GARP SCR: Understanding Albedo effect

 This question was first posed by one of the group member Divya Papneja from the Linkedin group (https://www.linkedin.com/groups/12842133/). 

The Albedo effect, also known as Albedo, refers to the measure of the reflectivity or reflective properties of a surface. It quantifies how much of the incoming solar radiation (sunlight) is reflected back into space, as opposed to being absorbed by the surface. Albedo is typically expressed as a percentage, with 0% indicating perfect absorption (all incoming radiation is absorbed), and 100% indicating perfect reflection (all incoming radiation is reflected).

(Although various components of the Earth's surface display huge variable ranges in the amount of light they absorb or reflect, the global average reflectance/absorption of Earth, known as Albedo, has remained constant at ~31%. KEN GOULD, NEW YORK STATE REGENTS EARTH SCIENCE. Source:Forbes)

To put it simply, the whiter the surface is, higher the reflectivity and higher the "Albedo effect".  To put this in context of climate science, the Albedo effect at the poles of the earth is highest as it is covered in snow. Snow being "white" in color reflects most of the sunlight back. As the temperature rises due to climate change, this snow melts exposing the underlying ground, grass and rocks. The reflectivity or "Albedo effect" of these features is much smaller than "white snow".  This means, sunlight is reflected less and less and absorbed more and more. As the sunlight absorption increases, it causes the temperature to rise leading to further melting of snow. As more and more snow melts, the entire cycle repeats leading to more and more temperature rise. As snow melts into water, sea-level rises too which has its own implications.

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To express it mathematically, 

 

• P  = Projected heat on to a surface (experessed in watts per square meter)
• A  = Albedo effect Albedo effect (Albedo effect is expressed in % e.g Albedo effect of  a region is 80%. This means the region reflects 80% of the energy)
• R  = Reflected energy
• AB = Absorbed energy 

Simple equations:

Equation #1  :  R = P x A   --> This implies how much of the power is reflected depends upon the reflectivity property of the surface.

Equation #2 :   P = R + AB  --> This implies the power incident on a surface is either absorbed or reflected to put it simply.

Numerical examples involving the Albedo effect can help illustrate how changes in surface reflectivity impact the Earth's energy balance and climate. Here are a few numerical scenarios:

1. Snow Albedo Change:

   - Scenario: In a snowy region, the albedo of the snow-covered surface is initially 80%, reflecting 80% of incoming solar radiation.

   - Calculation: If the snow melts, and the surface changes to bare ground with an albedo of 20%, calculate the change in absorbed solar energy.

   - Initial albedo (A1) = 80%

   - Final albedo   (A2) = 20%

   - Change in albedo (ΔA) = A2 - A1 = 20% - 80% = -60%

   - Change in absorbed solar energy = ΔA * Incoming solar radiation

   - If the incoming solar radiation is 1000 watts per square meter, the change in absorbed energy would be -60% * 1000 watts/m² = -600 watts/m².

2. Climate Feedback Loop:

   - Scenario: Due to global warming, Arctic sea ice has decreased, and the albedo of the region has decreased from 60% to 30%.

   - Calculation: Calculate the additional solar energy absorbed per square meter due to this albedo change.

   - Initial albedo (A1) = 60%

   - Final albedo (A2) = 30%

   - Change in albedo (ΔA) = A2 - A1 = 30% - 60% = -30%

   - Change in absorbed solar energy = ΔA * Incoming solar radiation

   - If incoming solar radiation is 200 watts per square meter, the additional energy absorbed is -30% * 200 watts/m² = -60 watts/m².

These numerical examples demonstrate how changes in albedo, whether caused by natural processes or human activities, can impact the absorption of solar energy and, subsequently, temperatures and climate conditions. Positive values in the calculations indicate increased energy absorption, while negative values indicate reduced energy absorption due to changes in albedo.

Few other interesting examples - should interest readers who are travel enthusiastic

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In the textbook,  the Albedo effect is usually explained by referencing them to the polar regions of the Earth. However, there are many places across the globe where the inhabitants have adapted their housing (that make use of Albedo effect) in order to adapt to high temperatures that their regions experience. I am sure you would have probably read, heard about or might have even travelled to many such places. Let me share with you some examples.  

Before I share a list of such places, I have a request to make:

If you belong to such places or like to share some more examples, please leave your comments in the comment section and share more examples or information with other readers here. You can also invite them to visit such places. Sounds good?

1. Santorini, Greece:

Santorini is a beautiful place in Greece. Pre-air conditioning, the people of Greece had an innovative solution. We know that light colours absorb less heat than darker colours, so painting their houses white made the hot Greek summers more bearable. A clever solution!

2. Jodhpur, Rajasthan, India:

As you can see in the above image, almost all the houses are painted in blue in the city. In Jodhpur, weather remains bright and sunny all around the year, and the temperature rises to 40 degrees centigrade and above. Residents over the last couple of centuries have adapted to living in such hot temperatures. In order to keep the houses cool, the residents paint their houses in blue colour. Blue colour helps in keeping the houses cool in the heat, which is very vital.

 

3. Almeria, Spain:

 Since the 1980s, Almería in southern Spain has developed the largest concentration of greenhouses in the world, covering 26,000 hectares. The greenhouses reflect so much sunlight back into the atmosphere that they are actually cooling the province, Spanish researchers have found. While temperatures in the rest of Spain have climbed at rates above the world average, meteorological observatories located in the so-called sea of plastic have shown them moving in the opposite direction, with a decline of 0.3 degrees per decade. The strange phenomenon had not gone unnoticed in scientific circles, and now a study has suggested a plausible explanation: the white colour of the plastic reflects sunlight into the atmosphere as if it were a mirror, and it slows the warming of the surface. In this way, the greenhouses at a local level offset the rising temperatures associated with global warming.

https://geographyfieldwork.com/AlmeriaClimateChange.htm

 

Other useful information from the same chapter

Climate measurement proxies

Global warming

El nino

What is Radiative forcing?

What is Albedo Effect?

Few questions to try from Chapter 1

Question of the day based on Chapter-1 

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