Greenhouse effect

Lore & Background

The greenhouse effect occurs when certain gases in a planet’s atmosphere trap heat, preventing the planet from losing thermal energy to space and thereby raising its surface temperature. This heating can originate from an internal source, such as Jupiter’s core, or from an external source like a host star. On Earth, the Sun emits shortwave radiation—sunlight—that passes through greenhouse gases and warms the surface. The Earth then emits longwave radiation, which greenhouse gases largely absorb, slowing the planet’s rate of cooling. Without this effect, Earth’s average surface temperature would be far colder than the 20th-century average of about 15 °C (59 °F). Since the Industrial Revolution, human activities such as burning fossil fuels have increased atmospheric carbon dioxide and methane, causing global warming of roughly 1.2 °C by 2023, with surface temperatures rising about 0.18 °C per decade since 1981. All objects above absolute zero emit thermal radiation; the Sun, at a much higher temperature, radiates mostly shortwave energy, while Earth’s cooler surface emits longwave infrared radiation. A gas qualifies as a greenhouse gas if it absorbs this longwave radiation. Earth’s atmosphere absorbs only 23% of incoming shortwave radiation but captures 90% of the longwave radiation from the surface, accumulating energy and warming the planet. The greenhouse effect can be measured as a temperature change of about 33 °C—the difference between Earth’s actual average surface temperature and what it would be without the effect. Alternatively, it is measured as an energy flow: longwave radiation leaves the surface at roughly 398 watts per square meter, but only 239 W/m² reaches space, meaning 159 W/m² (about 40%) is trapped. The term “greenhouse effect” was first applied by Nils Gustaf Ekholm in 1901, though the concept was proposed by Joseph Fourier in 1824 and refined by Claude Pouillet in 1827 and 1838. In 1856, Eunice Newton Foote showed that humid air warms more under sunlight than dry air, and carbon dioxide enhances this effect further. John Tyndall later measured infrared absorption by various gases, demonstrating that water vapor and small amounts of carbon dioxide and hydrocarbons are responsible, while the main atmospheric gases have no effect. Svante Arrhenius made the first quantitative prediction of global warming from a doubling of carbon dioxide in

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.

The phenomenon arises because greenhouse gases in the atmosphere absorb longwave radiation emitted by the Earth's surface, preventing that heat from escaping directly into space. While the atmosphere absorbs only a small fraction of incoming shortwave sunlight, it absorbs the vast majority of the longwave radiation the surface radiates upward, thereby accumulating energy and warming the planet. All objects above absolute zero emit thermal radiation, but the Sun's high temperature means it emits mostly shortwave energy, whereas the cooler Earth emits longwave radiation. A gas qualifies as a greenhouse gas if it absorbs this longwave radiation. The natural greenhouse effect is measured either as a temperature increase of about 33 °C above the frigid −18 °C that would exist without it, or as an energy flow imbalance: longwave radiation leaves the surface at a rate of 398 W/m², yet only 239 W/m² reaches space, meaning 159 W/m² (about 40%) is retained by the atmosphere. The concept was first proposed in 1824 by Joseph Fourier, with later experimental work by Eunice Newton Foote in 1856 showing that water vapor and carbon dioxide enhance solar warming. John Tyndall subsequently measured the infrared absorption of various gases, and Svante Arrhenius made the first quantitative prediction of warming from doubled carbon dioxide in 1896. The term "greenhouse effect" was coined by Nils Gustaf Ekholm in 1901, though the analogy is imperfect: greenhouses primarily block convection, while the atmospheric effect restricts radiative heat loss.

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).