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Equivalent emission altitude

One simplification is to treat all outgoing longwave radiation as being emitted from an altitude where the air temperature equals the overall effective temperature for planetary emissions, T e f f {\displaystyle T_{\mathrm {eff} }}. Some authors have referred to this altitude as the effective radiating level (ERL), and suggest that as the CO concentration increases, the ERL must rise to maintain the same mass of CO above that level.

This approach is less accurate than accounting for variation in radiation wavelength by emission altitude. However, it can be useful in supporting a simplified understanding of the greenhouse effect. For instance, it can be used to explain how the greenhouse effect increases as the concentration of greenhouse gases increase.

Earth's overall equivalent emission altitude has been increasing with a trend of 23 m (75 ft) /decade, which is said to be consistent with a global mean surface warming of 0.12 °C (0.22 °F) /decade over the period 1979–2011.