Explaining the Earth's Albedo

In a recent post I mentioned the albedo of the planet. Technically this is the bond albedo and refers to the amount of energy, both visible and invisible, that is reflected from a planet. The albedo of a planet varies from 0 (no energy is reflected) to 1 (all the energy is reflected). In general, a higher albedo decreases the amount of energy we receive from the sun. From a fact sheet provided by NASA the earth has an albedo around 0.3 and for the moon is 0.11. Since the earth reflects more energy than the moon, from space the earth will appear much brighter visually than the moon.

These numbers are strictly averages. The albedo is different for the different surface types over the earth. An article from The Natural Environment details the differences in albedo for different surface types

Surface Type	Albedo
cloud-thin	25-60%
cloud-thick	50-90%
snow	50-90%
water	8%
grass	0-25%
forest	15-20%
desert	35%
soil	10-25%
asphalt	5-10%
concrete	15-25%

Ever notice on a hot summer day when a cloud roles through, how much cooler it feels. The cloud is reflecting the sun's rays back into space and the cooling is immediate. In fact, thick cloud cover may reflect as much of 90% of the sun's energy away from the planet.

A similar effect comes with snow cover on the ground. When the ground is covered in snow as much as 90% of the sun's rays are reflected. Anyone who lives any length of time where snow is on the ground knows that those cold winter days with the bright sunshine calls for a pair of sunglasses. Because that energy is reflected instead of being absorbed and warming the ground, the snow cover stays and isn't melted by the sun.

One interesting point is comparing the albedo of concrete/asphalt to that of grass/forest. They both absorb roughly the same amount of energy but on a hot summer day the forest will always feel cooler than the city. One possible explanation is that the energy in the grass/forest is being used by photosynthesis to produce oxygen and the energy in the concrete/asphalt is being radiated back as infrared heat.

The article from The Natural Environment goes on to state:

The relationship between cloud cover and Earth's climate is quite complex and a major unknown in studies of climate change. On one hand, more cloud cover causes higher albedo and less sunlight absorbed by the Earth, causing cooling. On the other hand, more cloud cover means less radiation from the surface escapes to space, causing warming.

I tend to disagree with this statement. Cloud cover in any amount will increase the albedo of the planet and reduce the amount of energy on the planet. Since the amount of energy coming in is the primary driver for the temperature of the earth, an increase in the albedo over an extended period of time will reduce the temperature of the planet.

On the next hot summer day, find yourself an object with a low albedo and sit down underneath it. We normal people call these low albedo objects you can sit under a shade. It goes well with a cold beverage of some kind.

Related posts:
Man Made Global Warming
Are Plants Starving for Carbon Dioxide
Greenhouse Effect
Carbon Dioxide Saturation in the Atmosphere