page_title: Radiative forcing
section_title: History
hierarchical_section_title: Radiative forcing / History
caption_attribution_description: English: This graph shows changes in radiative forcing of long-lived greenhouse gases between 1979-2012. These gases are carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), chlorofluorocarbon-12 (CFC-12), CFC-11, and fifteen other minor, long-lived, halogenated gases. The 15 other halogenated gases are CFC-113, tetrachloromethane (CCl4), trichloromethane (CH3CCl3); hydrochlorofluorocarbons (HCFCs) 22, 141b and 142b; hydrofluorocarbons (HFCs) 134a, 152a, 23, 143a, and 125; sulfur hexafluoride (SF6), and halons 1211, 1301 and 2402). The graph does not include other forcings, such as aerosols and changes in solar activity. Summary Total forcing in 1979 was 1.712 watts per square metre (W.m-2), and has steadily increased over time to 2.873 W.m-2 in 2012. Between 1979-2012, the largest contributors to radiative forcing have been CO2 and CH4. In 2012, the percentage contributions of each gas to total forcing was approximately: CO2: 64% CH4: 18% N2O: 6% CFC-12: 6% CFC-11: 2% 15 minor gases: 4% Forcing data are briefly summarized below. All the data are available in a later section as comma-separated values. The first value is the year, followed by forcing values (in W.m-2) for CO2, CH4, N2O, CFC-12, CFC-11, the 15-minor halogenated gases, and total forcing, respectively: 1979: 1.027, 0.419, 0.104, 0.092, 0.039, 0.031, 1.712 1980: 1.058, 0.426, 0.104, 0.097, 0.042, 0.034, 1.761 1990: 1.293, 0.472, 0.129, 0.154, 0.065, 0.065, 2.178 2000: 1.513, 0.494, 0.151, 0.173, 0.066, 0.083, 2.481 2010: 1.791, 0.504, 0.174, 0.170, 0.060, 0.106, 2.805 2012: 1.846, 0.507, 0.181, 0.168, 0.059, 0.111, 2.873 References: Butler, J.H. and S.A. Montzka&#32;(2013-08-01)&#32;THE NOAA ANNUAL GREENHOUSE GAS INDEX (AGGI)[1], NOAA/ESRL Global Monitoring Division
context_page_description: Radiative forcing or climate forcing is the difference between insolation absorbed by the Earth and energy radiated back to space. Changes to Earth's radiative equilibrium, that cause temperatures to rise or fall over decadal periods, are called climate forcings. Positive radiative forcing means Earth receives more incoming energy from sunlight than it radiates to space. This net gain of energy will cause warming. Conversely, negative radiative forcing means that Earth loses more energy to space than it receives from the sun, which produces cooling. A system in thermal equilibrium has zero radiative forcing.
  Radiative forcing is meaningfully quantified at the tropopause and at the top of the stratosphere as flux of watts per square meter of the Earth's surface.
  Radiative forcing varies with insolation, the atmospheric concentrations of radiatively active gases, commonly known as greenhouse gases, and aerosols.
context_section_description: The table below (derived from atmospheric radiative transfer models) shows changes in radiative forcing between 1979 and 2018. The table includes the contribution to radiative forcing from carbon dioxide (CO
  2), methane (CH
  ₄), nitrous oxide (N
  ₂O); chlorofluorocarbons (CFCs) 12 and 11; and fifteen other minor, long-lived, halogenated gases. The table includes the contribution to radiative forcing of long-lived greenhouse gases. It does not include other forcings, such as aerosols and changes in solar activity.
  The table shows that CO
  2 dominates the total forcing, with methane and chlorofluorocarbons (CFC) becoming relatively smaller contributors to the total forcing over time. 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.
  It might be observed that the total forcing for year 2016, 3.027 W m⁻², together with the commonly accepted value of climate sensitivity parameter λ, 0.8 K /(W m⁻²), results in an increase in global temperature of 2.4 K, much greater than the observed increase, about 1.2 K. Part of this difference is due to lag in the global temperature achieving steady state with the forcing. The remainder of the difference is due to negative aerosol forcing and/or climate sensitivity being less than the commonly accepted value, or some combination thereof.
  The table also includes an "Annual Greenhouse Gas Index" (AGGI), which is defined as the ratio of the total direct radiative forcing due to long-lived greenhouse gases for any year for which adequate global measurements exist to that which was present in 1990. 1990 was chosen because it is the baseline year for the Kyoto Protocol. This index is a measure of the inter-annual changes in conditions that affect carbon dioxide emission and uptake, methane and nitrous oxide sources and sinks, the decline in the atmospheric abundance of ozone-depleting chemicals related to the Montreal Protocol. and the increase in their substitutes (hydrogenated CFCs (HCFCs) and hydrofluorocarbons (HFC). Most of this increase is related to CO
  2. For 2013, the AGGI was 1.34 (representing an increase in total direct radiative forcing of 34% since 1990). The increase in CO
  2 forcing alone since 1990 was about 46%. The decline in CFCs considerably tempered the increase in net radiative forcing.
  An alternative table prepared for use in climate model intercomparisons conducted under the auspices of IPCC and including all forcings, not just those of greenhouse gases, is available at http://www.climatechange2013.org/images/report/WG1AR5_AIISM_Datafiles.xlsx
caption: Changes in radiative forcing of long-lived greenhouse gases between 1979 and 2012.
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