Sensitivity of global carbon pools and fluxes to human and potential climatic impacts

Besides the emissions from fossil sources, the anthropogenic land use changes (clearings and similar influences) the CO₂ fertilization effect on the biosphere, and potential climatic fluctuations may have influenced the global carbon balance and the CO₂ concentration of the atmosphere in the period 1860-1981. A sensitivity study was carried out to compare the importance of these impacts for the behaviour of fluxes and pools in biosphere, atmosphere and ocean. The Osnabriick Biosphere Model, a regionalized carbon flux model for the terrestrial biosphere, was coupled with a box diffusion Ocean model and a one-box atmosphere model. A regional land use pattern was derived from the World Atlas of Agriculture. Its dynamics were introduced using data of global land use changes. For the simulation of climatic variations, standardized changed levels as well as gradients of temperature and precipitation were used. In the period 1860-1981, land-use changes and the CO₂ fertilization effects are similarly important and roughly amount to 4/5 of the fossil source. Effects of potential climatic fluctuations may not exceed 1/5 of that amount.