I’d like to speak with you about your mother’s albedo. That’s right, her albedo.
No, I’m not referring to her insatiable drive for reproduction, her creative energy, how wet she is (well, not entirely), or those places where the sun don’t shine, I’m talking about how all her exposed parts just seem to glisten.
And by your mother, of course, I mean Gaia. Mother Earth.
Get your mind out of the gutter.
So what, exactly, am I talking about?
Your mom’s--okay, the Earth’s--albedo is the amount of sunlight that hits the surface and reflects; that which isn’t absorbed. Usually albedo is more of an astronomical term for the general amount of sunlight that a planet or other celestial body reflects, but since we have a planet covered in all sorts of different solids, liquids, gasses, plants, animals, and fungi, we can break the surface of the planet down and look at how much each thing reflects.
So how does it work? Simply measure the amount of incident light striking a surface, and the amount of light that reflects off of it. The ratio of reflected light to incident light is the albedo, sometimes read as a percentage.
So why is this a cool thing? (Haha!...ah, you’ll get it in a bit)
First, let’s talk space. When the sun shines electromagnetic radiation (some of it in the form of visible light) on objects in our solar system, they reflect these waves back at us, and from those reflections we can get an idea of what those objects are composed of, or “how the weather is out there.” In the case of planets and moons, we can tell how much ice cover they have, or what the surface might look like. Our own moon has an albedo of around 7%, which is enough to light up the landscape on a good night like last weekend’s. One of Saturn’s moons, the ice-encrusted Enceladus, has an albedo of 99%, meaning that it reflects almost all the sunlight that hits it. From the albedo of other space rocks like asteroids, we can figure out their metallic properties from how they reflect waves outside the visible spectrum.
But let’s get back to your mom, er, the Earth. You may have noticed that this planet is covered in all sorts of different surfaces, from oceans, deserts and tropical forests to the ice caps, huge buildings and cherry pies. Each of these surfaces has its own individual albedo, and conversely, absorbs a different amount of light.
So what does all of this matter to you? One thing to consider is that water, which covers about 70% of the Earth's surface, has a pretty low albedo, making it a good way to absorb the Sun's radiation and warm up the planet, supporting things like, y'know, life. Soaking up warmth in the day and maintaining it through the night is a good way to keep the temperature stable enough for us to survive, unlike on waterless orbs like the moon, where the temperature difference between day and night is about 356˚C. Our atmosphere is a big help, too, because it helps store this saved heat.
On the flip side, the sandy deserts near the equator and the snowy ice sheets near the poles have a higher albedo, up to 90% in the case of fresh snow. When these regions reflect a lot of light, they tend to stay a little bit cooler.
Most of the planet is somewhere between these extremes, however, with the majority of land covered in different kinds of plant cover, soil, and pies. Through local and satellite measurements, we can determine the albedo of these different surfaces, and also see a inverse correlation with the local temperature. The trees in tropical rain forests have a pretty low albedo, absorbing much of the incident sunlight (of which they get a lot), which in turn makes for higher local temperatures. However, if you're a farmer wise enough to cut down the rain forest for the excellent topsoil underneath, the decrease in albedo from green trees to dark brown soil will cause the temperature to go up on your new plot of land, making it even harder to grow anything while contributing to global warming.
Speaking of global warming, what happens if we're not reflecting as much light as we should? What if the highly reflective surfaces like the polar ice caps start shrinking, or if we create more dark surfaces, like giant parking lots and buildings and millions of miles of paved roads?
For the former, this presents a big problem, in that the melting of the ice caps initiates a positive feedback loop. Smaller ice sheet means smaller area of high albedo, which means less reflection and more absorption, which means higher temperature, which melts more ice, which means less area of high albedo... you get the picture. It's this positive feedback loop that has climatologists worried, because as it progresses, the ice at our poles will be melting at faster rates, and global temperatures will rise even faster. As far as rising ocean levels go, melting of the floating ice wouldn't drown us, but as soon as the ice on top of Antarctica and Greenland starts melting, we might start sailing on the Sacramento Bay.
So what about all the blacktop on our buildings and roads? In some places (like Maine), it's been common knowledge that having a black rooftop keeps your heating bill down and helps keep snow from piling up. However, urban planners are starting to figure out that all of this tar on our Walmarts and freeways is contributing to global warming, and is part of the reason why it gets so damn hot on the ubiquitously paved New York City (where everyone's wearing black, oddly) on an otherwise mild day. A new solution: paint everything white. Cool roof technology is a new engineering movement to paint the roofs of buildings white, increasing their albedo and consequently decreasing local and global temperatures. Other projects underway involve cloud seeding, where the creation of more cloud cover will reflect more of the sun's light, and spraying reflective aerosols into the stratosphere to keep some light from coming anywhere near the planet. While still in the infant stages, they may be part of the solution to combating global warming.