Editing Greenhouse effect (section)

== Simplified models ==
{{further|Idealized greenhouse model}}
[[File:Greenhouse Effect (2017 NASA data).svg|thumb|upright=1.35|right|Energy flows between space, the atmosphere, and Earth's surface, with greenhouse gases in the atmosphere absorbing and emitting radiant heat, affecting [[Earth's energy budget|Earth's energy balance]]. Data as of 2007.]]
Simplified models are sometimes used to support understanding of how the greenhouse effect comes about and how this affects surface temperature.

=== Atmospheric layer models ===
The greenhouse effect can be seen to occur in a [[idealized greenhouse model|simplified model]] in which the air is treated as if it is single uniform layer exchanging radiation with the ground and space.<ref name="acs-single">{{cite web |title=ACS Climate Science Toolkit - Atmospheric Warming - A Single-Layer Atmosphere Model |url=https://www.acs.org/climatescience/atmosphericwarming/singlelayermodel.html |accessdate=2 October 2022 |publisher=[[American Chemical Society]] |archive-date=25 May 2023 |archive-url=https://web.archive.org/web/20230525201203/https://www.acs.org/climatescience/atmosphericwarming/singlelayermodel.html |url-status=dead }}</ref> Slightly more complex models add additional layers, or introduce convection.<ref name="acs-multi">{{cite web |title=ACS Climate Science Toolkit - Atmospheric Warming - A Multi-Layer Atmosphere Model |url=https://www.acs.org/content/acs/en/climatescience/atmosphericwarming/multilayermodel.html |accessdate=2 October 2022 |publisher=[[American Chemical Society]] |archive-date=30 November 2022 |archive-url=https://web.archive.org/web/20221130202305/https://www.acs.org/content/acs/en/climatescience/atmosphericwarming/multilayermodel.html |url-status=dead }}</ref>

=== 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, <math>T_\mathrm{eff}</math>.<ref name="Benestad2017">{{cite journal |last1=Benestad |first1=R. E. |date=2017 |title=A mental picture of the greenhouse effect |journal=Theor Appl Climatol |volume=128 |issue=3–4 |pages=679–688 |doi=10.1007/s00704-016-1732-y |s2cid=123923155 |doi-access=free}}</ref> Some authors have referred to this altitude as the ''effective radiating level'' (ERL), and suggest that as the {{CO2}} concentration increases, the ERL must rise to maintain the same mass of {{CO2}} above that level.<ref name="aosuw">{{cite web |title=Radiation Balance of the Earth-Atmosphere System |url=https://www.aos.wisc.edu/~aos121br/radn/radn/sld001.htm |access-date=1 June 2023 |website=Atmospheric and Oceanic Sciences |publisher=University of Wisconsin |quote=Based on the account in Horel & Geisler (1996) 'Global Environmental Change: An Atmospheric Perspective'}}</ref>

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.<ref name="Benestad2017" /> For instance, it can be used to explain how the greenhouse effect increases as the concentration of greenhouse gases increase.<ref name="Rasmus2016">{{cite web |last1=Benestad |first1=R. E. |date=2016 |title=What is the best description of the greenhouse effect? |url=https://www.realclimate.org/index.php/archives/2016/02/what-is-the-best-description-of-the-greenhouse-effect/ |access-date=1 June 2023 |website=RealClimate}}</ref><ref name="aosuw" /><ref name="Tziperman2022" />

Earth's overall equivalent emission altitude has been increasing with a trend of {{convert|23|m|abbr=on}}/decade, which is said to be consistent with a global mean surface warming of {{convert|0.12|C-change}}/decade over the period 1979–2011.<ref name="Benestad2017" />