The Carbon Sink Strength of Forests in Europe: a Synthesis of Results

The terrestrial sink for carbon is estimated to be of the order of 2±1 Gt C — y-1 (IPCC 2000) However the accumulation of C02 in the atmosphere as documented by atmospheric stations around the globe for the past 40 years can vary by a factor of two from one year to the next, which is equivalent to several Gt C per year. Such changes reflect interannual shifts in the carbon uptake of land and oceans of the same magnitude as the average uptake itself. Fossil fuel emissions changes tend to be smooth in time: year-to-year variations are less than 4% of the total. Both ocean data and global ocean carbon models suggest that the air-sea carbon fluxes are rather stable. The land biosphere may thus explain most of the observed C02 interannual growth rate variation. Several studies, utilizing different techniques, have shown that, in the northern hemisphere, the terrestrial biosphere is currently absorbing carbon (Dixon et al. 1994; Myneni et al. 1997). Most, if not all, of these methods depend on indirect estimates of the carbon fluxes, like isotopic analysis and inversion methods from C02 concentrations measurements (Ciais et al. 1995), remote sensing (Myneni et al. 1997), growth trend analysis (Dixon et al. 1994; Kauppi et al. 1992), and modeling. All these methods provide the necessary global and continental scale perspective for carbon balance calculations.