J.G., Kirschbaum, M.U.F., Kurz, W.A., Sanz, M.-J., Schlamadinger, B.,
Abstract. The capacity to partition the natural, indirect, and direct human-induced effects on terrestrial carbon (C) sources and sinks is a fundamental prerequisite to be able to predict future dynamics of the net terrestrial C sink and its contribution to atmospheric CO2 growth. It will take a number of years before we can fully attribute quantitative estimates to the contribution of various C processes to the net C balance. In a policy context, factoring out natural and indirect human-induced effects on C sources and sinks from the direct human-induced influences is seen as a requirement of a C accounting approach that establishes a clear and unambiguous connection between human activities and the assignment of C credits and debits.
We present options for factoring out these various groups of influences, including the legacies from forest management prior to the reference year (1990):
i) selecting longer accounting or measurement periods to reduce the effects of interannual variability;
ii) correction of national inventory results for inter-annual variability;
iii) use of activity-based accounting and C response curves;
iv) use of baseline scenarios or benchmarks at the national level; and
v) stratification of the landscape into units with distinct average C stocks.
Other, more sophisticated modeling approaches (e.g., demographic models in combination with forest inventories; process-based models) are possible options for future C accounting systems but their complexity and data requirements make their present adoption more difficult in an inclusive international C accounting system.
Keywords: AFOLU; carbon cycle; forests; Kyoto Protocol; LULUCF; Marrakech Accords; C sink processes; C source processes.