Fig. 4: Global changes in the fraction of C4 plants, GPP and Δ13C over 1982–2016.
Fraction of C4 plants (F4) from our model for (a) natural grasslands (green), crops (orange) and both natural grasses and crops (violet) and (b) total F4 compared to that from Still2009 (brown) and Luo2024 (light pink). GPP weighted by the fraction of C3/C4 plants (in PgC yr−1) for natural grasslands (green), crops (orange) and both natural grasses and crops (violet) in C3 (c) and C4 (d) plants and (e) for all plants (including C3 and C4 plants; Eq. 3c) using our maps and those. Δ13C weighted by the fraction of C3/C4 plants (in ‰) for natural grasslands (green), crops (orange) and both natural grasses and crops (violet) in C3 (f) and C4 (g) plants and (h) for all plants (including C3 and C4 plants; Eq. 4) using our map, Still2009 and Luo2024. The light shade is the uncertainty calculated as the 95% confidence interval of the simulated mean (a, b, f, g, h) or sum (c–e) plus the sum of uncertainties from the input data (assumed to be ±2% of the global average values). The uncertainty range of the C4 cropland area derived from LUHv2-2019 (orange) is assumed to be ±10% of the global average values following Luo.
