The effects of air pollution on vegetation may provide another important control on the carbon cycle that has not yet been widely considered. Prolonged exposure to high levels of ozone, in particular, has been observed to inhibit photosynthesis by direct cellular damage within the leaves and through changes in stomatal conductance. We have incorporated simple empirical equations derived for hardwoods, pines, and crops into the Terrestrial Ecosystem Model (TEM, version 4.3) to explore spatial and temporal variations of ozone effects on net primary productivity (NPP) and carbon sequestration across the globe. Although our results show up to a 2% reduction in annual NPP as a result of historical ozone levels during the late 1980s-early 1990s, regionally this reduction is much larger. The largest decreases (up to 39% in some locations) occur in the eastern U.S., Europe, and China, during months with high ozone levels and substantial production. Carbon sequestration during the early 1990s is reduced by as much as 0.43 PgC/yr, or 15%, with the presence of ozone. Thus the effects of ozone on net primary production and carbon sequestration should be factored into future calculations of the global carbon budget.