The greenhouse effect is a well-known mechanism. It was discovered in the 19th Century : Joseph Fourier described it as early as 1824. Briefly: the gases in the atmosphere absorb some of the energy of sunlight and, in doing so, heat the planet. The more gases there are, the more they heat the planet. There are many gases: water vapour, CO2, methane, nitrous oxide, etc. Thanks to these gases, the Earth's average temperature is compatible with our existence. Without them, it would go down to -18°C.
In 1896, the Swedish researcher Arrhenius calculated that if the amount of CO2 in the atmosphere doubled, the average temperature would go up by 4°C.
A historical modification
Human activity has considerably increased certain greenhouse gases. For CO2, the world atmospheric concentration went from about 280 ppm (parts per million) in 1750 to 380 ppm in 2005. This increase is mainly due to the use of fossil fuels (transport...