Elevated CO${}_2$ negates O${}_3$ impacts on terrestrial carbon and nitrogen cycles

Increasing tropospheric concentrations of ozone (e[O${}_3$]) and carbon dioxide (e[CO${}_2$]) 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[O${}_3$] and e[CO${}_2$] 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[O${}_3$] 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[CO${}_2$]. More importantly, simultaneous increases in [CO${}_2$] and [O${}_3$] negate or even overcompensate the negative effects of e[O${}_3$3] on ecosystem functions and carbon and nitrogen cycles. Therefore, the negative effects of e[O${}_3$] on terrestrial ecosystems would be overestimated if e[CO${}_2$] impacts are not considered, stressing the need for evaluating terrestrial carbon and nitrogen feedbacks to concurrent changes in global atmospheric composition.