A global chemical transport model of the atmosphere [the Model for Ozone and Related Tracers, version 2 (MOZART-2)] driven by prescribed surface emissions and by meteorological fields provided by the ECHAM5/Max Planck Institute Ocean Model (MPI-OM-1) coupled atmosphere–ocean model is used to assess how expected climate changes (2100 versus 2000 periods) should affect the chemical composition of the troposphere. Calculations suggest that ozone changes resulting from climate change only are negative in a large fraction of the troposphere because of enhanced photochemical destruction by water vapor. In the Tropics, increased lightning activity should lead to larger ozone concentrations. The magnitude of the climate-induced ozone changes in the troposphere remains smaller than the changes produced by enhanced anthropogenic emissions when the Special Report on Emission Scenarios (SRES) A2P is adopted to describe the future evolution of these emissions. Predictions depend strongly on future trends in atmospheric methane levels, which are not well established. Changes in the emissions of NOx by bacteria in soils and of nonmethane hydrocarbons by vegetation associated with climate change could have a significant impact on future ozone levels.