1Department of Physics, University of Helsinki, 00014, Helsinki, Finland
2Finnish Meteorological Institute, 00101, Helsinki, Finland
3Department of Physical Geography and Ecosystems Analysis, Lund University, 223 62, Lund, Sweden
4Institute of Meteorology and Climate Research, Karlsruhe Institute for Technology, 82467 Garmisch-Partenkirchen, Germany
5Department of Forest Science, University of Helsinki, 00014, Helsinki, Finland
Abstract. The number of cloud droplets determines several climatically relevant cloud properties. A major cause for the high uncertainty in the indirect aerosol forcing is the availability of cloud condensation nuclei (CCN), which in turn is highly sensitive to atmospheric new particle formation. Here we present the effect of new particle formation on anthropogenic aerosol forcing in present-day (year 2000) and future (year 2100) conditions. The total aerosol forcing (−1.61 W m−2 in year 2000) is simulated to be greatly reduced in the future, to −0.23 W m−2, mainly due to decrease in SO2 emissions and resulting decrease in new particle formation. With the total aerosol forcing decreasing in response to air pollution control measures taking effect, warming from increased greenhouse gas concentrations can potentially increase at a very rapid rate.