Fig. 1. Simplified carbon cycle. Fluxes are expressed in PgCy−1and refer to the average for the period 2000–2009. Fluxes betweenthe atmosphere and the terrestrial biosphere include freshwater outgassing, net land-use change (in red), net land fluxes androck weathering; fluxes between oceans and the terrestrial biosphere to the lithosphere consist of CaCO3sedimentation; fluxesbetween the lithosphere and the atmosphere include volcanism, fossil fuels and cement production (the latter two in red).Lithosphere carbon stocks include conventional fossil fuel reserves and, in brackets, estimated total fossil fuels that couldultimately be recovered (tar and heavy oil) (Field et al., 2012). They do not include CaCO3deposits and methane hydrates incontinental shelf sediments. (For interpretation of the references to color in this figure legend, the reader is referred to the webversion of this article.)Source: Adapted from Ciais and Sabine (2013).