Dealing
with uncertainty in greenhouse gas inventories

Since the mid-1990s developed-country parties to the United Nations Framework Convention on Climate Change (UNFCCC) have been publishing annual or periodic inventories of greenhouse gas (GHG) sources and sinks to keep track of changes and estimate their uncertainty. Seventeen papers from the second Uncertainty Workshop held at IIASA on the uncertainty in greenhouse gas inventories have just been published in a Special Issue of the Springer journal Climatic Change. While the Intergovernmental Panel on Climate Change (IPCC) stresses the value of conducting uncertainty analyses for inventories and offers guidance on executing them, the recommendations from the new research go well beyond any suggestions it has made to date.

A major finding in the new research was the lack of transparency regarding the methodologies used in national inventories. Researchers found that comparability of national inventories and their uncertainties can be achieved only if details of the methodologies used in analyses are clearly laid out and the results understood in a methodology-dependent context. Researchers found that as uncertainty analyses are still too inconsistent from country to country, inter-country emission-uncertainty analyses/comparisons should not be carried out under the Kyoto Protocol in its current form, which looks at the technosphere and part of the terrestrial biosphere. Thus, as an alternative for the time being, for ideally, global compliance purposes, only the best-known GHGs and subsystems (basically carbon dioxide (CO2) from fossil fuel burning) could be covered in country reporting. The non-CO2 GHGs and the entire biosphere, could fall under global reporting. Moreover, the methodology recommended by IPCC GHG inventory guidelines, which recommends splitting emission sources into direct and indirect emissions for analysis using error propagation methodology, was found to be too simplistic. Covering these sources as statistically interdependent with a more elaborate Monte Carlo algorithm, showed greater uncertainty in overall national GHG inventory uncertainty than was obtained using the IPCC method.

The current partial accounting approach to national inventories under the UNFCCC and the Kyoto Protocol was also critiqued. Researchers strongly recommended verified full greenhouse gas accounting, including all sources and sinks of both the technosphere and the biosphere, considered continuously over time, as a prerequisite for reducing uncertainties. The entire system should be looked at bottom-up and top-down so that the system’s subsystems can be understood and the uncertainties reduced from both sides (top-down and bottom-up). However, such a bottom-up/top-down monitoring system is not yet in place and it will still take some time until such a system can be implemented.

The current policy approach of ignoring inventory uncertainty altogether at the country, sectoral, corporate, or other level, was also deemed problematical, as uncertainty is inherently higher for some GHGs and sectors of an inventory than others. For instance, nitrous oxide emission estimates tend to be more uncertain than those of methane. In the design of future policy agreements, researchers argued, some GHG inventory components would benefit from differentiated treatment. Researchers called on policymakers to decide whether a post-Kyoto agreement will have clear rules for incorporating uncertainty and which parts of an emissions inventory will undergo stringent compliance; and which will be consistently monitored and will undergo stringent reporting (see paragraph 2).

Researchers also considered the fact that inventory uncertainty is not considered to have a bearing on trading of emissions “permits.” They advised incorporating reliably and quantitatively assessed uncertainty into emissions trading to allow the required level of emission reductions to be more precisely determined.

The researchers have recently met for a third Uncertainty Workshop held in September 2010 at the Lviv Polytechnic National University and co-sponsored by IIASA. It discussed a number of approaches to addressing uncertainty to improve national inventories and thereby strengthen their usefulness under a compliance and/or global monitoring and reporting framework.

Last edited: 28 August 2012