Summary and key terms | B.2

What is emissivity?

Emissivity is the ratio of the power emitted per unit area by an object to the power emitted by a perfect black body of the same size and temperature.

What does albedo represent?

Albedo is the ratio of the average energy reflected off a macroscopic system to the energy incident on the system.

What is the solar constant?

The solar constant represents the average intensity of electromagnetic radiation incident on the Earth’s outer atmosphere.

What is the mean value of the incoming intensity of sunlight on Earth?

The mean value of the incoming intensity of sunlight is S4 or 340 W m−2.

What is the natural greenhouse effect's significance?

The natural greenhouse effect is essential for sustaining life on Earth.

How do human activities affect the greenhouse effect?

Human activities, such as the combustion of fossil fuels, increase the concentration of greenhouse gases in the atmosphere, leading to the enhanced greenhouse effect.

List the greenhouse gases mentioned.

The greenhouse gases are carbon dioxide, nitrous oxide, methane, and water vapour.

Why do greenhouse gases absorb infrared radiation?

Greenhouse gases absorb infrared radiation because its frequency matches the natural frequency of the greenhouse gas molecules.

What role does the law of conservation of energy play in the Earth atmosphere system?

The law of conservation of energy can be applied to the Earth surface–atmosphere system to explain why its thermal equilibrium is at risk.

What happens when a photon of infrared radiation is absorbed by greenhouse gases?

The difference in the atoms’ energy levels equals the energy carried by a photon of infrared radiation, leading to the absorption of the photon.