Before revision: Because CO2 is close to saturation with high concentrations and few infrared absorption bands, the radiation budget and hence the greenhouse effect has low sensitivity to changes in CO2 concentration; Harnung, Sven E. and Johnson, Matthew S.; Chemistry and the Environment, p. 365 the increase in temperature is roughly logarithmic.
After revision: Because CO2 is close to saturation with high concentrations and few infrared absorption bands, the radiation budget and hence the greenhouse effect has low sensitivity to changes in CO2 concentration; the increase in temperature is roughly logarithmic.