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Could we control our climate?
Could we control our climate?

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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 shows two satellite images of the whole disc of the Earth, clearly showing land, sea and clouds. Figure 4a shows Africa and the Middle East; Figure 4b shows North America.
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

The correct answers are:
  • 1 = e
  • 2 = a
  • 3 = d
  • 4 = b
  • 5 = c

Answer

The correct answer, with typical albedo ranges (α), is:

  1. fresh snow (0.75–0.95)
  2. thick cloud (0.7–0.9)
  3. sea ice (0.2–0.3)
  4. agricultural crops (0.16–0.26)
  5. coniferous forest (0.05–0.15)

(Sea ice values are from IPCC (2013), cloud values are from Schneider et al. (2011), and other values are from Campbell and Norman (1998)).

Earth has an average albedo of 0.30 so it reflects around 30% of the incoming energy from the Sun. As an Energy Balance Consultant, how might you increase this number?