Comment on "Recent global decline of CO 2 fertilization effects on vegetation photosynthesis".

Wang . (Research Articles, 11 December 2020, p. 1295) reported a large decline in the CO fertilization effect (CFE) on global photosynthesis, on the basis of changing regression coefficients of CO (β) for satellite proxies/products of photosynthesis. We show that their methods cannot robustly estimate CFE, leading to incorrect attribution, and largely neglect CO effects on the photosynthetic enzyme ribulose-1,5-bisphosphate carboxylase-oxygenase (RuBisCO).