Beyond equilibrium climate sensitivity -LSB-...] Newer metrics relating global warming directly to the total emitted CO2 show that in order to keep warming to within 2 °C, future CO2 emissions have to remain strongly limited, irrespective of climate sensitivity being at the high or low end.»
What could hypothetically happen if a very large change in GHG amount / type is made, is that the forcing could increase
beyond a point where it becomes saturated at the tropopause level at all wavelengths — what can happen then is that the
equilibrium climate sensitivity to the nearly zero forcing from additional GHGs may approach infinity, because in
equilibrium the tropopause has to shift upward enough to reach a level where there can be some net LW flux up through it.