Climate: what are greenhouse gases and how do they warm the planet?


DECRYPTION – The average temperature of the Earth, wrapped in a kind of heating blanket that covers the ground and the seas, is rising more and more.

Without an atmosphere, the Earth would be a frozen ball. It is the presence of greenhouse gases that allows us to conserve a large part of the energy that comes to us from the Sun. But how does this happen? Heated by the Sun, our planet re-emits some of this energy – especially at night – in the form of infrared radiation. Greenhouse gases will absorb this radiation and re-emit some of it in all directions. Some will be captured by other greenhouse gases and so on. In the end, the Earth is enveloped in a kind of heating blanket that covers the ground and the seas and causes the temperature to rise.

Each gas that comes into play in the greenhouse effect has its own warming capacity which depends on its chemistry and its residence time in the air. The first of these, in order of importance, is water vapor. But the overall volume of water contained in the atmosphere remains stable over time: its impact is therefore negligible.

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