The influence of chronic ozone exposure on global carbon and water cycles

In addition to directly increasing radiative forcing as a greenhouse gas, O₃ indirectly impacts climate through altering the plant processes of photosynthesis and transpiration. While global estimates of gross primary productivity (GPP) have incorporated the effects of O₃, few studies have explicitly determined the independent effects of O₃ on transpiration.

In this study, the authors include effects of O₃ on photosynthesis and stomatal conductance from a recent literature review to determine the impact on GPP and transpiration and highlight uncertainty in modeling plant responses to O₃. Using the Community Land Model, the authors estimate that present-day O₃ exposure reduces GPP and transpiration globally by 8%-12% and 2%-2.4%, respectively. The largest reductions were in midlatitudes, with GPP decreasing up to 20% in the eastern United States, Europe, and Southeast Asia and transpiration reductions of up to 15% in the same regions.