Editing Greenhouse effect (section)

=== Radiative balance ===

The temperature of a planet depends on the [[Earth's energy budget|balance]] between incoming radiation and outgoing radiation. If incoming radiation exceeds outgoing radiation, a planet will warm. If outgoing radiation exceeds incoming radiation, a planet will cool. A planet will tend towards a state of [[radiative equilibrium]], in which the power of outgoing radiation equals the power of absorbed incoming radiation.<ref name="cimss">{{cite web |title=Earth's Radiation Balance |url=https://cimss.ssec.wisc.edu/wxwise/homerbe.html |website=CIMSS: University of Wisconsin |access-date=25 April 2023}}</ref>

Earth's [[Earth's energy budget|energy imbalance]] is the amount by which the power of incoming sunlight absorbed by Earth's surface or atmosphere exceeds the power of outgoing longwave radiation emitted to space. Energy imbalance is the fundamental measurement that drives surface temperature.<ref name="SciAmEEB">{{cite web |title=Don't Worry about CO2, Worry about the Earth's 'Energy Balance' |url=https://www.scientificamerican.com/article/dont-worry-about-co2-worry-about-the-earths-energy-balance/ |publisher=Scientific American |access-date=2 June 2023}}</ref> A [[United Nations|UN]] presentation says "The EEI is the most critical number defining the prospects for continued global warming and climate change."<ref name="UNeei"/> One study argues, "The absolute value of EEI represents the most fundamental metric defining the status of global climate change."<ref name="vsh2016">{{cite journal |last1=von Schuckmann |first1=K. |last2=Palmer |first2=M. |last3=Trenberth |first3=K. |last4=Cazenave |first4=A. |last5=Chambers |first5=D. |last6=Champollion |first6=N. |last7=Hansen |first7=J. |last8=Josey |first8=S. A. |last9=Loeb |first9=N. |last10=Mathiew |first10=P.P. |last11=Meyssignac |first11=B. |last12=Wild |first12=M. |title=An imperative to monitor Earth's energy imbalance |journal=Nature Climate Change |date=2016 |volume=6 |issue=2 |pages=138–144 |doi=10.1038/nclimate2876|bibcode=2016NatCC...6..138V |url=http://nora.nerc.ac.uk/id/eprint/512751/1/vonSchuckmannPostprint.pdf }}</ref>

Earth's energy imbalance (EEI) was about 0.7 W/m{{sup|2}} as of around 2015, indicating that Earth as a whole is accumulating thermal energy and is in a process of becoming warmer.<ref name="ipcc-ar6wg1-ch7" />{{rp|934}}

Over 90% of the retained energy goes into warming the oceans, with much smaller amounts going into heating the land, atmosphere, and ice.<ref>{{cite web |last1=Hawkins |first1=Ed |title=Earth's energy imbalance |url=https://www.climate-lab-book.ac.uk/2016/earths-energy-imbalance/ |website=Climate Lab Book |access-date=16 July 2023 |date=27 January 2016}}</ref>
[[File:Outgoing radiation with and without Greenhouse effect.svg|thumb|upright=2.5|Comparison of Earth's upward flow of longwave radiation in reality and in a hypothetical scenario in which greenhouse gases and clouds are removed or lose their ability to absorb longwave radiation—without changing Earth's albedo (i.e., reflection/absorption of sunlight). Top shows the balance between Earth's heating and cooling as measured at the top of the atmosphere (TOA). Panel (a) shows the real situation with an active greenhouse effect.<ref name="rrtmeeb">{{cite web |title=RRTM Earth's Energy Budget |url=http://climatemodels.uchicago.edu/rrtm/index.html |publisher=University of Chicago |access-date=9 June 2023}}</ref> Panel (b) shows the situation immediately after absorption stops; all longwave radiation emitted by the surface would reach space; there would be more cooling (via longwave radiation emitted to space) than warming (from sunlight). This imbalance would lead to a rapid temperature drop. Panel (c) shows the final stable steady state, after the surface cools sufficiently to emit only enough longwave radiation to match the energy flow from absorbed sunlight.<ref name="rrtmeeb"/>]]