Why is there a short-term increase in global precipitation in response to diminished CO₂ forcing?

[1] Recently, it was found that a reduction in atmospheric CO₂ concentration leads to a temporary increase in global precipitation. We use the Hadley Center coupled atmosphere-ocean model, HadCM3L, to demonstrate that this precipitation increase is a consequence of precipitation sensitivity to changes in atmospheric CO₂ concentrations through fast tropospheric adjustment processes. Slow ocean cooling explains the longer-term decrease in precipitation. Increased CO₂ tends to suppress evaporation/precipitation whereas increased temperatures tend to increase evaporation/precipitation. When the enhanced CO₂ forcing is removed, global precipitation increases temporarily, but this increase is not observed when a similar negative radiative forcing is applied as a reduction of solar intensity. Therefore, transient precipitation increase following a reduction in CO₂-radiative forcing is a consequence of the specific character of CO₂ forcing and is not a general feature associated with decreases in radiative forcing.