Greenhouse gas inventories or GHG inventories are emission inventories of greenhouse gas (GHG). Scientists use inventories of natural and anthropogenic (human-caused) GHG emissions as tools when developing atmospheric models. Policy makers use inventories to develop strategies and policies for emissions reductions and to track the progress of those policies.
Regulatory agencies and corporations also rely on inventories to establish compliance records with allowable emission rates. Businesses, the public, and other interest groups use inventories to better understand the sources and trends in emissions.
Unlike some other air emission inventories, greenhouse gas inventories include not only emissions from source categories, but also removals by carbon sinks. These removals are typically referred to as carbon sequestration.
Greenhouse gas inventories typically use global warming potential (GWP) values to combine emissions of various greenhouse gases into a single weighted value of emissions.
Examples Some of the key examples of greenhouse gas inventories include: All Annex I countries are required to report annual emissions and sinks of greenhouse gases under the United Nations Framework Convention on Climate Change (UNFCCC) National governments that are Parties to the UNFCCC and/or the Kyoto Protocol are required to submit annual inventories of all anthropogenic greenhouse gas emissions from sources and removals from sinks. The Kyoto Protocol includes additional requirements for national inventory systems, inventory reporting, and annual inventory review for determining compliance with Articles 5 and 8 of the Protocol. Project developers under the Clean Development Mechanism of the Kyoto Protocol prepare inventories as part of their project baselines.
Greenhouse gas emissions accounting
Greenhouse gas emissions accounting is measuring the amount of greenhouse gases (GHG) emitted during a given period of time by a polity, usually a country but sometimes a region or city. Such measures are used to conduct climate science and climate policy.
There are two main, conflicting ways of measuring GHG emissions: production-based (also known as territorial-based) and consumption-based. The Intergovernmental Panel on Climate Change defines production-based emissions as taking place “within national territory and offshore areas over which the country has jurisdiction”. Consumption-based emissions take into account the effects of trade, encompassing the emissions from domestic final consumption and those caused by the production of its imports. From the perspective of trade, consumption-based emissions accounting is thus the reverse of production-based emissions accounting, which includes exports but excludes imports (Table 1).
The choice of accounting method can have very important effects on policymaking, as each measure can generate a very different result. Thus, different values for a National greenhouse gas Emissions Inventory (NEI) could result in a country choosing different optimal mitigation activities, the wrong choice based on wrong information being potentially damaging. The application of production-based emissions accounting is currently favoured in policy terms as it is easier to measure, but it is criticised in the literature principally for its inability to allocate emissions embodied in international trade/transportation and the potential for carbon leakage.
Almost all countries in the world are parties to the Paris Agreement, which requires them to provide regular production-based GHG emissions inventories to the United Nations Framework Convention on Climate Change (UNFCCC), in order to track both countries achievement of their nationally determined contributions and climate policies as well as regional climate policies such as the EU Emissions Trading Scheme (ETS), and the world's progress in limiting global warming.
Comparison of production based and consumption-based accounting
Over the last few decades emissions have grown at an increasing rate from 1.0% yr−1 throughout the 1990s to 3.4% yr−1 between 2000 and 2008. These increases have been driven not only by a growing global population and per-capita GDP, but also by global increases in the energy intensity of GDP (energy per unit GDP) and the carbon intensity of energy (emissions per unit energy). These drivers are most apparent in developing markets (Kyoto non-Annex B countries), but what is less apparent is that a substantial fraction of the growth in these countries is to satisfy the demand of consumers in developed countries (Kyoto Annex B countries). This is exaggerated by a process known as Carbon Leakage whereby Annex B countries decrease domestic production in place of increased importation of products from non-Annex B countries where emission policies are less strict. Although this may seem the rational choice for consumers when considering local pollutants, consumers are inescapably affected by global pollutants such as GHG, irrespective of where production occurs. Although emissions during the 2008 financial crisis, the longer-term trend of increased emissions has resumed.
Today, much international effort is put into slowing the anthropogenic release of GHG and resulting climate change. In order to set benchmarks and emissions targets for - as well as monitor and evaluate the progress of - international and regional policies, the accurate measurement of each country's NEI becomes imperative. + A comparison of the production-based and consumption-based national emissions inventories (NEI). CriteriaProduction-based NEIConsumption-based NEI Emissions coveredAdministered territoryGlobal AllocationDomestic productionDomestic consumption Allocation of tradeIncludes exports, not importsIncludes imports, not exports Mitigation focusDomestic activities including exportsDomestic activities and imports (exports excluded) ComparabilityConsistent with GDPConsistent with national consumption Consistent with trade policyNoYes Annex I emissions coverageLowerHigher ComplexityLowHigh TransparencyHighLow UncertaintyLower Higher Current country coverageRelatively highLow with current data Mitigation analysisDomestic mitigation onlyGlobal mitigation
Production-based accounting
As production-based emissions accounting is currently favoured in policy terms, its methodology is well established. Emissions are calculated not directly but indirectly from fossil fuel usage and other relevant processes such as industry and agriculture according to 2006 guidelines issued by the IPCC for GHG reporting. The guidelines span numerous methodologies dependent on the level of sophistication (Tiers 1–3 in Table 2). The simplest methodology combines the extent of human activity with a coefficient quantifying the emissions from that activity, known as an ‘emission factor’. For example, to estimate emissions from the energy sector (typically contributing over 90% of emissions and 75% of all GHG emissions in developed countries) the quantity of fuels combusted is combined with an emission factor - the level of sophistication increasing with the accuracy and complexity of the emission factor. Table 2 outlines how the UK implements these guidelines to estimate some of its emissions-producing activities.
+ Table 2. Some emissions producing activities and methods used to estimate emissions. IPCC tier represents one of three tiers, each tier indicating an additional layer of sophistication. These tiers indicate which method of emissions calculations is used from the IPCC 1996 Guidelines. Activity GHG IPCC Tier Method used to estimate emissions Public electricity and heat productionCO2 2 An emissions factor is applied to fuel consumption data from DUKES. Some data are also collected from individual point sources at generation facilities. The emissions factors are UK specific factors obtained by sampling average UK carbon content of fuels. Road transportationCO2, CH4, N2O 3 Emissions from road transport are estimated from a combination of total fuel consumption data taken from the Digest of UK Energy Statistics and fuel properties, and from a combination of drive related emission factors and road traffic data on fuel use, car type, miles driven, road types, and fuel type from the Department for Transport. Domestic aviation CO2, CH4, N2O3 Data from the Department for Transport and Civil Aviation Authority on aircraft movements is broken down by aircraft type at each UK airport. The model takes into account the lengths of time spent on different parts of an aircraft's take off and landing cycle and different types of aircraft used in the UK. Refrigeration and air conditioning equipmentHFC 2 Data on the numbers of UK domestic and commercial refrigerators is obtained from the UK Market Transformation Programme and activity data supplied by industry. Data on mobile air conditioning systems is obtained from the UK Society of Motor Manufacturers and Traders. Once the numbers and size of refrigerators is known, an emissions factor which was derived to reflect UK refrigeration fluids applied to estimate emissions Enteric FermentationCH4 2 Enteric fermentation is a digestive process in ruminant animals which produces methane. Emissions are estimated from animal production data from the June agricultural census. Emissions factors for milk producing cattle, lambs and deer are calculated using a tier 2 approach which takes into account the sizes, ages and types of UK animals. Agricultural soilsN2O1 and 2 The method involves estimating the contributions from the use of inorganic fertilizer, biological fixation of nitrogen by crops, ploughing in crop residues, cultivation of organic soils, spreading animal manure on land, and manures dropped by animals grazing in the field using data from DEFRA and the British Survey of Fertiliser Practice. For some of these areas IPCC default methods are used and for other UK specific methods are used. Wastewater handlingCH4, N2O2 The estimate is based on the work of Hobson et al. (1996) who estimated emissions of methane for the years 1990–95. Subsequent years are extrapolated on the basis of population. Sewage disposed to landfill is included in landfill emissions Emissions from burning wood are counted against the country where the trees were felled rather than the country where they are burnt.
Consumption-based accounting Consumption-based emissions accounting has an equally established methodology using Input-Output Tables. These "display the interconnection between different sectors of production and allow for a tracing of the production and consumption in an economy" and were originally created for national economies. However, as production has become increasingly international and the import/export market between nations has flourished, Multi-Regional Input-Output (MRIO) models have been developed. The unique feature of MRIO is allowing a product to be traced across its production cycle, "quantifying the contributions to the value of the product from different economic sectors in various countries represented in the model. It hence offers a description of the global supply chains of products consumed". From this, assuming regional- and industry-specific data for CO2 emissions per unit of output are available, the total amount of emissions for the product can be calculated, and therefore the amount of emissions the final consumer is allocated responsibility for.