Practical applications of uncertainty analysis for national greenhouse gas inventories∗

International policy-makers and climate researchers use greenhouse gas emissions inventory estimates in a variety of ways. Because of the varied uses of the inventory data, as well as the high uncertainty surrounding some of the source category estimates, considerable effort has been devoted to understanding the causes and magnitude of uncertainty in national emission inventories. In this paper we focus on two aspects of the rationale for quantifying uncertainty: (a) the direct benefits of the process of investigating uncertainty in terms of improvements in inventory methods and quality, and (b) the uses of the quantified uncertainty estimates in policy as a means of adjusting inventories used to determine compliance. We find that it is difficult to develop uncertainty estimates for a national inventory that account for significant types of uncertainty, are objective, and will be comparable across countries. Consequently, the quality of quantitative uncertainty data associated with national inventories is insufficient to warrant its use for policy purposes. While statistically valid methods for adjusting inventories to account for uncertainty exist, there is no unique method for adjusting inventory estimates to account for uncertainty, further complicating the issue of adjustments, and of reaching consensus on a method. The best use of uncertainty analysis may be in extracting lessons for improving the quality of inventory methods and data. In other words, the richest use of uncertainty estimates may come from the process of investigating data quality, which is instructive concerning the sources of uncertainty and means by which uncertainty can be reduced.