«Fs», the fixed SST forcing, is a combination of the flux change at the top of (and throughout) the atmosphere and of the global
surface air temperature change after the forcing and with observed sea surface temperature (SST) and sea ice (SI) held fixed.
Relationships between the
change in net top - of - atmosphere radiative flux, N, and global - mean
surface -
air -
temperature change, ΔT,
after an instantaneous quadrupling of CO2.