Science, Maths & Technology

Become an OU student

Could we control our climate?

Start this free course now. Just create an account and sign in. Enrol and complete the course for a free statement of participation or digital badge if available.

3.2 Earth’s albedo

Figure 4 shows the Earth from space in two photos known as ‘Blue Marble 2012’. They show that the brightness of Earth’s surface is very varied.

Albedo (from the Latin for ‘white’) is the fraction of the solar radiation that hits the Earth (we call this the “incident” radiation) that is reflected.

Albedo is denoted by alpha α, with no units, because it is a fraction, the higher the value, the greater amount of solar radiation that is reflected. Surfaces that reflect more radiation tend to appear light (white or silver) and those that reflect less tend to appear dark. Different surfaces on the Earth have different values of albedo, as do different types and depths of cloud and particles in the atmosphere, such as dust or the sulfate aerosols you studied in Session 3.

Figure 4 ‘Blue Marble 2012’ images of the Earth showing (a) Africa and the Middle East, and (b) North America.

Activity 3

Timing: Allow approximately 5 minutes

Arrange these surfaces into order of decreasing albedo:

Using the following two lists, match each numbered item with the correct letter.

1. 1. (highest albedo)

2. 2.

3. 3.

4. 4.

5. 5.

• a.thick cloud

• b.agricultural crops

• c.coniferous forest

• d.sea ice

• e.fresh snow

• 1 = e
• 2 = a
• 3 = d
• 4 = b
• 5 = c