# Explain why increasing the concentration of greenhouse gases in the atmosphere causes the effective radiating level of the Earth to rise to a higher altitude, and explain how this leads to an increase in the Earth's average surface temperature.

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

> The effective radiating level is the average altitude from which infrared radiation escapes to space. As greenhouse gas concentrations increase, this level rises to a higher, cooler altitude.

## Mark scheme (4 marks)

1. A greater concentration of greenhouse gas molecules means the atmosphere absorbs infrared radiation more strongly / over a shorter path length, so the altitude at which the atmosphere becomes transparent to outgoing infrared radiation increases.
2. At a higher altitude the temperature of the atmosphere is lower, so the effective radiating level is at a lower temperature.
3. Because the radiating level is cooler, the power radiated to space (Stefan–Boltzmann law / P ∝ T⁴) is reduced, so the Earth radiates less energy to space than it receives from the Sun — creating an energy imbalance / net energy gain.
4. This net energy surplus causes the whole atmosphere–surface system to warm until the radiating level's temperature is restored to a value that once again balances incoming and outgoing radiation, resulting in a higher average surface temperature.

## Key terms

- [effective radiating level](https://www.gradenine.co.uk/glossary/effective-radiating-level)
- [greenhouse gas](https://www.gradenine.co.uk/glossary/greenhouse-gas)

## 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)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-increasing-the-concentration-of-f1f69495) · Published by Druglandscape Ltd.