Evolution of anthropogenic CO2 sources and sinks, 1765-2005. S Khatiwala et al., 2009.

This graph shows the evolution of the various sources and sinks of anthropogenic CO2 between ad 1765 and ad 2005. Our results indicate that the terrestrial biosphere was a source of Cant until the 1940s, roughly in line with previous model-based estimates3, 18, after which it turned into a sink of anthropogenic CO2. Taken over the entire industrial period, and accounting for uncertainties, we estimate that the terrestrial biosphere has been anywhere from neutral to a net source of CO2, contributing up to half as much Cant as has been taken up by the ocean over the same period. Fossil fuel burning30 (including a small contribution from cement production) is the only source considered here, and is shown as positive values. Sinks, shown as negative values, include the atmosphere, ocean, and land biosphere. Error envelope (as in Fig. 1 legend), indicated by broken lines and the shaded area, includes a 5% uncertainty in fossil fuel emissions17.

S Khatiwala et al., Reconstruction of the history of anthropogenic CO2 concentrations in the ocean, Nature 462, 346-349 (2009) doi:10.1038/nature08526