I did an RRTM run with H2O mole fraction 0.00025 (approximating the Arctic) and got the following results.
Removal of all CO2 decreases downwelling longwave radiation by 14%, and increasing CO2 by 10X increases downwelling longwave radiation by 7%
So new we have the Earth constrained. CO2 is responsible for 1.3% of the greenhouse effect in the tropics, 2.5% in the mid latitudes, and 14% in the polar regions. These numbers are a far cry from the bloated garbage which Gavin publishes.