Figure 1.
Annual mean net carbon uptake (NEE, defined as negative when CO2 is taken up by the biosphere) versus isotopic discrimination integrated over Northern Hemisphere land area. The slope of the green regression line is -0.28±0.13 ‰/PgCyr-1. Error bars show 1-σ standard deviations based on four alternative approaches to the data assimilation estimates (see Table S2 of the Suppl. Info). Inset shows the temporal correlation between the two time-series (r=-0.86), partly explained by a secular trend in both variables, but mostly by correlated interannual variations (r=-0.74, see Methods).