Greenhouse effect, illustration. The greenhouse effect is a process by which the Earth warms up. It occurs naturally, but human activities are increasing its effect, leading to global warming. Greenhouse gases in the Earth's atmosphere behave like the glass of a greenhouse. Solar radiation (arrows) passes through and re-radiates at a longer (infrared, IR) wavelength. Naturally some of this IR passes through the atmosphere back into space, but the build-up of greenhouse gases such as methane and carbon dioxide traps the energy, producing a warming effect. Carbon dioxide is emitted by the burning of fossil fuels and is a major greenhouse gas. Global warming could have dire consequences for the planet.