Editing Radiative forcing (section)

== Definition and fundamentals ==
''Radiative forcing'' is defined in the [[IPCC Sixth Assessment Report]] as follows: "The change in the net, downward minus upward, radiative flux (expressed in W/m<sup>2</sup>) due to a change in an external driver of climate change, such as a change in the concentration of carbon dioxide (CO<sub>2</sub>), the concentration of volcanic aerosols or the output of the Sun."<ref name=":0">IPCC, 2021: [https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_AnnexVII.pdf Annex VII: Glossary] [Matthews, J.B.R., V. Möller, R. van Diemen, J.S. Fuglestvedt, V. Masson-Delmotte, C.  Méndez, S. Semenov, A. Reisinger (eds.)]. In [https://www.ipcc.ch/report/ar6/wg1/ Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change] [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 2215–2256, doi:10.1017/9781009157896.022.</ref>{{rp|2245}}

There are some different types of radiative forcing as defined in the literature:<ref name=":0" />{{rp|2245}}

* ''Stratospherically adjusted radiative forcing: "''when all tropospheric properties held fixed at their unperturbed values, and after allowing for stratospheric temperatures, if perturbed, to readjust to radiative-dynamical equilibrium."
* ''Instantaneous radiative forcing:'' "if no change in stratospheric temperature is accounted for". 
* ''Effective radiative forcing'': "once both stratospheric and tropospheric adjustments are accounted for".

The radiation balance of the Earth (i.e. the balance between absorbed and radiated energy) determines the [[average global temperature]]. This balance is also called [[Earth's energy budget|Earth's energy balance]]. Changes to this balance occur due to factors such as the intensity of [[solar energy]], reflectivity of clouds or gases, absorption by various [[greenhouse gas]]es or surfaces and heat emission by various materials. Any such alteration is a ''radiative forcing'', which along with its [[Climate change feedback|climate feedbacks]], ultimately changes the balance. This happens continuously as sunlight hits the surface of Earth, clouds and aerosols form, the concentrations of atmospheric gases vary and seasons alter the [[groundcover]].

''Positive radiative forcing'' means Earth receives more incoming energy from sunlight than it radiates to space. This net gain of energy will cause [[global warming]]. Conversely, ''negative radiative forcing'' means that Earth loses more energy to space than it receives from the Sun, which produces cooling ([[global dimming]]). 

=== History ===
Transport of energy and matter in the Earth-atmosphere system is governed by the principles of [[equilibrium thermodynamics]] and more generally [[non-equilibrium thermodynamics]].  During the first half of the 20th century, physicists developed a comprehensive description of [[radiative transfer]] that they began to apply to stellar and planetary atmospheres in [[radiative equilibrium]].  Studies of radiative-convective equilibrium (RCE) followed and matured through the 1960s and 1970s.  RCE models began to account for more complex material flows within the energy balance, such as those from a water cycle, and thereby described observations better.

Another application of equilibrium models is that a [[perturbation theory|perturbation]] in the form of an [[thermodynamic operation|externally imposed intervention]] can estimate a change in [[thermodynamic state|state]].  The RCE work distilled this into a ''forcing-feedback framework'' for change, and produced [[climate sensitivity]] results agreeing with those from [[general circulation model|GCM]]s.  This [[conceptual framework]] asserts that a homogeneous disturbance (effectively imposed onto the top-of-atmosphere energy balance) will be met by slower responses (correlated more or less with changes in a planet's surface temperature) to bring the system to a new equilibrium state. ''Radiative forcing'' was a term used to describe these disturbances and gained widespread traction in the literature by the 1980s.<ref name="nrcrf"/>{{rp|19-23}}

=== Related metrics ===
The concept of radiative forcing has been evolving from the initial proposal, named nowadays ''instantaneous radiative forcing'' (IRF), to other proposals that aim to relate better the radiative imbalance with global warming (global surface mean temperature). For example, researchers explained in 2003 how the ''adjusted troposphere and stratosphere forcing'' can be used in [[General circulation model|general circulation models]].<ref>{{Cite journal |last1=Shine |first1=Keith P. |last2=Cook |first2=Jolene |last3=Highwood |first3=Eleanor J. |last4=Joshi |first4=Manoj M. |date=23 October 2003 |title=An alternative to radiative forcing for estimating the relative importance of climate change mechanisms |journal=Geophysical Research Letters |volume=30 |issue=20 |pages=2047 |bibcode=2003GeoRL..30.2047S |doi=10.1029/2003GL018141 |s2cid=59514371 |doi-access=free}}</ref> 

The adjusted radiative forcing, in its different calculation methodologies, estimates the imbalance once the stratosphere temperatures has been modified to achieve a radiative equilibrium in the stratosphere (in the sense of zero radiative heating rates). This new methodology is not estimating any ''adjustment'' or ''feedback'' that could be produced on the troposphere (in addition to stratospheric temperature adjustments), for that goal another definition, named ''effective radiative forcing'' has been introduced.<ref>{{Cite journal |last1=Sherwood |first1=Steven C. |last2=Bony |first2=Sandrine |last3=Boucher |first3=Olivier |last4=Bretherton |first4=Chris |last5=Forster |first5=Piers M. |last6=Gregory |first6=Jonathan M. |last7=Stevens |first7=Bjorn |date=2015-02-01 |title=Adjustments in the Forcing-Feedback Framework for Understanding Climate Change |url=http://centaur.reading.ac.uk/38337/1/sherwood15forcefeed.pdf |url-status=live |journal=Bulletin of the American Meteorological Society |language=en |volume=96 |issue=2 |pages=217–228 |bibcode=2015BAMS...96..217S |doi=10.1175/bams-d-13-00167.1 |issn=0003-0007 |s2cid=12515303 |archive-url=https://web.archive.org/web/20190428115201/http://centaur.reading.ac.uk/38337/1/sherwood15forcefeed.pdf |archive-date=2019-04-28 |access-date=2019-12-16}}</ref> In general the ERF is the recommendation of the CMIP6 radiative forcing analysis <ref>{{Cite journal |last1=Forster |first1=Piers M. |last2=Richardson |first2=Thomas |last3=Maycock |first3=Amanda C. |last4=Smith |first4=Christopher J. |last5=Samset |first5=Bjorn H. |last6=Myhre |first6=Gunnar |last7=Andrews |first7=Timothy |last8=Pincus |first8=Robert |last9=Schulz |first9=Michael |date=2016-10-27 |title=Recommendations for diagnosing effective radiative forcing from climate models for CMIP6 |url=http://eprints.whiterose.ac.uk/111875/17/Forster_et_al-2016-Journal_of_Geophysical_Research__Atmospheres.pdf |url-status=live |journal=Journal of Geophysical Research: Atmospheres |language=en |volume=121 |issue=20 |pages=12,460–12,475 |bibcode=2016JGRD..12112460F |doi=10.1002/2016jd025320 |issn=2169-897X |s2cid=59367633 |archive-url=https://web.archive.org/web/20190925083723/http://eprints.whiterose.ac.uk/111875/17/Forster_et_al-2016-Journal_of_Geophysical_Research__Atmospheres.pdf |archive-date=2019-09-25 |access-date=2019-09-25}}</ref> although the stratospherically adjusted methodologies are still being applied in those cases where the adjustments and feedbacks on the troposphere are considered not critical, like in the well mixed greenhouse gases and ozone.<ref>{{Cite journal |last1=Stevenson |first1=D. S. |last2=Young |first2=P. J. |last3=Naik |first3=V. |last4=Lamarque |first4=J.-F. |last5=Shindell |first5=D. T. |last6=Voulgarakis |first6=A. |last7=Skeie |first7=R. B. |last8=Dalsoren |first8=S. B. |last9=Myhre |first9=G. |date=2013-03-15 |title=Tropospheric ozone changes, radiative forcing and attribution to emissions in the Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP) |url=http://eprints.lancs.ac.uk/63025/1/Atmos._Chem._Phys._2013_Stevenson.pdf |url-status=live |journal=Atmospheric Chemistry and Physics |language=en |volume=13 |issue=6 |pages=3063–3085 |bibcode=2013ACP....13.3063S |doi=10.5194/acp-13-3063-2013 |issn=1680-7316 |s2cid=15347857 |archive-url=https://web.archive.org/web/20211121144029/http://eprints.lancs.ac.uk/id/eprint/63025/1/Atmos._Chem._Phys._2013_Stevenson.pdf |archive-date=2021-11-21 |access-date=2019-09-04 |doi-access=free}}</ref><ref>{{Cite journal |last1=Checa-Garcia |first1=Ramiro |last2=Hegglin |first2=Michaela I. |last3=Kinnison |first3=Douglas |last4=Plummer |first4=David A. |last5=Shine |first5=Keith P. |date=2018-04-06 |title=Historical Tropospheric and Stratospheric Ozone Radiative Forcing Using the CMIP6 Database |url=http://centaur.reading.ac.uk/75867/8/Checa-Garcia_et_al-2018-Geophysical_Research_Letters.pdf |url-status=live |journal=Geophysical Research Letters |language=en |volume=45 |issue=7 |pages=3264–3273 |bibcode=2018GeoRL..45.3264C |doi=10.1002/2017gl076770 |issn=0094-8276 |s2cid=53471515 |archive-url=https://web.archive.org/web/20190430055312/http://centaur.reading.ac.uk/75867/8/Checa-Garcia_et_al-2018-Geophysical_Research_Letters.pdf |archive-date=2019-04-30 |access-date=2019-12-16}}</ref> A methodology named ''radiative kernel approach'' allows to estimate the climate feedbacks within an offline calculation based on a linear approximation <ref>{{Cite journal |last1=Soden |first1=Brian J. |last2=Held |first2=Isaac M. |last3=Colman |first3=Robert |last4=Shell |first4=Karen M. |last5=Kiehl |first5=Jeffrey T. |last6=Shields |first6=Christine A. |date=2008-07-01 |title=Quantifying Climate Feedbacks Using Radiative Kernels |journal=Journal of Climate |language=en |volume=21 |issue=14 |pages=3504–3520 |bibcode=2008JCli...21.3504S |citeseerx=10.1.1.141.653 |doi=10.1175/2007jcli2110.1 |issn=0894-8755 |s2cid=14679991}}</ref>