Table 3

The global carbon budget for two time periods (Pg C year−1). There are different arrangements to account for elements of the global C budget (see also table S6). Here, the accounting was based on global C sources and sinks. The terrestrial sink was the residual derived from constraints of two major anthropogenic sources and the sinks in the atmosphere and oceans. We used the C sink in global established forests as a proxy for the terrestrial sink.

Sources and sinks1990–19992000–2007
Sources (C emissions)
Fossil fuel and cement*6.5 ± 0.47.6 ± 0.4
Land-use change†1.5 ± 0.71.1 ± 0.7
Total sources8.0 ± 0.88.7 ± 0.8
Sinks (C uptake)
Atmosphere†3.2 ± 0.14.1 ± 0.1
Ocean‡2.2 ± 0.42.3 ± 0.4
Terrestrial (established forests)§2.5 ± 0.42.3 ± 0.5
Total sinks7.9 ± 0.68.7 ± 0.7
Global residuals||0.1 ± 1.00.0 ± 1.0

*See (2).

†See (4, 7, 25). The global land-use change emission is approximately equal to the tropical land-use change emission, because the net carbon balance of land-use changes in temperate and boreal regions is neutral (24, 38).

‡See (4).

§Estimates of C sinks in the global established forests (that are outside the areas of tropical land-use changes) from this study. Note that the carbon sink in tropical regrowth forests is excluded because it is included in the term of land-use change emission (see above and Table 1).

||Global C residuals are close to zero when averaged over a decade. Uncertainties in the global residuals indicate either a land sink or source in the 212 Mha of forest not included here, on nonforest land, or systematic error in other source (overestimate) or sink (underestimate) terms, or both.