Greenhouse Gas Emissions

The availability of good, reliable and timely basic energy statistics and energy balances is fundamental for the estimation of greenhouse gas (GHG) emissions and to address global concerns about climate change. Basic energy statistics and energy balances are the main sources of data for the calculation of energy-related GHG emissions, because the IPCC Guidelines are based on the same conceptual framework. Countries are encouraged to make additional efforts to verify the compiled data and make any necessary adjustments to ensure that the calculated emissions are internationally comparable [IRES, Ch. XI, para. 11.34, PDF p. 154, 2018] — recommendations tracker row XI/11.34.

Climate change and GHG emissions: background

Human interference with the climate system, driven by the so-called “greenhouse effect”, started being acknowledged as a global problem in 1979, at the First World Climate Conference. Ten years later, in 1988, the IPCC was established by the United Nations Environment Programme (UNEP) and the World Meteorological Organization (WMO), with a mission to provide a clear scientific view of the knowledge on climate change and its potential environmental and socio-economic impacts [IRES, Ch. XI, para. 11.35, PDF pp. 154–155, 2018].

The latest available scientific assessment of climate change from IPCC at the time of IRES’s writing was the IPCC Fifth Assessment Report (AR5), published in 2013. The report underlines that “warming of the climate system is unequivocal” and that “it is extremely likely that more than half of the observed increase in global average surface temperature from 1951 to 2010 was caused by the anthropogenic increase in greenhouse gas concentrations and other anthropogenic forcings together.” AR5 not only corroborated but reinforced the findings of the IPCC Fourth Assessment Report (AR4), published in 2007. These assessments are consistent with ongoing climate observations reported by WMO. AR5 emphasizes that “continued emissions of GHGs will cause further warming and changes in all components of the climate system”, and that “limiting climate change will require substantial and sustained reductions of greenhouse gas emissions” [IRES, Ch. XI, para. 11.36, PDF p. 155, 2018].

The international community responded to growing concerns about climate change by putting in place three key international treaties: the United Nations Framework Convention on Climate Change (UNFCCC), the Kyoto Protocol to UNFCCC, and the Paris Agreement under UNFCCC. Reporting on GHG emissions, including emissions from the energy sector, is a key obligation of the Parties to these treaties [IRES, Ch. XI, para. 11.37, PDF p. 155, 2018].

IPCC Guidelines for estimating GHG emissions

An important function of IPCC is to provide methodological guidance on the estimation of national GHG emissions as part of the preparation of national GHG inventories. The first consolidated and extensive guidance on the estimation of GHG emissions was issued by IPCC in 1995, and revised and published as the Revised 1996 IPCC Guidelines for National Greenhouse Gas Inventories (IPCC 1997). It was followed by the Good Practice Guidance and Uncertainty Management in National Greenhouse Gas Inventories (IPCC 2000) and the Good Practice Guidance for Land Use, Land-Use Change and Forestry (IPCC 2003) [IRES, Ch. XI, para. 11.38, PDF p. 155, 2018].

The 2006 IPCC Guidelines for National Greenhouse Gas Inventories were prepared at the invitation of UNFCCC. According to decision 24/CP.19 of the Conference of the Parties to UNFCCC (Warsaw, Poland, 11–23 November 2013), Annex I Parties to UNFCCC are required to use the 2006 IPCC Guidelines in their national GHG inventory submissions from 2015. While there is no formal decision on the use of the 2006 IPCC Guidelines by non-Annex I Parties to date, some developing countries have started using the Guidelines in preparing national submissions on climate change, and it is likely that more will follow [IRES, Ch. XI, para. 11.39, PDF p. 155, 2018].

The IPCC Guidelines address emissions of direct and indirect GHGs. The direct GHGs covered by the Guidelines are carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulphur hexafluoride (SF6) and some others. The indirect GHGs considered in the Guidelines are nitrogen oxides (NOX), ammonia (NH3), non-methane volatile organic compounds (NMVOC), carbon monoxide (CO) and sulphur dioxide (SO2) [IRES, Ch. XI, para. 11.40, PDF p. 155, 2018].

The methods for estimating GHG emissions in the IPCC Guidelines are structured into a three-tier sectoral approach and a reference approach; these are described in Box 11.1 [IRES, Ch. XI, para. 11.41, PDF p. 155, 2018].

Box 11.1 — Methods for the estimation of GHG emissions from fossil fuel combustion

Sectoral approach

• Tier 1 method. Used to estimate emissions from all sources of combustion on the basis of the quantities of fuel combusted (usually taken from national energy statistics) and average (default) emission factors. This method is fairly accurate for CO2 emissions, but much less so for non-CO2 gases because emission factors for these gases may depend considerably on the combustion technology and operating conditions.
• Tier 2 method. In the Tier 2 method for energy, emissions from combustion are estimated from similar fuel statistics as in the Tier 1 method, but country-specific emission factors are used instead of the Tier 1 defaults. Since available country-specific emission factors might differ for different fuels, combustion technologies or individual plants, activity data could be further disaggregated to properly reflect such disaggregated sources. Tier 2 estimates can be more accurate than Tier 1 estimates but require more data.
• Tier 3 method. In the Tier 3 method for energy, either detailed emission models or measurements and data at individual plant level are used where appropriate. Properly applied, the Tier 3 method should provide better estimates, especially for non-CO2 emissions, though at the cost of more extensive data requirements and greater estimation efforts.

Reference approach

The reference approach, which is applied to CO2 emissions from fuel combustion, can be used as an independent check of the sectoral approach and as a first-order estimate of national GHG emissions. This is a “top-down” approach assuming that all carbon coming into a national economy is either released into the atmosphere in the form of a greenhouse gas, or diverted (e.g., into increases of fuel stocks). The reference approach methodology is implemented in 5 steps:

1. Estimate apparent fuel consumption in original units
2. Convert to a common energy unit
3. Multiply by carbon content to compute the total carbon
4. Compute the excluded carbon
5. Correct for unoxidised carbon and convert to CO2 emissions

The reference approach requires statistics on the production of fuels, on their external trade, as well as on changes in their stocks. It also requires some data on the consumption of fuels used for non-energy purposes.

[IRES, Ch. XI, Box 11.1, PDF p. 156, 2018]

Energy emissions and energy statistics

The “energy sector” in the IPCC definition includes exploration and exploitation of primary energy sources, conversion of primary energy sources into more useable energy forms in refineries and power plants, transmission and distribution of fuels, and the use of fuels in stationary and mobile applications. In terms of emission sources, two major categories are distinguished:

(a) Emissions from fuel combustion — further disaggregated into the subcategories of energy industries, manufacturing industries and construction, transport, other sectors, and non-specified;

(b) Fugitive emissions — intentional or unintentional releases of gases during the production, processing, transmission, storage and use of fuels, further disaggregated into emissions from solid fuels (such as methane emissions from coal mining) and emissions from oil and natural gas.

[IRES, Ch. XI, para. 11.42, PDF p. 156, 2018]

The energy sector is the major source of GHG emissions. According to the IPCC AR5, around 70 per cent of global GHG emissions in 2010 related to energy supply and use, with CO2 from fuel combustion accounting for a major part. It is therefore important, even critical, to accurately estimate energy-related emissions and CO2 emissions in particular [IRES, Ch. XI, para. 11.43, PDF p. 157, 2018].

The emissions equation

Estimates are normally done at the level of individual emission sources that may correspond to a physical facility (e.g. a power plant) or to an industrial or economic group (e.g. cement production). These estimates are then summed up to obtain sectoral and national totals by individual gases, as well as the total of all gases calculated as a weighted average in terms of the so-called CO2-equivalent. The number of individual source categories may vary depending on data availability, the organizational and methodological frameworks of the assessment, and the resources available. For each individual source category, CO2 emissions are often estimated using an equation of the type:

Emissionsfuel = FuelCombustedfuel × EmissionFactorfuel, tech

where Emissionsfuel are CO2 emissions by type of fuel (for a given source category), FuelCombustedfuel is the quantity of fuel combusted, and EmissionFactorfuel, tech is the CO2 emission factor by type of fuel and combustion technology used. Sometimes a carbon oxidation factor is added to this equation. While the equation is simple, estimating values for the amount of fuel combusted and selecting emission factors consistent with the definitions of the IPCC emission categories may be difficult [IRES, Ch. XI, para. 11.44, PDF p. 157, 2018].

Data quality dependence

Regardless of the tier used, consumption of fuels by fuel/product type is the very first basic step in the estimation of CO2 emissions from fuel combustion. If this basic step is not done properly, the subsequent steps cannot result in an accurate estimate. Data on the production and consumption of fuels and energy products are part of national energy statistics, normally in the form of national energy balances. It is therefore unequivocal that the quality of GHG estimates depends critically on the quality of national energy statistics — see Data Quality. This dependence is fully recognized by the IPCC Guidelines, which encourage the use of fuel statistics collected by official national bodies, as this usually provides the most appropriate and accessible data [IRES, Ch. XI, para. 11.45, PDF p. 157, 2018].

If national data sources are unavailable or have gaps, IPCC suggests using data from international organizations (based normally on national submissions from countries). The two main sources of international energy statistics are the United Nations Statistics Division (UNSD) and the International Energy Agency (IEA). Both collect data from the national administrations of their member countries through questionnaires (thus collecting “official data”), and they exchange data to ensure consistency and prevent duplication of efforts by reporting countries [IRES, Ch. XI, para. 11.46, PDF p. 157, 2018].

Estimating non-CO2 emissions from fuel combustion normally requires more specific methods than for CO2 emissions and more detailed information, such as the characteristics of fuel composition, combustion conditions, combustion technologies and emission control methods. Specific methods and data are also used for estimating fugitive CO2 and non-CO2 emissions. Such methods and associated data requirements can be found in the corresponding sections of the IPCC Guidelines. It is quite clear also in the Guidelines that for these emissions national energy statistics are indispensable for obtaining a solid emissions estimate [IRES, Ch. XI, para. 11.47, PDF p. 157, 2018].

A number of references related to GHG emission estimates are provided in the bibliography to IRES [IRES, Ch. XI, para. 11.48, PDF p. 157, 2018].

Related

• IRES Chapter XI — Uses of Basic Energy Statistics and Balances — the chapter digest this page supports (Section D)
• Intergovernmental Panel on Climate Change — author of the GHG-inventory Guidelines lineage this page’s Box 11.1 draws from
• United Nations Framework Convention on Climate Change — the treaty framework that mandates the 2006 IPCC Guidelines for Annex I Parties from 2015
• Energy Balance — the accounting framework providing the fuel-consumption data at the base of every emissions estimate, per para 8.3(e)
• Energy Products — the fuel/product-type detail the emissions equation and reference approach operate on
• Data Quality — the quality dimensions GHG-estimate accuracy depends on
• Energy Indicators — Table 11.3’s ENV1 indicator is built directly on GHG emissions data