A constraint on historic growth in global photosynthesis due to rising CO2

Theory predicts that rising CO2 increases global photosynthesis, a process known as CO2 fertilisation, and that this is responsible for much of the current terrestrial carbon sink. The estimated magnitude of the historic CO2 fertilization, however, differs by an order of magnitude between long-term proxies, remote sensing-based estimates and terrestrial biosphere models. Here, 2022 Abdul Latif Jameel Water and Food Systems Lab principal investigator César Terrer and colleagues constrain the likely historic effect of CO2 on global photosynthesis by combining terrestrial biosphere models, ecological optimality theory, remote sensing approaches and an emergent constraint based on global carbon budget estimates. Their analysis suggests that CO2 fertilisation increased global annual terrestrial photosynthesis by 13.5 ± 3.5% or 15.9 ± 2.9 PgC (mean ± s.d.) between 1981 and 2020. The results help resolve conflicting estimates of the historic sensitivity of global terrestrial photosynthesis to CO2 and highlight the large impact anthropogenic emissions have had on ecosystems worldwide.