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The Albedo Effect and Global Warming

Posted on 30 July 2013 by gpwayne

This post is a new 'basic' level rebuttal of the myth: "Earth’s Albedo has risen in the past few years..."

What the science says...

The long term trend from albedo is of cooling. Recent satellite measurements of albedo show little to no trend.

The Unsettled Science of Albedo

“Clouds are very pesky for climate scientists…”

Karen M. Shell, Associate Professor,  College of Earth, Ocean, and Atmospheric Sciences,  Oregon State University, writing about cloud feedback for RealClimate

Albedo is a measure of the reflectivity of a surface. The albedo effect when applied to the Earth is a measure of how much of the Sun's energy is reflected back into space. Overall, the Earth's albedo has a cooling effect. (The term ‘albedo’ is derived from the Latin for ‘whiteness’).

The basic principle is analogous to strategies employed by people who live in hot places. Building are finished with white exteriors to keep them cool, because white surfaces reflect the sun’s energy. Black surfaces reflect much less. People wear light colours in summer rather than dark ones for the same reason.

The Earth’s surface is a vast patchwork of colours, ranging from the dazzling white of ice and snow, to the dark surfaces of oceans and forests. Each surface has a specific effect on the Earth’s temperature. Snow and ice reflect a lot of the sun’s energy back into space. The darker oceans absorb energy, which warms the water. Oceans help keep the Earth warm because they absorb a lot of heat (approximately 90%). This warming increases water vapour, which acts as a greenhouse gas and helps to keep temperatures within ranges humans have largely taken for granted for millennia.

A Cloudy Outlook

It isn’t just the Earth’s surface that has a reflective quality. Clouds also reflect sunlight, contributing to the cooling effect of albedo. They also contribute to warming at the same time, because they consist of condensed water vapour, which retains heat.

And if clouds complicate matters, so too do the seasons. Every year, albedo peaks twice. The first peak occurs when the Antarctic sea-ice is at its winter maximum. The second peak, which is larger, occurs when there is snow cover over much of the Northern Hemisphere.

Albedo also changes due to human interaction. Forests have lower albedo than topsoil; deforestation increases albedo. Burning wood and fossil fuels adds black carbon to the atmosphere. Some black carbon settles on the surface of the ice, which reduces albedo.

Albedo and Global Warming

The most significant projected impact on albedo is through future global warming. With the exception of Antarctic sea-ice, recently increasing by 1% a year, nearly all the ice on the planet is melting. As the white surfaces decrease in area, less energy is reflected into space, and the Earth will warm up even more.

The loss of Arctic ice is of particular concern. The ice is disappearing quite fast; not only is albedo decreasing, but the loss triggers a positive feedback. By exposing the ocean surface to sunlight, the water warms up. This melts the ice from underneath, while man-made CO2 in the atmosphere warms the surface. Humidity also increases; water vapour is a powerful greenhouse gas.  More ice therefore melts, which exposes more water, which melts more ice from underneath…

This loop fuels itself, the effect getting more and more pronounced. This is a good example of a positive feedback. Increased water vapour also has another effect, which is to increase the amount of cloud. As mentioned already, clouds can increase albedo (a negative feedback), but also warming (a positive feedback).

Measuring Albedo

The albedo of a surface is measured on a scale from 0 to 1, where 0 is a idealised black surface with no reflection, and 1 represents a white surface that has perfect reflection. 

Taking measurements of something with so many variables and influences is clearly going to be a challenge. Satellite data is constrained by the orbit of the satellite. Clouds can be hard to distinguish from white surfaces.

Indirect measurement may also be problematic. The Earthshine project investigated a phenomenon where light reflected by Earth illuminates the dark side of the moon. By measuring the brightness, the amount of albedo - reflectivity - could be estimated.

The project reported a counter-intuitive finding. The Earth’s albedo was rising, even as the planet was warming. This seems contradictory, as Anthony Watts was quick to note when he voiced his sceptical argument in 2007. If higher albedo was having a cooling effect, how could global warming be taking place?

Tricky Business

Science constantly seeks to improve itself. The first Earthshine paper (Palle 2004) claimed to have discovered a very significant cooling effect through a big increase in global albedo.

The results were problematic.  They flatly contradicted the NASA CERES satellite observations, and the discrepancy became the subject of investigation. In 2004, a new telescope was installed at the Big Bear observatory, where the project was located. It became evident that the original analysis was inaccurate. Once corrected, the Earthshine project and the satellite measurements were more consistent.

Figure 1: Earth albedo anomalies as measured by earthshine. In black are the albedo anomalies published in 2004 (Palle 2004). In blue are the updated albedo anomalies after improved data analysis, which also include more years of data (Palle 2008).

Over a five-year period, scientists found that albedo did increase slightly. Since 2003 the CERES satellite records shows a very slight reduction.

 Figure 2: CERES Terra SW TOA flux and MODIS cloud fraction for 30S–30N between March 2000 and February 2010 (Loeb 2012 - PDF)

Global versus Local

There are contradictory assessments of current trends in global albedo, possibly because the changes and effects are small. Research is being conducted into the role of clouds, both as forcings and feedbacks, and the role of albedo in cloud formation.

Recent research indicates that global albedo is fairly constant, and having no material effect on global temperatures. Local effects may be more pronounced. Loss of albedo in the Arctic could heat the water sufficiently to release methane stored in ice crystals called clathrates. (Methane is a greenhouse gas far more potent than CO2).

Loss of albedo in the Arctic will accelerate warming across adjacent permafrost, releasing methane. Melting permafrost may reduce its albedo, another positive feedback that will accelerate warming. Ocean warming from reduced Arctic albedo will also accelerate melting at the edges of the Greenland ice cap, speeding up sea level rise.


Albedo is a subject needing a lot more research. It’s an important feature of our climate, and a complex one. It is not yet possible to make definitive statements about what the future may hold. In fact, it is a good example of the ‘unsettled’ nature of climate change science.

We know the planet is warming, and that human agency is causing it. What we cannot say yet is how climate change is affecting albedo, how it might be affected in the future, and what contribution to climate change - positive or negative - it may make.

Basic rebuttal by GPWayne

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Comments 1 to 16:

  1. Hi. Great explanation, as usual here on SKS. But I must say that the first line, "The long term trend from albedo is of cooling." is somewhat confusing. It could be read as though we're experiencing a cooling effect.

    I'd suggest changing it to "A higher albedo has a cooling effect on the earth."

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  2. It would be really nice to update the graphs to include more recent data.

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    Moderator Response:

    [GPW] - Silence (and MA Rodger). Thanks for the comment. Sorry about the old graph, now updated to Loeb 2012 (same graph as MA Roger linked to, but without the bit cut off).

  3. There is a Loeb et al 2011 presentation here which has on its last frame a graph of the CERES & MODIS data spanning March 2000 to Feb 2010 but for 30N to 30S. (Note the top graph fig 4a is hidden - well it is in the form I see it on line - it reappears if you download-cut-paste).

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  4. I think this excellent post might be just a bit clearer if the discussion made a concrete distinction between the global or planetary albedo (which lumps together all the effects of clouds, aerosols, and surface changes and which may be increasing slightly) and the surface albedo (which does NOT include atmospheric effects for the most part). The surface albedo clearly is decreasing owing to the loss of snow and ice, and this allows more of the sun's energy to be absorbed by the system, even though there may be less of it entering the top of the atmosphere.   

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    Moderator Response:

    [DB] Thank you, Dr. Francis.  Your insights are always valued and welcome.

  5. There seems to be one little localized negative feed back occuring this year.  Due to a persistant low pressure area over the Arctic Ocean, it is cloudier than it has been and this is reflecting heat back into space.  The ice extent graph hasn't reached last year's values.  The low pressure area may be due to the earlier cracking of the ice north of Alaska, releasing heat and water vapour to the atmosphere or thinner ice doing likewise.  Gaia is trying to fight back. 

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  6. francis@4,

    Can you tell us why such distinction (planetary vs surface A) is important? My uneducated guess is that surface A may have large impact on arctic amplification (positive feedback in mid-to-high N lattitudes), while planetary A feedback may be confined to lower lattitudes only. But that's just may guess and I'd like to know your expert opinion.

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  7. Maybe I'm being dense, but this article isn't clear to me. I'm left with the impression that the Earthshine data still shows increasing albedo. The CERES graph is something of a cipher.

    Dr. Francis makes good points. Just because there may be a cloud-driven increase in albedo in the higher atmosphere doesn't mean the albedo below is also increasing, nor does it mean that the planet's surface is cooling. In fact, those same clouds could be acting as a blanket, capturing a larger share of the energy that does penetrate. Again, this isn't clear from the write-up.

    In fact, this piece doesn't read like a rebuttal at all, let alone a basic one, but a discussion with no strong conclusion. Time for re-draft, with the conclusion stated clearly at the top, and then supported by discussion?

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  8. william at 06:43 AM on 1 August, 2013

    releasing heat and water vapour to the atmosphere or thinner ice doing likewise. Gaia is trying to fight back.

    Right on!  Totally agree!  We humanoids think we're "all that", and we HAVE evolved "intellects" which have gotten ALL of Gaia endangered...

    but.."what we are for" ( as close as I can intuit/express it) is to see what the INNATE intelligence of the "larger system" is trying to "do", and help it along.



    For instance, there is a focused change anticipated in weather patterns in the Northern Pacific, which is anticipated to drive precipitation into Northern Nevada.  Why??   So that rain can fall on the pH 10 (or so) alkaliine soils found so abundantly in that locale, in the Great Basin.


    Thus cometh (pat pending) 

    "Carbon Dioxide Direct Air Capture and Sequestration Utilizing Endorheic Basin Alkaline Deposits to Effect Mineral Carbonation"

    all WE have to do, is quit being a "ME", and become open to ??whatever is apparent to do.."

    We are all in this together.

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  9. davidnewell @8, any mention of gaia that is not purely metaphorical is simply mysticism.  Humans are not "for" anything within the purview of science; and if we are "for" something, that thing will be found within the texts of some traditional religion.  Further, absent a direct causal link between the presence of highly alkaline soils and increased rainfall, claims that anticipated increased rainfall on one region with such soils have a teleological basis are (yet again) mysticism.  Don't for a moment imagine that your new religion has any basis in science.

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  10. This is not a new "religion", it is an observable fact that we are not separate from our environment:  and the principles of quantum physics support the premise.  You may object to "Gaia"because of it's "in the poppys" overtone..

    But don't think for a moment that "science" is a complete or sufficient matrix to describe phenomenae.

    What you see is what you get:  What you get is what you look for:  What you look for is what you see.

    If you want to look for something we are NOT "for",

    examine the nature of activity hamans have conducted on this planet  which threaten Life on it.

    "Science", the "intellect" and "the ego",  thinking that it is separate from "context", has led to this situation.   Now, "science" , and "the intellect"  have GOT to be employed to "get us out" of this situation.  Only one change, Tom.  "you" and "I" and "the planet" are NOT separate. 

    You can dispute this only in the face of incredibly overwhelming facts staring you in the face.

    I'll call it Gaia, and have a sense of what I'm talking about, and it ain't "religion".



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  11. dn @10 whatever ....

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  12. David, Gaia is not simply about the obvious interconnectedness of everything.  There is the suggestion made by its proponents that the Earth has an agenda -- if not forethought, a program that strives toward a goal.  There's no evidence for this.  Appealing to the unknown and then defining it according to your own needs is not good thinking, and that's what most people do when they seek to supplement science with another method.  You can't define with any sort of authority (beyond your own assumption of your own authority) what the supplement looks like.  Who is Gaia?  The part of Gaia that is beyond science is a figment of your imagination, differing in quality (sometimes radically) from every other human's concept of beyond-science Gaia.  If you don't have any rigorously-discovered evidence for this reality undiscoverable by science, and you don't even have a consistent logic for confirming what counts as evidence, then you're not going anywhere. 

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  13. ???  Well, we could descend into trivia on this point, but thank you for explaining to me what the term means to you.  I would have to defer to your comment aboput saying "what we ar e FOR": it was an error, although a slight one, in my own estimation of my intent.

    However, having stated that screwing up the planet is an example of what we are "NOT FOR" is another way to state that a terminal cancer is NOT FOR individual health.

    You agree that there is an obvious interconnectedness of everything,   You, for example, and me?  How about if it was you and me and everybody else and the Earth, and we call it "Gaia" and try to figure out what is needed for "thriving?"


    Mostly, you are projecting your own perceptions on me, and then "tilting" at them.


    Let's agree that ther is only one god, and we and everyone else bow down to it.

    That god is "God Reality", capitals provided only for efffect.

    Wiat, have to go pay my Gaia taxes.




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  14. Reading about resent NASA satellite data on finding increase heat loss to space makes me wonder how this increase in heat loss is consistent with the Radiative Forcing theory of the IPCC. My understanding of that theory is that as atmospheric CO2 increase it hold in more heat and makes the surface temperature hotter like a blanket effect while the heat loss to space remains the same. The NASA data does not seem to support the Radiative Forcing theory or I must not understand the Radiative Forcing theory. Where is the extra heat coming from?

    Also reading about the “heat island” effect from big cities (up to 15’F difference between urban and suburban) makes me wonder could this be related to the NASA data on heat loss? Has population gotten big enough to have an impact on global warming? The “heat island” effect is caused by the much lower albedo (reported as 0.04, cloud free) of urban areas vs the earth as a whole (reported at 0.31). Using IPCC data one can calculate that an albedo change of only 0.15% (+1’C) is needed to account for all of the temperature change from 1880 until now. (that is a hard to detect 0.001%/year). While we are waiting on that detection level we can use related data to estimate man-made albedo change like population or atmospheric CO2.
    The earth’s urban area is reported at 3.1% of the total area of the earth. The urban area back in 1880 (start of IPCC global warming data) is estimated at 0.7% (proportional to population) over 4X change. In 1880’s the “heat island” albedo effect was probably insignificant plus there was not many black parking lots or paved roads. The IPCC reports a 1’C rise in temperature since 1880. Using published information one can calculate the heat rise of the current 3.1% urban area at 4’C rise (since 1880) in earth temperate just from the urban area albedo change. (Using IPCC data of sun’s radiation to the earth at 1367w/m^2 and surface temperature rise correlation of 0.5 ‘C/w/m^2). The calculated 4’C rise is more heat than necessary to account for the 1’C observed this is probably due the reflective increase in clouds (water evaporation that eventually become clouds and reflects sun light) that would come with more heat from urban area. This overly simplified estimate of the man-made albedo effect suggests a more scientific version of albedo change should be included in any global warming model or theory. As the population of the earth gets bigger and urban areas grow this effect will get bigger. There are also other man-made albedo effects (destruction of rain forest, forest fires, melting of sea ice, and agricultural practices) which would be proportional to their % of the earth’s surface and their individual albedos.

    The earth’s population should be a good indicator of urban area increase and thus man-made albedo change. Atmospheric CO2 is also corelated to population should also be a good indicator of urban area increase (albedo decrease). Are CO2 and albedo confounded in their correlation to global warming? Which force is bigger? The above calculation suggest albedo. NASA's ongoing map of the earth's cloud free albedo should be a big help in including albedo in global warming models, initial results seem to support the above.


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    Moderator Response:

    [BL] Please learn to format your comments for readability.

    Much of your comment is off-topic for this thread.

    It does not look like you have improved your understanding of the physics of climate change since your last post here over two years ago.

    In your first paragraph, you are correct in saying "I must not understand the Radiative Forcing theory." The fundamental aspect of greenhouse warming of the atmosphere is that adding CO2 reduces the IR loss to space and increases the blanket effect - until the system heats up to restore the balance. Once balance is restored, IR loss will equal solar absorbed - but that may be at different values due to albedo feedback effects.

    For discussion of the urban heat island - how it works, how it relates to our measurements of temperature trends, please go to this thread. Hint: it's not just albedo effects.

    In order to avoid off-topic posts, please take the time to review the Comments Policy and ensure future comments are in full compliance with it.  Thanks for your understanding and compliance in this matter.


  15. blaisct - first off, this is somewhat offtopic here, and urban heat island effect is entirely off topic. Try posting to thread such discussions or moderators will remove you post.

    As to increased heat loss to space - consider the blanket analogy. The blanket doesnt stop heat loss, but it slows it so person in the bed stays warm. Now, what do you expect to happen to measurement of heat loss through the blanket if you put two people in the bed (or the person has a fever?). More detail on the science can be found in the actual paper which I believe is this one. 

    As to whether this contradicts radiative theory, lets see what that paper have to say. Note that EEI is "Earth energy imbalance" - if energy out is less than energy in, then earth heats up.

    "The excellent agreement between satellite and in situ trends in EEI obtained in this study demonstrates the benefits of having independent satellite TOA radiation observations and ocean heat content measurements for tracking changes in EEI. That both produce nearly identical results provides confidence that the trend toward an increased EEI reported here is robust, since it is unlikely to be due to artifacts in both observing systems." Ie expected result.

    Note too also that IPCC doesnt have theories - it simply reports on the science consensus.

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  16. blaisct @14,

    You say you are curious about recent NASA satellite data "finding increase heat loss to space." And you correctly add, the forcing due to increased GHGs will restrict "heat loss to space," this resulting in an energy imbalance and planetary warming.

    I'm not entirely sure what it is you enquire about, but this NASA web page 'NASA Satellites See Upper Atmosphere Cooling and Contracting Due to Climate Change' does report a measured cooling of the mesosphere from which they inferred "more heat is lost to space" from the mesosphere.

    Assuming this to be what prompts your enquiry:-

    The mesosphere roughly lies between 60km and 90km above the surface, sitting above the stratosphere. Both these regions of the atmosphere sit above the mechanism which results in global warming. Both these high-up regions of the atmosphere are cooling as would be expected with CO2-induced global warming. CO2 is well-mixed up to about 50km and lower altitude increases will also impact levels above 50km.

    The blanket analogy does not properly capture what is going on as an increase in a greenhouse gas like CO2 cools as well as warms due to mechanisms not present in blankets.

    The atmosphere radiates to space (indeed radiates anywhere) only via greenhouse gases. The other atmospheric gases do not radiate at the relatively low atmospheric temperatures. If GHGs are added to a bit of atmosphere, there will be more molecules to radiate so radiation flying about. Also the amount of radiation depends on the gas temperature which increases collisions with GHGs and so stimulates more radation.

    In the lower troposphere, the level of GHGs is high enough such that the radiation cannot travel far before it encounters another GHG molecule and is reabsorbed by the atmosphere. Down low, none of it gets to space. What is important for global warming is the altitude above which the GHG density becomes low enough to allow emissions to space. As the lower atmosphere becomes cooler with increased altitude and the level of radiation is dependent on temperature, the higher this altitude is, the cooler the atmosphere radiating to space is and the cooler t is the less radiation can reach space. And if you add GHGs, that altitude rises resulting in less space-bound radiation and thus a warming planet.

    But go above that critical point above which radiation can reach space and an increase in GHGs means more radiation flying about and more of it being "lost to space." This is why the mesosphere with rising CO2 levels is expected to cool with global warming. (The stratosphereric cooling is a different story again.)

    Hope that helps explain that NASA webpage statement "Scientists have long predicted this [mesosphere cooling] effect of human-driven climate change."

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