### Radiative forcing

#### Indicators:

- Radiative Forcing

  Relative contributions to Radiative Forcing:

  - Sum of positive and negative contributors
  - Positive contributors
  - Negative contributors

  Anthropogenic greenhouse gases and black carbon and aerosols affect the climate system by altering the balance between absorbed solar radiation and emitted infrared radiation. The indicators of radiative forcing presented in this box (calculated by the Upwelling-Diffusion Climate Model, UDCM) quantify the imbalance in net downward radiation (combined solar and infrared) at the tropopause. Variability of solar radiation and the injection of aerosols into the atmosphere by volcanic eruptions are also relevant. However, since these processes are variable in time and unpredictable, they are not taken into account in IMAGE 2.4.

  Gases and aerosols can have a warming or cooling effect on the troposphere. The most important greenhouse gas with a warming effect is CO2. Sulphate aerosols have a cooling effect in the troposphere. Here, the absolute change in radiative forcing relative to the pre-industrial age (1765) and the relative contribution to the total change in radiative forcing since 1765 by the various contributing compounds is presented. As positive and negative contributors to the change in radiative forcing are distinguished, the most important ''warmers' and 'coolers' of the troposphere can be identified.

  | #### Radiative Forcing
  | unit: W/m2 (Watt per square meter) dimension: contributor

  This indicator summarizes the contribution since the pre-industrial age (1765) to radiative forcing by CO2, CH4, N2O, chlorinated compounds, bromocarbons, perfluorocarbons and SF6, hydrofluorocarbons, tropospheric ozone, stratospheric ozone (O3), stratospheric water vapour, direct sulphate aerosols, indirect sulphate aerosol effects, black and organic carbon aerosols, and direct biomass burning aerosols.

  The radiative forcing by the various contributors is obtained as follows:

  - major greenhouse gases: with simple expressions taken from Table 6.2 of IPCC (2001).
  - chlorinated compounds, bromocarbons, perfluorocarbons, SF6 and hydrofluorocarbons: from Table 6.7 of IPCC (2001).
  - tropospheric O3: 0.042 W/m2/DU.
  - stratospheric water vapour, stratospheric ozone and direct and indirect effects of sulphate aerosols are calculated according to Appendix 2 of .
  - black and organic carbon aerosols: scaled linearly with the energy and industry emissions of SOx from the TIMER Emissions Model of IMAGE 2.4 (TEM). The 1990 level is assumed to be 0.1 W/m2.
  - biomass burning aerosols: scaled linearly with the SOx emissions from biomass burning generated by the land use emission model (LUEM). The 1970 level is assumed to be -0.146 W/m2.

  IPCC, 2001. Climate Change 2000. The science of climate change. Contribution of working group I to the third assessment report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge.

  | #### Sum of positive and negative contributors
  | unit: - dimension: contributor

  This indicator shows the relative contribution to the change in total radiative forcing since the pre-industrial age (1765) of the various positive and negative contributors.

  | #### Positive contributors
  | unit: - dimension: contributor

  This indicator shows the relative contribution of the various positive contributors (CO2, CH4, N2O, chlorinated compounds, bromocarbons, perfluorocarbons and SF6, hydrofluorocarbons, tropospheric ozone, stratospheric water vapour and black and organic carbon aerosols) to the change in radiative forcing since the pre-industrial age (1765).

  | #### Negative contributors
  | unit: - dimension: contributor

  This indicator shows the relative contribution of the various negative contributors (stratospheric ozone, direct sulphate aerosols, indirect sulphate aerosol effects, direct biomass burning aerosols) to the change in total radiative forcing since the pre-industrial age (1765).