Editing Albedo (section)

==Terrestrial albedo==
{| class="wikitable floatright"
|+ 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
 | access-date=27 August 2007
 | archive-url= https://web.archive.org/web/20070829153207/http://eetd.lbl.gov/HeatIsland/Pavements/Albedo/
 | archive-date= 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
 | access-date=27 August 2007
 | doi=10.1029/96JD03876
 | bibcode=1997JGR...10228901B
 | archive-url=https://web.archive.org/web/20070930184719/http://www.agu.org/pubs/crossref/1997/96JD03876.shtml
 | archive-date=30 September 2007<!--Added by DASHBot-->
 | doi-access=free
}}</ref> 0.09 to 0.15<ref name="mmutrees" />
|-
| [[Deciduous forest]] || 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
 |publisher=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" />
|-
| [[Aluminium]] || 0.85<ref>{{cite journal | pmid=31822767 | pmc=6904492 | doi=10.1038/s41598-019-55272-x | title=The effects of surface albedo and initial lignin concentration on photodegradation of two varieties of Sorghum bicolor litter | journal=Scientific Reports | date=10 December 2019 | volume=9 | page=18748 | last1=Ruhland | first1=Christopher T. | last2=Niere | first2=Joshua A. | issue=1 | bibcode=2019NatSR...918748R }}</ref><ref>{{cite web | url=https://www.pvsyst.com/help/albedo.htm | title=Physical models used > Irradiation models > Albedo usual coefficients }}</ref>
|}
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 |access-date=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.

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.{{citation needed|date=July 2023}}

Earth's average surface temperature due to its albedo and the [[greenhouse effect]] is currently about {{convert|15|C|F}}. If Earth were frozen entirely (and hence be more reflective), the average temperature of the planet would drop below {{convert|−40|C|F}}.<ref name="washington" /> If only the continental land masses became covered by glaciers, the mean temperature of the planet would drop to about {{convert|0|C|F}}.<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 {{convert|27|C|F}}.<ref name="Smith Robin" />

<!--===Variability and recent/spatiotemporal changes===-->
In 2021, scientists reported that Earth dimmed by ~0.5% over two decades (1998–2017) as measured by earthshine using modern photometric techniques. This may have both been co-caused by [[climate change]] as well as a substantial increase in global warming. However, the link to climate change has not been explored to date and it is unclear whether or not this represents an ongoing trend.<ref>{{cite news |last1=Gray |first1=Jennifer |title=The Earth isn't as bright as it once was |url=https://edition.cnn.com/2021/10/04/weather/earth-dimming-climate/index.html |access-date=19 October 2021 |work=CNN}}</ref><ref>{{cite journal |last1=Goode |first1=P. R. |last2=Pallé |first2=E. |last3=Shoumko |first3=A. |last4=Shoumko |first4=S. |last5=Montañes-Rodriguez |first5=P. |last6=Koonin |first6=S. E. |title=Earth's Albedo 1998–2017 as Measured From Earthshine |journal=Geophysical Research Letters |date=2021 |volume=48 |issue=17 |pages=e2021GL094888 |doi=10.1029/2021GL094888 |bibcode=2021GeoRL..4894888G |s2cid=239667126 |language=en |issn=1944-8007|doi-access=free }}</ref>

===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" />

===Changes to albedo due to human activities===
[[File:2000- Albedo (reflectivity) of Earth.svg|thumb|Earth's albedo as monitored by the [[Clouds and the Earth's Radiant Energy System|CERES]] satellite system shows a darkening of Earth that has caused 1.7{{nbsp}}W/m<sup>2</sup> warming since 2010.<ref name=Hansen_20250203/> That amount, only some of which is [[Radiative forcing|climate forcing]], is equivalent to a 138 ppm increase of atmospheric carbon dioxide.<ref name=Hansen_20250203>{{cite journal |last1=Hansen |first1=James E. |last2=Kharecha |first2=Pushker |last3=Sato |first3=Makiko |last4=Tselioudis |first4=George |last5=Kelly |first5=Joseph |last6=Bauer |first6=Susanne E. |last7=Ruedy |first7=Reto |last8=Jeong |first8=Eunbi |last9=Jin |first9=Quijian |last10=Rignot |first10=Eric |last11=Velicogna |first11=Isabella |last12=Schoeberl |first12=Mark R. |last13=von Schuckmann |first13=Karina |last14=Amponsem |first14=Joshua |last15=Cao |first15=Junji |last16=Keskinen |first16=Anton |last17=Li |first17=Jing |last18=Pokela |first18=Anni |title=Global Warming Has Accelerated: Are the United Nations and the Public Well-Informed? |journal=Environment |date=3 February 2025 |volume=67 |issue=1 |pages=6–44 |doi=10.1080/00139157.2025.2434494|doi-access=free |bibcode=2025ESPSD..67....6H }} Figure 6.</ref>]]
[[File:ISS041-E-90107 - View of Spain.jpg|thumb|Greenhouses of El Ejido, Almería, Spain]]
Human activities (e.g., deforestation, farming, and urbanization) change the albedo of various areas around the globe.<ref>{{Cite journal |last1=Sagan |first1=Carl |last2=Toon |first2=Owen B. |last3=Pollack |first3=James B. |date=1979 |title=Anthropogenic Albedo Changes and the Earth's Climate |journal=Science |volume=206 |issue=4425 |pages=1363–1368 |bibcode=1979Sci...206.1363S |doi=10.1126/science.206.4425.1363 |issn=0036-8075 |jstor=1748990 |pmid=17739279 |s2cid=33810539}}</ref> [[Human impact on the environment|Human impacts]] to "the physical properties of the land surface can perturb the climate by altering the Earth’s radiative energy balance" even on a small scale or when undetected by satellites.<ref name=":0">{{Cite journal |last1=Campra |first1=Pablo |last2=Garcia |first2=Monica |last3=Canton |first3=Yolanda |last4=Palacios-Orueta |first4=Alicia |date=2008 |title=Surface temperature cooling trends and negative radiative forcing due to land use change toward greenhouse farming in southeastern Spain |journal=Journal of Geophysical Research |volume=113 |issue=D18 |bibcode=2008JGRD..11318109C |doi=10.1029/2008JD009912 |doi-access=free}}</ref>

[[Urbanization]] generally decreases albedo (commonly being 0.01–0.02 lower than adjacent [[croplands]]), which contributes to [[global warming]]. Deliberately increasing albedo in urban areas can mitigate the [[urban heat island]] effect. An estimate in 2022 found that on a global scale, "an albedo increase of 0.1 in worldwide urban areas would result in a cooling effect that is equivalent to absorbing ~44 [[Gigatons|Gt]] of CO<sub>2</sub> emissions."<ref>{{Cite journal |last1=Ouyang |first1=Zutao |last2=Sciusco |first2=Pietro |last3=Jiao |first3=Tong |last4=Feron |first4=Sarah |last5=Li |first5=Cheyenne |last6=Li |first6=Fei |last7=John |first7=Ranjeet |last8=Peilei |first8=Fan |last9=Li |first9=Xia |last10=Williams |first10=Christopher A. |last11=Chen |first11=Guangzhao |last12=Wang |first12=Chenghao |last13=Chen |first13=Jiquan |date=July 2022 |title=Albedo changes caused by future urbanization contribute to global warming |journal=Nature Communications |volume=13 |issue=1 |page=3800 |bibcode=2022NatCo..13.3800O |doi=10.1038/s41467-022-31558-z |pmc=9249918 |pmid=35778380}}</ref>

Intentionally enhancing the albedo of the Earth's surface, along with its daytime [[thermal emittance]], has been proposed as a [[Solar Radiation Management|solar radiation management]] strategy to mitigate [[Energy crisis|energy crises]] and global warming known as [[passive daytime radiative cooling]] (PDRC).<ref name=":1">{{Cite journal |last1=Wang |first1=Tong |last2=Wu |first2=Yi |last3=Shi |first3=Lan |last4=Hu |first4=Xinhua |last5=Chen |first5=Min |last6=Wu |first6=Limin |date=2021 |title=A structural polymer for highly efficient all-day passive radiative cooling |journal=Nature Communications |volume=12 |issue=365 |page=365 |doi=10.1038/s41467-020-20646-7 |pmc=7809060 |pmid=33446648 |quote=Accordingly, designing and fabricating efficient PDRC with sufficiently high solar reflectance (𝜌¯solar) (λ ~ 0.3–2.5 μm) to minimize solar heat gain and simultaneously strong LWIR thermal emittance (ε¯LWIR) to maximize radiative heat loss is highly desirable. When the incoming radiative heat from the Sun is balanced by the outgoing radiative heat emission, the temperature of the Earth can reach its steady state.}}</ref><ref name=":5">{{Cite journal |last1=Chen |first1=Meijie |last2=Pang |first2=Dan |last3=Chen |first3=Xingyu |last4=Yan |first4=Hongjie |last5=Yang |first5=Yuan |date=October 2021 |title=Passive daytime radiative cooling: Fundamentals, material designs, and applications |journal=EcoMat |volume=4 |doi=10.1002/eom2.12153 |s2cid=240331557 |quote=Passive daytime radiative cooling (PDRC) dissipates terrestrial heat to the extremely cold outer space without using any energy input or producing pollution. It has the potential to simultaneously alleviate the two major problems of energy crisis and global warming. |doi-access=free }}</ref><ref name=":02">{{Cite journal |last=Munday |first=Jeremy |date=2019 |title=Tackling Climate Change through Radiative Cooling |journal=Joule |volume=3 |issue=9 |pages=2057–2060 |doi=10.1016/j.joule.2019.07.010 |s2cid=201590290 |doi-access=free|bibcode=2019Joule...3.2057M }}</ref> Efforts toward widespread implementation of PDRCs may focus on maximizing the albedo of surfaces from very low to high values, so long as a thermal emittance of at least 90% can be achieved.<ref name=":22">{{Cite journal |last1=Anand |first1=Jyothis |last2=Sailor |first2=David J. |last3=Baniassadi |first3=Amir |date=February 2021 |title=The relative role of solar reflectance and thermal emittance for passive daytime radiative cooling technologies applied to rooftops |url=https://www.sciencedirect.com/science/article/abs/pii/S2210670720308295 |journal=Sustainable Cities and Society |volume=65 |page=102612 |doi=10.1016/j.scs.2020.102612 |bibcode=2021SusCS..6502612A |s2cid=229476136 |quote=Thus, as manufactures consider development of PDRC materials for building applications, their efforts should disproportionately focus on increasing surface solar reflectance (albedo) values, while retaining the conventional thermal emissivity. |via=Elsevier Science Direct}}</ref>

The tens of thousands of [[hectare]]s of greenhouses in [[Province of Almería|Almería, Spain]] form a large expanse of whitened plastic roofs. A 2008 study found that this anthropogenic change lowered the local surface area temperature of the high-albedo area, although changes were localized.<ref name=":0" /> A follow-up study found that "CO2-eq. emissions associated to changes in surface albedo are a consequence of land transformation" and can reduce surface temperature increases associated with climate change.<ref>{{Cite journal |last1=Muñoz |first1=Ivan |last2=Campra |first2=Pablo |date=2010 |title=Including CO2-emission equivalence of changes in land surface albedo in life cycle assessment. Methodology and case study on greenhouse agriculture |url=https://www.researchgate.net/publication/226490855 |journal=Int J Life Cycle Assess |volume=15 |issue=7 |pages=679–680 |bibcode=2010IJLCA..15..672M |doi=10.1007/s11367-010-0202-5 |s2cid=110705003 |via=Research Gate}}</ref>