This paper describes results of a modeling study aimed at simulating the effects of global climate change on climate and air quality over the northeastern United States with a focus on the New York City metropolitan area. The model systems used for this study are the Goddard Institute for Space Studies (GISS) Global Atmosphere-Ocean Model; the PennState/NCAR MM5 mesoscale meteorological model; the Sparse Matrix Operator Kernel Emissions Modeling System (SMOKE); and the Community Multiscale Air Quality (CMAQ) model for simulating air quality. Simulations were performed for five summer seasons each during the 1990s and future decades. An evaluation of the present-day climate and air quality predictions indicates that the modeling system largely captures the observed climate-ozone system. This is established through map-typing analyses, comparison of observed and predicted distributions of meteorological variables and ozone, as well as a comparison of observed and predicted extreme heat and pollution events. Analysis of future-year predictions shows an increase in temperature and humidity as well as mean and extreme ozone concentrations under the IPCC A2 emission scenario. In addition to the analysis of mean summertime temperature, precipitation, mixing height, and pollutant concentrations, an analysis of the changes in the severity and duration of extreme heat and pollution events is presented. Furthermore, through a series of sensitivity studies the question is addressed whether changes in meteorology due to global climate change or changes in emissions have the largest impact on predicted ozone concentrations. Model predictions of current and future climate and air quality in the New York City metropolitan area are combined with health impact functions derived specifically for this area to assess the public health effects of predicted changes.