Definition of the greenhouse effect

Summary

The greenhouse effect is the process by which certain gases and other atmospheric constituents absorb and re-emit infrared (longwave) radiation, reducing the amount of heat that escapes from a planet’s surface to space. On Earth, sunlight (shortwave radiation) passes through the atmosphere and warms the surface, which then emits longwave radiation. Greenhouse gases, clouds, and some aerosols absorb much of this outgoing longwave radiation and re-radiate it, slowing the rate of cooling and causing the surface to be warmer than it would be without this effect. Formally, the greenhouse effect is defined as the infrared radiative effect of all infrared-absorbing constituents in the atmosphere: greenhouse gases (GHGs), clouds, and some aerosols absorb terrestrial radiation emitted by the Earth’s surface and elsewhere in the atmosphere. The “enhanced greenhouse effect” refers to the strengthening of the natural greenhouse effect due to increased concentrations of greenhouse gases from human activities, which increases the infrared trapping and leads to additional warming.

Key Points

• 1

  Greenhouse gases (along with clouds and some aerosols) absorb outgoing longwave (infrared) radiation and re-emit it, reducing heat loss to space.

• 2

  On Earth, this causes the surface to warm relative to the planet’s effective temperature; without the greenhouse effect, Earth’s average surface temperature would be much colder.

• 3

  The enhanced greenhouse effect describes how human-driven increases in greenhouse gas concentrations strengthen the natural greenhouse effect.