The adjoints of the GEOS-Chem Chemical Transport Model and a comprehensive cloud droplet parameterization are coupled to study the sensitivity of cloud droplet number concentration (N<inf>d</inf>) over US regions and Central Europe to global emissions of anthropogenic fine mode aerosol precursors. Simulations reveal that the N<inf>d</inf> over the midwestern and southeastern US is mostly sensitive to SO<inf>2</inf> emissions during August, and to NH<inf>3</inf> emissions during February. Over the western US, N<inf>d</inf> is mostly sensitivity to SO<inf>2</inf> and primary organic aerosol emissions. In Central Europe, N<inf>d</inf> is most sensitive to NH<inf>3</inf> and NO<inf>x</inf> emissions. As expected, local emissions strongly affect N<inf>d</inf>; long-range transport, however, is also important for the western US and Europe. Emissions changes projected for the year 2050 are estimated to have the largest impacts on cloud albedo and N<inf>d</inf> over Central Europe during August (42% and 82% change, respectively) and western US during February (12% and 36.5% change, respectively). © 2012. American Geophysical Union. All Rights Reserved.