archiveurl= https://web.archive.org/web/20081022223827/http://www.johnstonsarchive.net/astro/tnodiam.html| archivedate= 22 October 2008<!--Added by DASHBot-->}}</ref> and [[asteroid belt]] have low albedos down to about 0.05.<ref name="astalbedo">{{cite web
  |date=28 June 2003
  |title=Asteroid albedos: graphs of data
  |publisher=Johnston's Archive
  |author=Wm. Robert Johnston
  |url=http://www.johnstonsarchive.net/astro/astalbedo.html
  |accessdate=16 June 2008| archiveurl= https://web.archive.org/web/20080517100307/http://www.johnstonsarchive.net/astro/astalbedo.html| archivedate= 17 May 2008<!--Added by DASHBot-->}}</ref> A typical [[comet nucleus]] has an albedo of 0.04.<ref name="dark">{{cite web
  |date=29 November 2001
  |title=Comet Borrelly Puzzle: Darkest Object in the Solar System
  |publisher=Space.com
  |author=Robert Roy Britt
  |url=http://www.space.com/scienceastronomy/solarsystem/borrelly_dark_011129.html
  |accessdate=1 September 2012| archiveurl= https://web.archive.org/web/20090122074028/http://www.space.com/scienceastronomy/solarsystem/borrelly_dark_011129.html| archivedate= 22 January 2009}}</ref> Such a dark surface is thought to be indicative of a primitive and heavily [[space weathering|space weathered]] surface containing some [[organic compound]]s.

The overall albedo of the [[Moon]] is measured to be around 0.14,<ref name="CERESmoon">
{{cite journal
| title = Celestial body irradiance determination from an underfilled satellite radiometer: application to albedo and thermal emission measurements of the Moon using CERES
| journal = Applied Optics
| volume = 47 | issue = 27
| date = 2008
| bibcode = 2008ApOpt..47.4981M
| last1 = Matthews
| first1 = G.
| pages = 4981–4993

|doi = 10.1364/AO.47.004981
| pmid=18806861}}
</ref> but it is strongly directional and non-[[Lambertian reflectance|Lambertian]], displaying also a strong [[opposition effect]].<ref name="medkeff" /> Although such reflectance properties are different from those of any terrestrial terrains, they are typical of the [[regolith]] surfaces of airless Solar System bodies.

Two common albedos that are used in astronomy are the (V-band) [[geometric albedo]] (measuring brightness when illumination comes from directly behind the observer) and the [[Bond albedo]] (measuring total proportion of electromagnetic energy reflected). Their values can differ significantly, which is a common source of confusion.

{| class="wikitable"
|-
! Planet
! Geometric
! Bond
|-
| Mercury
| 0.14 <ref name="Mallama_et_al"/>
| 0.09 <ref name="Mallama"/>
|-
| Venus
| 0.69 <ref name="Mallama_et_al"/>
| 0.76  <ref name="Haus_et_al"/>
|-
| Earth
| 0.43 <ref name="Mallama_et_al"/>
| 0.31 <ref>[http://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html Earth Fact Sheet, NASA]</ref>
|-
| Mars
| 0.17 <ref name="Mallama_et_al"/>
| 0.25 <ref>[http://nssdc.gsfc.nasa.gov/planetary/factsheet/marsfact.html Mars Fact Sheet, NASA]</ref>
|-
| Jupiter
| 0.54 <ref name="Mallama_et_al"/>
| 0.50 <ref name="Li_et_al"/>
|-
| Saturn
| 0.50 <ref name="Mallama_et_al"/>
| 0.34 <ref name="Hanel_et_al"/>
|-
| Uranus
| 0.49 <ref name="Mallama_et_al"/>
| 0.30 <ref name="Pearl_et_al_Uranus"/>
|-
| Neptune
| 0.44 <ref name="Mallama_et_al"/>
| 0.29 <ref name="Pearl_et_al_Neptune"/>
|}

In detailed studies, the directional reflectance properties of astronomical bodies are often expressed in terms of the five [[Hapke parameters]] which semi-empirically describe the variation of albedo with [[phase angle (astronomy)|phase angle]], including a characterization of the opposition effect of [[regolith]] surfaces.

The correlation between astronomical (geometric) albedo, [[Absolute magnitude#Absolute magnitude for planets (H)|absolute magnitude]] and diameter is:<ref name="bruton">{{cite web
 |title=Conversion of Absolute Magnitude to Diameter for Minor Planets
 |publisher=Department of Physics & Astronomy (Stephen F. Austin State University)
 |author=Dan Bruton
 |url=http://www.physics.sfasu.edu/astro/asteroids/sizemagnitude.html
 |accessdate=7 October 2008
 |archiveurl=https://web.archive.org/web/20081210190134/http://www.physics.sfasu.edu/astro/asteroids/sizemagnitude.html
 |archivedate=10 December 2008
 |url-status=dead
}}</ref>
<math>A =\left ( \frac{1329\times10^{-H/5}}{D} \right ) ^2</math>,

where <math>A</math> is the astronomical albedo, <math>D</math> is the diameter in kilometers, and <math>H</math> is the absolute magnitude. absorbing lots of light energy black would be better

==Examples of terrestrial albedo effects==

===Illumination===
Albedo is not directly dependent on illumination because changing the amount of incoming light proportionally changes the amount of reflected light, except in circumstances where a change in illumination induces a change in the Earth's surface at that location (e.g. through melting of reflective ice). That said, albedo and illumination both vary by latitude. Albedo is highest near the poles and lowest in the subtropics, with a local maximum in the tropics.<ref name=Winston>{{cite journal| first=Jay |last=Winston |title=The Annual Course of Zonal Mean Albedo as Derived From ESSA 3 and 5 Digitized Picture Data |journal=Monthly Weather Review |volume=99 |pages=818–827| bibcode=1971MWRv...99..818W| date=1971| doi=10.1175/1520-0493(1971)099<0818:TACOZM>2.3.CO;2| issue=11}}</ref>

===Insolation effects===
The intensity of albedo temperature effects depends on the amount of albedo and the level of local [[insolation]] (solar irradiance); high albedo areas in the [[arctic]] and [[antarctic]] regions are cold due to low insolation, whereas areas such as the [[Sahara Desert]], which also have a relatively high albedo, will be hotter due to high insolation.  [[Tropical]] and [[sub-tropical]] [[rainforest]] areas have low albedo, and are much hotter than their [[temperate forest]] counterparts, which have lower insolation. Because insolation plays such a big role in the heating and cooling effects of albedo, high insolation areas like the tropics will tend to show a more pronounced fluctuation in local temperature when local albedo changes.{{citation needed|date=November 2013}}

Arctic regions notably release more heat back into space than what they absorb, effectively cooling the [[Earth]]. This has been a concern since arctic ice and [[snow]] has been melting at higher rates due to higher temperatures, creating regions in the arctic that are notably darker (being water or ground which is darker color) and reflects less heat back into space. This [[Ice-albedo feedback|feedback loop]] results in a reduced albedo effect.<ref>{{Cite journal|url=https://www.economist.com/news/briefing/21721364-commercial-opportunities-are-vastly-outweighed-damage-climate-thawing-arctic|title=The thawing Arctic threatens an environmental catastrophe|journal=The Economist|access-date=8 May 2017|date=29 April 2017}}</ref>

===Climate and weather===
Albedo affects [[climate]] by determining how much [[radiation]] a planet absorbs.<ref>{{Cite book|url=https://books.google.com/books?id=av7q4N8Ib6sC&pg=PA53|title=Encyclopedia of Climate and Weather: Abs-Ero|last=Schneider|first=Stephen Henry|last2=Mastrandrea|first2=Michael D.|last3=Root|first3=Terry L.|date=2011|publisher=Oxford University Press|isbn=978-0-19-976532-4|page=53}}</ref> The uneven heating of Earth from albedo variations between land, ice, or ocean surfaces can drive [[weather]].

===Albedo–temperature feedback===
When an area's albedo changes due to snowfall, a snow–temperature [[feedback]] results. A layer of snowfall increases local albedo, reflecting away sunlight, leading to local cooling. In principle, if no outside temperature change affects this area (e.g., a warm [[air mass]]), the raised albedo and lower temperature would maintain the current snow and invite further snowfall, deepening the snow–temperature feedback. However, because local [[weather]] is dynamic due to the change of [[season]]s, eventually warm air masses and a more direct angle of sunlight (higher [[insolation]]) cause melting. When the melted area reveals surfaces with lower albedo, such as grass or soil, the effect is reversed: the darkening surface lowers albedo, increasing local temperatures, which induces more melting and thus reducing the albedo further, resulting in still more heating.

===Snow===
Snow albedo is highly variable, ranging from as high as 0.9 for freshly fallen snow, to about 0.4 for melting snow, and as low as 0.2 for dirty snow.<ref>Hall, D.K. and Martinec, J. (1985), ''Remote sensing of ice and snow''. Chapman and Hall, New York, 189 pp.</ref> Over [[Antarctica]] snow albedo averages a little more than 0.8. If a marginally snow-covered area warms, snow tends to melt, lowering the albedo, and hence leading to more snowmelt because more radiation is being absorbed by the snowpack (the ice–albedo [[positive feedback]]).

Just as fresh snow has a higher albedo than does dirty snow, the albedo of snow-covered sea ice is far higher than that of sea water. Sea water absorbs more solar radiation than would the same surface covered with reflective snow. When sea ice melts, either due to a rise in sea temperature or in response to increased solar radiation from above, the snow-covered surface is reduced, and more surface of sea water is exposed, so the rate of energy absorption increases. The extra absorbed energy heats the sea water, which in turn increases the rate at which sea ice melts. As with the preceding example of snowmelt, the process of melting of sea ice is thus another example of a positive feedback.<ref>"All About Sea Ice." National Snow and Ice Data Center. Accessed 16 November 2017. /cryosphere/seaice/index.html.</ref> Both positive feedback loops have long been recognized as important for [[global warming]].{{citation needed|date=January 2018}}

[[Cryoconite]], powdery windblown [[dust]] containing soot, sometimes reduces albedo on glaciers and ice sheets.<ref name = "Nat. Geo">[http://ngm.nationalgeographic.com/2010/06/melt-zone/jenkins-text/3 "Changing Greenland – Melt Zone"] page 3, of 4, article by Mark Jenkins in ''[[National Geographic (magazine)|National Geographic]]'' June 2010, accessed 8 July 2010</ref>

The dynamical nature of albedo in response to positive feedback, together with the effects of small errors in the measurement of albedo, can lead to large errors in energy estimates. Because of this, in order to reduce the error of energy estimates, it is important to measure the albedo of snow-covered areas through remote sensing techniques rather than applying a single value for albedo over broad regions.{{citation needed|date=January 2018}}

===Small-scale effects===
Albedo works on a smaller scale, too. In sunlight, dark clothes absorb more heat and light-coloured clothes reflect it better, thus allowing some control over body temperature by exploiting the albedo effect of the colour of external clothing.<ref name="ranknfile-ue">{{cite web|url=http://www.ranknfile-ue.org/h&s0897.html |title=Health and Safety: Be Cool! (August 1997) |publisher=Ranknfile-ue.org |accessdate=19 August 2011}}</ref>

=== Solar photovoltaic effects ===
Albedo can affect the [[electrical energy]] output of solar [[photovoltaic system|photovoltaic devices]]. For example, the effects of a spectrally responsive albedo are illustrated by the differences between the spectrally weighted albedo of solar photovoltaic technology based on hydrogenated amorphous silicon (a-Si:H) and crystalline silicon (c-Si)-based compared to traditional spectral-integrated albedo predictions. Research showed impacts of over 10%.<ref>{{cite journal | last1 = Andrews | first1 = Rob W. | last2 = Pearce | first2 = Joshua M. | date = 2013 | title = The effect of spectral albedo on amorphous silicon and crystalline silicon solar photovoltaic device performance | journal = Solar Energy | volume = 91 | pages = 233–241 | doi = 10.1016/j.solener.2013.01.030 |bibcode = 2013SoEn...91..233A | url = https://www.academia.edu/3081684 }}</ref> More recently, the analysis was extended to the effects of spectral bias due to the specular reflectivity of 22 commonly occurring surface materials (both human-made and natural) and analyzes the albedo effects on the performance of seven photovoltaic materials covering three common photovoltaic system topologies: industrial (solar farms), commercial flat rooftops and residential pitched-roof applications.<ref>{{cite journal | last1 = Brennan | first1 = M.P. | authorlink4 = J. M. Pearce | last2 = Abramase | first2 = A.L. | last3 = Andrews | first3 = R.W. | last4 = Pearce | first4 = J. M. | date = 2014 | title = Effects of spectral albedo on solar photovoltaic devices | journal = Solar Energy Materials and Solar Cells | volume = 124 | pages = 111–116 | doi = 10.1016/j.solmat.2014.01.046 | url = https://www.academia.edu/6222506 }}</ref>

===Trees===
Because forests generally have a low albedo, (the majority of the ultraviolet and [[visible spectrum]] is absorbed through [[photosynthesis]]), some scientists have suggested that greater heat absorption by trees could offset some of the carbon benefits of afforestation (or offset the negative climate impacts of [[deforestation]]). In the case of evergreen forests with seasonal snow cover albedo reduction may be great enough for deforestation to cause a net cooling effect.<ref>{{cite journal | last1 = Betts | first1 = RA | date = 2000 | title = Offset of the potential carbon sink from boreal forestation by decreases in surface albedo | journal = Nature | volume = 408 | issue = 6809| pages = 187–190 | doi = 10.1038/35041545 | pmid=11089969|bibcode = 2000Natur.408..187B }}</ref> Trees also impact climate in extremely complicated ways through [[evapotranspiration]]. The water vapor causes cooling on the land surface, causes heating where it condenses, acts a strong greenhouse gas, and can increase albedo when it condenses into clouds.<ref>{{cite journal | last1 = Boucher | date = 2004 | title = Direct human influence of irrigation on atmospheric water vapour and climate | journal = Climate Dynamics | volume = 22 | issue = 6–7| pages = 597–603 | doi=10.1007/s00382-004-0402-4|display-authors=etal|bibcode = 2004ClDy...22..597B | url = https://www.academia.edu/25329256}}</ref> Scientists generally treat evapotranspiration as a net cooling impact, and the net climate impact of albedo and evapotranspiration changes from deforestation depends greatly on local climate.<ref>{{cite journal | last1 = Bonan | first1 = GB | date = 2008 | title = Forests and Climate Change: Forcings, Feedbacks, and the Climate Benefits of Forests | journal = Science | volume = 320 | issue = 5882| pages = 1444–1449 | doi = 10.1126/science.1155121 | pmid=18556546|bibcode = 2008Sci...320.1444B  | url = https://zenodo.org/record/1230896 }}</ref>

In seasonally snow-covered zones, winter albedos of treeless areas are 10% to 50% higher than nearby forested areas because snow does not cover the trees as readily. [[Deciduous trees]] have an albedo value of about 0.15 to 0.18 whereas [[coniferous trees]] have a value of about 0.09 to 0.15.<ref name="mmutrees" /> Variation in summer albedo across both forest types is correlated with maximum rates of photosynthesis because plants with high growth capacity display a greater fraction of their foliage for direct interception of incoming radiation in the upper canopy.<ref name="Ollinger">{{cite journal
| title = Canopy nitrogen, carbon assimilation and albedo in temperate and boreal forests: Functional relations and potential climate feedbacks
| journal = Proceedings of the National Academy of Sciences
| volume = 105
| issue = 49
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| first18 = H.P.
| page = 19335

}}</ref> The result is that wavelengths of light not used in photosynthesis are more likely to be reflected back to space rather than being absorbed by other surfaces lower in the canopy.

Studies by the [[Hadley Centre]] have investigated the relative (generally warming) effect of albedo change and (cooling) effect of [[carbon sequestration]] on planting forests. They found that new forests in tropical and midlatitude areas tended to cool; new forests in high latitudes (e.g., Siberia) were neutral or perhaps warming.<ref name="Betts" />

===Water===
[[File:water reflectivity.jpg|thumb|upright=1.3|Reflectivity of smooth water at 20&nbsp;°C (refractive index=1.333)]]
Water reflects light very differently from typical terrestrial materials. The reflectivity of a water surface is calculated using the [[Fresnel equations]] (see graph).

At the scale of the wavelength of light even wavy water is always smooth so the light is reflected in a locally [[specular reflection|specular manner]] (not [[Diffuse reflection|diffusely]]). The glint of light off water is a commonplace effect of this. At small [[angle of incidence (optics)|angles of incident]] light, [[waviness]] results in reduced reflectivity because of the steepness of the reflectivity-vs.-incident-angle curve and a locally increased average incident angle.<ref name="Fresnel" />

Although the reflectivity of water is very low at low and medium angles of incident light, it becomes very high at high angles of incident light such as those that occur on the illuminated side of Earth near the [[terminator (solar)|terminator]] (early morning, late afternoon, and near the poles). However, as mentioned above, waviness causes an appreciable reduction. Because light specularly reflected from water does not usually reach the viewer, water is usually considered to have a very low albedo in spite of its high reflectivity at high angles of incident light.

Note that white caps on waves look white (and have high albedo) because the water is foamed up, so there are many superimposed bubble surfaces which reflect, adding up their reflectivities. Fresh 'black' ice exhibits Fresnel reflection.
Snow on top of this sea ice increases the albedo to 0.9.{{Citation needed|date=December 2017}}

===Clouds===
[[Cloud albedo]] has substantial influence over atmospheric temperatures. Different types of clouds exhibit different reflectivity, theoretically ranging in albedo from a minimum of near 0 to a maximum approaching 0.8. "On any given day, about half of Earth is covered by clouds, which reflect more sunlight than land and water. Clouds keep Earth cool by reflecting sunlight, but they can also serve as blankets to trap warmth."<ref name="livescience">{{cite web|url=http://www.livescience.com/environment/060124_earth_albedo.html |title=Baffled Scientists Say Less Sunlight Reaching Earth |publisher=LiveScience |date=24 January 2006 |accessdate=19 August 2011}}</ref>

Albedo and climate in some areas are affected by artificial clouds, such as those created by the [[contrail]]s of heavy commercial airliner traffic.<ref>{{cite journal|title=Contrails reduce daily temperature range|url=http://facstaff.uww.edu/travisd/pdf/jetcontrailsrecentresearch.pdf|journal=Nature |accessdate=7 July 2015|archiveurl=https://web.archive.org/web/20060503192714/http://facstaff.uww.edu/travisd/pdf/jetcontrailsrecentresearch.pdf|archivedate=3 May 2006|page=601|volume=418|issue=6898|date=8 August 2002|url-status=dead|doi=10.1038/418601a|bibcode = 2002Natur.418..601T|pmid=12167846|last1=Travis|first1=D. J.|last2=Carleton|first2=A. M.|last3=Lauritsen|first3=R. G.}}</ref> A study following the burning of the Kuwaiti oil fields during Iraqi occupation showed that temperatures under the burning oil fires were as much as 10&nbsp;°C colder than temperatures several miles away under clear skies.<ref name="harvard">{{cite journal |title=The Kuwait oil fires as seen by Landsat |date=30 May 1991|bibcode=1992JGR....9714565C |last1=Cahalan |first1=Robert F. |volume=97 |issue=D13 |page=14565 |journal=Journal of Geophysical Research: Atmospheres |doi=10.1029/92JD00799|url=https://www.researchgate.net/publication/23842551 }}</ref>

===Aerosol effects===
[[Aerosols]] (very fine particles/droplets in the atmosphere) have both direct and indirect effects on Earth's radiative balance. The direct (albedo) effect is generally to cool the planet; the indirect effect (the particles act as [[cloud condensation nuclei]] and thereby change cloud properties) is less certain.<ref name="girda">{{cite web|url=http://www.grida.no/climate/ipcc_tar/wg1/231.htm#671 |title=Climate Change 2001: The Scientific Basis |publisher=Grida.no |accessdate=19 August 2011| archiveurl= https://web.archive.org/web/20110629175429/http://www.grida.no/climate/ipcc_tar/wg1/231.htm| archivedate= 29 June 2011<!--Added by DASHBot-->}}</ref> As per Spracklen et al.<ref name="DOMINICK" /> the effects are:
<blockquote>
<!-- Aerosol radiative forcing. -->
* ''Aerosol direct effect.'' Aerosols directly scatter and absorb radiation. The scattering of radiation causes atmospheric cooling, whereas absorption can cause atmospheric warming.
* ''Aerosol indirect effect.'' Aerosols modify the properties of clouds through a subset of the aerosol population called [[cloud condensation nuclei]]. Increased nuclei concentrations lead to increased cloud droplet number concentrations, which in turn leads to increased cloud albedo, increased light scattering and radiative cooling (''first indirect effect''), but also leads to reduced precipitation efficiency and increased lifetime of the cloud (''second indirect effect'').
</blockquote>

===Black carbon===
Another albedo-related effect on the climate is from [[black carbon]] particles. The size of this effect is difficult to quantify: the [[Intergovernmental Panel on Climate Change]] estimates that the global mean [[radiative forcing]] for black carbon aerosols from fossil fuels is +0.2 W m<sup>−2</sup>, with a range +0.1 to +0.4 W m<sup>−2</sup>.<ref name="girda 1">{{cite web|url=http://www.grida.no/climate/ipcc_tar/wg1/233.htm |title=Climate Change 2001: The Scientific Basis |publisher=Grida.no |accessdate=19 August 2011| archiveurl= https://web.archive.org/web/20110629180154/http://www.grida.no/climate/ipcc_tar/wg1/233.htm| archivedate= 29 June 2011<!--Added by DASHBot-->}}</ref> Black carbon is a bigger cause of the melting of the polar ice cap in the Arctic than carbon dioxide due to its effect on the albedo.<ref>James Hansen & Larissa Nazarenko, ''Soot Climate Forcing Via Snow and Ice Albedos'', 101 Proc. of the Nat'l. Acad. of Sci. 423 (13 January 2004) ("The efficacy of this forcing is »2 (i.e., for a given forcing it is twice as effective as CO<sub>2</sub> in altering global surface air temperature)"); ''compare'' Zender Testimony, ''supra'' note 7, at 4 (figure 3); See J. Hansen & L. Nazarenko, ''supra'' note 18, at 426. ("The efficacy for changes of Arctic sea ice albedo is >3. In additional runs not shown here, we found that the efficacy of albedo changes in Antarctica is also >3."); ''See also'' Flanner, M.G., C.S. Zender, J.T. Randerson, and P.J. Rasch, ''Present-day climate forcing and response from black carbon in snow'', 112 J. GEOPHYS. RES. D11202 (2007) ("The forcing is maximum coincidentally with snowmelt onset, triggering strong snow-albedo feedback in local springtime. Consequently, the "efficacy" of black carbon/snow forcing is more than three times greater than forcing by CO<sub>2</sub>.").</ref>

===Human activities===
Human activities (e.g., deforestation, farming, and urbanization) change the albedo of various areas around the globe. However, quantification of this effect on the global scale is difficult.{{citation needed|date=November 2013}}

==Other types of albedo==
[[Single-scattering albedo]] is used to define scattering of electromagnetic waves on small particles. It depends on properties of the material ([[refractive index]]); the size of the particle or particles; and the wavelength of the incoming radiation.

==See also==
<!-- Please keep entries in alphabetical order & add a short description [[WP:SEEALSO]] -->
{{Div col|colwidth=20em|small=yes}}
* [[Cool roof]]
* [[Daisyworld]]
* [[Emissivity]]
* [[Exitance]]
* [[Global dimming]]
* [[Irradiance]]
* [[Kirchhoff's law of thermal radiation]]
* [[Opposition surge]]
* [[Polar see-saw]]
* [[Solar radiation management]]
{{div col end}}
<!-- please keep entries in alphabetical order -->

==References==
{{Reflist|refs=
<ref name="Goode">{{Cite journal |last=Goode |first=P. R. |date=2001 |title=Earthshine Observations of the Earth's Reflectance |journal=[[Geophysical Research Letters]] |volume=28 |issue=9 |pages=1671–1674 |url=http://www.agu.org/journals/ABS/2001/2000GL012580.shtml |doi=10.1029/2000GL012580 |bibcode = 2001GeoRL..28.1671G |display-authors=etal}}</ref>

<ref name="NASA">{{cite web|url=http://modis.gsfc.nasa.gov/data/atbd/atbd_mod09.pdf|title=MODIS BRDF/Albedo Product: Algorithm Theoretical Basis Document, Version 5.0|accessdate=2 June 2009| archiveurl= https://web.archive.org/web/20090601063932/http://modis.gsfc.nasa.gov/data/atbd/atbd_mod09.pdf| archivedate= 1 June 2009<!--Added by DASHBot-->}}</ref>

<ref name="washington">{{cite web|url=http://www.atmos.washington.edu/~sgw/PAPERS/2002_Snowball.pdf|title=Snowball Earth: Ice thickness on the tropical ocean|accessdate=20 September 2009}}</ref>

<ref name="clim-past">{{cite web|url=http://www.clim-past.net/2/31/2006/cp-2-31-2006.pdf|title=Effect of land albedo, CO2, orography, and oceanic heat transport on extreme climates|accessdate=20 September 2009}}</ref>

<ref name="Smith Robin">{{cite web|url=http://www.mpimet.mpg.de/fileadmin/staff/smithrobin/IC_JClim-final.pdf|title=Global climate and ocean circulation on an aquaplanet ocean-atmosphere general circulation model|accessdate=20 September 2009| archiveurl= https://web.archive.org/web/20090920212836/http://www.mpimet.mpg.de/fileadmin/staff/smithrobin/IC_JClim-final.pdf| archivedate= 20 September 2009<!--Added by DASHBot-->}}</ref>
<ref name="medkeff">{{cite web
| url         = http://jeff.medkeff.com/astro/lunar/obs_tech/albedo.htm
| title       = Lunar Albedo
| first       = Jeff
| last        = Medkeff
| authorlink  = Jeffrey S. Medkeff
| date        = 2002
| archiveurl  = https://web.archive.org/web/20080523151225/http://jeff.medkeff.com/astro/lunar/obs_tech/albedo.htm
| archivedate = 23 May 2008
| accessdate  = 5 July 2010
}}
</ref>

<!-- <ref name="Dickinson">{{cite journal | last1 = Dickinson | first1 = R. E. | last2 = Kennedy | first2 = P. J. | date = 1992 | title = Impacts on regional climate of Amazon deforestation | url = | journal = Geophys. Res. Lett. | volume = 19 | issue = | pages = 1947–1950 | doi=10.1029/92gl01905 | bibcode=1992GeoRL..19.1947D}}</ref> -->

<!-- <ref name="mit">[http://web.mit.edu/12.000/www/m2006/final/characterization/abiotic_water.html http://web.mit.edu/12.000/www/m2006/final/characterization/abiotic_water.html] Project Amazonia: Characterization – Abiotic – Water</ref> -->

<ref name="mmutrees">{{cite web|url=http://www.ace.mmu.ac.uk/Resources/gcc/1-3-3.html |archive-url=https://web.archive.org/web/20030301133707/http://www.ace.mmu.ac.uk/Resources/gcc/1-3-3.html |url-status=dead |archive-date=1 March 2003 |title=The Climate System |publisher=Manchester Metropolitan University |accessdate=11 November 2007 }}</ref>

<ref name="Betts">{{cite journal | doi = 10.1038/35041545 | date = 2000 | last1 = Betts | first1 = Richard A. | journal = Nature | volume = 408 | issue = 6809 | pages = 187–190 | pmid = 11089969 | title = Offset of the potential carbon sink from boreal forestation by decreases in surface albedo |bibcode = 2000Natur.408..187B }}</ref>

<ref name="Fresnel">{{cite web|url=http://vih.freeshell.org/pp/01-ONW-St.Petersburg/Fresnel.pdf |title=Spectral Approach To Calculate Specular reflection of Light From Wavy Water Surface |publisher=Vih.freeshell.org |accessdate=16 March 2015}}</ref>

<ref name="DOMINICK">{{cite journal | doi = 10.1098/rsta.2008.0201 | title = Boreal forests, aerosols and the impacts on clouds and climate | date = 2008 | last1 = Spracklen | first1 = D. V | last2 = Bonn | first2 = B. | last3 = Carslaw | first3 = K. S | journal = Philosophical Transactions of the Royal Society A | volume = 366 | issue = 1885 | pages = 4613–4626 |url=http://homepages.see.leeds.ac.uk/~eardvs/papers/spracklen08c.pdf |bibcode = 2008RSPTA.366.4613S | pmid=18826917}}</ref>

<ref name="BlueskyAlbedo">{{Cite journal |last=Roman |first=M. O. |author2=C.B. Schaaf|author3=P. Lewis|author4=F. Gao|author5=G.P. Anderson|author6=J.L. Privette|author7=A.H. Strahler|author8=C.E. Woodcock|author9=M. Barnsley |date=2010 |title=Assessing the Coupling between Surface Albedo derived from MODIS and the Fraction of Diffuse Skylight over Spatially-Characterized Landscapes |journal=Remote Sensing of Environment |volume=114 |pages=738–760 |doi=10.1016/j.rse.2009.11.014 |issue=4  |url=https://www.academia.edu/406124|bibcode = 2010RSEnv.114..738R }}</ref>

<ref name="Mallama_et_al">{{cite journal |title=Comprehensive wide-band magnitudes and albedos for the planets, with applications to exo-planets and Planet Nine |journal=Icarus |first1=Anthony |last1=Mallama |first2=Bruce |last2=Krobusek |first3=Hristo |last3=Pavlov |volume=282 |pages=19–33 |date=2017 |doi=10.1016/j.icarus.2016.09.023 |bibcode=2017Icar..282...19M |arxiv=1609.05048 }}</ref>

<ref name="Mallama">{{cite journal |title=The spherical bolometric albedo for planet Mercury |first1=Anthony |last1=Mallama |date=2017 |arxiv=1703.02670 }}</ref>

<ref name="Haus_et_al">{{cite journal |title=Radiative energy balance of Venus based on improved models of the middle and lower atmosphere |journal=Icarus |first1=R. |last1=Haus|display-authors=et al |volume=272 |pages=178–205 |date=July 2016 |doi=10.1016/j.icarus.2016.02.048 |bibcode=2016Icar..272..178H |url=https://elib.dlr.de/109285/1/Haus%20et%20al%202017_ICARUS.pdf }}</ref>

<ref name="Li_et_al">{{cite journal |title=Less absorbed solar energy and more internal heat for Jupiter |first1=Liming |last1=Li|display-authors=et al |journal=Nature Communications |volume=9 |issue=1 |pages=3709 |date=2018 |doi=10.1038/s41467-018-06107-2 |pmid=30213944 |pmc=6137063 }}</ref>

<ref name="Hanel_et_al">{{cite journal |title=Albedo, internal heat flux, and energy balance of Saturn |first1=R.A. |last1=Hanel|display-authors=et al |journal=Icarus |volume=53 |issue=2 |pages=262–285 |date=1983 |doi=10.1016/0019-1035(83)90147-1 |bibcode=1983Icar...53..262H }}</ref>

<ref name="Pearl_et_al_Uranus">{{cite journal |title=The albedo, effective temperature, and energy balance of Uranus, as determined from Voyager IRIS data |first1=J.C. |last1=Pearl|display-authors=et al |journal=Icarus |volume=84 |issue=1 |pages=12–28 |date=1990 |doi=10.1016/0019-1035(90)90155-3 |bibcode=1990Icar...84...12P }}</ref>

<ref name="Pearl_et_al_Neptune">{{cite journal |title=The albedo, effective temperature, and energy balance of Neptune, as determined from Voyager data |first1=J.C. |last1=Pearl|display-authors=et al |journal=J. Geophys. Res. |volume=96 |pages=18,921–18,930 |date=1991 |doi=10.1029/91JA01087 |bibcode=1991JGR....9618921P }}</ref>

}}

==External links==
{{wiktionary}}
* [https://sites.google.com/site/albedoproject/home Albedo Project]
* [http://www.eoearth.org/article/Albedo Albedo – Encyclopedia of Earth]
* [https://web.archive.org/web/20060505132944/http://www-modis.bu.edu/brdf/product.html NASA MODIS BRDF/albedo product site]
* [https://web.archive.org/web/20081125082044/http://www.eumetsat.int/Home/Main/Access_to_Data/Meteosat_Meteorological_Products/Product_List/SP_1125489019643?l=en Surface albedo derived from Meteosat observations]
* [https://web.archive.org/web/20080523151225/http://jeff.medkeff.com/astro/lunar/obs_tech/albedo.htm A discussion of Lunar albedos]
* [http://www.tvu.com/metalreflectivityLR.jpg reflectivity of metals (chart)]

{{Global warming}}
[[Category:Land surface effects on climate]]
[[Category:Climate feedbacks]]
[[Category:Climate forcing]]
[[Category:Climatology]]
[[Category:Electromagnetic radiation]]
[[Category:Radiometry]]
[[Category:Scattering, absorption and radiative transfer (optics)]]
[[Category:Radiation]]
[[Category:Words coined in the 1760s]]