Greenhouse effect
Heat-trapping gases raise Earth's surface temperature above freezing.
The greenhouse effect is the process by which heat-trapping gases in a planet's atmosphere prevent the planet from losing heat to space, raising its surface temperature. On Earth, the Sun emits shortwave radiation that passes through greenhouse gases to heat the surface, which then emits longwave radiation that is mostly absorbed by those gases, reducing the rate at which Earth cools. Without this effect, Earth's average surface temperature would be −18 °C, far below the 20th century average of about 14 °C.
- first proposed
- 1824 by Joseph Fourier
- key early experimenter
- Eunice Newton Foote (1856)
- rate of temperature increase since 1981
- 0.18 °C per decade
Lore & Background
The existence of the greenhouse effect was proposed as early as 1824 by Joseph Fourier, though not named as such. In 1856, Eunice Newton Foote demonstrated that the warming effect of the sun is greater for air with water vapor than for dry air, and even greater with carbon dioxide, concluding that an atmosphere of that gas would give Earth a high temperature.
Reader's Guide
The greenhouse effect is central to understanding Earth's climate. It explains why Earth's average surface temperature is about 15 °C rather than −18 °C, a difference of 33 °C. Human activities, especially burning fossil fuels, have increased atmospheric carbon dioxide and methane, strengthening the effect. The enhanced greenhouse effect is directly observed through increased radiative forcing, mainly from CO₂.
Did You Know?
- Eunice Newton Foote in 1856 showed that carbon dioxide in air produces greater warming than water vapor.
- Earth's atmosphere absorbs 90% of longwave radiation emitted by the surface but only 23% of incoming shortwave radiation.
- Without the greenhouse effect, Earth's average surface temperature would be −18 °C (−0.4 °F).
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