A radiative forcing is a change imposed on the planetary radiation balance. It is measured by the net radiative flux change (in the unit of W/m2), at some level in the atmosphere, calculated to occur in response to the perturbation. There are several alternative definitions of radiative forcing (Fi,Fa, Fg, Fs), as shown below.
The adjusted forcing, Fa is most commonly used, but here we will give the "effective forcing" which is defined as
Fe = Ea x Fa =~ΔTs / 0.463⚬C/(W/m2),
where Ea is the efficacy and ΔTs is the global surface air temperature change in response to the forcing agent. (See the references below.) Fe provides a good prediction of the response to different forcing amounts.
The time dependent effective forcings relative to 1750 for the agents used in our computations are shown individually and as the total in the graph below.
Figure in PDF.
References
Hansen, J., M. Sato, R. Ruedy, et al. (2000) Global Warming In the Twenty First Century: An Alternative Scenario, Proc. Natl. Acad. Sci., 97, 9875-9880
Hansen, J., M. Sato, R. Ruedy, et al. (2005) Efficacy of climate forcings, J. Geophys. Res., 110, D18104.
Hansen, J., M. Sato, R. Ruedy, et al. (2007) Climate simulations for 1880-2003 with GISS modelE, Clim. Dyn. 29, 661-696.
Hansen, J., M. Sato, P. Kharecha, and K. von Schuckmann (2011) Earth's energy imbalance and implications, Atmos. Chem. Phys. 11, 13421-13449.
Hansen, J., M. Sato, P. Kharecha, et al. (2017) Young people's burden: Requirement of negative CO2 emissions, Earth System Dynamics 8 577-616.
Hansen, J., M. Sato, L. Simons, et al. (2023) Global Warming in the Pipeline, Oxford Open Climate Change, 3, kgad008.