National Greenhouse Gas Inventories: Understanding Uncertainties vs. Potential for Improving Reliability

Abstract An investigation of the national Austrian greenhouse gas emission inventory allows reconstructing reliability and usability of such inventories. Overall uncertainty of the inventory (95% confidence interval) is just over 10% of the total emissions, with N2O from soils clearly providing the largest impact. Uncertainty of the trend - the difference between two years - is only about 5% points, as important sources like soil N2O are not expected to show different behavior between the years, and thus exhibit a high co variance. The result is very typical for industrialized countries, with subjective decisions of individuals during uncertainty assessment being responsible for the major part of discrepancies between countries. For this reason uncertainty assessment can not help to evaluate if emission targets have been met. Instead, for this purpose a more rigid emission accounting system is proposed, which allows for little individual flexibility in order to provide a harmonized evaluation not influenced by the respective targets. Such an accounting system may increase uncertainty in terms of greenhouse gas fluxes to the atmosphere. More importantly, it will decrease uncertainty in a comparison between countries and thus allow for a fair burden-sharing. Setting of post-Kyoto emission targets will require the evaluation of achievements, by an independent assessment of emissions. This can in part be achieved by emission inventory validation and thorough uncertainty assessment.