Figure 25: Projcted CO2
emissions permitting stabilisation of atmospheric CO2 concentrations
at different final values. Panel (a) shows the assumed trajectories of
CO2 concentration (WRE scenarios) and panels (b) and (c)
show the implied CO2 emissions, as projected with two fast carbon cycle
models, Bern-CC and ISAM. The model ranges for ISAM were obtained by tuning the
model to approximate the range of responses to CO2 and climate from
model intercomparisons. This approach yields a lower bound on uncertainties in
the carbon cycle response. The model ranges for Bern-CC were obtained by combining
different bounding assumptions about the behaviour of the CO2 fertilisation
effect, the response of heterotrophic respiration to temperature and the turnover
time of the ocean, thus approaching an upper bound on uncertainties in the carbon
cycle response. For each model, the upper and lower bounds are indicated by the
top and bottom of the shaded area. Alternatively, the lower bound (where hidden)
is indicated by a hatched line. [Based on Figure 3.13]
