What is the albedo effect? The albedo effect is how much a surface is able to reflect sunlight. Light colored surfaces reflect more, and dark colored surfaces reflect more.
The word “albedo” comes from the Latin word “albus”, which means “whiteness”. It is a way of measuring how much sunlight an object can reflect, and it goes from 0 to 1. 0 is something black that will absorb all sunlight, and 1 is something white that will reflect all sunlight. Everything else lies in between. There is nothing on Earth that has an albedo of 0 because it is not possible to get pure black. Manmade products like Vantablack come closest, but they can only absorb 99.965% of light. And likewise, there is nothing that has an albedo of 1 because there is nothing on Earth that is pure white and can reflect all of the sunlight that hits it. Everything absorbs something.
To begin with, we need to look at why black things absorb light and white things reflect light. Although, actually, I have that the wrong way round. Black things don’t absorb light. Things that absorb all of the visible light appear black to us. And white things don’t reflect light. Things that reflect all of the visible light appear white to us. Our eyes receive reflected light wavelengths, and our brains turn those into colors. Light is energy that comes from the sun. This energy is spread across a whole range of wavelengths, and we have evolved to be able to see the wavelengths in the middle. Some light has more energy than others, and this is reflected in the frequency of the wave. The more energy light has, the faster it moves and the higher its frequency. So, why is some light absorbed and some reflected? It all depends on the natural frequency of the electrons around the atoms of the object. All electrons vibrate at a specific frequency. If light energy of the same frequency hits these electrons, they absorb it, and it makes them vibrate more. They release this energy as thermal energy. This is why things that appear black get hot in sunlight. Conversely, if the frequency of the light doesn’t match the frequency of the electrons, the electrons absorb the energy, but they get rid of it as fast as possible and release it as another light photon. This light photon heads back out of the object and, if we were looking, is what we see as a color.
So, what is the albedo effect? It is basically a way of quantifying how much a material reflects or absorbs light. If the level is close to 0, it is more likely to absorb the light energy and if the level is closer to 1, it is more likely to reflect the light. This is the case all across Earth and every material can be given an albedo value. The albedo value of asphalt is 0.04, and the value of the ocean is 0.06. The albedo value of concrete is 0.55, and fresh snow is 0.8. Aluminium has an albedo value of 0.85. That means asphalt absorbs 96% of the sunlight that hits it, and aluminium reflects back 85% of the sunlight that hits it. And remember that if something has a low albedo number, it absorbs the energy from the sunlight and turns it into thermal energy, which is why asphalt is hot to the touch and aluminium left in direct sunlight won’t be very hot to touch.
You have probably heard about the albedo effect in relation to climate change and the greenhouse effect. Just like a road, the darker the surface is, the hotter it gets. A snow covered road in sunlight isn’t as hot as bare asphalt in direct sunlight. The more ice there is on the surface of a planet, the lower the surface temperature will be because the ice will reflect a lot more of the light than the ground or the ocean. If our Earth were covered completely in ice, the average surface temperature would drop to -40℃. We obviously don’t want that. If there was no ice, or even land on Earth, and there were only oceans, the average temperature on Earth would be 27℃ because oceans absorb a lot of light energy and produce a lot of heat. Picture Kevin Costner. We don’t want that either. With the current balance of ocean, land, and ice, the average temperature is 15℃, which is a little hot, but we can live with it. We need to keep the albedo of the Earth in the small range where we can live with it, which means keeping the ice we have. And that is what I learned today.
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Sources
https://www.physicsclassroom.com/class/light/Lesson-2/Light-Absorption,-Reflection,-and-Transmission