As the global population becomes increasingly urbanised, so interest has grown in the potential climate change impacts on city infrastructure, services, and environmental quality. However, urban areas are only beginning to be represented explicitly in the land-surface schemes of dynamical climate models through modified energy and moisture budgets. This paper summarises recent evidence of urban impacts on climate and vice versa. The technique of statistical downscaling is then introduced through exemplar studies of London's future urban heat island and peak ozone concentrations. Projections of both indices are derived from atmospheric variables supplied by four general circulation models, driven by a medium-high (A2) emissions scenario for the 2050s. The results show further intensification of the nocturnal heat island and higher ozone concentrations that are most pronounced in summer. These changes reflect sensitivity to variations in regional climate alone, so omit other factors such as changes in land use, emissions. climate feedbacks, or synergies between air quality and heat islands. Nonetheless, the downscaled scenarios are consistent with an emerging picture of increasing risks to human health in urban areas unless appropriate adaptation measures are taken.