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Greenhouse gases warm Earth by absorbing and re-emitting infrared radiation, slowing heat loss to space.
Greenhouse gases (GHGs) are atmospheric gases that trap heat by absorbing and re-emitting infrared radiation emitted by Earth’s surface. This absorption reduces the rate at which heat escapes to space, warming the planet. Without greenhouse gases, Earth’s average surface temperature would be far colder (about −18 °C) than it is today (about 15 °C). The main greenhouse gases include water vapor, carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and ozone, with additional human-relevant gases such as CFCs, HCFCs, HFCs, perfluorocarbons, SF6, and NF3. The strength of the greenhouse effect depends on how gases interact with radiation (they are “infrared active”), their atmospheric abundance, and their lifetime. Radiative forcing is a common way to quantify how changes in greenhouse gas concentrations alter Earth’s energy balance at the top of the atmosphere; increased greenhouse gases produce positive forcing (warming), while some other factors can produce negative forcing (cooling). Water vapor is the largest contributor to the greenhouse effect, but its global concentration is mainly controlled by temperature rather than direct human emissions, making it a key feedback mechanism. To compare different gases, scientists use global warming potential (GWP), which expresses how much heat a gas traps over a specified time relative to CO2. Because methane has a shorter atmospheric lifetime than CO2, its GWP is much larger over shorter time horizons (e.g., 20 years) but smaller over longer periods (e.g., 100 years). Human activities since the Industrial Revolution have increased CO2 and methane substantially, driving enhanced (human-caused) warming, while natural carbon and methane cycles partially offset emissions but do not fully prevent long-term accumulation of CO2.
Greenhouse gases warm Earth by absorbing and re-emitting infrared radiation, slowing heat loss to space.
Radiative forcing quantifies how changes in greenhouse gas concentrations shift Earth’s top-of-atmosphere energy balance toward warming.
Water vapor is the largest greenhouse contributor but acts mainly through temperature-driven feedback rather than direct emissions.
Global warming potential (GWP) compares gases by their heat-trapping effect relative to CO2 over a chosen time horizon, strongly influenced by atmospheric lifetime.
The process by which greenhouse gases absorb and re-emit infrared radiation, reducing heat loss to space and warming a planet’s surface and lower atmosphere.
A gas in an atmosphere that traps heat by absorbing and emitting infrared radiation in the same long-wavelength range as Earth’s thermal emission.
A metric (in watts per square meter) representing the immediate change in Earth’s top-of-atmosphere energy balance caused by a factor such as increased greenhouse gas concentrations.
A climate feedback in which warming increases atmospheric water vapor, which then enhances the greenhouse effect and further warming.
A dimensionless measure of how much heat a greenhouse gas traps over a specified time relative to the same mass of CO2.
A common unit that converts emissions of different greenhouse gases into the amount of CO2 that would produce the same warming effect using GWP.
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