Final Government Distribution Annex II IPCC AR6 WGIII
Table of Contents
Annex II: Definitions, Units & Conventions .......................................................................................... 1
Part I: Definitions and units ................................................................................................................ 3
1. Classification schemes for countries and areas ........................................................................... 3
2. Standard units and unit conversions............................................................................................ 6
Part II: Conventions .......................................................................................................................... 10
3. Levelised cost metrics ............................................................................................................... 10
4. Growth rates .............................................................................................................................. 12
5. Trends calculations between years and over decades ............................................................... 13
6. Primary energy accounting ....................................................................................................... 13
7. The concept of risk.................................................................................................................... 13
8. GHG emission metrics .............................................................................................................. 16
Part III: Emissions Datasets .......................................................................................................... 18
9. Historical data ........................................................................................................................... 18
10. Indirect emissions ................................................................................................................... 29
Part IV: Assessment methods ........................................................................................................... 30
11. Methodology adopted for assessing the feasibility of mitigation response options ................ 30
12. Methodology adopted for assessing synergies and trade-offs between mitigation options and
the SDGs ....................................................................................................................................... 32
References ......................................................................................................................................... 33
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Final Government Distribution Annex II IPCC AR6 WGIII
This annex on Definitions, Units and Conventions provides background information on material used
in the Working Group III contribution to the Intergovernmental Panel on Climate Change (IPCC) Sixth
Assessment Report (WGIII AR6). The material presented in this annex documents metrics and common
datasets that are typically used across multiple chapters of the report. In a few instances there are no
updates to what was adopted by WGIII during the production of the Fifth Assessment Report (AR5), in
which case this annex refers to Annex II of AR5 (Krey et al. 2014).
The annex comprises four parts: Part I introduces standards, metrics and common definitions adopted
in the report; Part II presents methods to derive or calculate certain quantities and identities used in the
report; Part III provides more detailed background information about common data sources; and Part
IV presents integrative methodologies used in the assessment. While this structure may help readers to
navigate through the annex, it is not possible in all cases to unambiguously assign a certain topic to one
of these parts, naturally leading to some overlap between the parts.
Part I: Definitions and units
1. Classification schemes for countries and areas
In this report, three different levels of classification are used as a standard to present the results of
analysis. The basis for the classification is the UN Statistics Division Standard Country or Area Codes
for Statistical Use, also known as the M49 Standard (UNSD 1999). This covers geographical regions,
and also identifies developed regions, developing regions and least developed countries.
The high-level classification has six categories (Table 1): one for all developed countries and five
covering developing countries. The high-level classification is an expansion of the RC5 (Regional
Categorisation 5) adopted in WG III AR5, with Africa and the Middle East now identified separately.
The intermediate-level classification (ten categories) divides Developed Countries into three
geographical regions, and Asia and Developing Pacific into three sub-regions. The low-level
classification (twenty-one regions) further sub-divides Developed Countries, Latin America and the
Caribbean, Africa and Asia.
The high- and intermediate-level classification schemes reflect schemes used in many global models
and statistical sources. The sectoral and cross-cutting chapters of the report, which go into more detail,
may make use of the low level-classification. Where the report synthesises data, only these standard
classification schemes have been used. On occasions, the underlying literature may deviate from the
standard classification scheme and direct citations may unavoidably refer to alternative classifications.
This is dealt with on a case-by-case basis and does not imply any endorsement of the scheme used in
the underlying literature by the IPCC or the authors of this report.
The detailed composition of countries and areas to the low-level classification is shown in section 1.1.
The classification scheme deviates from the UN regional classification to ensure that Annex I, Annex
II and non-Annex I countries as defined under the UN Framework Convention on Climate Change
(UNFCCC) are distinguished. Some Annex I countries in Western Asia and countries in Eastern Europe
which are not members of the European Union are allocated to Eastern Europe and West-Central Asia
(EEA). In AR5, these formed part of the Economies in Transition group. The remainder of Western
Asia (non-Annex I) is allocated to the Middle East.
Following the practice of the UN Statistics Division, we note that the designations employed and the
presentation of material in this report do not imply the expression of any opinion by the United Nations,
the IPCC or the authors of this report concerning the legal status of any country, territory, city or area
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Final Government Distribution Annex II IPCC AR6 WGIII
or of its authorities, or concerning the delimitation of its frontiers or boundaries. The term “country” as
used in this material also refers, as appropriate, to territories or areas.
1.1. Low level of regional classification
Western Africa: Cabo Verde, Côte d'Ivoire, Ghana, Nigeria, Saint Helena, Ascension and Tristan da
Cunha, Benin, Burkina Faso, Gambia (the), Guinea, Guinea-Bissau, Liberia, Mali, Mauritania, Niger
(the), Senegal, Sierra Leone, Togo
Eastern Africa: British Indian Ocean Territory (the), French Southern Territories (the), Kenya,
Mauritius, Mayotte, Réunion, Seychelles, Zimbabwe, Burundi, Comoros (the), Djibouti, Eritrea,
Ethiopia, Madagascar, Malawi, Mozambique, Rwanda, Somalia, South Sudan, Uganda, Tanzania,
United Republic of, Zambia
Southern and middle Africa: Botswana, Eswatini, Namibia, South Africa, Lesotho, Cameroon, Congo
(the), Equatorial Guinea, Gabon, Angola, Central African Republic (the), Chad, Congo (the Democratic
Republic of the), Sao Tome and Principe
Northern Africa: Algeria, Egypt, Libya, Morocco, Tunisia, Western Sahara, Sudan (the)
Middle East: Bahrain, Iran (Islamic Republic of), Iraq, Israel, Jordan, Kuwait, Lebanon, Oman, Qatar,
Saudi Arabia, Palestine, State of, Syrian Arab Republic, United Arab Emirates (the), Yemen
Caribbean: Anguilla, Antigua and Barbuda, Aruba, Bahamas (the), Barbados, Bonaire, Sint Eustatius
and Saba, Virgin Islands (British), Cayman Islands (the), Cuba, Curaçao, Dominica, Dominican
Republic (the), Grenada, Guadeloupe, Jamaica, Martinique, Montserrat, Puerto Rico, Saint Barthélemy,
Saint Kitts and Nevis, Saint Lucia, Saint Martin (French part), Saint Vincent and the Grenadines, Sint
Maarten (Dutch part), Trinidad and Tobago, Haiti, Turks and Caicos Islands (the), Virgin Islands (U.S.)
Meso America: Belize, Costa Rica, El Salvador, Guatemala, Honduras, Mexico, Nicaragua, Panama
South America: Argentina, Bolivia (Plurinational State of), Bouvet Island, Brazil, Chile, Colombia,
Ecuador, Falkland Islands (the) [Malvinas], French Guiana, Guyana, Paraguay, Peru, South Georgia
and the South Sandwich Islands, Suriname, Uruguay, Venezuela (Bolivarian Republic of)
USA & Canada: United States of America (the), Canada
Greenland, Bermuda & others: Bermuda, Greenland, Saint Pierre and Miquelon
Eastern Asia: China, Korea (the Republic of), Korea (the Democratic People's Republic of), Mongolia
India & Sri Lanka
Rest of Southern Asia: Maldives, Pakistan, Afghanistan, Bangladesh, Bhutan, Nepal
South-East Asia: Brunei Darussalam, Indonesia, Malaysia, Philippines (the), Singapore, Thailand,
Viet Nam, Cambodia, Lao People's Democratic Republic (the), Myanmar, Timor-Leste
Developing Pacific: Fiji, New Caledonia, Papua New Guinea, Solomon Islands, Vanuatu, Guam,
Marshall Islands (the), Micronesia (Federated States of), Nauru, Northern Mariana Islands (the), Palau,
United States Minor Outlying Islands (the), Kiribati, American Samoa, Cook Islands (the), French
Polynesia, Niue, Pitcairn, Samoa, Tokelau, Tonga, Wallis and Futuna, Tuvalu
Northern and Western Europe: Åland Islands, Denmark, Estonia, Faroe Islands (the), Finland,
Iceland, Ireland, Isle of Man, Latvia, Lithuania, Norway, Svalbard and Jan Mayen, Sweden, United
Kingdom of Great Britain and Northern Ireland (the), Austria, Belgium, France, Germany,
Liechtenstein, Luxembourg, Monaco, Netherlands (the), Switzerland, Guernsey, Jersey
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Southern and eastern Europe: Andorra, Cyprus, Croatia, Gibraltar, Greece, Holy See (the), Italy,
Malta, Portugal, San Marino, Slovenia, Spain, Bulgaria, Czechia, Hungary, Poland, Romania, Slovakia,
Turkey, Albania, Bosnia and Herzegovina, Montenegro, Serbia, Ukraine
Australia & New Zealand
Asia-Pacific Developed (others): Japan, Christmas Island, Cocos (Keeling) Islands (the), Heard Island
and McDonald Islands, Norfolk Island
Eastern Europe and West-Central Asia1: Belarus, Russian Federation (the), Republic of North
Macedonia, Moldova (the Republic of), Armenia, Azerbaijan, Georgia, Kazakhstan, Kyrgyzstan,
Tajikistan, Turkmenistan, Uzbekistan
International shipping
International Aviation
1.2. High, intermediate and low levels of regional classification
Table 1 below presents the high, intermediate and low levels of the classification scheme. For country
mapping to the low level of regional classification see section 1.1 above.
Table: 1 | Classification schemes for countries and areas
WGIII AR6
High Level (6) Intermediate level (10) Low Level (21)
USA & Canada
North America
Greenland, Bermuda + others
Northern and western Europe
Developed Countries (DEV) Europe
Southern and eastern Europe
Australia & New Zealand
Asia-Pacific Developed
Asia-Pacific Developed (others)
Eastern Europe and West- Eastern Europe and West-Central Eastern Europe and West-Central
Central Asia (EEA) Asia Asia
Caribbean
Latin America and Caribbean
Latin America and Caribbean Meso America
(LAM)
South America
Western Africa
Eastern Africa
Africa (AF) Africa
Southern and middle Africa
Northern Africa
FOOTNOTE1 In some instances in the report, this region might be labelled: Eurasia.
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Middle East (ME) Middle East Middle East
Eastern Asia Eastern Asia
Asia and developing Pacific India & Sri Lanka
(APC) Southern Asia
Rest of Southern Asia
South-East Asia and developing South-East Asia
Pacific Developing Pacific
International shipping,
International Shipping & Aviation
International Aviation
2. Standard units and unit conversions
The following sections introduce standard units and unit conversions used throughout this report.
2.1. Standard units
Standard units of measurements include Système International (SI) units, SI-derived units, and other
non-SI units as well the standard prefixes for basic physical units.
Table: 2 | Système International (SI) units
Physical Quantity Unit Symbol
Length meter m
Mass kilogram kg
Time second s
Thermodynamic temperature kelvin K
Amount of Substance mole mol
Table: 3 | Special names and symbols for certain SI-derived units.
Physical Quantity Unit Symbol Definition
Force Newton N kg m s^2
Pressure Pascal Pa kg m^–1 s^–2 (= N m^–2)
Energy Joule J kg m^2 s^–2
Power Watt W kg m^2 s^–3 (= J s^–1)
Frequency Hertz Hz s^–1 (cycles per second)
Ionizing Radiation Dose sievert Sv J kg^-1
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Table: 4 | Non-SI standard units.
Monetary units Unit Symbol
Currency (Market Exchange Rate, MER) constant US Dollar 2015 USD2015
Currency (Purchasing Power Parity, PPP) constant International Dollar Int$2015
2015
Emission- and Climate- related units
Unit Symbol
Emissions Metric tonnes t
CO2 Emissions Metric tonnes CO2 tCO2
CO2-equivalent Emissions2 Metric tonnes CO2-equivalent tCO2-eq
Abatement Costs and Emissions Prices/Taxes constant US Dollar 2015 USD2015 /t
per metric tonnes
CO2 concentration or Mixing Ratio (μmol mol–1) Parts per million (10^6) ppm
CH4 concentration or Mixing Ratio (nmol mol–1) Parts per billion (10^9) ppb
N2O concentration or Mixing Ratio (nmol mol–1) Parts per billion (10^9) ppb
2
Radiative forcing Watts per square meter W/m
Energy-related units Unit Symbol
Energy Joule J
Electricity and Heat generation Watt Hours Wh
Power (Peak Capacity) Watt (Watt thermal, Watt W (Wth, We)
electric)
Capacity Factor Percent %
Technical and Economic Lifetime Years yr
Specific Energy Investment Costs US Dollar 2015 per kW USD2015 /kW
(peak capacity)
Energy Costs (e.g., LCOE) and Prices constant US Dollar 2015 per GJ USD2015 /GJ and
or US Cents 2015 per kWh USct2015 /kWh
Passenger-Distance passenger-kilometer pkm
Payload-Distance3 tonne-kilometer tkm
Land-related units Unit Symbol
Area Hectare ha
Note that all monetary and monetary-related units are expressed in constant US Dollar 2015 (𝑈𝑆𝐷2015)
or constant International Dollar 2015 (𝐼𝑛𝑡$2015 ).
Table: 5 | Prefixes for basic physical units.
Multiple Prefix Symbol Fraction Prefix Symbol
1E+21 zeta Z 1E-01 deci d
1E+18 exa E 1E-02 centi c
1E+15 peta P 1E-03 milli m
FOOTNOTE 2 A measure of aggregate greenhouse gas GHG emissions. This report uses the GHG metric Global
Warming Potential with a time horizon of 100 years (GWP100); for details see section 8.
FOOTNOTE 3 The is a unit of measure of freight transport which represents the transport of one tonne of goods
(including packaging and tare weights of intermodal transport units) by a given transport mode (road, rail, air, sea,
inland waterways, pipeline etc.) over a distance of one kilometre. The tonne measure here is not the same unit of
measure as metric tonnes earlier in the third row of Table 4.
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Final Government Distribution Annex II IPCC AR6 WGIII
1E+12 tera T 1E-06 micro μ
1E+09 giga G 1E-09 nano n
1E+06 mega M 1E-12 pico p
1E+03 kilo k 1E-15 femto f
1E+02 hecto h 1E-18 atto a
1E+01 deca da 1E-21 zepto z
2.2. Physical units conversion
Table: 6 | Conversion table for common mass units (IPCC 2001).
To: kg t lt St lb
From: multiply by:
Kilogram kg 1 1.00E-03 9.84E-04 1.10E-03 2.20E+00
Tonne t 1.00E+03 1 9.84E-01 1.10E+00 2.20E+03
long ton lt 1.02E+03 1.02E+00 1 1.12E+00 2.24E+03
short ton st 9.07E+02 9.07E-01 8.93E-01 1 2.00E+03
Pound lb 4.54E-01 4.54E-04 4.46E-04 5.00E-04 1
Table: 7 | Conversion table for common volumetric units (IPCC 2001).
To: gal US gal UK bbl ft3 l m3
From: multiply
by:
US Gallon gal 1 8.33E-01 2.38E- 1.34E- 3.79E 3.80E
US 02 01 +00 -03
UK/Imperial gal 1.20E 1 2.86E- 1.61E- 4.55E 4.50E
Gallon UK +00 02 01 +00 -03
Barrel bbl 4.20E 3.50E+01 1 5.62E 1.59E 1.59E
+01 +00 +02 -01
Cubic foot ft3 7.48E 6.23E+00 1.78E- 1 2.83E 2.83E
+00 01 +01 -02
Liter l 2.64E- 2.20E-01 6.30E- 3.53E- 1 1.00E
01 03 02 -03
Cubic meter m3 2.64E 2.20E+02 6.29E 3.53E 1.00E 1
+02 +00 +01 +03
Table: 8 | Conversion table for common energy units (NAS 2007; IEA 2019).
To: TJ Gcal Mtoe Mtce MBtu GWh
Fro multiply
m: by:
Tera Joule TJ 1 2.39E 2.39E- 3.41E- 9.48E 2.78E-
+02 05 05 +02 01
Giga Calorie Gc 4.19E- 1 1.0E- 1.43E- 3.97E 1.16E-
al 03 06 07 +00 03
Mega Tonne Oil Mt 4.19E 1.0E+ 1 1.43E 3.97E 1.16E
Equivalent oe +04 08 +00 +07 +04
Mega Tonne Coal Mt 2.93E 7.0E+ 7.00E- 1 2.78E 8.14E
Equivalent ce +04 06 01 +07 +03
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Final Government Distribution Annex II IPCC AR6 WGIII
Million British M 1.06E- 2.52E- 2.52E- 3.60E- 1 2.93E-
Thermal Units Btu 03 01 08 08 04
Giga Watt Hours G 3.60E 8.60E 8.60E- 1.23E- 3.41E 1
Wh +00 +02 05 4 +03
In addition to the above physical units, datasets often report carbon emissions in either units of carbon
(C) or carbon dioxide (CO2). In this report we report carbon dioxide (CO2) emissions where possible,
using the conversion factor (44/12) to convert from units of C into CO2. Finally, we note that the
conversion from GJ to kWh is as follows: 1 GJ= ~ 277,78 kWh.
Where aggregate greenhouse gas emissions are reported, this report uses the Global Warming Potential
with a time horizon of 100 years (GWP100); for details see section 8.
2.3. Monetary unit conversion
To achieve comparability across cost und price information from different regions, where possible
monetary quantities reported in the WGIII AR6 have been expressed in constant US Dollar 2015
(𝑈𝑆𝐷2015 ) or constant International Dollar 2015 (𝐼𝑛𝑡$2015), as suitable.
To facilitate a consistent monetary unit conversion process, a simple and transparent procedure to
convert different monetary units from the literature to USD2015 is established and described below.
In order to convert from year X local currency unit (𝐿𝐶𝑈𝑋 ) to 2015 US Dollars (𝑈𝑆𝐷2015 ) two steps
are needed:
1. inflating or deflating from year X to 2015, and
2. converting from 𝐿𝐶𝑈 to 𝑈𝑆𝐷.
In practice, the order of applying these two steps will lead to different results. In this report, the
conversion route adopted is 𝐿𝐶𝑈𝑋 -> 𝐿𝐶𝑈2015 -> 𝑈𝑆𝐷2015, i.e., national or regional deflators are used
to measure country- or region-specific inflation between year X and 2015 in local currency, then current
(2015) exchange rates are used to convert to 𝑈𝑆𝐷2015. The reason for adopting this rout is when the
economy’s GDP deflator is used to convert to a common base year, i.e. 2015, it captures the changes in
prices of all goods and services that the economy produces. To convert from 𝐿𝐶𝑈2015 to 𝑈𝑆𝐷2015 , the
official 2015 exchange rates are used. Note that exchange rates often fluctuate significantly in the short
term.
In order to be consistent with the choice of the World Bank databases as the primary source for gross
domestic product (GDP) and other financial data throughout the report, deflators and exchange rates
from the World Bank Development Indicators are used4.
To summarize, the following procedure has been adopted to convert monetary quantities reported in
𝐿𝐶𝑈𝑋 to 𝑈𝑆𝐷2015 :
1. Use the country- / region-specific deflator and multiply with the deflator value to convert from 𝐿𝐶𝑈𝑋
to 𝐿𝐶𝑈2015. In case national / regional data are reported in non-LCU units (e.g., 𝑈𝑆𝐷𝑋 or 𝐸𝑢𝑟𝑜𝑋 ), which
is often the case in multi-national or global studies, apply the corresponding currency deflator to convert
to 2015 currency (i.e., the US deflator and the Eurozone deflator in the examples above).
Example of converting GDP from 𝐿𝐶𝑈2010 prices to 𝐿𝐶𝑈2015 prices:
FOOTNOTE 4 For instance, the data for GDP deflators for all countries can be downloaded following this link:
https://data.worldbank.org/indicator/NY.GDP.DEFL.ZS?locations=US
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Final Government Distribution Annex II IPCC AR6 WGIII
𝐿𝐶𝑈 GDP deflator
𝐺𝐷𝑃2015 (in 𝐿𝐶𝑈2015 prices) = 𝐺𝐷𝑃2010 (in 𝐿𝐶𝑈2010 prices) * 𝐿𝐶𝑈2010 GDP deflator
2015
2. Use the appropriate 2015 exchange rate to convert from 𝐿𝐶𝑈2015 to 𝑈𝑆𝐷2015.
Part II: Conventions
3. Levelised cost metrics
Across this report, a number of different metrics to characterise cost of climate change mitigation are
employed. To facilitate a meaningful economic comparison across diverse options at the technology
level, the metric of ‘levelised costs’ is used throughout several chapters of this report in various forms.
The most used metrics are the levelised cost of energy (LCOE), the levelised cost of conserved energy
(LCCE), and the levelised cost of conserved carbon (LCCC). These metrics are used throughout the
WGIII AR6 to provide a benchmark for comparing different technologies or practices of achieving the
respective output. Each comes with a set of context-specific caveats that need to be taken into account
for correct interpretation. Various literature sources caution against drawing too strong conclusions
from these metrics. Annex II in AR5, namely section A.II.3.1., includes a detailed discussion on
interpretations and caveats. Below is an introduction to each of these metrics and how they are derived.
3.1. Levelised cost of energy
The levelised cost of energy (LCOE) can be defined as the unique break-even cost-price where
discounted revenues (price x quantities) are equal to the discounted net expenses (Moomaw et al. 2011),
which is expressed as follows:
𝐸 ∗𝐿𝐶𝑂𝐸 𝐸𝑥𝑝𝑒𝑛𝑠𝑒𝑠
∑𝑛𝑡=0 𝑡 = ∑𝑛𝑡=0 (1+𝑖)𝑡 𝑡 (1)
(1+𝑖)𝑡
where 𝐸𝑡 is the energy delivered in year 𝑡 (might vary from year to year), Expenses cover all (net)
expenses in the year 𝑡, 𝑖 is the discount rate and 𝑛 the lifetime of the project.
solving for 𝐿𝐶𝑂𝐸:
𝐸𝑥𝑝𝑒𝑛𝑠𝑒𝑠𝑡
∑𝑛
𝑡=0 (1+𝑖)𝑡
𝐿𝐶𝑂𝐸 = 𝐸 (2)
∑𝑡=0 𝑡 𝑡
𝑛
(1+𝑖)
The lifetime expenses comprise investment costs 𝐼, operation and maintenance cost 𝑂&𝑀 (including
waste management costs), fuel costs 𝐹, carbon costs 𝐶, and decommissioning costs 𝐷. In this case,
levelised cost can be determined by (IEA 2010):
𝐼 +𝑂&𝑀𝑡 +𝐹𝑡 +𝐶𝑡 +𝐷𝑡
∑𝑛
𝑡=0
𝑡
(1+𝑖)𝑡
𝐿𝐶𝑂𝐸 = 𝐸 ∗ (3)
∑𝑡=0 𝑡 𝑡
𝑛
(1+𝑖)
Assuming energy 𝐸 provided annually is constant during the lifetime of the project, one can rewrite (3)
as follows:
CRF · NPV (Lifetime Expenses) Annuity (Lifetime Expenses)
𝐿𝐶𝑂𝐸 = = (4)
𝐸 𝐸
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Final Government Distribution Annex II IPCC AR6 WGIII
𝑖
where 𝐶𝑅𝐹 = 1−(1−𝑖)−𝑛 is the capital recovery factor and 𝑁𝑃𝑉 the net present value of all lifetime
expenditures (Suerkemper et al. 2012).
For the simplified case, where the annual costs are also assumed constant over time, this can be further
simplified to (𝑂&𝑀 costs and fuel costs 𝐹 constants):
CRF · I+O&M+F
𝐿𝐶𝑂𝐸 = 𝐸
(5)
Where 𝐼 is the upfront investment, 𝑂&𝑀 are the annual operation and maintenance costs, 𝐹 are the
annual fuel costs, and 𝐸 is the annual energy provision. The investment 𝐼 should be interpreted as the
sum of all capital expenditures needed to make the investment fully operational discounted to 𝑡 = 0.
These might include discounted retrofit payments during the project lifetime and discounted
decommissioning costs at the end of the lifetime. Where applicable, annual 𝑂&𝑀 costs have to take
into account revenues for by-products and existing carbon costs must be added or treated as part of the
annual fuel costs.
3.2. Levelised cost of conserved energy
The levelised cost of conserved energy (LCCE) annualises the investment and operation and
maintenance cost differences between a baseline technology and the energy-efficient alternative and
divides this quantity by the annual energy savings.
The conceptual formula for 𝐿𝐶𝐶𝐸 is essentially the same as Equation (4) above, with 𝛥𝐸 measuring in
this context the amount of energy saved annually (Suerkemper et al. 2012):
𝐶𝑅𝐹.𝑁𝑃𝑉(𝛥𝐿𝑖𝑓𝑒𝑡𝑖𝑚𝑒 𝐸𝑥𝑝𝑒𝑛𝑠𝑒𝑠) 𝐴𝑛𝑛𝑢𝑖𝑡𝑦(𝛥𝐿𝑖𝑓𝑒𝑡𝑖𝑚𝑒 𝐸𝑥𝑝𝑒𝑛𝑠𝑒𝑠)
𝐿𝐶𝐶𝐸 = = (6)
𝛥𝐸 𝛥𝐸
In the case of assumed annually constant 𝑂&𝑀 costs over the project lifetime, one can rewrite (6) as
follows:
𝐶𝑅𝐹 · ΔI + ΔO&M
𝐿𝐶𝐶𝐸 = 𝛥𝐸
(7)
where 𝛥𝐼 is the difference in investment costs of an energy saving measure (e.g., in USD) as compared
to a baseline investment; 𝛥𝑂&𝑀 is the difference in annual operation and maintenance costs of an
energy saving measure (e.g., in USD) as compared to the baseline in which the energy saving measure
is not implemented; 𝛥𝐸 is the annual energy conserved by the measure (e.g., in 𝑘𝑊ℎ) as compared to
the usage of the baseline technology; and 𝐶𝑅𝐹 is the capital recovery factor depending on the discount
rate i and the lifetime of the measure in years as defined above. It should be stressed once more that this
equation is only valid if 𝛥𝑂&𝑀 and 𝛥𝐸 are constant over the project lifetime. As 𝐿𝐶𝐶𝐸 are designed to
be compared with complementary levelised cost of energy supply, they do not include the annual fuel
cost difference. Any additional monetary benefits that are associated with the energy saving measure
must be taken into account as part of the 𝑂&𝑀 difference.
3.3. Levelised cost of conserved carbon
The levelised cost of conserved carbon can be used for comparing mitigation costs per unit of avoided
carbon emissions and comparing these specific emission reduction costs for different options. This
concept can be applied to other pollutants.
The conceptual formula for 𝐿𝐶𝐶𝐶 is similar to Equation (6) above, with 𝛥𝐶 is the annual reduction in
carbon emissions, which can be expressed as follows:
𝐶𝑅𝐹.𝑁𝑃𝑉(𝛥𝐿𝑖𝑓𝑒𝑡𝑖𝑚𝑒 𝐸𝑥𝑝𝑒𝑛𝑠𝑒𝑠) 𝐴𝑛𝑛𝑢𝑖𝑡𝑦(𝛥𝐿𝑖𝑓𝑒𝑡𝑖𝑚𝑒 𝐸𝑥𝑝𝑒𝑛𝑠𝑒𝑠)
𝐿𝐶𝐶𝐶 = 𝛥𝐶
= 𝛥𝐶
(8)
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In the case of assumed annually constant 𝑂&𝑀 costs over the lifetime, one can rewrite (8) as follows:
𝐶𝑅𝐹 · ΔI + ΔO&M−ΔB
𝐿𝐶𝐶𝐶 = 𝛥𝐶
(9)
where 𝛥𝐼 is the difference in investment costs of a mitigation measure (e.g., in USD) as compared to a
baseline investment; 𝛥𝑂&𝑀 is the difference in annual operation and maintenance costs (e.g., in USD)
and 𝛥𝐵 denotes the annual benefits, all compared to a baseline for which the option is not implemented.
Note that annual benefits include reduced expenditures for fuels, if the investment project reduces
emissions via a reduction in fuel use. As such 𝐿𝐶𝐶𝐶 depend on energy prices. An important
characteristic of this equation is that 𝐿𝐶𝐶𝐶 can become negative if 𝛥𝐵 is bigger than the sum of the
other two terms in the numerator.
4. Growth rates
4.1. Emissions growth rates
In order to ensure consistency throughout the reported growth rates for emissions in WGIII AR6, this
section establishes the convention for calculating these rates.
The annual growth rate of emissions in percent per year for adjacent years is given by:
(𝐸𝐹𝐹 (𝑡0 −1)−𝐸𝐹𝐹 (𝑡0 ))
𝑟= 𝐸𝐹𝐹 (𝑡0 )
∗ 100 (10)
where 𝐸𝐹𝐹 stands for fossil fuel CO2 emissions, but can also be applied to other pollutants.
When relevant a leap-year adjustment is required in order to ensure valid interpretation of annual growth
rates in the case of adjacent years. A leap-year affects adjacent years growth rate by approximately
1
0.3% 𝑦𝑟 −1 (365) which causes growth rates to go up approximately 0.3% if the first year is a leap year,
and down 0.3% if the second year is a leap year (Friedlingstein et al. 2019).
The relative growth rate of 𝐸𝐹𝐹 over time periods of greater than one year is derived as follows.
Starting from:
𝐸𝐹𝐹 (𝑡 + 𝑛) = 𝐸𝐹𝐹 (𝑡) ∗ (1 + 𝑟)𝑛 (11)
solving for 𝑟:
𝐸 (𝑡+𝑛) 1/𝑛
𝑟 = ( 𝐹𝐹 (𝑡) ) −1 (12)
𝐸𝐹𝐹
4.2. Economic growth rates
A number of different methods exist for calculating economic growth rates (e.g., GDP), all of which
lead to slightly different numerical results. If not stated otherwise, the annual growth rates shown in the
report are derived using the Log Difference Regression technique or Geometric Average techniques
which can be shown to be equivalent.
The Log Difference Regression growth rate 𝑟𝐿𝐷 is calculated as follows:
1
𝑟𝐿𝐷 = 𝑒 𝛽 − 1 with 𝛽 = 𝑇−1 ∑𝑇𝑡=2 ∆𝑙𝑛𝑋𝑡 (13)
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The Geometric Average growth rate 𝑟𝐺𝐸𝑂 is calculated as shown below:
1
𝑋 𝑇−1
𝑟𝐺𝐸𝑂 = ( 𝑋𝑇 ) −1 (14)
1
Other methods that are used to calculate annual growth rates include the Ordinary Least Square
technique and the Average Annual Growth Rate technique.
5. Trends calculations between years and over decades
In order to compare or contrast trends between two different years, for instance comparing 2000 and
2010 cumulative CO2 emissions, the year 2000 runs from 1st of January to 31st of December and
similarly the year 2010 runs from 1st of January to 31st of December.
In order to undertake a timeseries calculation over a decade, the 10-year period should be defined as
follows: from 1st of January 2001 to 31st of December 2010, that is 2001-2010.
6. Primary energy accounting
Primary energy accounting methods are used to report primary energy from non-combustible energy
sources, i.e., nuclear energy and all renewable energy sources except biomass. Annex II of AR5, namely
section A.II.4., includes a detailed discussion of the three main methods dominant in the literature. The
method adopted in AR6 is the direct equivalent method which counts one unit of secondary energy
provided from non-combustible sources as one unit of primary energy, i. e., 1 kWh of electricity or heat
is accounted for as 1 kWh = 3.6 MJ of primary energy. This method is mostly used in the long-term
scenarios literature, including multiple IPCC reports (IPCC 1995; Morita et al. 2001; Fisher et al. 2007;
Fischedick et al. 2011), because it deals with fundamental transitions of energy systems that rely to a
large extent on low-carbon, non-combustible energy sources.
7. The concept of risk
The concept of risk is a key aspect of how the IPCC assesses and communicates to decision-makers the
potential adverse impacts of, and response options to, climate change. For the AR6 cycle, the definition
of risk was revised (see below). Authors and IPCC Bureau members from all three Working Groups
produced a Guidance (Reisinger et al. 2020) for authors on the concept of risk in order to ensure a
consistent and transparent application across Working Groups.
This section summarises this Guidance briefly with a focus on issues related to WGIII, i.e., with focus
on mitigation.
7.1. The definition of risk
Definition (see Annex I: Glossary):
Risk is the potential for adverse consequences for human or ecological systems, recognising the
diversity of values and objectives associated with such systems. In the context of climate change, risks
can arise from potential impacts of climate change as well as human responses to climate change.
Relevant adverse consequences include those on lives, livelihoods, health and wellbeing, economic,
social and cultural assets and investments, infrastructure, services (including ecosystem services),
ecosystems and species.
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• In the context of climate change impacts, risks result from dynamic interactions between
climate-related hazards with the exposure and vulnerability of the affected human or ecological
system to the hazards. Hazards, exposure and vulnerability may each be subject to uncertainty
in terms of magnitude and likelihood of occurrence, and each may change over time and space
due to socio-economic changes and human decision-making (see also risk management,
adaptation, mitigation).
• In the context of climate change responses, risks result from the potential for such responses
not achieving the intended objective(s), or from potential trade-offs with, or negative side-
effects on, other societal objectives, such as the Sustainable Development Goals. Risks can
arise for example from uncertainty in implementation, effectiveness or outcomes of climate
policy, climate-related investments, technology development or adoption, and system
transitions.
7.2. The definition of risk management
Plans, actions, strategies or policies to reduce the likelihood and/or magnitude of adverse potential
consequences, based on assessed or perceived risks (see also risk assessment, risk perception, risk
transfer).
7.3. The uses of the term risk and risk management
In this report, with the aim of improving the ability of decision-makers to understand and manage risk,
the term is used when considering the potential for adverse outcomes and the uncertainty relating to
these outcomes.
The term risk is not used as a simple substitute for probability or chance, to describe physical hazards,
or as generic term for ‘anything bad that may happen in future’. While the probability of an adverse
outcome does not necessarily have to be quantified, it needs to be characterised in some way to allow a
risk assessment to inform responses via risk management.
In the AR6, risk refers to the potential for adverse consequences only. The term hazard is used where
climatic events or trends has an identified potential for having adverse consequences to specific
elements of an affected system. The contribution of Working Group I to the AR6 uses the more general
term ‘climatic impact driver’ where a specific change in climate could have positive or negative
consequences, and where a given climatic change may therefore act as a driver of risk or of an
opportunity.
7.4. Examples of application in the context of mitigation
Food security
Climate-related risk to food security arises from multiple drivers that include both climate change
impacts, responses to climate change and other stressors.
In the context of responses to climate change, drivers of risk include the demand for land from climate
change responses (both adaptation and mitigation), the role of markets (e.g., price spikes related to
biofuel demand in other countries), governance (how are conflicts about access to land and water
resolved) and human behaviour more generally (e.g., trade barriers, dietary preferences).
Given the multitude of drivers, the risk to food security depends on assumptions about what drivers of
risk are changing and which are assumed to remain constant. Such assumptions are important for
analytical robustness and are stated where relevant.
Risk in the investment and finance literature
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The investment and finance literature and practitioner community broadly distinguish between
‘physical risk’ and ‘transition risk’. The term ‘physical risk’ generally refers to risks arising from
climate change impacts and climate-related hazards, while the term ‘transition risk’ typically refers to
risks associated with the transition to a low carbon economy. These two types of risk may interact and
create cascading or compounding risks.
Physical Risk
In much of the business and financial literature, the term ‘physical risk’ relates to those derived from
the hazard × exposure × vulnerability framework. Physical risks arise from the potential for climate
change impacts on the financial value of assets such as industrial plants or real estate, risks to facilities
and infrastructure, impact on operations, water and raw material availability and supply chain
disruptions. Physical risks have direct financial consequences for organisations where those risks are
realised, as well as up-front insurance and investment related costs and downstream effects for users of
relevant goods and services.
Transition risk
Transition risks typically refer to risks associated with transition to a low carbon economy, which can
entail extensive policy, legal, technology, and market changes to address mitigation and adaptation
requirements related to climate change. Depending on the nature, speed, and focus of these changes,
transition risks may pose varying levels of financial and reputational risk to organizations. Transition
risks, if realised, can result in stranded assets, loss of markets, reduced returns on investment, and
financial penalties, as well as adverse outcomes for governance and reputation.
A key issue is the stranding of assets that may not provide the expected financial returns and may end
up as large financial liabilities.
Examples of types of Transition Risk relating to business, finance and investments
• Risk related to an asset losing its value: the potential for loss of investment in infrastructure.
• Risk related to losing some or all of the principal of an investment (or invested capital)
• Solvency risk: the risk from reduction in credit ratings due to potential adverse consequences
of climate change or climate policy. This includes liquidity risk or the risk of not being able to
access funds. Another example is suffering a downgraded credit rating.
• Risk of lower than expected return on investment.
• Liability risk: Lack of response to climate change creates risk of liability for failure to
accurately assess risk of climate change to infrastructure and people.
• Technology risk: reliance on a particular technology to achieve an outcome creates the potential
for adverse consequences if the technology fails to be developed or deployed.
• Policy risk: Changes in policy or regulations in response to climate change could result in the
loss of value of some assets.
• Market risk: Changes in relative prices from increased prices of CO2 for instance, could reduce
financial returns and hence increase risks to investors.
• Residual risk: in parts of the financial literature, this concept refers to adverse consequences
that cannot be quantified in probabilistic terms. Note that this is different from how the term
‘residual risk’ is generally used in IPCC, especially Working Group II, where it means the risk
remaining after adaptation and risk reduction efforts.
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8. GHG emission metrics
Comprehensive mitigation policy relies on consideration of all anthropogenic forcing agents, which
differ widely in their atmospheric lifetimes and impacts on the climate system. GHG emission metrics5
provide simplified information about the effect that emissions of different GHGs have on global
temperature or other aspects of climate, usually expressed relative to the effect of emitting CO2. An
assessment of different GHG emission metrics from a mitigation perspective is provided in Cross-
Chapter Box 2 and Chapter 2 supplementary material, building on the assessment of GHG emission
metrics from a physical science perspective in AR6 WGI (Forster et al., 2021, Section 7.6).
The WGIII contribution to the AR6 reports aggregate emissions and removals using updated values for
the Global Warming Potential with a time horizon of 100 years (GWP100) from AR6 WGI unless stated
otherwise. These updated GWP100 values reflect updated scientific understanding of the response of the
climate system to emissions of different gases, and include a methodological update to incorporate
climate-carbon cycle feedbacks associated with the emission of non-CO2 gases (Forster et al. 2021).
For the second-most important anthropogenic greenhouse gas, methane, the updated GWP100 value of
27 is similar but slightly lower than the value of 28 reported in the AR5 without climate-carbon cycle
feedbacks. A full set of GWP100 values used in this report, based on the assessment of WGI (Forster et
al., 2021, Section 7.6 and Table 7.SM.7), is provided in Table 9.
GWP100 was chosen in the WGIII contribution to the AR6 as the default GHG emissions metric for both
procedural and scientific reasons.
Procedural reasons are to provide continuity with the use of GWP100 in past IPCC reports and the
dominant use of GWP100 in the literature assessed by WGIII, and to match decisions made by
Governments as part of the Paris Agreement Rulebook. Parties to the Paris Agreement decided to report
aggregated emissions and removals (expressed as CO2-eq) based on the Global Warming Potential with
a time horizon of 100 years (GWP100), using values from IPCC AR5 or from a subsequent IPCC report
as agreed upon by the CMA6, and to account for future nationally determined contributions (NDCs) in
accordance with this approach. Parties may also report supplemental information on aggregate
emissions and removals, expressed as CO2-eq, using other GHG emission metrics assessed by the IPCC
(4/CMA.1 and 18/CMA.1: UNFCCC 2019).
Scientific reasons for the use of GWP100 as default GHG emission metric in WGIII are that GWP100
approximates the relative damages caused by the two most important anthropogenic GHGs CO 2 and
CH4 for social discount rates around 3%. In addition, for pathways that likely limit warming to 2°C or
lower, using GWP100 to inform cost-effective abatement choices between gases would achieve these
long-term temperature goals at close to least global cost within a few percent (high confidence; see
Cross-Chapter Box 2).
However, all emission metrics have limitations and uncertainties, given that they simplify the
complexity of the physical climate system and its response to past and future GHG emissions. The most
suitable metric for any given climate policy application, depends on judgements about the specific
context, policy objectives and the way in which a metric would be used.
Wherever emissions, removals and mitigation potentials are expressed as CO2-eq in this report, efforts
have been made to recalculate those values consistently in terms of GWP 100 values from AR6 WGI.
However, in some cases it was not possible or feasible to disentangle conclusions from the existing
literature into individual gases and then re-aggregate those emissions using updated GWP100 values.
FOOTNOTE 5 Emission metrics also exist for aerosols, but these are not commonly used in climate policy. This
assessment focuses on GHG emission metrics only.
FOOTNOTE 6 The CMA is the Conference of the Parties serving as the meeting of the Parties to the Paris
Agreement.
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The existing literature assessed by WGIII uses a range of GWP100 values from previous IPCC reports;
for CH4, these values vary between 21 (based on the IPCC Second Assessment Report) to 28 or even
34 (based on the IPCC Fifth Assessment Report and depending on whether the study included or
excluded climate-carbon cycle feedbacks). Consistent application of any metric is challenging as
individual GHG emission species are not always provided in the literature assessed by WGIII. Where a
full recalculation of CO2-eq emissions or mitigation potentials into GWP100 AR6 values was not
possible or feasible, and especially if non-CO2 emissions constitute only a minor fraction of total
emissions or abatement, individual chapters note this inconsistency and provide an indication of the
potential magnitude of inconsistency.
To further reduce ambiguity regarding actual climate outcomes over time from any given set of
emissions, the WGIII contribution to the AR6 reports emissions and mitigation options for individual
gases where possible based on the available literature, and reports CO2-eq emissions where this is
judged to be policy relevant by author teams in addition to, not instead of individual gases.
Table: 9 | 𝑮𝑾𝑷𝟏𝟎𝟎 values and atmospheric lifetimes for a range of GHGs, based on WGI AR6 (Forster et
al. 2021)
Gas AR6 - GWP_100 Lifetime
CO2 1 N/A
CH4 (biogenic) 27.0 11.8
CH4 (fossil - combustion)7 27.0 11.8
CH4 (fossil – fugitive and process) 29.8 11.8
N2O 273 109
HFC-32 770 5.4
HFC-143a 5,807 51
CF4 7,379 50000
C2F6 12,410 10000
C3F8 9,289 2600
C4F10 10,022 2600
C5F12 9,218 4100
C6F14 8,617 3100
C7F16 8,409 3000
c-C4F8 13,902 3000
HFC-125 3,744 30
HFC-134a 1,526 14
HFC-152a 164 1.6
HFC-227ea 3,602 36
HFC-23 14,590 228
HFC-236fa 8,689 213
FOOTNOTE 7 The biogenic CH4 GWP100 value applies here, given Tier 1 IPCC CO2 emissions factors which
are based on total carbon content. The associated emissions are estimated on the bases of complete (100%)
oxidation to CO2 of carbon contained in combusted mass.
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HFC-245fa 962 7.9
HFC-365mfc 913 8.9
HFC-43-10-mee 1,599 17
SF6 25,184 3200
NF3 17,423 569
Part III: Emissions Datasets
In this section we report on the historical emissions data used in the report (section 9), the sectoral
mapping on emissions sources (section 9.1), the methane emissions sources (section 9.2), and indirect
emissions (section 10).
9. Historical data
Historic emissions data for countries, regions and sectors are presented throughout the report, but
especially in Chapters 2, 6-7, 9-11, the Technical Summary and Summary for Policymakers. To ensure
consistency and transparency we use the same emissions data across these chapters, with a single
methodology, division of emissions sources, and following the classification scheme of countries and
areas in section 1 above.
Our primary data source is the Emissions Database for Global Atmospheric Research (EDGAR) (Crippa
et al. 2021; Minx et al. 2021). This dataset provides annual CO2, CH4, N2O and F-gas emissions on a
country and emissions source level for the time span 1970 to 2019. The fossil fuel combustion
component of EDGAR is closely linked to and sourced from International Energy Agency (IEA 2021)
energy and emissions estimates. Section 2.2.1 in Chapter 2 of this report describes the differences
between and coverage of different global emissions datasets.
In addition to EDGAR, land-use CO2 emissions are sourced as the mean of three bookkeeping models,
in a convention established by the Global Carbon Project (Friedlingstein et al. 2020) and consistent with
the Working Group I approach. The bookkeeping models are BLUE (Bookkeeping of Land Use
Emissions) Hansis et al. (2015), Houghton and Nassikas (2017) and OSCAR (Gasser et al. 2020).
Global total greenhouse gas emissions reported throughout AR6 are the sum of EDGAR and land-use
CO2 emissions. Significant uncertainties are associated with each gas and emissions source. These
uncertainties are comprehensively treated in Section 2.2.1 of Chapter 2.
9.1. Mapping of emission sources to sectors
The list below shows how emission sources in EDGAR are mapped to sectors throughout the WGIII
AR6. This defines unambiguous system boundaries for the sectors as represented in Chapters 6, 7 and
9-11 in the report and enables a discussion and representation of emission sources without double-
counting.
Emission sources follows the definitions by the IPCC Task Force on National Greenhouse Gas
Inventories (TFI) (IPCC 2019). EDGARv6 identifies each source as either “Fossil” or “Bio”. The “Bio”
label indicates the biomass component of fuel combustion, while “Fossil” is the default label for all
other emissions sources (including, e.g. agricultural GHG emissions).
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Table: 10 | Mapping Emission Sources to Sectors
Chapter
Subsector title EDGAR code IPCC 2019 Gases
title
Biomass
4F1 (bio), 4F2 (bio), 4F3
AFOLU burning (CO2, 3.C.1.b (bio) CH4, N2O
(bio), 4F4 (bio), 4F5 (bio)
CH4)
4A1-d (fossil), 4A1-n 3.A.1.a.i (fossil), 3.A.1.a.ii (fossil),
Enteric (fossil), 4A2 (fossil), 4A3 3.A.1.b (fossil), 3.A.1.c (fossil),
AFOLU Fermentation (fossil), 4A4 (fossil), 4A5 3.A.1.d (fossil), 3.A.1.e (fossil), CH4
(CH4) (fossil), 4A6 (fossil), 4A7 3.A.1.f (fossil), 3.A.1.g (fossil),
(fossil), 4A8 (fossil) 3.A.1.h (fossil)
4D12 (fossil), 4D13
(fossil), 4D14 (fossil),
Managed soils
4D15 (fossil), 4D2 (fossil), 3.C.4 (fossil), 3.C.5 (fossil), 3.C.6
AFOLU and pasture N2O, CO2
4D3a (fossil), 4D3b (fossil), 3.C.3 (fossil), 3.C.2 (fossil)
(CO2, N2O)
(fossil), 4D4a (fossil),
4D4b (fossil)
4B1-d (fossil), 4B1-n
3.A.2.a.i (fossil), 3.A.2.a.ii (fossil),
(fossil), 4B2 (fossil), 4B3
Manure 3.A.2.b (fossil), 3.A.2.c (fossil),
(fossil), 4B4 (fossil), 4B5
AFOLU management 3.A.2.i (fossil), 3.A.2.d (fossil), CH4, N2O
(fossil), 4B6 (fossil), 4B7
(N2O, CH4) 3.A.2.e (fossil), 3.A.2.f (fossil),
(fossil), 4B8 (fossil), 4B9
3.A.2.g (fossil), 3.A.2.h (fossil)
(fossil)
Rice cultivation
AFOLU 4C (fossil) 3.C.7 (fossil) CH4
(CH4)
Synthetic
fertilizer
AFOLU 4D11 (fossil) 3.C.4 (fossil) N2O
application
(N2O)
c-C4F8,
C4F10, CF4,
HFC-125,
Non-CO2 (all 2F3 (fossil), 2F4 (fossil), 2.F.3 (fossil), 2.F.4 (fossil), 2.G.2.c HFC-227ea,
Buildings 2F9a (fossil), 2F9c (fossil) (fossil)
buildings) HFC-23,
HFC-236fa,
HFC-134a,
HFC-152a
CH4, N2O,
Buildings Non-residential 1A4a (bio), 1A4a (fossil) 1.A.4.a (bio), 1.A.4.a (fossil)
CO2
CH4, N2O,
Buildings Residential 1A4b (bio), 1A4b (fossil) 1.A.4.b (bio), 1.A.4.b (fossil)
CO2
1B1a1 (fossil), 1B1a1r
Coal mining (fossil), 1B1a2 (fossil),
Energy 1.B.1.a (fossil), 1.B.1.c (fossil)
fugitive 1B1a3 (fossil), 1B1b2 CO2, CH4
systems
emissions (fossil), 1B1b4 (fossil)
1A1a1 (bio), 1A1a1
(fossil), 1A1a2 (bio),
1A1a2 (fossil), 1A1a3
(bio), 1A1a3 (fossil),
1.A.1.a.i (bio), 1.A.1.a.i (fossil),
Energy Electricity & 1A1a4 (bio), 1A1a4 CO2, CH4,
1.A.1.a.ii (bio), 1.A.1.a.ii (fossil),
systems heat (fossil), 1A1a5 (bio), N2O
1.A.1.a.iii (bio), 1.A.1.a.iii (fossil)
1A1a5 (fossil), 1A1a6
(bio), 1A1a6 (fossil),
1A1a7 (bio), 1A1a7
(fossil)
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1B2a1 (bio), 1B2a1
1.B.2.a.iii.2 (bio), 1.B.2.a.iii.2
(fossil), 1B2a2 (fossil),
(fossil), 1.B.2.a.iii.3 (fossil),
1B2a3-l (fossil), 1B2a4-l
1.B.2.a.iii.4 (fossil), 1.B.2.b.iii.2
Oil and gas (fossil), 1B2a4-t (fossil),
Energy (fossil), 1.B.2.b.iii.4 (fossil), CO2, CH4,
fugitive 1B2a5(e) (fossil), 1B2b1
systems 1.B.2.b.iii.5 (fossil), 1.B.2.b.iii.3 N2O
emissions (fossil), 1B2b3 (fossil),
(fossil), 1.B.2.b.ii (fossil), 1.B.2.a.ii
1B2b4 (fossil), 1B2b5
(fossil)
(fossil), 1B2c (fossil)
1A1c3 (bio), 1A1c3
(fossil), 1A1c4 (bio),
1.A.1.c.ii (bio), 1.A.1.c.ii (fossil),
1A1c5 (bio), 1A1c5
1.A.1.c.i (bio), 1.A.1.c.i (fossil),
(fossil), 1A4c1 (bio),
Energy Other (energy 1.A.4.c.i (bio), 1.A.4.c.i (fossil), CO2, CH4,
1A4c1 (fossil), 1A4d (bio),
systems systems) 1.A.5.a (bio), 1.A.5.a (fossil), N2O, SF6
1A4d (fossil), 1B1b3 (bio),
1.B.1.c (bio), 2.G.1.b (fossil), 5.B
2F8b (fossil), 7A1 (fossil),
(fossil), 5.A (fossil)
7A2 (fossil), 7B1 (fossil),
7C1 (fossil)
Energy Petroleum 1A1b (bio), 1A1b (fossil) 1.A.1.b (bio), 1.A.1.b (fossil) CO2, CH4,
systems refining N2O
Industry Cement 2A1 (fossil) 2.A.1 (fossil) CO2
1A2c (bio), 1A2c (fossil), CH4, N2O,
2A2 (fossil), 2A3 (fossil), CO2, c-
2A4a (fossil), 2A4b C4F8, C2F6,
(fossil), 2A7a (fossil), C3F8,
1.A.2.c (bio), 1.A.2.c (fossil), 2.A.2
2B1g (fossil), 2B1s C4F10,
(fossil), 2.A.4.d (fossil), 2.A.4.b
(fossil), 2B2 (fossil), 2B3 C5F12,
(fossil), 2.A.3 (fossil), 2.B.1
(fossil), 2B4a (fossil), C6F14, CF4,
(fossil), 2.B.2 (fossil), 2.B.3
2B4b (fossil), 2B5a HFC-125,
(fossil), 2.B.5 (fossil), 2.B.8.f
Industry Chemicals (fossil), 2B5b (fossil), HFC-134a,
(fossil), 2.B.8.b (fossil), 2.B.8.c
2B5d (fossil), 2B5e HFC-143a,
(fossil), 2.B.8.a (fossil), 2.B.4
(fossil), 2B5f (fossil), HFC-152a,
(fossil), 2.B.6 (fossil), 2.B.9.b
2B5g (fossil), 2B5g2 HFC-227ea,
(fossil), 2.D.3 (fossil), 2.G.3.a
(fossil), 2B5h1 (fossil), 2E HFC-32,
(fossil), 2.G.3.b (fossil)
(fossil), 2E1 (fossil), 3A HFC-
(fossil), 3B (fossil), 3C 365mfc,
(fossil), 3D (fossil), 3D1 NF3, SF6,
(fossil), 3D3 (fossil) HFC-23
1A1c1 (fossil), 1A1c2
(fossil), 1A2a (bio), 1A2a
(fossil), 1A2b (bio), 1A2b
1.A.1.c.i (fossil), 1.A.1.c.ii (fossil),
(fossil), 1B1b1 (fossil),
1.A.2.a (bio), 1.A.2.a (fossil),
2C1a (fossil), 2C1b
1.A.2.b (bio), 1.A.2.b (fossil), CO2, CH4,
Industry Metals (fossil), 2C1d (fossil), 2C2 N2O, C2F6,
1.B.1.c (fossil), 2.C.1 (fossil), 2.C.2
(fossil), 2C3a (fossil), CF4, SF6
(fossil), 2.C.3 (fossil), 2.C.4
2C3b (fossil), 2C4a
(fossil), 2.C.5 (fossil), 2.C.6 (fossil)
(fossil), 2C4b (fossil),
2C5lp (fossil), 2C5mp
(fossil), 2C5zp (fossil)
1A2d (bio), 1A2d (fossil), 1.A.2.d (bio), 1.A.2.d (fossil), CH4, N2O,
1A2e (bio), 1A2e (fossil), 1.A.2.e (bio), 1.A.2.e (fossil), CO2, HFC-
Industry Other (industry) 1A2f (bio), 1A2f (fossil), 1.A.2.f (bio), 1.A.2.f (fossil), 125, HFC-
1A2f1 (fossil), 1A2f2 1.A.2.k (fossil), 1.A.2.i (fossil), 134a, HFC-
(fossil), 1A5b1 (fossil), 1.A.5.b.iii (fossil), 2.F.1.a (fossil), 143a, HFC-
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Final Government Distribution Annex II IPCC AR6 WGIII
2F1a (fossil), 2F1b NA (fossil), 2.F.5 (fossil), 2.E.1 152a, HFC-
(fossil), 2F1c (fossil), (fossil), 2.E.2 (fossil), 2.E.3 (fossil), 227ea, HFC-
2F1d (fossil), 2F1e 2.G.1.a (fossil), 2.G.2.c (fossil), 236fa, HFC-
(fossil), 2F1f (fossil), 2F2a 2.G.2.b (fossil), 2.G.2.a (fossil), 245fa, HFC-
(fossil), 2F2b (fossil), 2F5 2.D.1 (fossil), 5.A (fossil) 32, HFC-
(fossil), 2F6 (fossil), 2F7a 365mfc,
(fossil), 2F7b (fossil), C3F8,
2F7c (fossil), 2F8a (fossil), C6F14, CF4,
2F9 (fossil), 2F9d (fossil), HFC-43-10-
2F9e (fossil), 2F9f (fossil), mee, HFC-
2G1 (fossil), 7B2 (fossil), 134, HFC-
7C2 (fossil) 143, HFC-
23, HFC-41,
c-C4F8,
C2F6, NF3,
SF6, HCFC-
141b,
HCFC-142b,
C4F10
6A1 (fossil), 6B1 (fossil),
4.A.1 (fossil), 4.D.2 (fossil), 4.D.1
6B2 (fossil), 6C (fossil), CH4, N2O,
Industry Waste (fossil), 4.C.1 (fossil), 4.C.2 (bio),
6Ca (bio), 6Cb1 (fossil), CO2
4.C.2 (fossil), 4.B (fossil)
6Cb2 (fossil), 6D (fossil)
Domestic CO2, CH4,
Transport 1A3a (fossil) 1.A.3.a.ii (fossil)
Aviation N2O
CH4, N2O,
Transport Inland Shipping 1A3d (bio), 1A3d (fossil) 1.A.3.d.ii (bio), 1.A.3.d.ii (fossil)
CO2
International CO2, CH4,
Transport 1C1 (fossil) 1.A.3.a.i (fossil)
Aviation N2O
International CH4, N2O,
Transport 1C2 (bio), 1C2 (fossil) 1.A.3.d.i (bio), 1.A.3.d.i (fossil)
Shipping CO2
1A3e (bio), 1A3e (fossil), 1.A.3.e.i (bio), 1.A.3.e.i (fossil),
Other CH4, N2O,
Transport 1A4c2 (fossil), 1A4c3 1.A.4.c.ii (fossil), 1.A.4.c.iii (bio),
(transport) CO2
(bio), 1A4c3 (fossil) 1.A.4.c.iii (fossil)
CH4, N2O,
Transport Rail 1A3c (bio), 1A3c (fossil) 1.A.3.c (bio), 1.A.3.c (fossil)
CO2
1.A.3.b_RES (bio), 1.A.3.b_RES CH4, N2O,
Transport Road 1A3b (bio), 1A3b (fossil)
(fossil) CO2
9.2. Methane emissions sources
In order to identify emission trends and mitigation opportunities by sector WG III allocates each
emission source to a sector and subsequently a subsector (check section 9 above). These trends and
mitigation opportunities are, in most cases and whenever possible, reported in the native unit of gases
as well as in CO2-eq using IPCC AR6 GWP100 values (section 8). In the case of methane (CH4), it
has two different GWP100 values according to its source. The relevant sources of methane are:
biogenic methane, fossil methane (source: combustion) and fossil methane (source: fugitive and
process).
The majority of biogenic methane emissions result from the AFOLU sector due to livestock and other
agricultural practices, but also from the energy systems, building, transport and industry (waste)
sectors. Meanwhile, fossil methane (combustion) emissions result from electricity and heat generation
in the energy systems sector as well as various combustion activities in all other sectors. Finally, fossil
methane (fugitive and process) is emitted from the extraction and transportation of fossil fuels (fugitive
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Final Government Distribution Annex II IPCC AR6 WGIII
methane), in addition to some activities in the industry sector (fugitive and process methane). See
Table 12 below for a comprehensive list.
There are two GWP100 values assigned to methane depending on its source: a GWP100 value of 27
for biogenic methane and fossil methane (combustion), and a higher GWP100 value of 29.8 for fossil
methane (fugitive and process), see Table 11 below. The difference between these two GWP100
values arises from treatment of the effect of methane conversion into CO2 during its chemical decay
in the atmosphere. The higher GWP100 value takes account of the warming caused by CO2 that
methane decays into, which adds to the warming caused by methane itself, while the lower GWP100
value does not.
In the case of biogenic methane, the correct GWP100 value is always the low value irrespective of the
specific source. This is because all CO2 originated from biomass is either already estimated and
reported as CO2 emissions from AFOLU sector, or in the case of short-rotation biomass, the original
removal of CO2 from the atmosphere is not reported and hence neither does the release of CO2 back
into the atmosphere need to be reported.
For fossil methane, the correct GWP100 value depends on the source, i.e., combustion source vs
fugitive and process sources. Fossil methane (fugitive and process) should use the higher GWP100
value because CO2 converted from methane in the atmosphere is not estimated anywhere else.
For fossil methane (combustion), despite it being fossil, the correct GWP100 value is always the low
one, for the dataset reported here. This is due to the fact that the emissions data provider EDGAR
(section 9) considers a complete oxidation to CO2 of all the carbon contained in the fossil fuel upon
combustion, which is then reflected in the CO2 emissions factors for the different sources based on the
carbon content of fuels. In other words, IPCC (IPCC 2019) methods and defaults (Tier 1 IPCC CO2
emissions factors) have been used where the associated CO2 emissions are estimated on the basis of
complete (100%) oxidation to CO2 of carbon contained in combusted mass, which includes not only
CO2 directly released to the atmosphere but also CO2 generated in the atmosphere from the carbon
released as methane and converted to CO2 only subsequently.
There are two exceptions applied to the above categorisation, both belong to the industry sector, sector
codes 6Cb1 (Waste incineration - uncontrolled municipal solid waste (MSW) burning) and 6D (other
waste). Uncontrolled MSW burning (6Cb1) includes both biogenic and fossil material, with
incomplete oxidation for this source even when the IPCC Tier 1 default emission/oxidation factor is
used. The GWP100 value adopted for this source is the low one, given that the fossil-origin methane
component is unlikely to be very large. The “other waste” (6D) source may also include both biogenic
and fossil methane. However, it is unclear what type of waste handling is included here. Furthermore,
the associated CO2 emissions are not estimated. Therefore, the high GWP100 value is used.
In total, the estimation of EDGAR methane emissions in 2019 using a GWP100 value of 27 across all
related sources results in 10.2 Gt CO2eq, compared to 10.6 Gt CO2eq using the higher GWP100 value
as described. This is primarily driven by the readjustment of methane emissions from hard coal mining,
gas production, and venting and flaring (sectors 1B1a1, 1B2b1 and 1B2c).
Table: 11 | Summary of methane GWP100 values in AR6 depending on type and source.
CH4 GWP100 value
CH4 (biogenic) 27
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Final Government Distribution Annex II IPCC AR6 WGIII
CH4 (fossil - combustion) 27
CH4 (fossil – fugitive and process) 29.8
Table: 12 | Methane Sources and Types
Sector code Description Sector Subsector CH4 type
Public Electricity
Generation
1A1a1 (biomass) Energy systems Electricity & heat CH4 Biogenic
Public Electricity
1A1a1 Generation Energy systems Electricity & heat CH4 Fossil (Combustion)
Public Combined
Heat and Power gen.
1A1a2 (biom.) Energy systems Electricity & heat CH4 Biogenic
Public Combined
1A1a2 Heat and Power gen. Energy systems Electricity & heat CH4 Fossil (Combustion)
Public Heat Plants
1A1a3 (biomass) Energy systems Electricity & heat CH4 Biogenic
1A1a3 Public Heat Plants Energy systems Electricity & heat CH4 Fossil (Combustion)
Public Electricity
Gen. (own use)
1A1a4 (biom.) Energy systems Electricity & heat CH4 Biogenic
Public Electricity
Generation (own
1A1a4 use) Energy systems Electricity & heat CH4 Fossil (Combustion)
Electricity
Generation
(autoproducers)
1A1a5 (biom.) Energy systems Electricity & heat CH4 Biogenic
Electricity
Generation
1A1a5 (autoproducers) Energy systems Electricity & heat CH4 Fossil (Combustion)
Combined Heat and
Power gen. (autopr.)
1A1a6 (biom.) Energy systems Electricity & heat CH4 Biogenic
Combined Heat and
Power gen.
1A1a6 (autoprod.) Energy systems Electricity & heat CH4 Fossil (Combustion)
Heat Plants
(autoproducers)
1A1a7 (biomass) Energy systems Electricity & heat CH4 Biogenic
Heat Plants
1A1a7 (autoproducers) Energy systems Electricity & heat CH4 Fossil (Combustion)
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Final Government Distribution Annex II IPCC AR6 WGIII
1A1b Refineries (biomass) Energy systems Petroleum refining CH4 Biogenic
1A1b Refineries Energy systems Petroleum refining CH4 Fossil (Combustion)
Fuel combustion
1A1c1 coke ovens Industry Metals CH4 Fossil (Combustion)
Blast furnaces (pig
1A1c2 iron prod.) Industry Metals CH4 Fossil (Combustion)
1A1c3 Gas works (biom.) Energy systems Other (energy systems) CH4 Biogenic
1A1c3 Gas works Energy systems Other (energy systems) CH4 Fossil (Combustion)
Fuel comb. charcoal
1A1c4 production (biom.) Energy systems Other (energy systems) CH4 Biogenic
Other transf. sector
1A1c5 (BKB, etc.) (biom.) Energy systems Other (energy systems) CH4 Biogenic
Other transformation
1A1c5 sector (BKB, etc.) Energy systems Other (energy systems) CH4 Fossil (Combustion)
Iron and steel
1A2a (biomass) Industry Metals CH4 Biogenic
1A2a Iron and steel Industry Metals CH4 Fossil (Combustion)
Non-ferrous metals
1A2b (biomass) Industry Metals CH4 Biogenic
1A2b Non-ferrous metals Industry Metals CH4 Fossil (Combustion)
1A2c Chemicals (biomass) Industry Chemicals CH4 Biogenic
1A2c Chemicals Industry Chemicals CH4 Fossil (Combustion)
Pulp and paper
1A2d (biomass) Industry Other (industry) CH4 Biogenic
1A2d Pulp and paper Industry Other (industry) CH4 Fossil (Combustion)
Food and tobacco
1A2e (biomass) Industry Other (industry) CH4 Biogenic
1A2e Food and tobacco Industry Other (industry) CH4 Fossil (Combustion)
Other industries
1A2f (stationary) (biom.) Industry Other (industry) CH4 Biogenic
Other industries
1A2f (stationary) (fos.) Industry Other (industry) CH4 Fossil (Combustion)
Off-road machinery:
1A2f1 construction (diesel) Industry Other (industry) CH4 Fossil (Combustion)
Off-road machinery:
1A2f2 mining (diesel) Industry Other (industry) CH4 Fossil (Combustion)
Domestic air
1A3a transport Transport Domestic Aviation CH4 Fossil (Combustion)
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Final Government Distribution Annex II IPCC AR6 WGIII
Road transport (incl.
1A3b evap.) (biom.) Transport Road CH4 Biogenic
Road transport (incl.
1A3b evap.) (foss.) Transport Road CH4 Fossil (Combustion)
Non-road transport
1A3c (rail, etc.)(biom.) Transport Rail CH4 Biogenic
Non-road transport
1A3c (rail, etc.) (fos.) Transport Rail CH4 Fossil (Combustion)
Inland shipping
1A3d (biom.) Transport Inland Shipping CH4 Biogenic
Inland shipping
1A3d (fos.) Transport Inland Shipping CH4 Fossil (Combustion)
Non-road transport
1A3e (biom.) Transport Other (transport) CH4 Biogenic
Non-road transport
1A3e (fos.) Transport Other (transport) CH4 Fossil (Combustion)
Commercial and
public services
1A4a (biom.) Buildings Non-residential CH4 Biogenic
Commercial and
1A4a public services (fos.) Buildings Non-residential CH4 Fossil (Combustion)
1A4b Residential (biom.) Buildings Residential CH4 Biogenic
1A4b Residential (fos.) Buildings Residential CH4 Fossil (Combustion)
Agriculture and
1A4c1 forestry (biom.) Energy systems Other (energy systems) CH4 Biogenic
Agriculture and
1A4c1 forestry (fos.) Energy systems Other (energy systems) CH4 Fossil (Combustion)
Off-road machinery:
1A4c2 agric./for. (diesel) Transport Other (transport) CH4 Fossil (Combustion)
1A4c3 Fishing (biom.) Transport Other (transport) CH4 Biogenic
1A4c3 Fishing (fos.) Transport Other (transport) CH4 Fossil (Combustion)
Non-specified other
1A4d (biom.) Energy systems Other (energy systems) CH4 Biogenic
Non-specified other
1A4d (fos.) Energy systems Other (energy systems) CH4 Fossil (Combustion)
Off-road machinery:
1A5b1 mining (diesel) Industry Other (industry) CH4 Fossil (Combustion)
Hard coal mining Coal mining fugitive
1B1a1 (gross) Energy systems emissions CH4 Fossil (Fugitive)
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Final Government Distribution Annex II IPCC AR6 WGIII
Methane recovery Coal mining fugitive
1B1a1r from coal mining Energy systems emissions CH4 Fossil (Fugitive)
Coal mining fugitive
1B1a2 Abandoned mines Energy systems emissions CH4 Fossil (Fugitive)
Coal mining fugitive
1B1a3 Brown coal mining Energy systems emissions CH4 Fossil (Fugitive)
Fuel transformation
1B1b1 coke ovens Industry Metals CH4 Fossil (Fugitive)
Fuel transformation
1B1b3 charcoal production Energy systems Other (energy systems) CH4 Biogenic
Oil production Oil and gas fugitive
1B2a1 (biom.) Energy systems emissions CH4 Biogenic
Oil and gas fugitive
1B2a1 Oil production Energy systems emissions CH4 Fossil (Fugitive)
Oil and gas fugitive
1B2a2 Oil transmission Energy systems emissions CH4 Fossil (Fugitive)
Oil and gas fugitive
1B2a3-l Tanker loading Energy systems emissions CH4 Fossil (Fugitive)
Tanker oil transport Oil and gas fugitive
1B2a4-l (crude and NGL) Energy systems emissions CH4 Fossil (Fugitive)
Transport by oil Oil and gas fugitive
1B2a4-t trucks Energy systems emissions CH4 Fossil (Fugitive)
Oil refineries Oil and gas fugitive
1B2a5(e) (evaporation) Energy systems emissions CH4 Fossil (Fugitive)
Oil and gas fugitive
1B2b1 Gas production Energy systems emissions CH4 Fossil (Fugitive)
Oil and gas fugitive
1B2b3 Gas transmission Energy systems emissions CH4 Fossil (Fugitive)
Oil and gas fugitive
1B2b4 Gas distribution Energy systems emissions CH4 Fossil (Fugitive)
Venting and flaring
during oil and gas Oil and gas fugitive
1B2c production Energy systems emissions CH4 Fossil (Fugitive)
International air
1C1 transport Transport International Aviation CH4 Fossil (Combustion)
International marine
1C2 transport (biom.) Transport International Shipping CH4 Biogenic
International marine
1C2 transport (bunkers) Transport International Shipping CH4 Fossil (Combustion)
Silicon carbide
2B4a production Industry Chemicals CH4 Fossil (Process)
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Final Government Distribution Annex II IPCC AR6 WGIII
Carbon black
2B5a production Industry Chemicals CH4 Fossil (Process)
2B5b Ethylene production Industry Chemicals CH4 Fossil (Process)
2B5d Styrene production Industry Chemicals CH4 Fossil (Process)
2B5e Methanol production Industry Chemicals CH4 Fossil (Process)
Other bulk chemicals
2B5g production Industry Chemicals CH4 Fossil (Process)
2C1d Sinter production Industry Metals CH4 Fossil (Process)
Ferroy Alloy
2C2 production Industry Metals CH4 Fossil (Process)
Enteric Fermentation
4A1-d Dairy cattle AFOLU (CH4) CH4 Biogenic
Enteric Fermentation
4A1-n Non-dairy cattle AFOLU (CH4) CH4 Biogenic
Enteric Fermentation
4A2 Buffalo AFOLU (CH4) CH4 Biogenic
Enteric Fermentation
4A3 Sheep AFOLU (CH4) CH4 Biogenic
Enteric Fermentation
4A4 Goats AFOLU (CH4) CH4 Biogenic
Enteric Fermentation
4A5 Camels and Lamas AFOLU (CH4) CH4 Biogenic
Enteric Fermentation
4A6 Horses AFOLU (CH4) CH4 Biogenic
Enteric Fermentation
4A7 Mules and asses AFOLU (CH4) CH4 Biogenic
Enteric Fermentation
4A8 Swine AFOLU (CH4) CH4 Biogenic
Manure Man.: Dairy Manure management
4B1-d Cattle (confined) AFOLU (N2O, CH4) CH4 Biogenic
Manure Man.: Non-
Dairy Cattle Manure management
4B1-n (confined) AFOLU (N2O, CH4) CH4 Biogenic
Manure Man.: Manure management
4B2 Buffalo (confined) AFOLU (N2O, CH4) CH4 Biogenic
Manure Man.: Sheep Manure management
4B3 (confined) AFOLU (N2O, CH4) CH4 Biogenic
Manure Man.: Goats Manure management
4B4 (confined) AFOLU (N2O, CH4) CH4 Biogenic
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Final Government Distribution Annex II IPCC AR6 WGIII
Manure Man.:
Camels and llamas Manure management
4B5 (confined) AFOLU (N2O, CH4) CH4 Biogenic
Manure Man.: Manure management
4B6 Horses (confined) AFOLU (N2O, CH4) CH4 Biogenic
Manure Man.: Mules Manure management
4B7 and asses (confined) AFOLU (N2O, CH4) CH4 Biogenic
Manure Man.: Swine Manure management
4B8 (confined) AFOLU (N2O, CH4) CH4 Biogenic
Manure Man.: Manure management
4B9 Poultry (confined) AFOLU (N2O, CH4) CH4 Biogenic
Rice cultivation
4C (CH4) AFOLU Rice cultivation (CH4) CH4 Biogenic
Field burning of Biomass burning (CH4,
4F1 agric. res.: cereals AFOLU N2O) CH4 Biogenic
Field burning of Biomass burning (CH4,
4F2 agric. res.: pulses AFOLU N2O) CH4 Biogenic
Field burning of
agric. res.: tuber and Biomass burning (CH4,
4F3 roots AFOLU N2O) CH4 Biogenic
Field burning of
agric. res.: sugar Biomass burning (CH4,
4F4 cane AFOLU N2O) CH4 Biogenic
Field burning of Biomass burning (CH4,
4F5 agric. res.: other AFOLU N2O) CH4 Biogenic
Managed waste
6A1 disposal on land Industry Waste CH4 Biogenic
6B1 Industrial wastewater Industry Waste CH4 Biogenic
Domestic and
commercial
6B2 wastewater Industry Waste CH4 Biogenic
Waste incineration -
6C hazardous Industry Waste CH4 Fossil (Combustion)
Waste incineration -
6Ca biogenic Industry Waste CH4 Biogenic
Waste incineration -
uncontrolled MSW
6Cb1 burning Industry Waste CH4 Fossil (Combustion)
Waste incineration -
6Cb2 other non-biogenic Industry Waste CH4 Fossil (Combustion)
6D Other waste Industry Waste CH4 Fossil (Process)
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Final Government Distribution Annex II IPCC AR6 WGIII
Coal fires
7A1 (underground) Energy systems Other (energy systems) CH4 Fossil (Combustion)
7A2 Oil fires (Kuwait) Energy systems Other (energy systems) CH4 Fossil (Combustion)
10. Indirect emissions
Carbon dioxide emissions resulting from fuel combusted to produce electricity and heat are traditionally
reported in the energy sector. An indirect emissions accounting principle allocates these emissions to
the end-use sectors (industry, buildings, transport, and agriculture) where the electricity and heat are
ultimately consumed. Attributing indirect emissions to consuming sectors makes it possible to assess
the full potential impact of demand-side mitigation actions that reduce electricity and heat consumption
(de la Rue du Can et al. 2015).
In order to estimate the indirect emissions of sectors and subsectors, the CO2 Emissions from Fuel
Combustion dataset of the International Energy Agency (IEA 2020a) is used. This database reports
direct and indirect CO2 emissions for IEA sectors, which are related to the IPCC (IPCC 2019)
classification of emissions sources. The IEA adopted a new methodology in 2020 that is in line with
the methodology used in Annex II of the WG III contribution to AR5 (Krey et al. 2014), namely section
A.II.4. The IEA now estimates individual electricity and heat specific emission factors and allocates
indirect emissions related to electricity and heat in the sectors where these forms of energy are used
respectively (IEA 2020b). In order to estimate the share of energy input that results in the production
of heat from the share that results in the production of electricity in Combined heat and Power plants,
the IEA fixes the efficiency for heat production equal to 90%, which is the typical efficiency of a heat
boiler and then allocates the remaining inputs to electricity production (IEA 2020b).
The base data for total global, regional and sectoral emissions in this report is the EDGAR database
(see section 9). Since there are some discrepancies between the electricity and heat emissions totals in
EDGAR and IEA, we make some adjustments in order to estimate indirect emissions in EDGAR using
the IEA data. First, we match the sectors in EDGAR and IEA. Second, for each country and emissions
source available in the IEA database, we take the IEA indirect emissions value and divide it by the total
IEA value for electricity and heat. Third, we multiply these values through by the EDGAR value for
electricity and heat. This procedure ensures that indirect emissions, in principle, sum to the correct total
(EDGAR) value of electricity and heat that we use elsewhere in the reporting. However, total indirect
emissions still do not sum to the total electricity and heat sector. This is due to an incomplete allocation
of electricity and heat emissions in the IEA dataset, equal to 0.008 Gt CO2 in 2018, or about 0.06% of
the total electricity and heat generation.
Additionally, a couple of adjustments were made to allocate emissions from IEA sector categories to
IPCC categories from IPCC Task force definition as described in IPCC (2019) Guidelines (see section
9). These include:
- Other non-specified sector: the IEA energy statistics report final energy and electricity use for three
end-use sectors: industry, transport, and other. The “other” category is further subdivided into
agriculture, fishing, commercial and public services, residential, and non-specified other. The
‘‘non-specified other” category includes energy used for agriculture, fishing, commercial and
public services, and residential sectors that has not been allocated to these end-use sectors by the
submitting countries. In most cases, there is no entry in the non-specified other category, indicating
that all end-use energy consumption has been allocated to other end-use sectors. However, for some
countries the energy reported in the non-specified other category needed to be allocated to the
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Final Government Distribution Annex II IPCC AR6 WGIII
appropriate end-use sectors. To perform this allocation, the energy use in the non-specified other
category was allocated to the other end-use sectors based on the share of energy allocated to each
of these sub-sectors for each region.
- Other energy industry own use: emissions from this category in the IEA statistics corresponds to
the IPCC Source/Sink categories 1A1b and 1A1c (see section 9) and contains emissions from fuel
combusted in energy transformation industries that are not producing heat and/or power and
therefore include oil refineries, coal mining, oil and gas extraction and other energy-producing
industries. These emissions were not reallocated to the end use sectors where final products are
ultimately consumed due to the lack of data.
Finally, it is also worth noting that indirect emissions only cover CO2 emissions and that a small portion
of non-CO2 are not included in the IEA dataset and therefore have not been allocated to the end use
sectors. Non-CO2 emissions from total electricity and heat generation represents 0.55% of all GHG
emissions from that sector.
Part IV: Assessment methods
In this section we report on assessment methods adopted in the report. Section 11 describes the
methodology adopted for assessing the feasibility of mitigation response options. Section 12 describes
the methodology adopted for assessing synergies and trade-offs between mitigation options and the
SDGs.
11. Methodology adopted for assessing the feasibility of mitigation response options
The feasibility assessment aims to identify barriers and enablers of the deployment of mitigation options
and pathways. The assessment organises evidence to support decision making on actions and policies
that would improve the feasibility of mitigation options and pathways, by removing relevant barriers
and strengthening enablers of change.
Feasibility of mitigation response options
The sectoral chapters in WG III AR6 assess six dimensions of feasibility, with each dimension
comprising a key set of indicators that can be evaluated by combining various strands of literature (see
Table 13). The feasibility of systems-level changes is addressed in Chapter 3 of this report.
Table: 13 | Feasibility dimensions and indicators to assess the barriers and enablers of implementing
mitigation options
Metric Indicators
Geophysical feasibility • Physical potential: physical constraints to implementation
• Geophysical resource availability (including geological storage
capacity): availability of resources needed to implementation
• Land use: claims on land when option would be implemented
Environmental-ecological • Air pollution: increase or decrease in air pollutants, such as NH4,
feasibility CH4, and fine dust
• Toxic waste, mining, ecotoxicity and eutrophication
• Water quantity and quality: changes in amount of water available for
other uses, including groundwater
• Biodiversity: changes in conserved primary forest or grassland that
affect biodiversity, and management to conserve and maintain land
carbon stocks
Technological feasibility • Simplicity: is the option technically simple to operate, maintain and
integrate
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• Technology scalability: can the option be scaled up, quickly
• Maturity and technology readiness: R&D and time needed to
implement to option
Economic feasibility • Costs now, in 2030 and in the long term, including investment costs,
costs in USD/tCO2-eq, and hidden costs
• Employment effects and economic growth
Socio-cultural feasibility • Public acceptance: extent to which the public supports the option and
changes behavior accordingly
• Effects on health and wellbeing
• Distributional effects: equity and justice across groups, regions, and
generations, including security of energy, water, food and poverty
Institutional feasibility • Political acceptance: extent to which politicians and governments
support the option
• Institutional capacity and governance, cross-sectoral coordination:
capability of institutions to implement and handle the option, and to
coordinate it with other sectors, stakeholder and civil society
• Legal and administrative capacity: extent to which supportive legal
and administrative changes can be achieved
The sectoral chapters in this report assess to what extent the indicators in Table 13 would be enablers
or barriers to implementation using the following scores (Nilsson et al. 2016):
- The indicator has a negative impact on the feasibility of the option, e.g., it is associated
with prohibitively high costs, levels of pollution or land use, or low public or political
acceptance.
± Mixed evidence: the indicator has mixed positive and negative impacts on the feasibility
of the option (e.g., more land use in some regions, while lower in other regions)
+ The indicator has a positive impact on the feasibility of the option, e.g., it is associated
with low costs, pollution, land use, or high public or political acceptance
0 / NA The indicator does not affect the feasibility of the option / criterion is not applicable for
the option
NE No evidence available to assess the impact on the feasibility of the option
LE Limited evidence available to assess the impact on the feasibility the option
Assessment
Each sectoral chapter assesses to what extent the indicators listed above would be an enabler or barrier
to the implementation of selected mitigation options, by using the above scores. Then the total number
of minus and plus points were computed, relative to the maximum possible number of points, per
feasibility dimensions, for each option; a + counts as two plus points, a - as two minus points, and a ±
as one plus and one minus point. The resulting scores reveal the extent to which each feasibility
dimension enables or inhibits the deployment of the relevant option, and indicates which type of
additional effort would be needed to reduce or remove barriers as to improve the feasibility of relevant
options.
The assessment is based on the literature, which is reflected in a line of sight. When appropriate, it is
indicated whether the feasibility of an option varies across context (e.g., region), scale (e.g., small,
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medium, full scale), time (e.g. implementation in 2030 versus 2050) and warming level (e.g., 1.5°C
versus 2°C).
Synergies and trade-offs may occur between the feasibility dimensions, and between specific mitigation
options. Therefore, chapters 3 and 4 employ a systems perspective and discuss the feasibility of
mitigation scenarios and pathways in the long term and near to mid-term, respectively, on the basis of
the feasibility assessments in the sectoral chapters taking into account such synergies and trade-offs.
Chapter 5 (demand, services and social aspects of mitigation), Chapter 13 (national and sub-national
policies and institutions), Chapter 14 (international cooperation), Chapter 15 (investment and finance)
and Chapter 16 (innovation, technology development and transfer) address technological, economic,
socio-cultural and institutional enabling conditions that can enhance the feasibility of options and
remove relevant barriers.
12. Methodology adopted for assessing synergies and trade-offs between mitigation
options and the SDGs
Adopting climate mitigation options can generate multiple positive (synergies) and negative (trade-offs)
interactions with sustainable development. Understanding these are crucial for selecting mitigation
options and policy choices that maximise the synergies, minimise trade-offs, and potentially offset
trade-offs (Roy et al. 2018). Chapter 5 in the IPCC’s Special Report on Global Warming of 1.5°C
examines the synergies and trade-offs of adaptation and mitigation measures with sustainable
development and UN’s Sustainable Development Goals (SDGs). Building on this, the sectoral chapters
in the WG III contribution to the AR6 include a qualitative assessment of the synergies and trade-offs
between mitigation options in different sectors and the SDGs based on existing literature. All these
assessments are collated and presented in Chapter 17 with a supplementary table including the details
of the synergies and trade-offs with a line of sight (Section 17.3.3.7 , Figure 17.1 and Supplementary
Material Table 17.1). The assessment also recognises that interactions of mitigation options with the
SDGs are context-specific and therefore provides a detailed explanation in the supplementary table of
Chapter 17.
For the assessment, the mitigation options were shortlisted from each of the sectoral chapters. The
sectoral chapters assessed the literature in terms of the impacts of each of these mitigation options on
the 17 SDGs. The assessment uses three signs:
‘+’ to denote positive interaction only (synergies),
‘-’ to denote negative interaction only (trade-offs) and
‘±’ to denote mixed interactions.
In some cases, where there is gap in literature, these are left blank denoting that these impacts have not
been assessed in the literature included in the sectoral chapters . To support these signs, brief statements
are provided followed by uncertainty qualifiers in the supplementary table of Chapter 17. These
uncertainty qualifiers denote the confidence levels (low, medium and high).
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