Talk:Albedo/Archive 1

Archive 1

(William M. Connolley 17:35, 26 Nov 2004 (UTC)) The following very old comments archived 2004/11/26.

I do not think this is a reliable source:

Kaczynski, T., 1991: The Unabomber Manifesto. Lispelite Press (F15), 40 pp.

I added the word 'allegedly' to facts attributed to Kaczynski, rather than just removing them. The 'allegedly' can be removed if a non-psychopathic source is found to corroborate the statements. In two other places I just removed the citation.

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Removed the following from list of sources:
   Neunke, M., 2001: White Pride Worldwide!! [Taken from http://www.whitepride.com/sorel.html]
I didn't see any information about albedo at that site... though I suppose white people may be proud of their higher than average albedo. (cough cough)

So if I have a higher albedo than blacks and whites with a decent tan, and therefore should be absorbing less radiation than them, why is it that my bald spot burns faster than dry leaves in a forest fire? -- Lee Daniel Crocker

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I also removed these, pending further investigation:

Walker, E., 1987: Pictures of Preschoolers Out in the Snow. Dishwasher Picture Publishing, Volume 26, 151-1103.

Thompson, S. I. U. A. M., 2001: Worldwide Monthly Climate Tables. [Taken from http://www.woolpit.com/]

Rocky, S., and E. Bullwinkle, 1970: The Climate of the North Polar Basin. World Survey of Climatology, Vol. 14, Elsevier Publishing Company, 373 pp.

These all look like hoaxes to me. Rocky and Bullwinkle? Pictures of children in the snow? --Jimbo Wales

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There are still several mentions of Rocky and Bullwinkle in the page itself. They weren't added recently. They're in the form of source notations; could they have replaced the real source notations long ago? Is there any way we can pull up the page from many moons ago to see whether those were real references?

Also, someone who knows this field should really review this whole page for other subtle munges. -- Rootbeer

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Can anyone find a real source that suggests albedo influences surfact temperature here on earth? I looked at Google and the only links I found claiming such an influence were educational projects for K-12 graders. - Tim

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An albedo calculation example For a lattitude of 52N on 4 january with fresh snow (albedo 0.8) the mid-day (clear sky) insolation is 68 W/m2

The albedo of a forest/town  = 0.15 

 0% forest/town | winter albedo 0.8   | insolation  68 W/m2 
10% forest/town | winter albedo 0.735 | insolation  90 W/m2 
20% forest/town | winter albedo 0.67  | insolation 113 W/m2 
30% forest/town | winter albedo 0.605 | insolation 135 W/m2 
40% forest/town | winter albedo 0.54  | insolation 157 W/m2 
50% forest/town | winter albedo 0.475 | insolation 179 W/m2 
60% forest/town | winter albedo 0.41  | insolation 201 W/m2 
70% forest/town | winter albedo 0.345 | insolation 223 W/m2 
80% forest/town | winter albedo 0.28  | insolation 245 W/m2 
90% forest/town | winter albedo 0.215 | insolation 268 W/m2 

100% forest/town | winter albedo 0.15 | insolation 290 W/m2

Insolation data derived using the insolation calculator download excel 2000 version http://members.lycos.nl/ErrenWijlens/co2/insol.zip

download excel 95 version http://members.lycos.nl/ErrenWijlens/co2/insol95.zip

You see that change of landuse has a dramatic effect on the winter energy balance.

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I write a quick perl script to convert all these Fs to C or K -- Tarquin 17:33 Mar 13, 2003 (UTC)

Wow, way harsh, dude! Like some of us surfer types took YEARS to learn "far in" height, and now yer like gonna push all this like "center grade" stuff on us and get us all confused and stuff. Dude! How 'bout, like, write your pearl surfing routine to, like, APPEND a center grade value so airheads like yurs trooly can like dig on both sides of the wave? Gnarly! --Surfer Dude 17:40 Mar 13, 2003 (UTC)

Lunar Albedo

The reference given doesn’t work anymore (http://jeff.medkeff.com/astro/lunar/obs_tech/albedo.htm), I also found a reference that gives a different value of lunar albedo, of 0.12 instead of 0.072 (http://www.universetoday.com/guide-to-space/the-moon/moon-albedo/). —Preceding unsigned comment added by Firstmatekevin (talk • contribs) 14:02, 4 July 2010 (UTC)

Terrestial vs. Ocean albedo unclear

The last sentence of the first paragraph is unclear; in comparison to land, do oceans typically have a higher or lower albedo, and do clouds contribute to higher albedo or to lower albedo? —Preceding unsigned comment added by 75.85.89.204 (talk) 11:23, 20 December 2009 (UTC)

WMC removing old stuff

"tropics" section is flawed.  Many factors control surface temperature, particularly those associated with vegetation.  I find fault with the statement "When Brazilian ranchers cut down dark, tropical rainforest trees to replace them with even darker soil in order to grow crops, the average temperature of the area appears to increase by an average of about 3 °C (5 °F) year-round, which is a significant amount"   as the lack of evapo-transpiration after forest is removed may have far more control over surface temperature than a change in albedo.  The statement should be supported with a reference or should be removed.23:47, 2 September 2006 (UTC)

This page looks weird to me. Some of it is definitely rubbish: the arctic ice stuff (there is no SW in winter...). Is anybody very fond of this page...? [WMC]

(William M. Connolley 19:55, 15 Sep 2003 (UTC)) OK, no-one spoke up, so I've started stripping out stuff that looks especially dodgy to me, and putting it here (note: stuff left is not necessarily OK, just less obviously not). If anyone thinks I've been unreasonably harsh, please feel free to revert, or perhaps better make comments on a per-para basis. I've put comments on what I've removed.

The albedo of an object can be used to help determine its chemical composition. Every molecule of every substance has its own albedo, but albedo can also refer to a collection of very many objects, and can even be applied to objects of a very large scale, such as the planet

Composition by albedo? Really?

Since albedo can greatly affect the temperature of an area, it is advantageous for people, especially in cold climates, to settle in areas where the albedo is very low, so that they can get as much warmth as possible from the sun. The reverse is true in desert and tropical climates; people want to live in areas where as much solar radiation as possible will be emitted back into space.

Apart from local stuff, like painting houses white (not mentioned here) I can't see any evidence for that.

The difference would most likely be more than 17°C (30°F) if the landscape of the rainforest was white instead of dark green. As evidence for this theory, scientists have climbed to the top of Mount Kilimanjaro in Tanzania, which is located in an area well described as "steaming jungle". But Kilimanjaro's temperatures remain well below freezing all year round, despite the fact that its summit is only about 20,000 feet above sea level. Assuming that the average temperature at sea level around Kilimanjaro is about 27°C (81°F) (this is the GHCN's record of the average temperature at Dar Es Salaam, a nearby sea-level weather station), and that the temperature up the mountain slope decreases only 1°C (2°F) per 1,000 feet because of the semi-moist environment, it seems that the temperature at the summit should be about 5°C (41°F), which is much warmer than the approximately -7°C (20°F) that it has been estimated that Kilimanjaro actually receives. By comparison, the Hawaiian volcano Mauna Loa, which peaks at about 14,000 feet, has an annual average temperature in the GHCN of approximately 4°C (40°F), despite the fact that Hawaii is a cooler and drier environment than northern Tanzania and thus the lapse rate there would be expected to be higher, thus resulting in a colder temperature at the summit of Mauna Loa.

Here we have a long chain of unsupported assumptions.

But there is no snow at the top of Mauna Loa to reflect back incoming solar radiation, and although the climate at the summit is very rainy, snow is relatively rare and the coldest recorded temperature is -10°C (14°F), which reduced to sea level at a rate of 1°C (2°F) gives 6°C (42°F), which is not much higher than the lowest temperatures recorded at other sea-level stations in Hawaii. And the average annual temperature at sea level in Hawaii is only about 23°C (74°F), and it is during the dry season a dry 25°C (77°F), so it can be seen that the lapse rate along the slope of Mauna Loa is not significantly higher than 1°C (2°F) per 1000 feet, whereas on Kilimanjaro the lapse rate is almost doubled, for no logical reason.

Err?

The only possible explanation is that on Kilimanjaro, a glacier built up when the climate was colder, and that this glacier never completely melted because its extremely high albedo reflected away enough heat to keep itself cold enough not to melt, and to keep the air temperature at the summit much lower than that atop Mauna Loa. This very wide gap in temperatures, of nearly 11°C (20°F), occurs despite the fact that the skies above both mountains are very cloudy and the climate of both is very wet, so not much solar radiation reaches either summit. If Mauna Loa were completely dry, it could be expected that its temperature would be even warmer, perhaps as warm as that of Tibet at 14,000 feet in summer.

Err, both are very wet, but above it sez that Hawaii is drier.

Another good example of albedo in action is Greenland. Greenland is an island covered almost completely with ice. In the winter, very little sunlight reaches Greenland, so albedo is not as important. But in the summertime, it makes a very big difference, making summertime temperatures even colder than they would normally be for a given latitude and elevation. For example, Eismitte is a weather station situated a bit south of the geographical center of the island (near 70°N) at an altitude of 9843 feet. The average temperature inland at 0 feet at 70°N in Eurasia and North America in July is about 13°C (55°F). Given a lapse rate of 1°C (2°F) per 1000 feet, we could expect the July average at Eismitte to be 2°C (35°F). In fact, 1°C (2°F) per 1000 feet is often an overestimate near the poles because of the unusual convective activity that causes inversions to arise there. But the actual average July temperature at Eismitte is only -12°C (10°F), and furthermore, the next warmest month is June, at only -17°C (2°F). June being warmer than August is a clear sign that there are some outside influences on the climate, in particular that sunlight plays an unusually large role in regulating temperature, because June is the sunniest month of the year in most of the northern part of the Northern Hemisphere. But we cannot ignore the fact that the temperatures in all summer months are much colder than the predicted values using the 1°C (2°F) lapse rate. This is obviously due to the very high albedo that Greenland's ice cap provides. Further evidence for this theory can be seen in the fact that other stations in Greenland have very low summer temperatures as well, and in fact are relatively consistent all year round with a 1°C (2°F) per 1000 feet lapse rate.

More imaginary lapse rates. Or am I being too harsh?

Some parts of the Arctic Ocean are frozen over with ice all year round. These areas have the unusual distinction of experiencing heat convection coming from the ocean below as well as the air above. The temperature of the purest Arctic Ocean water is roughly -2°C (28°F) at all depths, in all seasons. The temperature of the ice above, however, is much colder because it reflects away some of the heat of the water below it. During the summertime, the upward face of the ice reflects away solar heat and prevents itself from melting completely. The ice that does melt helps keep the average July temperatures at the North Pole at about -1°C (31°F).

This is confused.

Thus children, much skinnier than adults, need more clothes in the wintertime to keep them warm, even if they are dark-skinned.

Not albedo

There is a simple relationship between the albedo of an area of the earth's surface and its color. The lighter the color, the higher the albedo. A white substance would have an albedo of 1.00, or 100%, while a black substance would have an albedo of 0.00 or 0%. The human eye perceives green light especially well, so green substances have albedos somewhat lower than one might think.

Rewrites near this bit

, but with different values for latitude and day, they would be different. The reason for this is not because of the amount of sunlight coming in, which does not change a substance's albedo, but because the actual environments would be different in summer. For example, a cultivated field may come in as high as the low 20s, depending on the crop being cultivated. Because of increased photosynthesis, all of the values for the forests and swamp lands are nearly doubled in the summer. The grassy field, however, remains at 20% regardless of season or latitude. Near the equator, particularly in rainforest areas, the soil is very black, and its albedo is very close to 0. Some shallow lakes may have albedos as high as 45% during times when the sun is striking the lake from a very acute angle, and more of its light is reflected. Alpine areas often have strange albedo values because of the unusual land formations.

More kind of wurbly stuff removed.

In the real world, the maximum albedo depends on the environment. Thus, even in the middle of winter with a heavy snow cover, the albedo of weather stations in the pine-forested areas from Europe to Siberia and in the Americas rarely goes above 40%, and many stations in this area have averages around 25%. Deciduous trees lose their leaves, and their albedos may rise to the mid-50's in winter. Open prairie climates will average around 73%, and barren tundra averages about 80%.

Keep to the subject...

If the theory of global warming is true, and the polar regions of the planet are going to be rapidly warming up, then the magnitude and path of the warming trend will depend largely on the albedo of the earth's polar regions, and to a lesser extent on the albedo of the whole planet. Because warm days in the Arctic mean heavier snowfalls, the extra snow will have a negative feedback, tending to bring temperatures down, masking the warming effect. But if the temperature rises year-round, then summers in some areas will be warm enough to melt the snow and ice completely, and thus the feedback effect in the summer will become strongly positive. For example, currently the most northern part of the Davis Strait between Canada and Greenland is blocked with ice year-round, and summer temperatures are very cold even for its latitude because of the albedo. If the ice were to melt, the very high-albedo ice would be replaced with some very low-albedo water, and temperatures would rise enormously, perhaps as much as 8°C (15°F), which would make the area warmer than any other area at that latitude. (This is what accounts for the unusually warm summers on the islands of Svalbard, in Norway. But Svalbard is surrounded by ocean, whereas the Davis Strait is surrounded by land, and thus has the potential to become even warmer than Svalbard.

This wanders of into GW, which doesn't fit here. I've added a much simplified and shorter version to the page.

If the ice melted, then there would be a way for the warm waters of the Gulf Stream to penetrate deep into the Arctic, and warm spells would become increasingly frequent. This could accelerate the melting of the Arctic Ocean, a process which would feed on itself. A melted Arctic would help many people living in Arctic areas, but could possibly hurt many others living in other parts of the globe.

Perhaps, but not very albedo-relevant.

Albedo and frequency. There seems to be little mention of the fact that albedo is frequency dependent and objects which are white in visible light, (i.e. reflective), can be black (i.e. not reflective) in infra red, and so on for other frequencies. Most of the sun's energy comes to us as infra red heat. This means that apparent large changes in visible reflection are not necessarily significant in the main part of the spectrum. Someone said above that a molucule (or atom) has albedo, but this is highly frequency selective and is misleading if gross energy balances are being inferred in relation to global warming. For example it is often said that snow and crystals of ice have very high albedo, which is true in visible light, but they absorb at lower frequencies, otherwise, why would all the snow melt in summer?ProfSWback 16:44, 30 December 2006 (UTC)

While you're obviously right that albedo is frequency dependent (although not Bond albedo, which depends rather on the spectrum of the incident light), the sun's energy output IS highest in visible light which is the most energetically significant part of the Solar spectrum. See Solar radiation. Deuar 15:07, 5 January 2007 (UTC)

invalid reference

Please note that reference 13, http://lenah.freeshell.org/pp/01-ONW-St.Petersburg/Fresnel.pdf, seems no longer available. (9-nov-2007). —Preceding unsigned comment added by Jdekloe (talk • contribs) 13:15, 9 November 2007 (UTC)

Brazillian Ranchers

I removed "(refs???)" from the end of the following sentence. Perhaps someone could actually find a decent reference for it.

When Brazilian ranchers cut down dark, tropical rainforest trees to replace them with even darker soil in order to grow crops, the average temperature of the area allegedly increases by an average of about 3°C (5°F) year-round (refs???).

- Mark 05:25, 28 Jun 2004 (UTC)

Certainly needs ref because, as I understand it, when tropical forest is removed it is often replaced quite rapidly by pasture, which corresponds to an increase in albedo. The surface temperature increase is in response to the lower evaporation rate from pasture in spite of this albedo change. Deditos 11:24, 24 March 2006 (UTC).

Kuwait oil fires

Last bit, Kuwaiti Oil Fires: it seems contradictory, with the last sentence saying "impossible". Can someone who knows about this clear it up?

(William M. Connolley 17:36, 26 Nov 2004 (UTC)) Looking, the KOF stuff seems of rather dubious relevance to albedo. It was probably a confusion with BC or aerosol, so I've added sections for both.

Albedo 0.39

I don't know where this article got the 0.31 Albedo figure of Earth. Albedo 0.39 is what Kaufmann says; Pater and Lissauer say that Earth has a "bond albedo" of 0.29 and a "geometric albedo" of 0.37 source. I changed the page to quote the albedo 0.39 figure, since that seems to be a reasonable number (and a really good album to boot). Samboy 08:18, 22 December 2005 (UTC)

Sounds good to me. Every article needs more credible sources. Deco 09:19, 22 December 2005 (UTC)

I think both the bond albedo and geometric albedo should be given. I've usually seen the albedo given as 29 to 31 percent. Since Pater and Lissauer have both, I'll use them. -- Kjkolb 05:17, 5 January 2006 (UTC)

First, I think bond albedo and geometric albedo should be defined and it should be stated which one is being used when a number is given or both should be given. -- Kjkolb 05:21, 5 January 2006 (UTC)

Suggest 9 possible wiki links for Albedo.

An automated Wikipedia link suggester has some possible wiki link suggestions for the Albedo article:

• Can link electromagnetic radiation: ...re of reflectivity of a surface or body. It is the ratio of electromagnetic radiation reflected to the amount incident upon it. The fraction, usu...
• Can link angle of incidence: ...s the spectrum of [[visible light]]. It also depends on the angle of incidence of the radiation: unqualified, normal incidence. Fresh snow...
• Can link weather station: ...thousands of weather stations across the world, the college weather station at [[Fairbanks]], [[Alaska]], is about 3°C (5°F) warmer tha... (link to section)
• Can link solar radiation: ...s especially marked during the late [[winter]] months, when solar radiation is greater. ... (link to section)
• Can link natural environment: ...itional zones. Part of the reason for this is the different natural environment of cities in tropical regions, e.g., there are more very da... (link to section)
• Can link carbon sequestration: ...ly warming) effect of albedo change and (cooling) effect of carbon sequestration on planting forests. They found that new forests in tropica... (link to section)
• Can link Climate models: ...ing from a minimum of near 0% to a maximum in the high 70s. Climate models have shown that if the whole earth were to be suddenly cove... (link to section)
• Can link greenhouse effect: ...mperature change due to an increase in the magnitude of the greenhouse effect, "all" we would need to do is increase the earth's overall ... (link to section)
• Can link indirect effect: ...direct (albedo) effect is generally to cool the planet; the indirect effect (the particles act as [[CCN]]s and thereby change cloud pro... (link to section)

Notes: The article text has not been changed in any way; Some of these suggestions may be wrong, some may be right.
Feedback: I like it, I hate it, Please don't link to — LinkBot 11:14, 1 Dec 2004 (UTC)

• Definitely needs a link to the article on "global dimming" (I know nothing about how to do that!)

Done .. added See also section with link to Global dimming Kgrr 14:24, 13 March 2007 (UTC)

Useless Definition

I find the definition to be completely useless and unscientific. How are incident and reflected radiation to be measured, and how is albedo determined to 3-figure accuracy if the definition is given in essentially unquantifiable terms ? Are we talking about power here ? Power in a certain bandwidth ? Power weighted according to spectral distribution ? Get real ! Enough of this pseudo-scientific posturing and do the job properly, or not at all. Andrew Smith

"Climate models have shown that if the whole Earth were to be suddenly covered by white clouds..." removed pending source

I have removed the following text pending the supply of a source for the statement:

"Climate models have shown that if the whole Earth were to be suddenly covered by white clouds, the surface temperatures would drop to a value of about -150 °C (-240 °F). This model, though it is far from perfect, also predicts that to offset a 5 °C (9 °F) temperature change due to an increase in the magnitude of the greenhouse effect, "all" we would need to do is increase the Earth's overall albedo by about 12% by adding more white clouds."

This was marked with a "fact" template, which I think simply isn't enough. We should rather remove unsourced statements of this level of significance and query them (as I do here) on the talk page. --Tony Sidaway 15:39, 2 July 2006 (UTC)

clouds

The albedo values for clouds given here differ from those given at cloud albedo.4.232.6.75 21:59, 12 August 2006 (UTC)

First Line (again)

The first line (on 12 Feb 2010) states: "The albedo of an object is the extent to which it diffusely reflects light from light sources such as the Sun. It is therefore a more specific form of the term reflectivity. Albedo is defined as the ratio of diffusely reflected to incident electromagnetic radiation."

Restricting the description to "diffusely" implies that the specular reflection is ignored, which is not true. Rather, the albedo measures the total reflected light ("exitance", to be precise, ref 1 below) summed over all directions, including both the specular component (generally brightest in the glint direction) and the diffuse component (generally seen at all angles, but not constant). Unfortunately, there are multiple measures (definitions) of albedo, as described in the Astronomical Albedo section. But I don't think any of them exclude all of the specular (glint) component, except to perhaps avoid the peak of the glint.

I propose the following:

"The albedo of an object is a measure of how strongly it reflects light from light sources such as the Sun. It is therefore a more specific form of the term reflectivity. Albedo is defined as the ratio of total-reflected to incident electromagnetic radiation."

(1) Gutman, G.,"A Simple Method for Estimating Monthly Mean Albedo of Land Surfaces From AVHRR Data", Journal of Applied Meteorology, 1988, vol = 27, pp 973-988.

Chonny (talk) 20:49, 12 February 2010 (UTC)

Fairbanks vs. Van Nuys

Okay, the Fairbanks section says:

According to the National Climatic Data Center's GHCN 2 data, which is composed of 30-year smoothed climatic means for thousands of weather stations across the world, the college weather station at Fairbanks, Alaska, is about 3 °C (5 °F) warmer than the airport at Fairbanks, partly because of drainage patterns but also largely because of the lower albedo at the college resulting from a higher concentration of spruce trees and therefore less open snowy ground to reflect the heat back into space. Neunke and Kukla have shown that this difference is especially marked during the late winter months, when solar radiation is greater.

..but I read once that some climatologists said that if they plant about 10,000 trees in the ever-sunny steaming-hot San Fernando Valley of Los Angeles, that it could lower the average temperature of the Valley by several degrees, as the Valley's concrete sidewalks are reflecting the sunlight and heating up the air for several meters above the surface. So- which is right? or, is it that the trees will provide shade, heating up themselves to provide cooler air at the surface? I'm confused. - Eric 00:10, 25 December 2006 (UTC)

It's not albedo, Eric. While a small amount of the energy is used in photosynthesis, evapotranspiration would be the major cause of the cooling. Concrete and asphalt pavement reflect relatively little, the heating of the air is mainly due to conductive transfer. It takes about 600 calories of heat energy to change 1 gram of liquid water into a gas.(DW 20061231) 68.151.34.107 21:45, 31 December 2006 (UTC)

Clarify for non-scientists

The first paragraph should be in plain English for the many non-scientists who will read it. I don't have the expertise to be sure I write it correctly, but here's a draft idea:

Now it says,

Albedo is the ratio of reflected to incident electromagnetic radiation power. It is a unitless measure indicative of a surface's or body's reflectivity.

I think most readers will not understand "incident", "electromagnetic radiation power", or "unitless", or the way these things tie together. Suggested revision:

Albedo is a measure of how much electromagnetic energy (e.g., light) a surface reflects. When electromagnetic energy, such as light, hits a surface, such as a window or a mirror, it must either pass into the surface or be reflected. For example, when light hits a typical mirror, almost all the light is reflected; thus the mirror's albedo is high. When light hits a typical window, almost all the light passes through; thus the window's albedo is low. Most surfaces both reflect and absorb; for example, there are two way mirrors, and a window both allows sunlight through and reflects it -- you can see the glare.

Guanxi 18:07, 4 February 2007 (UTC)

Good point, I think. I would change the first sentence and a few words to be more informative, as per:

Albedo describes what proportion of electromagnetic energy (e.g., light) a surface reflects. When electromagnetic energy, such as light, hits a surface, such as a window or a mirror, it must either pass through the surface or be reflected. For example, when light hits a typical mirror, almost all the light is reflected; thus the mirror's albedo is high. When light hits a typical window head-on, almost all the light passes through; thus the window's albedo is low. Most surfaces both reflect and absorb; for example, there are two way mirrors, and a window both allows sunlight through and reflects it -- you can see the glare.

Deuar 17:13, 5 February 2007 (UTC)

Thanks. One more try below: The first sentence omits all but essential terminology; it's a little less precise but the interested reader can find plenty of detail further down the page. Also, I tried to remove a possible point of confusion (the angle of the light hitting the window) by widening the range of the proportion of light absorbed ("almost all" -> "most"); I hope that addresses your concern. Overall, do you know enough to say it's technically correct? It looks good to me, but 'I don't know what I don't know', as they say ...

The term Albedo describes how reflective a surface is when electromagnetic energy (e.g., light) hits it. When electromagnetic energy, such as light, encounters a surface, such as a window or a mirror, the energy must either pass through the surface or be reflected. For example, when light hits a typical mirror, almost all the light is reflected; thus the mirror's albedo is high. When light hits a typical window, most light passes through; thus the window's albedo is low. Most surfaces both reflect and absorb electromagnetic energy; for example, there are two way mirrors, and a window both allows some sunlight through and reflects the rest -- the glare that you see is the reflection.

Guanxi 23:16, 5 February 2007 (UTC)

Hi, you know I strongly think that the first sentence should be informative. Otherwise you get lots of words and no meaning. I agree that jargon should be watched out for, but "measure" and "proportion" are not particularly scary words. At least once we're in the full encyclopedia and not in interwiki:simple. I've put almost your original opening sentence back in.

Reading it all again, I was also struck that the comparison between mirrors and windows was a bit academic - most common materials absorb just as much or more than they transmit or reflect. When light hits a surface it can do one of three things: be reflected, go through, or be absorbed. I've tried to take this into account below.

Albedo is a measure of what proportion of electromagnetic energy (e.g., light) a surface reflects. When electromagnetic energy, such as light, encounters a surface, such as a window or a mirror, the energy must either be absorbed, pass through the surface, or be reflected. For example, when light hits a mirror or white sheet of paper, almost all the light is reflected; thus their albedo is high. When light hits a dull black object or a cave entrance, it does not come out; hence their albedos are low. A window is interesting in that when light hits it head on, most light passes through and the window's albedo is low, but when light hits the same window at a grazing angle it acts partly like a mirror, and its albedo becomes high. Most common surfaces act as some combination of the above behaviours.

Deuar 16:27, 9 February 2007 (UTC)

(I revised the following post. If you want to see the original version, look in the history, but at this point it's just spam so I removed it):

The first sentence looks good. I realize we're unnecessarily complicating our intro to Albedo by also discussing the behavior of light: Whether the light is transmitted or absorbed, albedo is still reduced, so let's cut out the light discussion (I'll linkify terms so readers can look them up) and phrase it in terms of albedo: 'Is it reflected or not?' With the transmit/absorb issue removed, I think a window and mirror are the simplest examples (I tried snow and asphalt, but I know people who have never seen snow, much less understand its reflective qualities. People intuitively understand mirrors and windows -- their purposes are to reflect and transmit).

Albedo is a measure of what proportion of electromagnetic energy (e.g., light) a surface reflects. When electromagnetic energy, such as light, encounters a surface, such as a mirror or a window, the surface reflects some of the energy. For example, when light hits a mirror, most of the light is reflected and thus the mirror's albedo is high. When light hits a window, little light is reflected and thus the window's albedo is low. Few surfaces reflect all light or no light: For example, even windows reflect some light and thus you can see a glare.

BTW, you know someone is going to change it 5 minutes after we post it!

Guanxi 17:55, 11 February 2007 (UTC)

I think our definition may not be technically correct. The following is from the Reflectivity article:

That part of incident light that is reflected from a body of water is specular and is calculated by the Fresnel equations. Fresnel reflection is directional and therefore does not contribute significantly to albedo which is primarily diffuse reflection.

I am curious why specular reflection contributes less to albedo, but I don't think this is the forum. I'm more concerned with how to define albedo properly. The definition in the current Abledo article also seems wrong (assuming the Reflectivity article is correct), since it doesn't distinguish between different kinds of reflection. Guanxi 18:09, 11 February 2007 (UTC)

Albedo Enhancement

Where should the topic of Albedo Enhancement be best handled? here? Global warming? Global dimming? Kgrr 02:11, 26 March 2007 (UTC)

Well, this article should be primarily about albedo as a general physical property, not limited to talk of Earth's albedo only. I think Earth's albedo should be a subsection including mention of potential future change (increase or decrease) and possible past change (20th century, e.g. global dimming, and paleo). Note that global dimming, global warming and climate change netion albedo already. Evidently, this article needs quite a bit of an overhaul... when I get the time, eh? Deditos 10:10, 26 March 2007 (UTC).

By "Albedo Enhancement" I was referring to artificially changing the albedo of the earth as a measure to slow or stop global warming should it spin out of control.

Incidentally, I'm surprised the article did not briefly mention or refer to Anders K. Ångström who did a lot of albedo research in the mid 1920's. see The Albedo of Various Surfaces of Ground Anders Angstrom Geografiska Annaler, Vol. 7, 1925 (1925), pp. 323-342 doi:10.2307/519495

A section on measuring albedo for both terrestrial and astronomical would have been nice.

Also, I would have thought the pop culture uses of Albedo such as Video Game Characters, Magazine titles, and Album titles are not relevant to the article and are already handled by the disambiguation top link to the more relevant articles and would have been removed from this article.Kgrr 11:20, 27 March 2007 (UTC)

Ah yes, my mistake, you mean Mitigation of global warming. Sounds like you have some sources in general, so I say be bold and make some changes to this article. Deditos 12:11, 27 March 2007 (UTC).

I'm currently working on Global dimming, but I would like to come back and help you with a short section that points to Mitigation of global warming where the big section needs to be. Thanks for finding the right place.Kgrr 15:01, 27 March 2007 (UTC)

Reflection

Sure the Albedo is highest if the light is reflected by objects that are white? --pizza1512 ^{Talk Autograph} 06:28, 30 April 2007 (UTC)

Desert Albedo

I've searched the web for specific references to the albedo effects of large-scale deserts, e.g. Sahara, on a hunch that the high albedo effect of such deserts may be a significant balance of Earth's temperature control mechanism. Suspiciously, such references are unavailable - nobody seems to have addressed that point.

I read something years ago concerning Gaia Theory and "Daisyworld", and a search brought up http://www.schumachercollege.org.uk/articles/college-articles/stephan/fromgaiatheory.html

In place of bright daisies, think deserts.

As we increasingly burn more fossil fuels we are heating the environment, with such heat being transferred globally, increasing the size of those deserts. Desertification is seen as bad, but I wonder if it is the only mechanism that currently we have to prevent runaway global warming? Deserts may become increasingly important as reflectors of heat back to space, to maintain temperature balance. Those countries (typically economically poor) may be supported economically by the world community, in the same way as is being proposed through the "carbon cap and trade" idea.

Much is being made of the value of using solar power farms as a green way of obtaining heat for our use, but surely they are yet more "black daisies" that will add to global warming.

Basically, we are hungry for energy, and are releasing it from within the Earth as fossil fuel, and will be trapping it on its arrival from the Sun (as solar energy farms). After we've finished with it, every bit of that energy ends up in the environment at large. We need to find a way of gathering that waste energy for redistribution.

Fractain 17:43, 1 May 2007 (UTC)

temperatures?

this is my first wikipedia article edit, so don't mind the mess I make of formatting...

several places this article cites temperatures that are innaccurate in some sense, because 3 degrees Celsius is simply not the same as 5.4 degrees fahrenheit.

unless there is something I am completely missing.

who wrote this?

Raging thunder (talk) 16:06, 11 December 2007 (UTC)

You have made the familiar error of confusing absolute and relative temperatures. 3 oC is not 5.4 oF. But a difference of 3 oC is a difference of 5.4 oF. Personally I'd just rid of all the oF's... 16:09, 11 December 2007 (UTC) —Preceding unsigned comment added by William M. Connolley (talk • contribs)

I removed some old vandalism (of my own)

I wrote this article as a mock research paper in high school and then put it on Wikipedia in 2001 as a prank: [1] I'm sorry for letting it sit here this long; I really didn't think about it after I did it, and it took me five years to remember that I had ever even edited the Albedo article, much less created it. I remembered when I came here looking for information on albedo for a real research paper, and reading through the article I realized I was reading some of my own words. So I removed most of it, but apparently either i missed some or the edits were restored. So this time I'm really cleaning up. Note: the info I'm removing isn't necessarily wrong; it's just that the original paper was only a mock paper, to teach us how to write research papers, so the factual accuracy of the information wasn't really important. I remember myself just skimming through some books on the subject and jotting down various notes. Once again, I apologize for vandalizing Wikipedia and for taking seven years to confess to it and clean up after myself. If you look at my recent contributions, you can see that I have ~2000 good faith edits and no bad ones. Soap ^Talk/_{Contributions} 17:05, 19 September 2008 (UTC)

Geoengineering

I think the geoengineering material should be removed. It is outside the scope of albedo as a physical concept and quantity, and while relevant geoengineering articles can link to this page, I don't think it warrants its own section here, and perhaps not even to be mentioned. Awickert (talk) 17:30, 31 January 2009 (UTC)

Removed. If re-added, I suggest that it is through more info on the albedo of different substances, through the current structure. Awickert (talk) 22:50, 1 February 2009 (UTC)

definition

I believe that the definition of albedo is the fraction of all sunlight reflected (all wavelengths not just visible wavelengths as stated in the article) Hke33ly (talk) 22:48, 13 April 2009 (UTC)

Not just the sun

A surface can have an albedo even if it has never been exposed to sunlight. So why mention the sun in its definition?--Singularitarian (talk) 10:08, 2 September 2009 (UTC)

True. But--mostly albedo is used in astronomy and climatology, so it makes sense that the sun would be in the definition. Also, the just because an object has not been exposed to sunlight does not mean it will not reflect a certain way if it is ever exposed to sunlight. Oh, and since we and everything around us is made of star stuff, everything has at one point been exposed to starlight, if you want to be pedantic. Not trying to be difficult here; just think it would be wrong to define albedo without sunlight. --Turboguppy (talk) 14:32, 2 November 2013 (UTC)

Not just climatology and astronomy

This article seems to be written from the perspective of a climatologist or an astronomer. However, albedo is an important concept in computer graphics and computer vision as well. It seems the article should be revised to account for these perspectives.--Singularitarian (talk) 10:04, 12 September 2009 (UTC)

The subject of albedo seems to be hard to find on the net as relates to computers--most references I found to it are related to using it exactly as described in this article--that is controlling lighting in a three-dimensional space, with regards to reflectivity of light sources. A small section might be added to address this, but hardly seems necessary as a computer programmer looking up albedo is likely to already know why it is needed, and need it for the reasons described; however, the point is valid that albedo is a concept in computer work, and deserves a mention.--Turboguppy (talk) 14:22, 2 November 2013 (UTC)

Reflectivity or reflectance?

The current version of the article says that albedo is a specific case of reflectivity. However, Wikipedia distinguishes between reflectivity and reflectance, and by my understanding albedo is a specific case of reflectance, not reflectivity.--Singularitarian (talk) 22:44, 15 September 2009 (UTC)

From Wikipedia on Reflectivity:

According to the CIE (the International Commission on Illumination),[3] reflectivity is distinguished from reflectance by the fact that reflectivity is a value that applies to thick reflecting objects.[4]

Therefore, Albedo is used for climatology and astronomy because it gives a reflectivity for thick objects, such as planets and moons and asteroids and such. Albedo is not considered reflectance because the total effects of the reflectivity in albedo's case depend on many different surfaces and even angles--not like a reflective surface such as a mirror. Camo pants have reflectivity, a mirror has reflectance. That's my understanding anyway-- anyone care to correct me?

--Turboguppy (talk) 14:08, 2 November 2013 (UTC)

Units used are inconsistent

Albedo units were reported in the article interchangeably as either proportions of 1 (i.e. the average albedo of the earth is approximately 0.3), or as percentages (i.e. the albedo of snow was reported as being 90%). In addition to this there are ambiguous statements where relative differences in reflectivity are given as percentages, in the same sentence as giving absolute albedo values, making the situation even more confusing. For example "winter albedos of treeless areas are 10% to 50% higher than nearby forested areas". Does this mean the albedo is 0.1 to 0.5 higher (in absolute terms) or 10-50% higher as a proportion of the albedo of forested areas? I have thus changed direct references to albedo values to be all expressed as a proportion of 1. I have left the above ambiguous statement in place because the original meaning of the author cannot be known with confidence. —Preceding unsigned comment added by 147.66.8.158 (talk) 04:01, 15 January 2010 (UTC)

There is no difference between 0.10 and 10%, they represent the exact same thing. In fact, the term "percent" is frequently used for both. Q Science (talk) 05:33, 15 January 2010 (UTC)

I agree they represent the same, and this is why it becomes confusing, if in the same context percentage units are used to compare measurements proportionally, rather than comparing absolute albedo measurements given as a percentage of light reflected. In the statement I provide above "winter albedos of treeless areas are 10% to 50% higher than nearby forested areas". Imagine the albedo of a forested area is 0.3 (30%). Does this mean the albedo of the nearby treeless areas is 0.33-0.45 (33-45% which is 10-50% higher measurement than the original), or 0.4-0.8 (40-80%, or an absolute albedo reading of 0.1-0.5 (10-50%) added to the original reading)? This ambiguous statement can be read both ways and using units consistently should avoid or at least minimise this. M. 19 January 2010. —Preceding unsigned comment added by 147.66.8.158 (talk) 03:06, 19 January 2010 (UTC)

Your point is good, but your change did not really address it. Also, I am sure that you are aware that 0.1 <> 0.10 (that is, in an article of this type, 0.1 is not the same value as 0.10). To me, this is a real issue with your changes. You can not simply change 10% to 0.1 because that may not be correct. In general, 0.10 would be more correct, but it really depends on what the references say. Q Science (talk) 06:09, 19 January 2010 (UTC)

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Needs mention of high-albedo roofing materials

Key for understanding concept of green roofs to reduce urban heat islands and slow global warming is concept of high-albedo construction materials.

Need a section here to point to from roofing or a new section on high-albedo roofing & paving materials, etc.

Mitigation via high albedo materials: See, e.g., http://en.wikipedia.org/wiki/Urban_heat_island#Mitigation

Relation to Global Warming: http://en.wikipedia.org/wiki/Urban_heat_island#Relation_to_global_warming

Ocdcntx (talk) 15:41, 16 February 2010 (UTC)

Visible vs. solar spectrum

Do the values given refer to some "reference" spectrum of white light or to sunlight (which is 50% IR)? This needs to be clarified. According to the "Percentiles" section of our page Planck's Law, 50% of sunlight is infrared at wavelengths > 711 nm. Therefore, the difference between solar and visible albedos becomes very large. In the case of snow, the near-IR albedo is roughly 50% less than the visible^[2], thus a visible albedo of 90% would be a total solar albedo of less than 70%, representing a 200% "increase" (!!!!) in absorbed energy. I wouldn't exactly call this negligible...

129.2.46.178 (talk) 00:58, 4 June 2010 (UTC)Nightvid

Low and High Angles

Section 3.5, the article says there is higher albedo from water early and late in the day, but calls this a high angle. The highest angle is normally (no pun intended) when the sun is directly overhead. The high albedo is at low angles, when the sun is near the horizon. The article is very unclear on these points. Ladarzak (talk) 05:57, 18 February 2012 (UTC)

Blue sky albedo

What is it? — Preceding unsigned comment added by Goatbar (talk • contribs) 18:25, 2 May 2016 (UTC)