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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., (© 2021. The Author(s), under exclusive licence to Springer Nature Limited.)

For over 30 years a central question in molecular evolution has been whether natural selection plays a substantial role in evolution at the DNA sequence level. Evidence has accumulated over the last decade that adaptive evolution does occur at the protein level, but it has remained unclear how prevalent adaptive evolution is. Here we present a simple method by which the number of adaptive substitutions can be estimated and apply it to data from Drosophila simulans and D. yakuba. We estimate that 45% of all amino-acid substitutions have been fixed by natural selection, and that on average one adaptive substitution occurs every 45 years in these species.