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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

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The albedo effect and global warming

What the science says...

Select a level... Basic Intermediate

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

Climate Myth...

It's albedo

"Earth’s Albedo has risen in the past few years, and by doing reconstructions of the past albedo, it appears that there was a significant reduction in Earth’s albedo leading up to a lull in 1997. The most interesting thing here is that the albedo forcings, in watts/sq meter seem to be fairly large. Larger than that of all manmade greenhouse gases combined." (Anthony Watts)

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 in 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 written by GPWayne

This rebuttal was updated by Kyle Pressler in September 2021 to replace broken links. The updates are a result of our call for help published in May 2021.

Last updated on 23 October 2016 by gpwayne. View Archives

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Argument Feedback

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Comments 126 to 132 out of 132:

  1. blaisct @125,

    Your URLs don't work but...

    I assume when you say @123 that "the psychometric chart in @106 shows the math" you mean that this Free Online Interactive Psychrometric Chart for HVAC engineers does the aritmentic. The "math" is your own. And I would suggest it includes questionable assumptions as well as error and is incomplete. Certainly the contradiction I posed @122 (that Costa et al [2007] showed increasing albedo rather than the required decreasing albedo yet still showed warming temperatures) remains unexplained.

  2. I don't know what went wrong but I tested these; Online psychrometric chart  and Tutorial

    Please except my assumption and online calculator results in the summary of the three conditions, they are only examples.
    Doing some further research on the clouds I found this site Cloud Ceiling Calc that had a correlation used by airplane pilots to predict cloud celling.

    Cloud ceiling (m) = (ground temp. – ground dew point)/2.6 *1000*0.3084
    The base case is virgin land with lots of trees and vegetation, and is simulated by adding water to the online psychrometric chart calculator. The water added (22% of total water) is typical of data for rain forest type land.
    I have added the cloud ceiling calculation to the summary to show that the LHAC cases increase the cloud ceiling no matter what the albedo is. The high albedo case is 20% higher albedo than the base case and much greater than your chart on W/m^2 vs time. The emphasis of the LHAC theory is that cities and cropland do not put as much water into the atmosphere as the orginal virgin land and this lack of water can reduce the cloud cover.


    Summary of these cases:
    Base case: 29.2’C and 70% RH with 23.3 dew point calculating 701 m ceiling
    Low albedo: 33.4’C and 47% RH with 21.4 dew point calculating 1543 m ceiling
    High albedo: 31.5’C and 55.5% RH with 21.4 dew point calculating 1171 m ceiling
    Cloud ceiling and cloud cover should have a correlation.

     

  3. blaisct @127,

    I'm not sure this interchange is going anywhere. You are not noting the obvious errors in these numbers you are throwing around and if they were corrected I don't see any relevance to the climate change occuring, either globally or regionally.

    On the errors thing, do note that your numbers from the Free Online Interactive Psychrometric Chart are wrong. Consider simplifying the process you are trying to represent. This is not some reversable process so all that matters is the start & end points, not the route between.

    Thus if you choose to start at 25°C & RH=80%, you can add the SH from 16g/kg to 18g/kg (that is 11% increase not 22%) giving RH rising to 89.4% & Enthalpy increasing from 66kJ/kg to 71kJ/kg.
    Now if you add further energy through warming with SH fixed at 18kJ/kg, the enthalpy will rise and the RH will drop with that warming.
    So your Case 3 with an endpoint of 72.3kJ/kg gives a temperature increased from +25°C to +26.2°C & RH drops to 83.6%.
    Your Case 1 with an endpoint of 74kJ/kg gives a temperature increase to +28°C & RH dropping to 75.5%.
    And your Case 2 with reduced albedo giving additional warming to +9.7kJ/kg from the same start conditions yields an endpoint of +29.3°C & RH dropping to 69.7%.

    But these are just numbers. I don't see them relating to what we see of the real world climate change.

  4. Rodger @128
    Once again thanks for your input and patience. My objective in these three cases was to show the difference in air quality (temp and RH) of possible man-made land changes. These air changes are related to the cloud ceiling.
    Sorry for the errors. I do not do a good job going from my excel sheet to this format. I should have shown the before water step in case 1, and I did copy the results of case 1 wrong.
    To correctly compare these cases a base case enthalpy change must be picked based on real world data that represents the middle part of the earth with the sun shining. I have made lots of temp vs RH plots and came up with 8 kJ/kg(da) as a good average change in enthalpy. The same data shows that adding 2g/kg dry air was typical of tropical conditions.
    The short cut you suggested is ok as long as it crosses the 18g/kg water line and the 74kJ/kg(da) (66+8) line simultaneously. The two albedo cases are ether side of the 8kJ/kg base case at 6.4 kJ/kg and 9.7kJ/kg. I corrected the cases to include the case 1 with out water added and the enthalpy difference for each case. All cases start at the same 25’C and 80%RH.
    Cloud ceiling (m) = (ground temp. – ground dew point)/2.6 *1000*0.3084
    I hope all the errors are out of these cases and we can discuss the conclusions.
    1. These simple cases show that the beginning (event 1) of the LHAC theory in @121is valid in that land changes that result in lower available moisture will produce higher temperatures and lower RH air even if the albedo is increased.
    2. This higher temperature lower humidity air is correlated to cloud ceiling.
    Base case water added: typical rain forest (other vegetation or water sources would have less water added)
    Base case no water: Just to show what the rain forest would look like without water added. Note same enthalpy change and same dew point of all the other cases.
    Low albedo: intended to simulate a UHI.
    High albedo: intended to simulate the rain forest conversion in Amazonia.
    Summary of these cases:
    Base case water added: 8kJ/kg(da), 27.9’C, 75.5% RH, 23.3 dew point calculating 561 m ceiling
    Base case no water: 8kJ/kg(da), 32.5’C, 52.0% RH, 21.4’C dew point calculating 1318 m ceiling
    Low albedo: 9,7kJ/kg(da), 33.4’C, 47.0% RH, 21.4’C dew point calculating 1543 m ceiling
    High albedo: 6.7kJ/kg(da), 31.5’C, 55.5% RH, 21.4’C dew point calculating 1171 m ceiling
    Cloud ceiling and cloud cover should have a negative correlation? This exercise also suggests that the LHAC theory is more related to cloud prevention than destruction. The real-world origins of the ceiling correlation to temp and dew point suggest the plume of hot low RH air reaches high into the atmosphere supporting the model in Figure 3 @121.
    Comments on how big (% of earth’s surface) this effect is? See event 2 calculation @121. I get 7.8% of the earth surface that could be affected by hot low RH air to some degree. Figure 2 @121 show a decreasing RH over time, suggesting low RH air is being produce.

  5. blaisct @129,

    The correction of the numbers is good but whether it leads you to anywhere useful is another matter entirely. I repeat my parting comment @128 - "But these are just numbers. I don't see them relating to what we see of the real world climate change."

    Perhaps you should read up on the literature examining the impact of UHI on climate. But be warned, to my understanding there is no evidence suggesting anything but local effects.

  6. I have been watching this discussion for a while, and I too have a really difficult time understanding what blaisct's real purpose or argument is. With respect to albedo, it seems as if he is implying that albedo causes the change in climate, while ignoring the possibility that other factors are changing the climate and albedo is responding to that - the classical albedo feedback that is a standard part of climate science.

    I have access to some high temporal resolution surface radiation data from a continental location. Let's look at four graphs of daily values:

    January radiation and albedo:

    January radiation

    January albedo

    ...and the same location in July

    July radiation

    July albedo

    Let's talk about the last two first. It's a mostly sunny day. with some morning cloud and mid-day scattered cloud. Global radiation peaks at over 1000 W/m2. There is a strong diurnal pattern to albedo - lowest in mid-day (less than 0.2), and highest around sunrise and sunset (around 0.3).

    Then let's compare these to the first two, from January. A similar day in the sense of morning cloud and afternoon clear skies, but global radiation is much lower - (peaks at about 300 W/m2). Albedo is quite different - it drops from about 0.9 in the morning to

    I also know a bit about the temperatures on each day. In July, it was much cooler in the morning and evening, and hottest in the early afternoon. January was much, much colder.

    Should I assume that the differences in albedo have caused those temperature differences? After all, there is a strong correlation: albedo drops, and temperature rises. Very high albedo? Very cold temperatures!

    ...but all I have done is shown that winter is colder than summer, so you can get snow on the ground instead of agricultural crops. After all, the energy input from solar radiation in January peaks at 30% of what it was on that July day, even if we don't account for the higher January albedo and shorter daylight period.

    And the diurnal cycle in July? It is well-known and well-documented that surface albedo shows variability with solar zenith angle in clear skies. The sun is high in the sky at solar noon (which is about 1pm clock time on these graphs), and low in the sky at sunrise and sunset. It's not the albedo that is driving temperature differences: it is the change in solar input.

    Nothing surprising here. Albedo differences are the result of other factors that affect weather and climate.

    I think the same applies to blaisct's humidity and cloud arguments. There is nothing that I can see in his comments that gives any evidence that albedo or humidity are the driving force behind changing climate - they can (and are more likely to be) the result of a changing climate. A feedback, not a forcing.

  7. Bob Loblaw @131,

    I also have struggled to identify any sign of a significant driver of climate in the arguments presented by blaisct. If we wind back to the initial proposal (in the 'Does Urban Heat Island effect exaggerate global warming trends?' thread @59), I feel the scoping of a direct potential forcing can be scoped quite simply** but refining such an analysis does not appear possible with commenter blaisct who now introduces further speculative feedbacks into the discussion, thus piling unhelpfulness on top of unhelpfulness.
    (**According to Wild et at [2015] fig2a, the average land albedo equates to 48Wm^-2(land) = 14Wm^-2(global). If urbaniseation reduced that to zero over 1M sq km, that would equate to a 0.1Wm^-2(global) forcing, thus a maximum value for a quantity which may not even be positive. Note Guo et al [2022] suggest the effect is negative over urbanisation in China.)

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