250 billion tons/year
||Andreas Bracher, Spencer M. Whitney, F. Ulrich Hartl, and Manajit Hayer-Hartl, Biogenesis and Metabolic Maintenance of Rubisco, Annu. Rev. Plant Biol. 2017. 68:6.1–6.32 DOI: 10.1146/annurev-arplant-043015-111633 p.6.2 top paragraph
||Field CB, Behrenfeld MJ, Randerson JT, Falkowski P. Primary production of the biosphere: integrating terrestrial and oceanic components. Science. 1998 Jul 10 281(5374)237-40PubMed ID9657713
||P.6.2 top paragraph: "Life on earth depends on the ability of photosynthetic organisms to sequester inorganic CO2 from the atmosphere into organic carbon compounds via the Calvin-Benson-Bassham cycle of photosynthesis (Figure 1). A key enzyme in this process is ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), the most abundant protein in nature (ref 26). The amount of CO2 fixed by Rubisco is estimated at 250 billion tons per year (primary source)."