Boundary layer nucleation influences the long term change in cloud drop number
Joonas Merikanto has shown that boundary layer nucleation has an important effect on the long term (pre-industrial to present day) change in cloud drop number, and therefore the indirect forcing.
Although particle formation increases global annual mean cloud drop concentrations by approximately the same amount in both 1860 and 2000(16.0% versus 13.5%), there are substantial regional effects of up to 50% enhancement
or suppression of the 1850–2000 albedo change. Over most modern-day polluted Northern Hemisphere regions particle formation suppresses the 1850–2000 increase in CDNC and cloud albedo. Over the Arctic the albedo change is suppressed by 23% in the annual mean and by 43% in summer when particle formation is taken into account. The albedo change of the persistent stratocumulus cloud deck west of Chile is enhanced by 49%.