Editing Radiative forcing (section)

=== Atmospheric observation ===
{{See also|Earth's energy imbalance}}
Earth's global [[radiation balance]] fluctuates as the planet rotates and orbits the Sun, and as global-scale thermal anomalies  arise and dissipate within the terrestrial, oceanic and atmospheric systems (e.g. [[ENSO]]).<ref>{{cite web |last=Rebecca |first=Lindsey |date=14 January 2009 |title=Climate and Earth's Energy Budget |url=https://earthobservatory.nasa.gov/features/EnergyBalance/page1.php |url-status=live |archive-url=https://web.archive.org/web/20210121082936/https://earthobservatory.nasa.gov/features/EnergyBalance/page1.php |archive-date=21 January 2021 |access-date=15 April 2021 |website=earthobservatory.nasa.gov}}</ref> Consequently, the planet's 'instantaneous radiative forcing' (IRF) is also dynamic and naturally fluctuates between states of overall warming and cooling. The combination of [[periodic function|periodic]] and [[complex system|complex]] processes that give rise to these natural variations will typically revert over periods lasting as long as a few years to produce a net-zero average IRF. Such fluctuations also mask the longer-term (decade-long) forcing trends due to human activities,  and thus make direct observation of such trends challenging.<ref name="kramer">{{cite journal |author=Kramer, R.J., H. He, B.J. Soden, L. Oreopoulos, G. Myhre, P.M. Forster, and C.J. Smith |date=2021-03-25 |title=Observational Evidence of Increasing Global Radiative Forcing |url=https://doi.org/10.1029/2020GL091585 |url-status=live |journal=Geophysical Research Letters |volume=48 |issue=7 |pages=e91585 |bibcode=2021GeoRL..4891585K |doi=10.1029/2020GL091585 |s2cid=233684244 |archive-url=https://web.archive.org/web/20211121144045/https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020GL091585 |archive-date=2021-11-21 |access-date=2021-04-17 |hdl-access=free |hdl=11250/2788616}}</ref>

[[File:NASA Earth Science Division Operating Missions.jpg|thumbnail|300px|right|NASA Earth Science Division Operating Missions<ref>{{cite web |title=NASA's Earth Observing System homepage |url=https://eospso.gsfc.nasa.gov/ |url-status=live |archive-url=https://web.archive.org/web/20210318000130/https://eospso.gsfc.nasa.gov/ |archive-date=2021-03-18 |accessdate=2021-04-16 |publisher=NASA EOS Project Science Office}}</ref>]]
Earth's radiation balance has been continuously monitored by NASA's [[Clouds and the Earth's Radiant Energy System]] (CERES)  instruments since year 1998.<ref>{{cite journal |author=Loeb, N.G., S. Kato, K. Loukachine, and N. Manalo-Smith |date=2005-04-01 |title=Angular Distribution Models for Top-of-Atmosphere Radiative Flux Estimation from the Clouds and the Earth's Radiant Energy System Instrument on the Terra Satellite. Part I: Methodology |journal=Journal of Atmospheric and Oceanic Technology |volume=22 |issue=4 |pages=338–351 |bibcode=2005JAtOT..22..338L |doi=10.1175/JTECH1712.1 |doi-access=free}}</ref><ref>{{cite journal |author=Loeb, N.G., F.G. Rose, S. Kato, D.A. Rutan, W. Su, H. Wang, D.R. Doelling, W.L. Smith, and A. Gettelman |date=2020-01-01 |title=Toward a Consistent Definition between Satellite and Model Clear-Sky Radiative Fluxes |journal=Journal of Climate |volume=33 |issue=1 |pages=61–75 |bibcode=2020JCli...33...61L |doi=10.1175/JCLI-D-19-0381.1 |doi-access=free}}</ref> Each scan of the globe provides an estimate of the total (all-sky) instantaneous radiation balance. This data record captures both the natural fluctuations and human influences on IRF; including changes in greenhouse gases, aerosols, land surface, etc. The record also includes the lagging radiative responses to the radiative imbalances; occurring mainly by way of Earth system feedbacks in temperature, surface albedo, atmospheric water vapor and clouds.<ref>{{cite journal |author=Sherwood, S.C., S. Bony, O. Boucher, C. Bretherton, P.M. Forster, J.M. Gregory, and B. Stevens |date=2015-02-01 |title=Adjustments in the Forcing-Feedback Framework for Understanding Climate Change |journal=Bulletin of the American Meteorological Society |volume=96 |issue=2 |pages=217–228 |bibcode=2015BAMS...96..217S |doi=10.1175/BAMS-D-13-00167.1 |s2cid=12515303 |doi-access=free |hdl-access=free |hdl=11858/00-001M-0000-0015-79FA-A}}</ref><ref>{{cite journal |author=Wielicki, B.A., R.D. Cess, M.D. King, D.A. Randall, and E.F. Harrison |date=1995-11-01 |title=Mission to Planet Earth: Role of Clouds and Radiation in Climate |journal=Bulletin of the American Meteorological Society |volume=76 |issue=11 |pages=2125–2154 |bibcode=1995BAMS...76.2125W |doi=10.1175/1520-0477(1995)076<2125:MTPERO>2.0.CO;2 |doi-access=free}}</ref>

Researchers have used measurements from CERES, [[atmospheric infrared sounder|AIRS]], [[CloudSat]] and other satellite-based instruments within NASA's [[Earth Observing System]] to parse out contributions by the natural fluctuations and system feedbacks. Removing these contributions within the multi-year data record allows observation of the anthropogenic trend in top-of-atmosphere (TOA) IRF. The data analysis has also been done in a way that is computationally efficient and independent of most related [[climate model|modelling]] methods and results. Radiative forcing was thus directly observed to have risen by +0.53&nbsp;W&nbsp;m<sup>−2</sup>&nbsp;(±0.11&nbsp;W&nbsp;m<sup>−2</sup>) from years 2003 to 2018. About 20% of the increase was associated with a reduction in the atmospheric aerosol burden, and most of the remaining 80% was attributed to the rising burden of greenhouse gases.<ref name="kramer" /><ref>{{cite web |author=Sarah Hansen |date=12 April 2021 |title=UMBC's Ryan Kramer confirms human-caused climate change with direct evidence for first time |url=https://news.umbc.edu/umbcs-ryan-kramer-confirms-human-caused-climate-change-with-direct-evidence-for-first-time/ |url-status=live |archive-url=https://web.archive.org/web/20210417044742/https://news.umbc.edu/umbcs-ryan-kramer-confirms-human-caused-climate-change-with-direct-evidence-for-first-time/ |archive-date=17 April 2021 |access-date=17 April 2021 |publisher=University of Maryland, Baltimore County}}</ref><ref>{{cite web |date=26 March 2021 |title=Direct observations confirm that humans are throwing Earth's energy budget off balance |url=https://phys.org/news/2021-03-humans-earth-energy.html |url-status=live |archive-url=https://web.archive.org/web/20210418072159/https://phys.org/news/2021-03-humans-earth-energy.html |archive-date=18 April 2021 |access-date=17 April 2021 |website=phys.org}}</ref>

A rising trend in the radiative imbalance due to increasing global {{CO2}} has been previously observed by ground-based instruments. For example, such measurements have been separately gathered under clear-sky conditions at two [[Atmospheric Radiation Measurement]] (ARM) sites in Oklahoma and Alaska.<ref>{{cite web |title=ARM Capabilities - Atmospheric Observatories |url=https://www.arm.gov/capabilities/observatories/ |url-status=live |archive-url=https://web.archive.org/web/20210425162041/https://www.arm.gov/capabilities/observatories/ |archive-date=2021-04-25 |accessdate=2021-04-25 |publisher=U.S. Department of Energy - Office of Science}}</ref> Each direct observation found that the associated radiative (infrared) heating experienced by surface dwellers rose by +0.2&nbsp;W&nbsp;m<sup>−2</sup>&nbsp;(±0.07&nbsp;W&nbsp;m<sup>−2</sup>) during the decade ending 2010.<ref>{{cite journal |author=Feldman, D.R., W.D. Collins, P.J. Gero, M.S. Torn, E.J. Mlawer, and T.R. Shippert |date=2015-02-25 |title=Observational determination of surface radiative forcing by CO2 from 2000 to 2010 |url=https://www.nature.com/articles/nature14240 |url-status=live |journal=Nature |volume=519 |issue=7543 |pages=339–343 |bibcode=2015Natur.519..339F |doi=10.1038/nature14240 |pmid=25731165 |s2cid=2137527 |archive-url=https://web.archive.org/web/20210405161008/https://www.nature.com/articles/nature14240 |archive-date=2021-04-05 |access-date=2021-04-25}}</ref><ref>{{cite web |author=Robert McSweeney |date=2015-02-25 |title=New study directly measures greenhouse effect at Earth's surface |url=https://www.carbonbrief.org/new-study-directly-measures-greenhouse-effect-at-earths-surface |url-status=live |archive-url=https://web.archive.org/web/20210418151415/https://www.carbonbrief.org/new-study-directly-measures-greenhouse-effect-at-earths-surface |archive-date=2021-04-18 |access-date=2021-04-25 |publisher=Carbon Brief}}</ref> In addition to its focus on [[outgoing longwave radiation|longwave radiation]] and the most influential forcing gas ({{CO2}}) only, this result is proportionally less than the TOA forcing due to its buffering by atmospheric absorption.