The greenhouse effect

The greenhouse effect is a direct application of radiation and its link with temperature. The Earth receives visible radiation from the Sun: the Sun has a surface temperature of $\sim 5800$ K and, by Wien’s displacement law, emits with its peak in the visible. The Earth, much colder ($\sim 290$ K), instead re-emits in the infrared, with its peak around $\sim 10\,\mu$m.

Here’s the crux: atmospheric gases (CO$_2$, H$_2$O, CH$_4$) are largely transparent to the incoming visible light, but opaque to the outgoing infrared. They thus trap part of the energy that the Earth would try to re-emit into space, raising the surface’s equilibrium temperature.

Greenhouse effect and global warming

The natural greenhouse effect is what makes the Earth habitable: without it, the average temperature would be well below freezing. Global warming is the anthropogenic amplification of this effect, due to the rising concentration of greenhouse gases from fossil fuels (Bloomfield 2016). See Riferimenti bibliografici.

The mechanism shows how a microscopic phenomenon — the differing opacity of certain molecules at different wavelengths — governs the climate of the whole planet through the Stefan-Boltzmann radiative balance.

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Topics: Termologia Concepts: Trasmissione del calore

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