Light Reflective Capacity of a Body or Surface
In the context of climate change, the term “albedo” (which means “whiteness” in Latin) refers to the light reflective capacity of a body or surface. Put simply, albedo is an object’s ability to reflect light. In the case of Planet Earth, it refers to Earth’s ability to reflect sunlight (and so stay cool). A scientist would say it is a measure of the diffuse reflection of sunlight by an astronomical body, such as Earth.
It is measured on a scale from 0 to 1, where 0 corresponds to the reflective capacity of a black body that absorbs all light, and 1 corresponds to a body that reflects all light. Unless calculated for a specific wavelength (known as spectral albedo), albedo refers to the entire spectrum of light. Albedo is an important element in climate science, where it acts as a climate feedback for global warming.
The average albedo of the Earth (planetary albedo) is roughly 0.3 (30 percent), mostly due to cloud cover. 1 However, albedo varies widely across the surface of the Earth because of different geographical and environmental features. 2 For example, the huge Antarctic ice sheet at the South Pole has a very high albedo because of the reflectivity of its snow and ice (the albedo of which is about 0.9), compared to green grass (0.25), conifer forest (0.08) and the open ocean (0.06).
- Light Reflective Capacity of a Body or Surface
- Does Albedo Affect Temperature?
- How Is Earth’s Albedo Measured?
- What Has The Highest Albedo?
- What Has The Lowest Albedo?
- Does Albedo Change With The Angle Of The Sun?
- What Happens To Snow’s Albedo If Snow Gets Dirty?
- List Of Albedos
- Does Earth’s Albedo Vary With The Season?
- Does Albedo Affect Global Warming?
- Forests Absorb More Solar Heat Than Snow
- The Mystery Of Clouds
- Effect of Aerosols On Albedo and Climate Change
Does Albedo Affect Temperature?
Yes. Since the Planet’s only source of heat energy is incoming sunlight, the amount that is immediately reflected back into space has a direct impact on the Earth’s climate system and temperature. Right now, with an average albedo of 0.3, Earth’s temperature is currently about 15°C. If Earth was entirely covered in snow (with therefore a higher albedo), the temperature of the planet would plummet to about minus 40°C. 3 If only the Earth’s land masses were snow covered, the mean temperature of the planet would fall to about 0°C. 4 If the entire Earth was covered by water, the average temperature would rise to about 27°C. 5
How Is Earth’s Albedo Measured?
Earth’s surface albedo is monitored regularly by observation satellite sensors such as NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS) on the Terra and Aqua satellites, and the Clouds and the Earth’s Radiant Energy System (CERES) instrument on the Suomi National Polar-orbiting Partnership (NPP) and on Joint Polar Satellite System (JPSS).
What Has The Highest Albedo?
Fresh snow – in Antarctica, Greenland or alpine regions – and fluffy cumulonimbus clouds (both 0.9) reflect 90 percent of the sunlight that hits them. Ocean water at dawn or sunset may be even higher. Stratocumulus Clouds (0.6) and Ocean ice (0.7) are also highly reflective.
What Has The Lowest Albedo?
Basically, anything that is black or very dark. Charcoal and fresh asphalt (both 0.04) have one of the lowest albedo values, closely followed by the open ocean (0.06).
Does Albedo Change With The Angle Of The Sun?
Yes. Most albedos are sensitive to the angle at which sunlight strikes the surface. Take water, for instance. When the Sun is at an angle of 40° or higher, the albedo of water is fairly constant (around 0.06), but as the sun goes down, the albedo increases dramatically, so at 10° it is about 0.5, and between 0.9 and 1.0 at sunset or sunrise. You can tell this by the glare coming off the water in the late evening or early morning.
What Happens To Snow’s Albedo If Snow Gets Dirty?
If snow gets dirty, its albedo drops. Ice and snow may start out relatively white and pure, but dust, dirt, and other discolorants can affect the albedo quite significantly. Curiously, a huge collection of brown algae was recently discovered growing on the Sermilik glacier, at the southern end of the Greenland Ice Sheet. 6 Overall, snow’s albedo varies from as high as 0.9 for fresh snow, to about 0.4 for melting snow, and as low as 0.2 for dirty snow. 7
List Of Albedos
Here is a short list of albedo measurements for some common examples of land cover.
0.07 – 0.15 11
0.09 to 0.15 12
0.18 max 12
0.18 max 13
0.40 max 13
0.70 max 14
Does Earth’s Albedo Vary With The Season?
Yes. The albedo of the earth is not constant but changes during the year according to the season. The earth’s albedo has two peaks. It reaches the first peak around New Year, when the Antarctic sea ice is at its maximum. Then it rises further, peaking in the early Spring when snow cover in the Northern Hemisphere is at its greatest extent.
Does Albedo Affect Global Warming?
Yes. When snow or cumulonimbus clouds reflect sunlight back into space, they have a direct (cooling) effect on the temperature of the Earth. This is one reason why the cryosphere – Earth’s frozen water – plays such an important role in climate change mitigation.
However, in certain situations, albedo is also a positive climate feedback. For example, as Arctic sea ice and northern snows melt during the Spring and Summer, the previously white (reflective) surface turns dark blue (sea) or green/brown (land), both of which are absorptive rather than reflective. As a result, more sunlight gets through to the surface of the Planet and temperatures rise. This in turn melts more snow, leading to more warming, and so on.
Land cover, the type of vegetation or other material covering the Earth’s surface has a small effect on climate, by virtue of the fact that trees and other plant life has a lower reflective capacity than soil, and a much lower albedo than deserts. (See also: Land Use and Climate Change.)
According to a recent scientific study, losing the albedo reflective power of Arctic sea ice would lead to an increase in global warming equivalent to the emission of one trillion tons of CO2. 17 To put this into context, humans have released 2.4 trillion tons of CO2 since pre-industrial times, including from land use changes.
Forests Absorb More Solar Heat Than Snow
Since forests have a far lower albedo than snow, some scientists argue that greater heat absorption by trees could reduce the carbon benefits of afforestation (or offset the negative impacts of deforestation).
Overall, research shows: (1) The large difference (10-50 percent) in winter albedo between snow-covered ground and neighboring snow-covered forest, suggests that deforestation here might be wholly offset by better reflectivity of sunlight. (2) New or very young forests in tropical and mid-latitude areas tended to exert a cooling effect, while new forests in northern latitudes (in Canada or Siberia) had a neutral or slightly warming effect, compared to previously bare ground. 18
The Mystery Of Clouds
Clouds reflect incoming sunlight due to their high albedo (cooling effect), but also absorb outgoing heat from the Earth, especially at night (warming effect). 19 No scientific consensus exists as to the net effect of clouds, although a slight cooling effect gets slightly more votes. For more on this, see our article: How do Clouds Affect Climate?
Effect of Aerosols On Albedo and Climate Change
Aerosols of soot and other particulate matter resulting from the incomplete combustion of fossil fuels and wood, tend to block sunlight from reaching Earth, thus exerting a cooling effect. This was confirmed once again by a 1991 study conducted during the burning of the Kuwaiti oil fields during Iraqi occupation, which showed that surface temperatures underneath the burning oil fires were up to 10°C colder than temperatures of other local areas under clear skies. 20
Scientists used to think that black carbon aerosols darkened snow-covered areas in northern polar regions, thus reducing the regional albedo. However, a recent study of satellite data from 1982 to 2014, indicated that although the Arctic was warming at a rate almost three times faster than the global average, the concomitant loss of surface albedo (roughly 1.4 percent per decade) was due almost entirely to melting ice, not soot absorption. 21
In contrast, other studies have shown a clear connection between black carbon emissions from routine gas flaring processes – conducted by the petroleum industry in northern high latitudes – and reduction in polar albedo. 22
Particles of dust and ash, hurled into the atmosphere during volcanic eruptions can have significant effects on our climate. Most of it forms dark clouds of air pollution that block incoming solar radiation, causing a cooling effect that can last for years. One interesting example is the Asian brown cloud that materializes over parts of India, Pakistan and Bangladesh during the winter dry season.
Emissions of sulfur dioxide are even more effective. They rise into the stratosphere and combine with water to form sulfuric acid aerosols, creating a haze of tiny droplets that reflects incoming sunlight. 23
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- Environmental Encyclopedia (3rd ed.) Thompson Gale. 2003. ISBN 978-0-7876-5486-3. (2)
- “Snowball Earth: Ice thickness on the tropical ocean.” Stephen G. Warren, Richard E. Brandt, Thomas C. Grenfell, and Christopher P. McKay. Journal of Geophysical Research. Vol 107, No. C10, 3167. (2002)
- “Effect of land albedo, CO2, orography, and oceanic heat transport on extreme climates” (PDF). “Effect of land albedo, CO2, orography, and oceanic heat transport on extreme climates.” V. Romanova, G. Lohmann, K. Grosfeld. Climate Past, 2, 31–42, 2006. (4)
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- “Radiative Heating of an Ice-Free Arctic Ocean.” Kristina Pistone, Ian Eisenman, Veerabhadran Ramanathan. Geophysical Research Letters. 20 June 2019 (17)
- “Offset of the potential carbon sink from boreal forestation by decreases in surface albedo“. Richard A. Betts. (2000). Nature. 408 (6809): 187–190. (18)
- “Baffled Scientists Say Less Sunlight Reaching Earth”. LiveScience. 24 January 2006. (19)
- “The Kuwait oil fires as seen by Landsat.” Robert F. Cahalan. Journal of Geophysical Research: Atmospheres. 97 (D13): 14565. May 30, 1991. (20)
- “Unraveling driving forces explaining significant reduction in satellite-inferred Arctic surface albedo since the 1980s.” Rudong Zhang, Hailong Wang, Qiang Fu, Philip J. Rasch, Xuanji Wang. PNAS November 11, 2019. (21)
- “A Missing Component of Arctic Warming: Black Carbon from Gas Flaring.” Mee-Hyun Cho et al. Environmental Research Letters 14, no. 9 (September, 2019).
- “How Volcanoes Influence Climate.” National Center for Atmospheric Research – University Corporation for Atmospheric Research. (22)