IPCC report
Even though the importance of aerosols for the formation of clouds is, in general, well understood, many uncertainties remain. In fact, the latest IPCC report considers aerosol-cloud interactions as one of the current major challenges in climate modeling in general. In particular, the number of droplets does not increase proportionally when more aerosols are present and can even decrease. Extrapolating the effects of particles on clouds observed on the microphysical scale to the regional, climatically relevant scale, is not straightforward.