Known as the partial trapping of solar radiation, makes the planet 40K hotter.
Magnitude of greenhouse effect is sensitive to greenhouse gases (gases that absorb IR radiation efficiently) CO2 and Water vapour are most important.
80-90% of greenhouse effect is due to water vapour and clouds, rest is due to C02 and CH4. Whilst N2 & O2 also absorb and emit IR radiation their radiative effect on temp is so weak they can be neglected. While CH4 is more potent than CO2 there's less of it. Although extremely small the conc. of CH4 increasing has lead to somewhat strengthening of greenhouse effect.
CO2 rates continue to rise at 4% per decade mainly due to burning of fossil fuels
A runaway increase in CO2 levels in atmosphere of venus has caused it's temperature to rise over 700K
Natural greenhouse effect which keeps the Earth warm and habitable, then there is Man-Made effect which is the enhancement of Earths natural greenhouse effect through burning fossil fuels (petroleum,coal,natural gas)
Greenhouse gases reduce the rate at which the earths surface loses IR radiation make the earths surface and lower atmosphere warmer than it would otherwise be