Reflecting RadiationThe proportion of incoming radiation that is reflected by a surface is called its albedo. Surfaces with a high albedo reflect more radiation than those with a low albedo (Figure 1). For example, clouds reflect a lot of radiation and have an average albedo of 40 % to 70 %. Forests do not reflect much radiation and have an average albedo of 10 % to 20 %.

albedo: ▶ the proportion of the Sun’s radiation that is reflected by a surface

TRY This Albedo bAsics

SkillS: Performing, Observing, Analyzing, Evaluating, Communicating

In this activity, you will observe the effect of albedo on temperature change, using a light source shining on different reflective surfaces.

Equipment and Materials: white and black construction paper; 2 thermometers; light source

1. Lay two thermometers side by side, 3 cm apart, on the lab bench. Cover the lower portion of one thermometer with a small piece of white paper. Cover the lower portion of the second thermometer with a small piece of black paper.

2. Record the initial temperatures.

3. Place the light source 20 cm directly above the thermometers. Check and record the temperature of each thermometer every 1 min for 10 min.

A. Plot a graph of the recorded temperatures. T/I C

B. Which colour of paper resulted in the higher temperature? T/I

C. Which colour of paper had the higher albedo? Explain. T/I C

D. Which surfaces on Earth might be represented by the white and black paper in this activity? T/I

3.A., 3.B.

8.7Wearing dark clothing on a sunny day usually makes you feel hotter than wearing light-coloured clothing. The reason is that lighter-coloured surfaces reflect more solar energy and so stay cooler.

albedo values

snow and ice 85 %

grasslands 20 %

Figure 1 Different surfaces reflect different amounts of the Sun’s radiation.

NEL316 Chapter 8 • Earth’s Climate System

8.7 Wrap Up • Albedo is the proportion of radiation reflected by a surface.

• An increase in Earth’s albedo can cause a drop in temperature. A decrease in Earth’s albedo can result in a rise in temperature.

CheCk Your leArning

1. Fresh snow has an albedo of about 85 %, and old snow has an albedo of about 50 %. Which will reflect more of the Sun’s radiation? Explain why. K/U C

2. You want to keep a bottle of pop cool on a sunny day, but you only have a white cloth and a black cloth with you. Which cloth would you use to wrap your pop and why? K/U C

3. How would a large volcanic eruption change Earth’s albedo? How would this change affect Earth’s temperature? K/U A

4. Scientists think that a giant meteorite crashed into Earth millions of years ago, resulting in the extinction of the dinosaurs. The meteorite’s impact produced a thick cloud of particles that prevented some sunlight from reaching Earth. Why do you think this might have led to the extinction of dinosaurs? T/I

5. The icecaps at Earth’s poles are becoming smaller as the ice melts. Explain how the melting of the polar icecaps might change Earth’s temperature. A C

Changes in Earth’s AlbedoIn Section 8.6, you saw that Earth’s temperature stays in a certain range when energy in equals energy out. Changes that affect albedo can affect Earth’s ability to maintain this energy balance (Figure 2).

If the ice in a region melts, then the albedo of the region decreases. Then, less incoming radiation from the Sun is reflected and more energy is absorbed. This causes Earth’s temperature to increase, which in turn causes more ice to melt, and so on.

Changes in albedo can also have a cooling effect. For example, volcanic eruptions can spew gas and ashes into the atmosphere. The gas and ashes reflect radiation, so less radiation can be absorbed. As a result, Earth’s temperature falls, the amount of snow and ice cover increases, and so on.

dig deeper

Did You Know?The Year with No Summer

In 1815, Mount Tambora in Indonesia erupted, sending 150 km3 of dust into the stratosphere. The next year was called “the year with no summer.” There was widespread famine in North America following summer snowfalls and frost.

more iceforms

more of Sun’sradiation re�ected

by the ice

Earth’stemperaturedecreases

coolingcycle

ice meltsless of Sun’s

radiation re�ected by the ice

Earth’stemperature

increases

warmingcycle

Figure 2 Changes in albedo can result in the warming and cooling of Earth.

NEL 8.7 Albedo 317