Figure 3.8: Modelled fluxes
of anthropogenic CO2 over the past century. (a) Ocean model results
from OCMIP (Orr and Dutay, 1999; Orr et al., 2000); (b), (c) terrestrial model
results from CCMLP (McGuire et al., 2001). Positive numbers denote fluxes to the
atmosphere; negative numbers denote uptake from the atmosphere. The ocean model
results appear smooth because they contain no interannual variability, being forced
only by historical changes in atmospheric CO2. The results are truncated
at 1990 because subsequent years were simulated using a CO2 concentration
scenario rather than actual measurements, leading to a likely overestimate of
uptake for the 1990s. The terrestrial model results include effects of historical
CO2 concentrations, climate variations, and land-use changes based
on Ramankutty and Foley (2000). The results were smoothed using a 10-year running
mean to remove short-term variability. For comparison, grey boxes denote observational
estimates of CO2 uptake by the ocean in panel (a) and by the land in
panel (b) (from Table 3.1). Land-use change flux estimates
from Houghton et al. (1999) are shown by the black line in panel (c). The grey
boxes in panel (c) indicate the range of decadal average values for the land-use
change flux accepted by the SRLULUCF (Bolin et al., 2000) for the 1980s and for
1990 to 1995.