Radiative forcing

Warming contributions of various GHGs, agents, factors [name the year that the contributions pertain to] [*correct reference given under the 'Talk' tab*]. Plus, the figure is inaccurate; at least wrt. to methane.
The assessment of radiative forcing and climate sensitivity shows which physical parameters are contributing to temperature changes.[1]: 7  Parameters shown with orange bars lead to a temperature increase (due to positive radiative forcings), whereas parameters shown with blue bars lead to a temperature decrease (due to negative radiative forcing).

Radiative forcing (or climate forcing[2]) is a concept used to quantify a change to the balance of energy flowing through a planetary atmosphere. Various factors contribute to this change in energy balance, such as concentrations of greenhouse gases and aerosols, and changes in surface albedo and solar irradiance. In more technical terms, it is defined as "the change in the net, downward minus upward, radiative flux (expressed in W/m2) due to a change in an external driver of climate change."[3]: 2245  These external drivers are distinguished from feedbacks and variability that are internal to the climate system, and that further influence the direction and magnitude of imbalance. Radiative forcing on Earth is meaningfully evaluated at the tropopause and at the top of the stratosphere. It is quantified in units of watts per square meter, and often summarized as an average over the total surface area of the globe.

A planet in radiative equilibrium with its parent star and the rest of space can be characterized by net zero radiative forcing and by a planetary equilibrium temperature.[4]

Radiative forcing is not a thing in the sense that a single instrument can independently measure it. Rather it is a scientific concept and entity whose strength can be estimated from more fundamental physics principles. Scientists use measurements of changes in atmospheric parameters to calculate the radiative forcing.[5]: 1–4 

The IPCC summarized the current scientific consensus about radiative forcing changes as follows: "Human-caused radiative forcing of 2.72 W/m2 in 2019 relative to 1750 has warmed the climate system. This warming is mainly due to increased GHG concentrations, partly reduced by cooling due to increased aerosol concentrations".[1]: 11 

The atmospheric burden of greenhouse gases due to human activity has grown especially rapidly during the last several decades (since about year 1950). For carbon dioxide, the 50% increase (C/C0 = 1.5) realized as of year 2020 since 1750 corresponds to a cumulative radiative forcing change (ΔF) of +2.17 W/m2.[6] Assuming no change in the emissions growth path, a doubling of concentrations (C/C0 = 2) within the next several decades would correspond to a cumulative radiative forcing change (ΔF) of +3.71 W/m2.

Radiative forcing can be a useful way to compare the growing warming influence of different anthropogenic greenhouse gases over time. The radiative forcing of long-lived and well-mixed greenhouse gases have been increasing in earth's atmosphere since the industrial revolution.[6] Carbon dioxide has the biggest impact on total forcing, while methane and chlorofluorocarbons (CFCs) play smaller roles as time goes on.[6] The five major greenhouse gases account for about 96% of the direct radiative forcing by long-lived greenhouse gas increases since 1750. The remaining 4% is contributed by the 15 minor halogenated gases.

  1. ^ a b IPCC, 2021: Summary for Policymakers. In: 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. 3−32, doi:10.1017/9781009157896.001.
  2. ^ Rebecca, Lindsey (14 January 2009). "Climate and Earth's Energy Budget: Feature Articles". earthobservatory.nasa.gov. Archived from the original on 10 April 2020. Retrieved 3 April 2018.
  3. ^ Cite error: The named reference :0 was invoked but never defined (see the help page).
  4. ^ Lissauer, Jack Jonathan; De Pater, Imke (16 September 2013). Fundamental planetary science: physics, chemistry, and habitability. New York City. ISBN 9780521853309. OCLC 808009225.{{cite book}}: CS1 maint: location missing publisher (link)
  5. ^ National Research Council (2005). Radiative Forcing of Climate Change: Expanding the Concept and Addressing Uncertainties. The National Academic Press. doi:10.17226/11175. ISBN 978-0-309-09506-8.
  6. ^ a b c Cite error: The named reference noaa aggi was invoked but never defined (see the help page).