The science of greenhouse gases: Uncertainties in sources and sinks, and implications for verification

Our present knowledge about the carbon cycle, governing the sources and sinks of the most important anthropogenically influenced greenhouse gas CO₂ is still far from satisfactory in the quantitative sense. This statement holds on all scales, from global to local. Therefore, long-term atmospheric measurements, on many locations, are absolutely needed, both to improve our quantitative knowledge of the carbon cycle, and to create a firm verification basis for mitigation measures. Yet, it is an illusion to think that source/sink characterisation by these atmospheric measurements will get to the detail that Kyoto Protocol actions can be surveyed and verified on a national level in the coming years (if ever !). Therefore, a combination of validation (on project basis) and verification (on a continental scale) is proposed. Mitigation measures through mere sink enhancement (afforestation) are at best a temporary solution. Therefore, not much (political) effort should be invested into this option.