Figure 3.6: Partitioning
the 1980s land-atmosphere flux for the tropics and the northern extratropics.
The residual terrestrial sink in different latitude bands can be inferred by subtracting
the land-use change flux for the 1980s (estimated by modelling studies: Houghton,
1999; Houghton and Hackler, 1999; Houghton et al., 2000; McGuire et al., 2001)
from the net land-atmosphere flux as obtained from atmospheric observations by
inverse modelling for the same period (Heimann, 2001; results from Figure
3.5). Positive numbers denote fluxes to the atmosphere; negative numbers denote
uptake from the atmosphere. This calculation is analogous to the global budget
calculation in Table 3.1, but now the model results
are broken down geographically and the land-atmosphere fluxes are obtained by
inverse modelling. The upper and lower bounds on the residual sink are obtained
by pairing opposite extremes of the ranges of values accepted for the two terms
in this calculation (for example, by subtracting the bottom of the range of values
for land-use change with the top of the range for the land-atmosphere flux). The
mid-ranges are obtained by combining similar extremes (for example, subtracting
the bottom of the range for land-use change emissions from the bottom of the range
land-atmosphere flux).