World Facts

What is Albedo?

The term albedo refers to the amount of solar energy that gets reflected off of the Earth and lands back in space.

Albedo is part of the energy from the sunlight that casts back into the atmosphere. These rays have a significant effect on our climate. When the albedo rises, the universe reflects light more and consequently, higher levels of radiation are sent back to space so the Earth cools down. Albedo determines the level of heat on the Earth. It is now well known that most of the light from the sun moves up once it hits the Earth. Research has shown that water absorbs light more thereby reflecting less light. If there is more water compared to a hard surface, then there is less solar emission. The Earth, the moon, or any other planet has the ability to transmit albedo.

What is Albedo?

Albedo can be defined as a way of quantifying how much radiation is reflected from the surface. It is a comparison between the reflection radiation from the surface to the amount of radiation that hits it. This term also refers to the quantity of radiation generated by electromagnetic rays which consequently reflects away.

Seasonal Effects on Albedo

Summer

To understand albedo better, we look at two scenarios. One, if you walk barefoot on the black soil during summer, you will feel a lot of heat and can even get burnt because the surface is absorbing and retaining more heat. Another person walking on white soil during the same season will not be burnt. This is basically because white surface tends to reflect more heat and absorb very little of it. Equally, if you touch a black car in summer it will feel much hotter than touching a white car. This is because black absorbs and retains heat while white car surface will reflect back the solar rays.

Winter

During this season, it is generally wet with either water or ice. Water reflects approximately 6% of the light and absorbs the rest. Ice, on the other hand, reflects 50% to 60% of the incoming solar heat, thereby remaining cooler. A snow-covered area reflects a lot of radiation, which is why skiers having a risk of getting sunburns while on the slopes. Albedo diminishes when the snow-covered places start to warm up.

How is Albedo Quantified?

Albedo helps us to know how well a surface reflects solar energy. It is measured on a scale of zero to one (0-1). Surfaces differ in absorbent ability but will always be in the range of between 0-1.

Value “0” - If a score of zero is given, then the conclusion is that the surface is highly receptive to light, meaning that the surface takes in all the light that comes into contact with it. It is characterized by black surfaces.

Value “1” - This score is evidence that the surface does not absorb incoming light. It is characterized by white surfaces.

The albedo of our planet is 0.367, whereas that of the moon stands at 0.12, meaning the moon reflects 12% out of the radiation that falls on it. There are many satellites set up to monitor the planet's albedo by use of sensors which measure the light from the Earth that reflects on the surface of the moon. NASA has set out what is called Terra and Aqua Satellites to assist identify any changes in albedo.

Various Studies

A. Danjon Studies (1928- 1954)

André-Louis Danjon, a French national, conducted studies on Albedo. He used an approach known as “The eyes of a cat”. He used light to make a bio image of the moon, permitting the sight checking of similarity and differences of the degrees of two research specimens of the moon surfaces. Using this approach, he ceased some light from the part with sunlight to correspond with the sunlight of the other side.

The research led to what is known as Danjon scale astrolabe which also led to enhanced accuracy of major visual astrometry. He further came up with a five-point measuring parameter for assessing the visual appearance and brightness of the moon when there is a total eclipse. He used letter “L” to denote high darkness.

L-O: Moon cannot be seen. This is characterized by the total to the medium dimness.

L-1: The details are visible but with some difficulty.

L-2: The shadows at the middle are very dim but the outer edge is a bit bright.

L-3: The umbral shadow has yellow color around it.

L-4: There is a blue looking shiny color around the moon. It has shades of either red or orange. It illuminates a lot of light.

Earth Surface Albedo Variations 1998- 2014

These were the second studies done within a total of sixteen years. During this period, man tried to understand the ratio of earthshine as compared to lunar shine. This was assessed both from the aerial satellites and on the ground for a period of sixteen years. The moon was the focus of the study.

De Pater and Lissauer Table of Albedo

De Peter and Lissauer categorized albedo into two sets namely Geometric and Bond albedo Geometric albedo means the quantity of radiation in comparison to the frequency which the wave's shape repeats itself while Bond albedo highlights the total radiation reflected from an object in comparison to the total incident radiation from the solar planets.

Albedo Drivers

Some of the factors that drive albedo include but are not limited to the following:

1. Change in land use –This refers to the way people do actions that alters the landscape. Examples range from the natural ecosystem to deforestation to subdividing into small-scale farms and setting up of urban cities leaving the ground bare.

2. Greenhouse emissions – Carbon dioxide and other gases emitted affects albedo.

3. Water degradation – The use of water has increased due to agricultural activities.

4. Pollution – Excess high-level nitrogen and phosphorus flow. This leads to pollution of water bodies and the atmosphere.

The Albedo Effect and Warming of the Universe

It was found that the global albedo has recently gone up and on a measuring scale, the watts per square meter is now greater. This is according to research by Anthony Watts.

The universe is gradually getting hotter due to deforestation. Better forest management skills should be embraced to mitigate effects of albedo. Trees reduce radioactive effects of solar reflection. We should also protect our wetlands and snow cover fractions. The loss of the Arctic is of great concern.

Many states are advocating reforestation since trees are darker and have reduced albedo emission rates. If one plants more trees he is remunerated based on a system called carbon credit. The clouds may at times reflect sunlight but can still hold heat thereby warming up the Earth.

Today climate scientists and researchers are concerned that if global warming continues it will make the polar ice caps to melt making the ocean water to absorb more solar light thereby increasing the global warming. It is in this context that all of us should work towards coming up with better models to curb its effect in future.

More in World Facts