Global Warming

Carbon dioxideand the carboncycle 33

Table 3.1Components of annual average global carbon budget for

1980s and 1990s – in Gt of carbon per yeara(positive values are fluxes

to the atmosphere, negative values represent uptake from the

atmosphere)

1980s 1990s

Emissions (fossil fuel, cement) 5. 4 ± 0. 36. 4 ± 0. 4
Atmospheric increase 3. 3 ± 0. 13. 2 ± 0. 1
Ocean–atmosphere flux − 1. 9 ± 0. 6 − 1. 7 ± 0. 5
Land–atmosphere flux∗ − 0. 2 ± 0. 7 − 1. 4 ± 0. 7
∗partitioned as follows

Land-use change 1.7 (0.6 to 2.5) 1.4 to 3.0

Residual terrestrial sink −1.9 (−3.8 to 0.3) −4.8 to−1.6

aThe entries in the first four rows are from Table 3.3 in Prenticeet al. 2001 (see

Note 2). Note that the ranges quoted represent sixty-seven per cent certainty.

The entries in the ‘partitioning of land-atmosphere flux’ are from Houseet al.

2003 (see Note 2).

Figure 3.3(a) Fossil carbon emissions (based on statistics of fossil fuel and

cement production) and estimates of global reservoir changes: atmosphere

(deduced from direct observations and ice core measurements), ocean

(calculated with the Geophysical Fluid Dynamics Laboratory (GFDL), University

of Princeton, ocean carbon model) and net terrestrial biosphere (calculated as

remaining imbalance) from 1840 to 1990. The calculation implies that the

terrestrial biosphere was a net source to the atmosphere prior to 1940 (negative

values) and has been a net sink since about 1960. (b) Estimates of contributions

to the carbon balance of the terrestrial biosphere. The curve showing the

terrestrial reservoir changes is taken from (a). Emissions from land-use changes

(including tropical deforestation) are plotted negatively because they represent a

loss of biospheric carbon. These estimates are subject to large uncertainties (see

uncertainty estimates in Table 3.1).