RETRACTED ARTICLE: A constraint on historic growth in global photosynthesis due to increasing CO 2

The global terrestrial carbon sink is increasing 1 – 3 , offsetting roughly a third of anthropogenic CO 2 released into the atmosphere each decade 1 , and thus serving to slow 4 the growth of atmospheric CO 2 . It has been suggested that a CO 2 -induced long-term increase in global photosynthesis, a process known as CO 2 fertilization, is responsible for a large proportion of the current terrestrial carbon sink 4 – 7 . The estimated magnitude of the historic increase in photosynthesis as result of increasing atmospheric CO 2 concentrations, however, differs by an order of magnitude between long-term proxies and terrestrial biosphere models 7 – 13 . Here we quantify the historic effect of CO 2 on global photosynthesis by identifying an emergent constraint 14 – 16 that combines terrestrial biosphere models with global carbon budget estimates. Our analysis suggests that CO 2 fertilization increased global annual photosynthesis by 11.85 ± 1.4%, or 13.98 ± 1.63 petagrams carbon (mean ± 95% confidence interval) between 1981 and 2020. Our results help resolve conflicting estimates of the historic sensitivity of global photosynthesis to CO 2 , and highlight the large impact anthropogenic emissions have had on ecosystems worldwide.