The greenhouse effect

In short: The greenhouse effect arises because certain gases in the atmosphere hold back the Earth’s heat radiation. Without it the mean temperature would be about −18 °C instead of roughly +15 °C.

In more detail: Sunlight warms the Earth. It gives off heat as infrared radiation. Gases such as water vapour, CO₂ and methane absorb part of it and radiate it back.

In detail

• Naturally necessary: The natural effect makes life on Earth possible in the first place.
• Strengthened by humans: More CO₂, methane and nitrous oxide from combustion, farming and industry strengthen it (kohlenstoffkreislauf).
• Greenhouse gases: Methane is much stronger per molecule than CO₂ but stays in the air for a shorter time.
• Consequences: Warming, glacier melt, sea level rise and more frequent extreme weather (klimawandel-grundlagen).
• Greenhouse comparison: A real greenhouse works differently (it prevents air exchange).