Albedo

The idea

Albedo is the fraction of solar radiation a surface reflects; high-albedo surfaces, light coloured or snow and ice, reflect more and stay cool, while low-albedo dark surfaces absorb more and heat up faster.

Hot road, cool wall

On a summer afternoon a dark road feels hot, while a white wall feels cooler.

What do you think makes the difference?

• How much sunlight each reflects
• The two are at the same temperature
• The road is nearer the Sun

Sort the surfaces

Put each surface in its group.

Reflect or absorb

Albedo tells how much of the sunlight a surface sends back. The more it reflects, the less it absorbs, so it stays cooler.

Albedo is the fraction of solar radiation a surface reflects. High albedo surfaces, light coloured or snow and ice, reflect more and stay cool. Low albedo, dark surfaces absorb more and heat up faster.

Notes

Albedo is the fraction of solar radiation a surface reflects. High albedo (light, snow, ice) stays cool. Low albedo (dark) absorbs more and heats up faster.

Check yourself

What is albedo?

Which surface stays cooler in strong sunlight?

Why are polar regions very cold, according to the chapter?

Black soil and ocean water have lower albedo. What does this mean for them?

• The fraction of solar radiation a surface absorbs. A surface with low albedo absorbs more, but albedo is the reflected fraction.
• The temperature of a surface at noon. Albedo is about reflection of solar radiation, not a temperature.
• The fraction of solar radiation a surface reflects — correct. Yes!
• One with high albedo — correct. Yes!
• One with low albedo. Low albedo surfaces reflect less and absorb more, so they heat up more quickly.
• A dark coloured road. Dark coloured roads absorb more sunlight and heat up more quickly.
• Snow and ice absorb most of the incoming solar radiation. Snow and ice have high albedo, so they reflect a large proportion of it.
• Snow and ice reflect a large proportion of incoming solar radiation — correct. Yes!
• Ocean water has the highest albedo there. Ocean water has lower albedo, so it absorbs more solar radiation.
• They reflect most sunlight and stay cool. Lower albedo means they reflect less, so they absorb more.
• They do not take in any solar radiation. They take in more solar radiation than high albedo surfaces do.
• They absorb more solar radiation and are relatively warmer — correct. Yes!