Policy Brief #01,  December 2007, highlights issues and challenges arising from uncertainty in estimates of greenhouse gas (GHG) emissions and removals, explores how this uncertainty can be dealt with, and points to the implications of uncertainty analysis for policymakers. The information contained in this briefing is from the Second International Workshop on Uncertainty in Greenhouse Gas Inventories, IIASA, 27–28 September 2007.


  • Calculations of greenhouse gas emissions (GHG) contain uncertainty for a variety of reasons such as the availability of sufficient and appropriate data and the techniques to process them.
  • Understanding the basic science of GHG gas sources and sinks requires an understanding of the uncertainty in their estimates.
  • Schemes to reduce human-induced global climate impact rely on confidence that inventories of GHG emissions allow the accurate assessment of emissions and emission changes. To ensure such confidence it is vital that the uncertainty present in emissions estimates is transparent. Clearer communication of the forces underlying inventory uncertainty may be needed so that the implications are better understood.
  • Uncertainty estimates are not necessarily intended to dispute the validity of national GHG inventories but they can help improve them.
  • Uncertainty is higher for some aspects of a GHG inventory than for others. For example, past experience shows that, in general, methods used to estimate nitrous dioxide (N2O) emissions are more uncertain than methane (CH4) and much more uncertain than carbon dioxide (CO2). If uncertainty analysis is to play a role in cross sectoral or international comparison or in trading systems or compliance mechanisms, then approaches to uncertainty analysis need to be robust and standardized across sectors and gases, as well as among countries.
  • Uncertainty analysis helps to understand uncertainties: better science helps to reduce them. Better science needs support, encouragement and greater investment. Full Carbon Accounting (FCA) – or full accounting of emissions and removals, including all GHGs – in national GHG inventories is important for advancing the science.
  • FCA is a prerequisite for reducing uncertainties in our understanding of the global climate system. From a policy viewpoint, FCA could be encouraged by including it in reporting commitments, but it might be separated from negotiation of reduction targets.
  • Future climate agreements will be made more robust, explicitly accounting for the uncertainties associated with emission estimates.