Future Development of the Carbon Cycle: the Role of the Biota/Forests within the IPCC Stabilization Scenarios
For the analyzed period between 1980 and 1989 a terrestrial biospheric sink of the order of 1.7 to 1.8 Gt C per year is required to close the CO2 budget between atmospheric CO2 input, observed atmospheric CO2 increase, CO2 ocean uptake and CO2 release from deforestation. The reasons for the additional terrestrial sink are still not completely clarified, however, the fertilization through additional atmospheric CO2 and deposition of nitrogen compounds are believed to be of importance in addition to factors associated with climate change, age class distribution of forests as well as land management practices. The IPCC (Intergovernmental Panel on Climate Change) has generated a series of atmospheric CO2 profiles leading to stabilization levels in the range 350 to 1000 ppmV. These profiles correspond to developments with very strong efforts, intermediate efforts, or nearly absent (at least during the next 30 to 50 years) efforts to stabilize greenhouse gases. In the present study, we examine the CO2 exchange between the land biota and the atmosphere studying in particular the long term development of a potential CO2 related fertilization effect for the profiles stabilizing atmospheric CO2 at 450 (S450), 650 (S650) and 1000 (S1000) ppmV. Two different biosphere box models, an ultra-simple two-box model (USBM) and the Bern four-box biosphere model as well as the high-resolution Frankfurt Biosphere Model (FBM) were investigated to study the long-term response (up to the year 2300) of the biota and soils.
We applied a linear pulse response function substitute model of the HILDA ocean model to calculate the oceanic CO2 uptake. Similar to the ocean behaviour the uptake of carbon by the biosphere follows the sigmoidal increase function of atmospheric CO2, both with the USBM, the Bern Biosphere Model as well as with the more detailed Frankfurt Biosphere Model. Biospheric carbon uptake is highest near the inflection point of the annual CO2 emissions into the atmosphere and then falls off at times beyond. We summarize in stating that a potential CO2 fertilization effect with respect to a biospheric carbon increase drops off during the first half of next century for the profiles S450 and S650 and somewhat later for the the S1000 scenario.
KeywordsBiomass Combustion Starch Dioxide Respiration
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