Physics B.2 The Greenhouse Effect

Term: Emissivity

Definition: Emissivity is a measure of a surface’s ability to emit thermal radiation compared to an ideal black body at the same temperature. It is given by the formula: emissivity = power radiated per unit area / (σT⁴), where σ is the Stefan-Boltzmann constant and T is the absolute temperature.

Term: Albedo

Definition: Albedo is the measure of the reflectivity of a surface, defined as the ratio of total scattered power to total incident power. It is given by the formula: albedo = total scattered power / total incident power.

Term: Solar constant

Definition: The solar constant is the amount of solar electromagnetic radiation received per unit area per unit time at the top of Earth’s atmosphere, typically measured in watts per square meter (W/m²).

Term: Greenhouse gases

Definition: Greenhouse gases are gases in Earth’s atmosphere that absorb and emit infrared radiation, contributing to the greenhouse effect. Examples include methane (CH₄), water vapor (H₂O), carbon dioxide (CO₂), and nitrous oxide (N₂O).

Term: Greenhouse effect

Definition: The greenhouse effect is the process by which greenhouse gases in Earth’s atmosphere trap heat, leading to an increase in the planet’s surface temperature. It is explained by the absorption and re-emission of infrared radiation by these gases.