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Verifying Greenhouse Gas Emissions: Methods to Support International Climate Agreements
compared to International Energy Agency (IEA) data, and statistics used to estimate agriculture emissions are compared to UN Food and Agriculture Organization (FAO) data. If anomalies are identified by this analysis, the review teams dig deeper into that country’s methods and data. Unless otherwise indicated, the inventory methods discussed in this chapter pertain to developed countries.
Reporting requirements are much less rigorous for developing countries. Emission inventories are reported only periodically in conjunction with a broader national report of climate change programs and activities. There is no set frequency for these national reports and their submission often depends on the provision of international funding. As a result, most developing countries have submitted only one national inventory to date. Reporting of only CO2, CH4, and N2O is required and only at the sector level, not for categories within each sector. Developing countries are not required to provide emissions trends over time or to document methods and data sources, and their inventories are not reviewed.
The IPCC’s National Greenhouse Gas Inventory Program is responsible for developing methods for creating national inventories of greenhouse gas emissions. The IPCC guidelines describe how to estimate national emissions of CO2, CH4, N2O, SF6, PFCs, and HFCs from anthropogenic sources and sinks using national statistics (activity data) and activity-based emission factors for the four sectors. Guidance is also provided on data sources, data collection methods, quantification of uncertainties, management of inventories, quality assurance and control, documentation, and data archiving. The guidelines have evolved over time to include more emissions sources and to improve and standardize the methodologies. The first edition of the IPCC guidelines was completed and approved in 1994; the most recent (2006) edition has not yet been endorsed by the UNFCCC and is thus not yet used for reporting purposes. However, the 2006 guidelines are expected to be adopted as the basis for reporting national inventories beginning in 2015.
The IPCC methodologies are intended to yield national greenhouse gas inventories that are transparent, complete, accurate, consistent over time, and comparable across countries. Because different countries have different capacities to produce inventories, the guidelines lay out tiers of methods (typically three) for each emissions source, with higher tiers (Tier 3 is normally the highest) being more complex and/or resource intensive than lower tiers. The higher-tier methods usually incorporate country-specific conditions, data, and emission factors and are thus considered more accurate than the lower-tier methods. For example, the Tier 1 method for calculating CO2 emissions from stationary combustion uses default emission factors for each fuel type, whereas the Tier 2 method requires each country to develop and use country-specific emission factors for each fuel type (see detailed guidance in Gómez et al., 2006). The Tier 3 method uses emission factors that are not only country-specific, but also differentiated by technology and operating conditions. The choice of method used for a particular source in a particular country depends on (1) the importance of that source to the level and trend of emissions in that country and (2) the resources available to prepare the inventory. Countries are encouraged to use country-specific data and emission factors to the extent possible. However, they are not expected to use higher-tier methods if doing so would jeopardize their ability to estimate other important emissions sources. The scope of the effort to prepare the U.S. inventory is described in Box 2.1.
Implications for Monitoring and Verification
Although multiple greenhouse gases are emitted from multiple activities in multiple sectors, the monitoring and verification problem is comparatively simple because only a few activities and greenhouse gases are responsible for the large majority of emissions. Table 2.1 summarizes emissions by sector for Annex I countries as a group, and Figure 2.1 compares emissions across sectors for Annex I and non-Annex I countries. The most important simplifying message is that well over 90 percent of global greenhouse gas emissions are in the energy and AFOLU sectors, making these sectors an obvious focus for monitoring. Energy alone is responsible for almost 90 percent of total net greenhouse gas emissions from Annex I countries and more than 40 percent of net emissions from developing countries. In both groups, CO2 from fossil-fuel