«The proportionality of warming to cumulative emissions depends in part on a cancellation of the saturation of carbon sinks with increasing cumulative emissions (leading to
a larger airborne fraction of cumulative emissions for higher emissions) and the logarithmic dependence of radiative forcing on atmospheric CO2 concentration [leading to a smaller increase in radiative forcing per unit increase in atmospheric CO2 at higher CO2 concentrations; Matthews et al. (2009)-RSB-.