Elevated CO₂ negates O₃ impacts on terrestrial carbon and nitrogen cycles

Increasing tropospheric concentrations of ozone (e[O₃]) and carbon dioxide (e[CO₂]) profoundly perturb terrestrial ecosystem functions through carbon and nitrogen cycles, affecting beneficial services such as their capacity to combat climate change and provide food. However, the interactive effects of e[O₃] and e[CO₂] on these functions and services remain unclear. Here, we synthesize the results of 810 studies (9,109 observations), spanning boreal to tropical regions around the world, and show that e[O₃] significantly decreases global net primary productivity and food production as well as the capacity of ecosystems to store carbon and nitrogen, which are stimulated by e[CO₂]. More importantly, simultaneous increases in [CO₂] and [O₃] negate or even overcompensate the negative effects of e[O₃] on ecosystem functions and carbon and nitrogen cycles. Therefore, the negative effects of e[O₃] on terrestrial ecosystems would be overestimated if e[CO₂] impacts are not considered, stressing the need for evaluating terrestrial carbon and nitrogen feedbacks to concurrent changes in global atmospheric composition.