Anthropogenic aerosols can influence the climate indirectly by changing the optical properties and precipitation formation of water clouds. An indirect effect that has not been considered involves the subset of anthropogenic aerosols that act as ice nuclei and thereby determines the lifetime of ice and mixed-phase clouds. If, in addition to mineral dust, a fraction of the hydrophilic soot aerosol particles is assumed to act as contact ice nuclei as evident from recent laboratory studies, then increases in aerosol concentration from pre-industrial times to present-day pose a new indirect effect, a glaciation indirect effect, on clouds. Here increases in contact ice nuclei in the present-day climate result in more frequent glaciation of clouds and increase the amount of precipitation via the ice phase. This effect can at least partly offset the solar indirect aerosol effect on water clouds.