# Explain why the Earth's surface temperature remains approximately constant despite the Earth continuously absorbing radiation from the Sun.

> IB DP Physics Standard Level (2023 syllabus) — B.2 Greenhouse effect · Explain · 4 marks

> The Earth absorbs solar radiation primarily in the visible and ultraviolet range. The atmosphere contains greenhouse gases such as carbon dioxide and water vapour.

## Mark scheme (4 marks)

1. The Earth re-emits radiation (as infrared / thermal radiation) back towards space.
2. Greenhouse gases in the atmosphere absorb some of this outgoing infrared radiation and re-emit it in all directions, including back towards the surface.
3. A balance (equilibrium) is reached where the rate of energy absorbed by the Earth equals the rate of energy emitted/radiated to space.
4. The Earth's surface emits radiation at a longer wavelength (infrared) than the incoming solar radiation (visible/UV) because the surface is at a lower temperature than the Sun.

## Related

- [Revision notes for IB DP Physics Standard Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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