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Greenhouse gas inventory

From Wikipedia, the free encyclopedia

Greenhouse gas inventories are emission inventories of greenhouse gas emissions that are developed for a variety of reasons. Scientists use inventories of natural and anthropogenic (human-caused) emissions as tools when developing atmospheric models. Policy makers use inventories to develop strategies and policies for emissions reductions and to track the progress of those policies.

Regulatory agencies and corporations also rely on inventories to establish compliance records with allowable emission rates. Businesses, the public, and other interest groups use inventories to better understand the sources and trends in emissions.

Unlike some other air emission inventories, greenhouse gas inventories include not only emissions from source categories, but also removals by carbon sinks. These removals are typically referred to as carbon sequestration.

Greenhouse gas inventories typically use Global warming potential (GWP) values to combine emissions of various greenhouse gases into a single weighted value of emissions.

Examples

Some of the key examples of greenhouse gas inventories include:

All Annex I countries are required to report annual emissions and sinks of greenhouse gases under the United Nations Framework Convention on Climate Change (UNFCCC)
National governments that are Parties to the UNFCCC and/or the Kyoto Protocol are required to submit annual inventories of all anthropogenic greenhouse gas emissions from sources and removals from sinks.
The Kyoto Protocol includes additional requirements for national inventory systems, inventory reporting, and annual inventory review for determining compliance with Articles 5 and 8 of the Protocol.
Project developers under the Clean Development Mechanism of the Kyoto Protocol prepare inventories as part of their project baselines.

Greenhouse gas emissions accounting

Greenhouse gas emissions accounting is measuring the amount of greenhouse gases (GHG) emitted during a given period of time by a polity, usually a country but sometimes a region or city. Such measures are used to conduct climate science and climate policy.

There are two main, conflicting ways of measuring GHG emissions: production-based (also known as territorial-based) and consumption-based. The Intergovernmental Panel on Climate Change defines production-based emissions as taking place “within national territory and offshore areas over which the country has jurisdiction”. Consumption-based emissions take into account the effects of trade, encompassing the emissions from domestic final consumption and those caused by the production of its imports. From the perspective of trade, consumption-based emissions accounting is thus the reverse of production-based emissions accounting, which includes exports but excludes imports (Table 1).

The choice of accounting method can have very important effects on policymaking, as each measure can generate a very different result. Thus, different values for a National greenhouse gas Emissions Inventory (NEI) could result in a country choosing different optimal mitigation activities, the wrong choice based on wrong information being potentially damaging. The application of production-based emissions accounting is currently favoured in policy terms as it is easier to measure, but it is criticised in the literature principally for its inability to allocate emissions embodied in international trade/transportation and the potential for carbon leakage.

Almost all countries in the world are parties to the Paris Agreement, which requires them to provide regular production-based GHG emissions inventories to the United Nations Framework Convention on Climate Change (UNFCCC), in order to track both countries achievement of their nationally determined contributions and climate policies as well as regional climate policies such as the EU Emissions Trading Scheme (ETS), and the world's progress in limiting global warming.

Comparison of production based and consumption-based accounting

Over the last few decades emissions have grown at an increasing rate from 1.0% yr⁻¹ throughout the 1990s to 3.4% yr⁻¹ between 2000 and 2008. These increases have been driven not only by a growing global population and per-capita GDP, but also by global increases in the energy intensity of GDP (energy per unit GDP) and the carbon intensity of energy (emissions per unit energy).These drivers are most apparent in developing markets (Kyoto non-Annex B countries), but what is less apparent is that a substantial fraction of the growth in these countries is to satisfy the demand of consumers in developed countries (Kyoto Annex B countries). This is exaggerated by a process known as Carbon Leakage whereby Annex B countries decrease domestic production in place of increased importation of products from non-Annex B countries where emission policies are less strict. Although this may seem the rational choice for consumers when considering local pollutants, consumers are inescapably affected by global pollutants such as GHG, irrespective of where production occurs. Although emissions have slowed since 2007 as a result of the global financial crisis, the longer-term trend of increased emissions is likely to resume.

Today, much international effort is put into slowing the anthropogenic release of GHG and resulting climate change. In order to set benchmarks and emissions targets for - as well as monitor and evaluate the progress of - international and regional policies, the accurate measurement of each country's NEI becomes imperative.

A comparison of the production-based and consumption-based national emissions inventories (NEI).
Criteria	Production-based NEI	Consumption-based NEI
Emissions covered	Administered territory	Global
Allocation	Domestic production	Domestic consumption
Allocation of trade	Includes exports, not imports	Includes imports, not exports
Mitigation focus	Domestic activities including exports	Domestic activities and imports (exports excluded)
Comparability	Consistent with GDP	Consistent with national consumption
Consistent with trade policy	No	Yes
Annex I emissions coverage	Lower	Higher
Complexity	Low	High
Transparency	High	Low
Uncertainty	Lower	Higher
Current country coverage	Relatively high	Low with current data
Mitigation analysis	Domestic mitigation only	Global mitigation

Production-based accounting

As production-based emissions accounting is currently favoured in policy terms, its methodology is well established. Emissions are calculated not directly but indirectly from fossil fuel usage and other relevant processes such as industry and agriculture according to 2006 guidelines issued by the IPCC for GHG reporting. The guidelines span numerous methodologies dependent on the level of sophistication (Tiers 1–3 in Table 2). The simplest methodology combines the extent of human activity with a coefficient quantifying the emissions from that activity, known as an ‘emission factor’. For example, to estimate emissions from the energy sector (typically contributing over 90% of CO₂ emissions and 75% of all GHG emissions in developed countries) the quantity of fuels combusted is combined with an emission factor - the level of sophistication increasing with the accuracy and complexity of the emission factor. Table 2 outlines how the UK implements these guidelines to estimate some of its emissions-producing activities.

Table 2. Some emissions producing activities and methods used to estimate emissions. IPCC tier represents one of three tiers, each tier indicating an additional layer of sophistication. These tiers indicate which method of emissions calculations is used from the IPCC 1996 Guidelines.
Activity	GHG	IPCC Tier	Method used to estimate emissions
Public electricity and heat production	CO₂	2	An emissions factor is applied to fuel consumption data from DUKES. Some data are also collected from individual point sources at generation facilities. The emissions factors are UK specific factors obtained by sampling average UK carbon content of fuels.
Road transportation	CO₂, CH₄, N₂O	3	Emissions from road transport are estimated from a combination of total fuel consumption data taken from the Digest of UK Energy Statistics and fuel properties, and from a combination of drive related emission factors and road traffic data on fuel use, car type, miles driven, road types, and fuel type from the Department for Transport.
Domestic aviation	CO₂, CH₄, N₂O	3	Data from the Department for Transport and Civil Aviation Authority on aircraft movements is broken down by aircraft type at each UK airport. The model takes into account the lengths of time spent on different parts of an aircraft's take off and landing cycle and different types of aircraft used in the UK.
Refrigeration and air conditioning equipment	HFC	2	Data on the numbers of UK domestic and commercial refrigerators is obtained from the UK Market Transformation Programme and activity data supplied by industry. Data on mobile air conditioning systems is obtained from the UK Society of Motor Manufacturers and Traders. Once the numbers and size of refrigerators is known, an emissions factor which was derived to reflect UK refrigeration fluids applied to estimate emissions
Enteric Fermentation	CH₄	2	Enteric fermentation is a digestive process in ruminant animals which produces methane. Emissions are estimated from animal production data from the June agricultural census. Emissions factors for milk producing cattle, lambs and deer are calculated using a tier 2 approach which takes into account the sizes, ages and types of UK animals.
Agricultural soils	N₂O	1 and 2	The method involves estimating the contributions from the use of inorganic fertilizer, biological fixation of nitrogen by crops, ploughing in crop residues, cultivation of organic soils, spreading animal manure on land, and manures dropped by animals grazing in the field using data from DEFRA and the British Survey of Fertiliser Practice. For some of these areas IPCC default methods are used and for other UK specific methods are used.
Wastewater handling	CH₄, N₂O	2	The estimate is based on the work of Hobson et al. (1996) who estimated emissions of methane for the years 1990–95. Subsequent years are extrapolated on the basis of population. Sewage disposed to landfill is included in landfill emissions

Emissions from burning wood are counted against the country where the trees were felled rather than the country where they are burnt.

Consumption-based accounting

Consumption-based emissions accounting has an equally established methodology using Input-Output Tables. These "display the interconnection between different sectors of production and allow for a tracing of the production and consumption in an economy" and were originally created for national economies. However, as production has become increasingly international and the import/export market between nations has flourished, Multi-Regional Input-Output (MRIO) models have been developed. The unique feature of MRIO is allowing a product to be traced across its production cycle, "quantifying the contributions to the value of the product from different economic sectors in various countries represented in the model. It hence offers a description of the global supply chains of products consumed". From this, assuming regional- and industry-specific data for CO₂ emissions per unit of output are available, the total amount of emissions for the product can be calculated, and therefore the amount of emissions the final consumer is allocated responsibility for.

The two methodologies of emissions accounting begin to expose their key differences. Production-based accounting is transparently consistent with GDP, whereas consumption-based accounting (more complex and uncertain) is consistent with national consumption and trade. However, the most important difference is that the latter covers global emissions - including those ‘embodied’ emissions that are omitted in production-based accounting - and offers globally based mitigation options. Thus the attribution of emissions embodied in international trade is the crux of the matter.

Emissions embodied in international trade

Figure 1 and Table 3 show extent of emissions embodied in international trade and thus their importance when attempting emissions reductions. Figure 1 shows the international trade flows of the top 10 countries with largest trade fluxes in 2004 and illustrates the dominance of trade from developing countries (principally China, Russia and India) to developed countries (principally USA, EU and Japan). Table 3 supports this showing that the traded emissions in 2008 total 7.8 gigatonnes (Gt) with a net CO₂ emissions trade from developing to developed countries of 1.6 Gt.

Table 3 also shows how these processes of production, consumption and trade have changed from 1990 (commonly chosen for baseline levels) to 2008. Global emissions have risen 39%, but in the same period developed countries seem to have stabilized their domestic emissions, whereas developing countries’ domestic emissions have doubled. This ‘stabilization’ is arguably misleading, however, if the increased trade from developing to developed countries is considered. This has increased from 0.4 Gt CO₂ to 1.6 Gt CO₂ - a 17%/year average growth meaning 16 Gt CO₂ have been traded from developing to developed countries between 1990 and 2008. Assuming a proportion of the increased production in developing countries is to fulfil the consumption demands of developed countries, the process known as carbon leakage becomes evident. Thus, including international trade (i.e. the methodology of consumption-based accounting) reverses the apparent decreasing trend in emissions in developed countries, changing a 2% decrease (as calculated by production-based accounting) into a 7% increase across the time period. This point is only further emphasized when these trends are studied at a less aggregated scale.

Table 3. Allocation of global emissions to Annex B and non-Annex B countries separated into domestic and internationally traded components.
	Component	1990 (Gt CO₂)	2008 (Gt CO₂)	Growth (%/y)
Annex B
Domestic	Annex B Domestic (Bdom)	11.3	10.8	-0.3
Trade component	Annex B to Annex B (B2B)	2.1	2.2	0.2
	Annex B to non-Annex B (B2nB)	0.7	0.9	1.8
Production	Annex B production (Bprod = Bdom + B2B + B2nB)	14.2	13.9	-0.1
Consumption	Annex B consumption (Bcons = Bdom + B2B + nB2B)	14.5	15.5	0.3
Non-Annex B
Domestic	Non-Annex B domestic (nBdom)	6.2	11.7	4.6
Trade component	Non-Annex B to Annex B (nB2B)	1.1	2.6	7.0
	Non-Annex B to non-Annex B (nB2nB)	0.4	2.2	21.5
Production	Non-Annex B production (nBprod = nBdom + nB2B + nB2nB)	7.7	16.4	5.9
Consumption	Non-Annex B consumption (nBcons = nBdom + B2nB + nB2nB)	7.4	14.8	5.3
Trade totals	Traded emissions (B2B + B2nB + nB2B + nB2nB)	4.3	7.8	4.3
	Trade balance (B2nB − nB2B)	-0.4	-1.6	16.9
	Global emissions (Bprod + nBprod = Bcons + nBcon)	21.9	30.3	2.0

Figure 2 shows the percentage surplus of emissions as calculated by production-based accounting over consumption-based accounting. In general, production-based accounting proposes lower emissions for the EU and OECD countries (developed countries) and higher emissions for BRIC and rest of the world (developing countries). However, consumption-based accounting proposes the reverse with lower emissions in BRIC and RoW, and higher emissions in EU and OECD countries. This led Boitier to term EU and OECD ‘CO₂ consumers’ and BRIC and RoW ‘CO₂ producers’.

The large difference in these results is corroborated by further analysis. The EU-27 in 1994 counted emissions using the consumption-based approach at 11% higher than those counted using the production-based approach, this difference rising to 24% in 2008. Similarly OECD countries reached a peak variance of 16% in 2006 whilst dropping to 14% in 2008. In contrast, although RoW starts and ends relatively equal, in the intervening years it is a clear CO₂ producer, as are BRIC with an average consumption-based emissions deficit of 18.5% compared to production-based emissions.

Peters and Hertwich completed a MRIO study to calculate emissions embodied in international trade using data from the 2001 Global Trade Analysis Program (GTAP). After manipulation, although their numbers are slightly more conservative (EU 14%; OECD 3%; BRIC 16%; RoW 6%) than Boitier the same trend is evident - developed countries are CO₂ consumers and developing countries are CO₂ producers. This trend is seen across the literature and supporting the use of consumption-based emissions accounting in policy-making decisions.

Tools and standards

ISO 14064

The ISO 14064 standards (published in 2006 and early 2007) are the most recent additions to the ISO 14000 series of international standards for environmental management. The ISO 14064 standards provide governments, businesses, regions and other organisations with an integrated set of tools for programs aimed at measuring, quantifying and reducing greenhouse gas emissions. These standards allow organisations take part in emissions trading schemes using a globally recognised standard.

Local Government Operations Protocol

The Local Government Operations Protocol (LGOP) is a tool for accounting and reporting greenhouse gas emissions across a local government's operations. Adopted by the California Air Resources Board (ARB) in September 2008 for local governments to develop and report consistent GHG inventories to help meet California's AB 32 GHG reduction obligations, it was developed in partnership with California Climate Action Registry, The Climate Registry, ICLEI and dozens of stakeholders.

The California Sustainability Alliance also created the Local Government Operations Protocol Toolkit, which breaks down the complexities of the LGOP manual and provides an area by area summary of the recommended inventory protocols.

Know IPCC Format for GHG Emissions Inventory

The data in the GHG emissions inventory is presented using the IPCC format (seven sectors presented using the Common Reporting Format, or CRF) as is all communication between Member States and the Secretariat of the United Nations Framework Convention on Climate Change (UNFCCC) and the Kyoto Protocol.

Advantages of consumption-based accounting

Consumption-based emissions accounting may be deemed superior as it incorporates embodied emissions currently ignored by the UNFCCC preferred production-based accounting. Other key advantages include: extending mitigation options, covering more global emissions through increased participation, and inherently encompassing policies such as the Clean Development Mechanism (CDM).

Extending mitigation options

Under the production-based system a country is punished for having a pollution intensive resource base. If this country has pollution intensive exports, such as Norway where 69% of its CO₂ emissions are the result of production for export, a simple way to meet its emissions reductions set out under Kyoto would be to reduce its exports. Although this would be environmentally advantageous, it would be economically and politically harmful as exports are an important part of a country's GDP. However, by having appropriate mechanisms in place, such as a harmonized global tax, border-tax adjustment or quotas, a consumption-based accounting system could shift the comparative advantage towards a decision that includes environmental factors. The tax most discussed is based on the carbon content of the fossil fuels used to produce and transport the product, the greater the level of carbon used the more tax being charged. If a country did not voluntarily participate then a border tax could be imposed on them. This system would have the effect of embedding the cost of environmental load in the price of the product and therefore market forces would shift production to where it is economically and environmentally preferable, thus reducing GHG emissions

Increasing participation

In addition to reducing emissions directly this system may also alleviate competitiveness concerns in twofold ways: firstly, domestic and foreign producers are exposed to the same carbon tax; and secondly, if multiple countries are competing for the same export market they can promote environmental performance as a marketing tool. A loss of competitiveness resulting from the absence of legally binding commitments for non-Annex B countries was the principal reason the US and Australia, two heavily emitting countries, did not originally ratify the Kyoto protocol (Australia later ratified in 2007). By alleviating such concerns more countries may participate in future climate policies resulting in a greater percentage of global emissions being covered by legally binding reduction policies. Furthermore, as developed countries are currently expected to reduce their emissions more than developing countries, the more emissions are (fairly) attributed to developed countries the more they become covered by legally bound reduction policies. Peters argues that this last prediction means that consumption-based accounting would advantageously result in greater emissions reductions irrespective of increased participation.

Encompassing policies such as the CDM

The CDM is a flexible mechanism set up under the Kyoto Protocol with the aim of creating ‘Carbon Credits’ for trade in trading schemes such as the EU ETS. Despite coming under heavy criticism (see Evans, p134-135; and Burniaux et al.,), the theory is that as the marginal cost of environmental abatement is lower in non-Annex B countries a scheme like this will promote technology transfer from Annex B to non-Annex B countries resulting in cheaper emissions reductions. Because under consumption-based emissions accounting a country is responsible for the emissions caused by its imports, it is important for the importing country to encourage good environmental behaviour and promote the cleanest production technologies available in the exporting country. Therefore, unlike the Kyoto Protocol where the CDM was added later, consumption-based emissions accounting inherently promotes clean development in the foreign country because of the way it allocates emissions. One loophole that remains relevant is carbon colonialism whereby developed countries do not mitigate the underlying problem but simply continue to increase consumption offsetting this by exploiting the abatement potential of developing countries.

Disadvantages of consumption-based accounting

Despite its advantages consumption-based emissions accounting is not without its drawbacks. These were highlighted above and in Table 1 and are principally: greater uncertainty, greater complexity requiring more data not always available, and requiring greater international collaboration.

Greater uncertainty and complexity

Uncertainty derives from three main reasons: production-based accounting is much closer to statistical sources and GDP which are more assured; the methodology behind consumption-based accounting requires an extra step over production-based accounting, this step inherently incurring further doubt; and consumption-based accounting includes data from all trading partners of a particular country which will contain different levels of accuracy. The bulk of data required is its second pitfall as in some countries the lack of data means consumption-based accounting is not possible. However, levels and accuracy of data will improve as more and better techniques are developed and the scientific community produce more data sets - examples including the recently launched global databases: EORA from the University of Sydney, EXIOPOL and WIOD databases from European consortia, and the Asian IDE-JETRO. In the short term it will be important to attempt to quantify the level of uncertainty more accurately.

Greater international co-operation

The third problem is that consumption-based accounting requires greater international collaboration to deliver effective results. A Government has the authority to implement policies only over emissions it directly generates. In consumption-based accounting emissions from different geo-political territories are allocated to the importing country. Although the importing country can indirectly oppose this by changing its importing habits or by applying a border tax as discussed, only by greater international collaboration, through an international dialogue such as the UNFCCC, can direct and meaningful emissions reductions be enforced.

Sharing emissions responsibility

Thus far it has been implied that one must implement either production-based accounting or consumption-based accounting. However, there are arguments that the answer lies somewhere in the middle i.e. emissions should be shared between the importing and exporting countries. This approach asserts that although it is the final consumer that ultimately initiates the production, the activities that create the product and associated pollution also contribute to the producing country's GDP. This topic is still developing in the literature principally through works by Rodrigues et al., Lenzen et al., Marques et al. as well as through empirical studies by such as Andrew and Forgie. Crucially it proposes that at each stage of the supply chain the emissions are shared by some pre-defined criteria between the different actors involved.

Whilst this approach of sharing emissions responsibility seems advantageous, the controversy arises over what these pre-defined criteria should be. Two of the current front runners are Lenzen et al. who say “the share of responsibility allocated to each agent should be proportional to its value added” and Rodrigues et al. who say it should be based on “the average between an agent's consumption-based responsibility and income-based responsibility” (quoted in Marques et al.). As no criteria set has been adequately developed and further work is needed to produce a finished methodology for a potentially valuable concept.

Trends

Measures of regions' GHG emissions are critical to climate policy. It is clear that production-based emissions accounting, the currently favoured method for policy-making, significantly underestimates the level of GHG emitted by excluding emissions embodied in international trade. Implementing consumption-based accounting which includes such emissions, developed countries take a greater share of GHG emissions and consequently the low level of emissions commitments for developing countries are not as important. Not only does consumption-based accounting encompass global emissions, it promotes good environmental behaviour and increases participation by reducing competitiveness.

Despite these advantages the shift from production-based to consumption-based accounting arguably represents a shift from one extreme to another. The third option of sharing responsibility between importing and exporting countries represents a compromise between the two systems. However, as yet no adequately developed methodology exists for this third way, so further study is required before it can be implemented for policy-making decisions.

Today, given its lower uncertainty, established methodology and reporting, consistency between political and environmental boundaries, and widespread implementation, it is hard to see any movement away from the favoured production-based accounting. However, because of its key disadvantage of omitting emissions embodied in international trade, it is clear that consumption-based accounting provides invaluable information and should at least be used as a ‘shadow’ to production-based accounting. With further work into the methodologies of consumption-based accounting and sharing emissions responsibility, both can play greater roles in the future of climate policy.

Carbon footprint

A carbon footprint (or greenhouse gas footprint) is a calculated value or index that makes it possible to compare the total amount of greenhouse gases that an activity, product, company or country adds to the atmosphere. Carbon footprints are usually reported in tonnes of emissions (CO₂-equivalent) per unit of comparison. Such units can be for example tonnes CO₂-eq per year, per kilogram of protein for consumption, per kilometer travelled, per piece of clothing and so forth. A product's carbon footprint includes the emissions for the entire life cycle. These run from the production along the supply chain to its final consumption and disposal.

Similarly, an organization's carbon footprint includes the direct as well as the indirect emissions that it causes. The Greenhouse Gas Protocol (for carbon accounting of organizations) calls these Scope 1, 2 and 3 emissions. There are several methodologies and online tools to calculate the carbon footprint. They depend on whether the focus is on a country, organization, product or individual person. For example, the carbon footprint of a product could help consumers decide which product to buy if they want to be climate aware. For climate change mitigation activities, the carbon footprint can help distinguish those economic activities with a high footprint from those with a low footprint. So the carbon footprint concept allows everyone to make comparisons between the climate impacts of individuals, products, companies and countries. It also helps people devise strategies and priorities for reducing the carbon footprint.

The carbon dioxide equivalent (CO₂eq) emissions per unit of comparison is a suitable way to express a carbon footprint. This sums up all the greenhouse gas emissions. It includes all greenhouse gases, not just carbon dioxide. And it looks at emissions from economic activities, events, organizations and services. In some definitions, only the carbon dioxide emissions are taken into account. These do not include other greenhouse gases, such as methane and nitrous oxide.

Various methods to calculate the carbon footprint exist, and these may differ somewhat for different entities. For organizations it is common practice to use the Greenhouse Gas Protocol. It includes three carbon emission scopes. Scope 1 refers to direct carbon emissions. Scope 2 and 3 refer to indirect carbon emissions. Scope 3 emissions are those indirect emissions that result from the activities of an organization but come from sources which they do not own or control.

For countries it is common to use consumption-based emissions accounting to calculate their carbon footprint for a given year. Consumption-based accounting using input-output analysis backed by super-computing makes it possible to analyse global supply chains. Countries also prepare national GHG inventories for the UNFCCC. The GHG emissions listed in those national inventories are only from activities in the country itself. This approach is called territorial-based accounting or production-based accounting. It does not take into account production of goods and services imported on behalf of residents. Consumption-based accounting does reflect emissions from goods and services imported from other countries.

Consumption-based accounting is therefore more comprehensive. This comprehensive carbon footprint reporting including Scope 3 emissions deals with gaps in current systems. Countries' GHG inventories for the UNFCCC do not include international transport. Comprehensive carbon footprint reporting looks at the final demand for emissions, to where the consumption of the goods and services takes place.

Definition

Comparison of the carbon footprint of protein-rich foods

A formal definition of carbon footprint is as follows: "A measure of the total amount of carbon dioxide (CO₂) and methane (CH₄) emissions of a defined population, system or activity, considering all relevant sources, sinks and storage within the spatial and temporal boundary of the population, system or activity of interest. Calculated as carbon dioxide equivalent using the relevant 100-year global warming potential (GWP100)."

Scientists report carbon footprints in terms of equivalents of tonnes of CO₂ emissions (CO₂-equivalent). They may report them per year, per person, per kilogram of protein, per kilometer travelled, and so on.

In the definition of carbon footprint, some scientists include only CO_2. But more commonly they include several of the notable greenhouse gases. They can compare various greenhouse gases by using carbon dioxide equivalents over a relevant time scale, like 100 years. Some organizations use the term greenhouse gas footprint or climate footprint to emphasize that all greenhouse gases are included, not just carbon dioxide.

The Greenhouse Gas Protocol includes all of the most important greenhouse gases. "The standard covers the accounting and reporting of seven greenhouse gases covered by the Kyoto Protocol – carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), hydrofluorocarbons (HFCs), perfluorocarbons (PCFs), sulfur hexafluoride (SF₆) and nitrogen trifluoride (NF₃)."

In comparison, the IPCC definition of carbon footprint in 2022 covers only carbon dioxide. It defines the carbon footprint as the "measure of the exclusive total amount of emissions of carbon dioxide (CO₂) that is directly and indirectly caused by an activity or is accumulated over the lifecycle stages of a product." The IPCC report's authors adopted the same definition that had been proposed in 2007 in the UK. That publication included only carbon dioxide in the definition of carbon footprint. It justified this with the argument that other greenhouse gases were more difficult to quantify. This is because of their differing global warming potentials. They also stated that an inclusion of all greenhouse gases would make the carbon footprint indicator less practical. But there are disadvantages to this approach. One disadvantage of not including methane is that some products or sectors that have a high methane footprint such as livestock appear less harmful for the climate than they actually are.

Types of greenhouse gas emissions

The greenhouse gas protocol is a set of standards for tracking greenhouse gas emissions. The standards divide emissions into three scopes (Scope 1, 2 and 3) within the value chain. Greenhouse gas emissions caused directly by the organization such as by burning fossil fuels are referred to as Scope 1. Emissions caused indirectly by an organization, such as by purchasing secondary energy sources like electricity, heat, cooling or steam are called Scope 2. Lastly, indirect emissions associated with upstream or downstream processes are called Scope 3.

Direct carbon emissions (Scope 1)

Direct or Scope 1 carbon emissions come from sources on the site that is producing a product or delivering a service. An example for industry would be the emissions from burning a fuel on site. On the individual level, emissions from personal vehicles or gas-burning stoves are Scope 1.

Indirect carbon emissions (Scope 2)

Indirect carbon emissions are emissions from sources upstream or downstream from the process being studied. They are also known as Scope 2 or Scope 3 emissions.

Scope 2 emissions are the indirect emissions related to purchasing electricity, heat, or steam used on site. Examples of upstream carbon emissions include transportation of materials and fuels, any energy used outside of the production facility, and waste produced outside the production facility. Examples of downstream carbon emissions include any end-of-life process or treatments, product and waste transportation, and emissions associated with selling the product. The GHG Protocol says it is important to calculate upstream and downstream emissions. There could be some double counting. This is because upstream emissions of one person's consumption patterns could be someone else's downstream emissions

Other indirect carbon emissions (Scope 3)

Scope 3 emissions are all other indirect emissions derived from the activities of an organization. But they are from sources they do not own or control. The GHG Protocol's Corporate Value Chain (Scope 3) Accounting and Reporting Standard allows companies to assess their entire value chain emissions impact and identify where to focus reduction activities.

Scope 3 emission sources include emissions from suppliers and product users. These are also known as the value chain. Transportation of good, and other indirect emissions are also part of this scope. In 2022 about 30% of US companies reported Scope 3 emissions. The International Sustainability Standards Board is developing a recommendation to include Scope 3 emissions in all GHG reporting.

Purpose and strengths

The current rise in global average temperature is more rapid than previous changes. It is primarily caused by humans burning fossil fuels. The increase in greenhouse gases in the atmosphere is also due to deforestation and agricultural and industrial practices. These include cement production. The two most notable greenhouse gases are carbon dioxide and methane. Greenhouse gas emissions, and hence humanity's carbon footprint, have been increasing during the 21st century. The Paris Agreement aims to reduce greenhouse gas emissions enough to limit the rise in global temperature to no more than 1.5°C above pre-industrial levels.

The carbon footprint concept makes comparisons between the climate impacts of individuals, products, companies and countries. A carbon footprint label on products could enable consumers to choose products with a lower carbon footprint if they want to help limit climate change. For meat products, as an example, such a label could make it clear that beef has a higher carbon footprint than chicken.

Understanding the size of an organization's carbon footprint makes it possible to devise a strategy to reduce it. For most businesses the vast majority of emissions do not come from activities on site, known as Scope 1, or from energy supplied to the organization, known as Scope 2, but from Scope 3 emissions, the extended upstream and downstream supply chain. Therefore, ignoring Scope 3 emissions makes it impossible to detect all emissions of importance, which limits options for mitigation. Large companies in sectors such as clothing or automobiles would need to examine more than 100,000 supply chain pathways to fully report their carbon footprints.

The importance of displacement of carbon emissions has been known for some years. Scientists also call this carbon leakage. The idea of a carbon footprint addresses concerns of carbon leakage which the Paris Agreement does not cover. Carbon leakage occurs when importing countries outsource production to exporting countries. The outsourcing countries are often rich countries while the exporters are often low-income countries. Countries can make it appear that their GHG emissions are falling by moving "dirty" industries abroad, even if their emissions could be increasing when looked at from a consumption perspective.

Carbon leakage and related international trade have a range of environmental impacts. These include increased air pollution, water scarcity, biodiversity loss, raw material usage, and energy depletion.

Scholars have argued in favour of using both consumption-based and production-based accounting. This helps establish shared producer and consumer responsibility. Currently countries report on their annual GHG inventory to the UNFCCC based on their territorial emissions. This is known as the territorial-based or production-based approach. Including consumption-based calculations in the UNFCCC reporting requirements would help close loopholes by addressing the challenge of carbon leakage.

The Paris Agreement currently does not require countries to include in their national totals GHG emissions associated with international transport. These emissions are reported separately. They are not subject to the limitation and reduction commitments of Annex 1 Parties under the Climate Convention and Kyoto Protocol. The carbon footprint methodology includes GHG emissions associated with international transport, thereby assigning emissions caused by international trade to the importing country.

Underlying concepts for calculations

The calculation of the carbon footprint of a product, service or sector requires expert knowledge and careful examination of what is to be included. Carbon footprints can be calculated at different scales. They can apply to whole countries, cities, neighborhoods and also sectors, companies and products. Several free online carbon footprint calculators exist to calculate personal carbon footprints.

Software such as the "Scope 3 Evaluator" can help companies report emissions throughout their value chain. The software tools can help consultants and researchers to model global sustainability footprints. In each situation there are a number of questions that need to be answered. These include which activities are linked to which emissions, and which proportion should be attributed to which company. Software is essential for company management. But there is a need for new ways of enterprise resource planning to improve corporate sustainability performance.

To achieve 95% carbon footprint coverage, it would be necessary to assess 12 million individual supply-chain contributions. This is based on analyzing 12 sectoral case studies. The Scope 3 calculations can be made easier using input-output analysis. This is a technique originally developed by Nobel Prize-winning economist Wassily Leontief.

Consumption-based emission accounting based on input-output analysis

Consumption-based emission accounting traces the impacts of demand for goods and services along the global supply chain to the end-consumer. It is also called consumption-based carbon accounting. In contrast, a production-based approach to calculating GHG emissions is not a carbon footprint analysis. This approach is also called a territorial-based approach. The production-based approach includes only impacts physically produced in the country in question. Consumption-based accounting redistributes the emissions from production-based accounting. It considers that emissions in another country are necessary for the home country's consumption bundle.

Consumer-based accounting is based on input-output analysis. It is used at the highest levels for any economic research question related to environmental or social impacts. Analysis of global supply chains is possible using consumption-based accounting with input-output analysis assisted by super-computing capacity.

Leontief created Input-output analysis (IO) to demonstrate the relationship between consumption and production in an economy. It incorporates the entire supply chain. It uses input-output tables from countries' national accounts. It also uses international data such as UN Comtrade and Eurostat. Input-output analysis has been extended globally to multi-regional input-output analysis (MRIO). Innovations and technology enabling the analysis of billions of supply chains made this possible. Standards set by the United Nations underpin this analysis. The analysis enables a Structural Path Analysis. This scans and ranks the top supply chain nodes and paths. It conveniently lists hotspots for urgent action. Input-output analysis has increased in popularity because of its ability to examine global value chains.

Combination with life cycle analysis (LCA)

Life cycle assessment (LCA) is a methodology for assessing all environmental impacts associated with the life cycle of a commercial product, process, or service. It is not limited to the greenhouse gas emissions. It is also called life cycle analysis. It includes water pollution, air pollution, ecotoxicity and similar types of pollution. Some widely recognized procedures for LCA are included in the ISO 14000 series of environmental management standards. A standard called ISO 14040:2006 provides the framework for conducting an LCA study. ISO 14060 family of standards provides further sophisticated tools. These are used to quantify, monitor, report and validate or verify GHG emissions and removals.

Greenhouse gas product life cycle assessments can also comply with specifications such as Publicly Available Specification (PAS) 2050 and the GHG Protocol Life Cycle Accounting and Reporting Standard.

An advantage of LCA is the high level of detail that can be obtained on-site or by liaising with suppliers. However, LCA has been hampered by the artificial construction of a boundary after which no further impacts of upstream suppliers are considered. This can introduce significant truncation errors. LCA has been combined with input-output analysis. This enables on-site detailed knowledge to be incorporated. IO connects to global economic databases to incorporate the entire supply chain.

Problems

Shifting responsibility from corporations to individuals

Critics argue that the original aim of promoting the personal carbon footprint concept was to shift responsibility away from corporations and institutions and on to personal lifestyle choices. The fossil fuel company BP ran a large advertising campaign for the personal carbon footprint in 2005 which helped popularize this concept. This strategy, employed by many major fossil fuel companies, has been criticized for trying to shift the blame for negative consequences of those industries on to individual choices.

Geoffrey Supran and Naomi Oreskes of Harvard University argue that concepts such as carbon footprints "hamstring us, and they put blinders on us, to the systemic nature of the climate crisis and the importance of taking collective action to address the problem".

Relationship with other environmental impacts

A focus on carbon footprints can lead people to ignore or even exacerbate other related environmental issues of concern. These include biodiversity loss, ecotoxicity, and habitat destruction. It may not be easy to measure these other human impacts on the environment with a single indicator like the carbon footprint. Consumers may think that the carbon footprint is a proxy for environmental impact. In many cases this is not correct. There can be trade-offs between reducing carbon footprint and environmental protection goals. One example is the use of biofuel, a renewable energy source and can reduce the carbon footprint of energy supply but can also pose ecological challenges during its production. This is because it is often produced in monocultures with ample use of fertilizers and pesticides.Another example is offshore wind parks, which could have unintended impacts on marine ecosystems.

The carbon footprint analysis solely focuses on greenhouse gas emissions, unlike a life-cycle assessment which is much broader and looks at all environmental impacts. Therefore, it is useful to stress in communication activities that the carbon footprint is just one in a family of indicators (e.g. ecological footprint, water footprint, land footprint, and material footprint), and should not be looked at in isolation. In fact, carbon footprint can be treated as one component of ecological footprint.

The "Sustainable Consumption and Production Hotspot Analysis Tool" (SCP-HAT) is a tool to place carbon footprint analysis into a wider perspective. It includes a number of socio-economic and environmental indicators. It offers calculations that are either consumption-based, following the carbon footprint approach, or production-based. The database of the SCP-HAT tool is underpinned by input–output analysis. This means it includes Scope 3 emissions. The IO methodology is also governed by UN standards. It is based on input-output tables of countries' national accounts and international trade data such as UN Comtrade, and therefore it is comparable worldwide.

Differing boundaries for calculations

The term carbon footprint has been applied to limited calculations that do not include Scope 3 emissions or the entire supply chain. This can lead to claims of misleading customers with regards to the real carbon footprints of companies or products.

Reported values

Greenhouse gas emissions overview

Greenhouse gas (GHG) emissions from human activities intensify the greenhouse effect. This contributes to climate change. Carbon dioxide (CO₂), from burning fossil fuels such as coal, oil, and natural gas, is the main cause of climate change. The largest annual emissions are from China followed by the United States. The United States has higher emissions per capita. The main producers fueling the emissions globally are large oil and gas companies. Emissions from human activities have increased atmospheric carbon dioxide by about 50% over pre-industrial levels. The growing levels of emissions have varied, but have been consistent among all greenhouse gases. Emissions in the 2010s averaged 56 billion tons a year, higher than any decade before. Total cumulative emissions from 1870 to 2022 were 703 GtC (2575 GtCO₂), of which 484±20 GtC (1773±73 GtCO₂) from fossil fuels and industry, and 219±60 GtC (802±220 GtCO₂) from land use change. Land-use change, such as deforestation, caused about 31% of cumulative emissions over 1870–2022, coal 32%, oil 24%, and gas 10%.

Carbon dioxide is the main greenhouse gas resulting from human activities. It accounts for more than half of warming. Methane (CH₄) emissions have almost the same short-term impact. Nitrous oxide (N₂O) and fluorinated gases (F-gases) play a lesser role in comparison. Emissions of carbon dioxide, methane and nitrous oxide in 2023 were all higher than ever before.

By products

Carbon footprint of EU diets by supply chain

The Carbon Trust has worked with UK manufacturers to produce "thousands of carbon footprint assessments". As of 2014 the Carbon Trust state they have measured 28,000 certifiable product carbon footprints.

Food

Plant-based foods tend to have a lower carbon footprint than meat and dairy. In many cases a much smaller footprint. This holds true when comparing the footprint of foods in terms of their weight, protein content or calories. The protein output of peas and beef provides an example. Producing 100 grams of protein from peas emits just 0.4 kilograms of carbon dioxide equivalents (CO₂eq). To get the same amount of protein from beef, emissions would be nearly 90 times higher, at 35 kgCO₂eq. Only a small fraction of the carbon footprint of food comes from transport and packaging. Most of it comes from processes on the farm, or from land use change. This means the choice of what to eat has a larger potential to reduce carbon footprint than how far the food has traveled, or how much packaging it is wrapped in.

By sector

The IPCC Sixth Assessment Report found that global GHG emissions have continued to rise across all sectors. Global consumption was the main cause. The most rapid growth was in transport and industry. A key driver of global carbon emissions is affluence. The IPCC noted that the wealthiest 10% in the world contribute between about one third to one half (36%–45%) of global GHG emissions. Researcheres have previously found that affluence is the key driver of carbon emissions. It has a bigger impact than population growth. And it counters the effects of technological developments. Continued economic growth mirrors the increasing trend in material extraction and GHG emissions. “Industrial emissions have been growing faster since 2000 than emissions in any other sector, driven by increased basic materials extraction and production,” the IPCC said.

Transport

There can be wide variations in emissions for transport of people. This is due to various factors. They include the length of the trip, the source of electricity in the local grid and the occupancy of public transport. In the case of driving the type of vehicle and number of passengers are factors. Over short to medium distances, walking or cycling are nearly always the lowest carbon way to travel. The carbon footprint of cycling one kilometer is usually in the range of 16 to 50 grams CO₂eq per km. For moderate or long distances, trains nearly always have a lower carbon footprint than other options.

By organization

Carbon accounting

Carbon accounting (or greenhouse gas accounting) is a framework of methods to measure and track how much greenhouse gas (GHG) an organization emits. It can also be used to track projects or actions to reduce emissions in sectors such as forestry or renewable energy. Corporations, cities and other groups use these techniques to help limit climate change. Organizations will often set an emissions baseline, create targets for reducing emissions, and track progress towards them. The accounting methods enable them to do this in a more consistent and transparent manner.

The main reasons for GHG accounting are to address social responsibility concerns or meet legal requirements. Public rankings of companies, financial due diligence and potential cost savings are other reasons. GHG accounting methods help investors better understand the climate risks of companies they invest in. They also help with net zero emission goals of corporations or communities. Many governments around the world require various forms of reporting. There is some evidence that programs that require GHG accounting help to lower emissions. Markets for buying and selling carbon credits depend on accurate measurement of emissions and emission reductions. These techniques can help to understand the impacts of specific products and services. They do this by quantifying their GHG emissions throughout their lifecycle (carbon footprint).

By country

CO₂ emissions of countries are typically measured on the basis of production. This accounting method is sometimes referred to as territorial emissions. Countries use it when they report their emissions, and set domestic and international targets such as Nationally Determined Contributions. Consumption-based emissions on the other hand are adjusted for trade. To calculate consumption-based emissions analysts have to track which goods are traded across the world. Whenever a product is imported, all CO₂ emissions that were emitted in the production of that product are included. Consumption-based emissions reflect the lifestyle choices of a country's citizens.

According to the World Bank, the global average carbon footprint in 2014 was about 5 tonnes of CO₂ per person, measured on a production basis. The EU average for 2007 was about 13.8 tonnes CO₂e per person. For the USA, Luxembourg and Australia it was over 25 tonnes CO₂e per person. In 2017, the average for the USA was about 20 metric tonnes CO₂e per person. This is one of the highest per capita figures in the world.

The footprints per capita of countries in Africa and India were well below average. Per capita emissions in India are low for its huge population. But overall the country is the third largest emitter of CO₂ and fifth largest economy by nominal GDP in the world.^[91] Assuming a global population of around 9–10 billion by 2050, a carbon footprint of about 2–2.5 tonnes CO₂e per capita is needed to stay within a 2 °C target. These carbon footprint calculations are based on a consumption-based approach using a Multi-Regional Input-Output (MRIO) database. This database accounts for all greenhouse gas (GHG) emissions in the global supply chain and allocates them to the final consumer of the purchased commodities.

Reducing the carbon footprint

Climate change mitigation

Efforts to reduce the carbon footprint of products, services and organizations help limit climate change. Such activities are called climate change mitigation.

Climate change mitigation (or decarbonisation) is action to limit the greenhouse gases in the atmosphere that cause climate change. Climate change mitigation actions include conserving energy and replacing fossil fuels with clean energy sources. Secondary mitigation strategies include changes to land use and removing carbon dioxide (CO₂) from the atmosphere. Current climate change mitigation policies are insufficient as they would still result in global warming of about 2.7 °C by 2100, significantly above the 2015 Paris Agreement's goal of limiting global warming to below 2 °C.

Reducing industry's carbon footprint

Carbon offsetting can reduce a company's overall carbon footprint by providing it with a carbon credit. This compensates the company for carbon dioxide emissions by recognizing an equivalent reduction of carbon dioxide in the atmosphere. Reforestation, or restocking existing forests that have previously been depleted, is an example of carbon offsetting.

A carbon footprint study can identify specific and critical areas for improvement. It uses input-output analysis and scrutinizes the entire supply chain. Such an analysis could be used to eliminate the supply chains with the highest greenhouse gas emissions.

History

The term carbon footprint was first used in a BBC vegetarian food magazine in 1999, though the broader concept of ecological footprint, which encompasses the carbon footprint, had been used since at least 1992, as also chronicled by William Safire in the New York Times.

In 2005, fossil fuel company BP hired the large advertising campaign Ogilvy to popularize the idea of a carbon footprint for individuals. The campaign instructed people to calculate their personal footprints and provided ways for people to "go on a low-carbon diet".

The carbon footprint is derived from the ecological footprint, which encompasses carbon emissions. The carbon footprint follows the logic of ecological footprint accounting, which tracks the resource use embodied in consumption, whether it is a product, an individual, a city, or a country. While in the ecological footprint, carbon emissions are translated into areas needed to absorb the carbon emissions, the carbon footprint on its own is expressed in the weight of carbon emissions per time unit. William Rees wrote the first academic publication about ecological footprints in 1992. Other related concepts from the 1990s are the "ecological backpack" and material input per unit of service (MIPS).

Trends and similar concepts

The International Sustainability Standards Board (ISSB) aims to bring global, rigorous oversight to carbon footprint reporting. It was formed out of the International Financial Reporting Standards. It will require companies to report on their Scope 3 emissions. The ISSB has taken on board criticisms of other initiatives in its aims for universality. It consolidates the Carbon Disclosure Standards Board, the Sustainability Accounting Standards Board and the Value Reporting Foundation. It complements the Global Reporting Initiative. It is influenced by the Task Force on Climate-Related Financial Disclosures. As of early 2023, Great Britain and Nigeria were preparing to adopt these standards.

The concept of total equivalent warming impact (TEWI) is the most used index for carbon dioxide equivalent (CO₂) emissions calculation in air conditioning and refrigeration sectors by including both the direct and indirect contributions since it evaluates the emissions caused by the operating lifetime of systems. The Expanded Total Equivalent Warming Impact method has been used for an accurate evaluation of refrigerators emissions.

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