Abstract

Observations of CO2 accumulation in the atmosphere and ocean show that they are approximately equal to the total amount emitted by burning of fossil fuels since 1850. A mass balance calculation is carried out with ocean uptake satisfying two observed constraints, and with net terrestrial emissions as the remainder. The calculation illustrates that before 1940, net terrestrial emissions were positive, and have been negative since then, making their cumulative contribution in 2008 rather small. The overall evidence strongly suggests that the increase of CO2 in the atmosphere is 100% due to human activities, and is dominated by fossil fuel burning. Some simple projections of atmospheric CO2, and therefore also of surface pCO2 for most of the ocean, are made with plausible future scenarios of fossil fuel emissions, only taking into account features of the carbon cycle that are quite well established.