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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 et.al. 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.

Conclusions

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

Comments 1 to 13:

  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 et.al. 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".

    regards,

    David

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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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