English Abstract Within the carbon cycle feedback mechanisms that
amplify or damp the exchange of carbon dioxide between the different
reservoirs to enhanced concentrations of carbon dioxide and increased
temperature from anthropogenic perturbations play a crucial role. Quite a
lot of these feedbacks are known, but most of them only potentially. This
report evaluates the role of a number of these feedback processes within the
carbon cycle. In order to assess their impact the feedbacks which at
present can be quantified reasonably are built into the Integrated Model to
Assess the Greenhouse Effect: IMAGE. Contrary to previous studies, this
study describes the scenario- and time dependent role of biogeochemical
feedbacks. A number of simulation experiments are performed with IMAGE to
make future projections of the concentration of carbon dioxide. Key
principle in this is that we use the modelled feedbacks to balance the past
and present carbon budget. This results in substantially lower projections
for atmospheric carbon dioxide than the IPCC-estimates: for the IPCC
'Business-as-Usual' scenario the difference is about 9%. Besides estimates
of their absolute importance, also the relative importance of individual
biogeochemical feedbacks is considered, by calculating the gain for each
feedback process. Finally the total gain is calculated, which appears to be
negative, caused by the dominant role of the fertilization
feedback.
