Figure 7.13. Predicted increase in the fraction of total emissions that add to atmospheric CO₂. Changes in the mean partitioning of emissions as simulated by the C⁴MIP models up to 2000 (black symbols) and for the entire simulation period to 2100 (red symbols). The letters represent the models as given in Table 7.4. The box shown by the dotted line is a constraint on the historical carbon balance based on records of atmospheric CO₂ increase, and estimates of total emissions (fossil fuel plus land use emissions) and the oceanic uptake of anthropogenic CO₂ (Sabine et al., 2004a). The black and red diamonds show the model-mean carbon partitioning for the historical period and the entire simulation period, respectively. The red line shows the mean tendency towards an increasing airborne fraction through the 21st century, which is common to all models.