The trapping of heat in an atmosphere by gases that absorb and re-emit infrared radiation.The greenhouse effect is the process by which an atmosphere traps heat near a planet's surface. Certain gases — called greenhouse gases — absorb infrared radiation emitted by the warmed surface and re-emit it in all directions, sending some energy back down instead of letting it escape to space. This natural mechanism keeps Earth about 33°C warmer than it would be otherwise, making it essential for life as we know it. However, human activities that increase the concentration of these gases strengthen the effect, leading to global warming and climate change.
The concept was first quantified by Svante Arrhenius in 1896, who calculated that doubling atmospheric CO2 could raise global temperatures by several degrees. Earlier, in the 1820s, Joseph Fourier had recognized that the atmosphere traps heat, and John Tyndall in the 1850s identified specific gases that do so.
Sunlight passes through the atmosphere and warms the planet's surface. The surface then radiates heat as infrared light. Greenhouse gases like carbon dioxide and water vapor have molecular vibrations that match the frequencies of this infrared radiation, so they absorb it. After absorbing, they re-emit the energy in random directions; about half of that returns to the surface, raising its temperature further. This is analogous to a blanket that lets sunlight in but slows the escape of heat.
Understanding the greenhouse effect is central to climate modeling, predicting global temperature rise, and designing mitigation strategies like carbon capture and renewable energy policies.
Venus's extreme surface temperature of about 465°C is primarily due to a runaway greenhouse effect from its thick CO2 atmosphere.















