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Greenhouse gas emissions from international aviation and allocation options

7 CO₂ Emissions from international aviation

This chapter is intended to give an overview of CO₂ emissions from domestic and international aviation activities. Section 7.1 describes some international conventions under which the Parties are obliged to report emissions from aviation activities. The convention of main concern for this project is United Nations Framework Convention on Climate Change (UNFCCC) under which emissions from domestic aviation are to be included in national totals whereas emissions from international aviation are not to be included in national totals but should be reported separately. Sections 7.1.2 and 7.1.2.1 describes in brief the main principles of the reporting guidelines for aviation under UNFCCC. Section 7.2 continues by describing the emissions of CO₂ reported by Parties to the UNFCCC. The UNFCCC data are supplemented by data from the International Energy Agency (IEA). The main reasons for also looking at IEA data are that the reporting by Annex I Parties to the UNFCCC of CO₂ emissions from domestic and international aviation is rather incomplete and furthermore that non-Annex I countries have not yet started reporting these emissions. The IEA have collected data on fuel sold for domestic and international aviation for decades and hold such data spanning back to 1971. Section 7.3 describes in brief some of the problems related to the data on emissions from domestic and international aviation reported by Parties to the UNFCCC.

7.1 International conventions and reporting obligations

This section gives a brief summary of the main reporting obligations for emissions from air transport.

7.1.1 UNECE Long Range Transboundary Air Pollution Convention

The Convention on Long Range Transboundary Air Pollution (LRTAP) was adopted in Geneva in 1979 and aims at preventing acid rain and photochemical smog. Several protocols are in force, dealing with different emissions. These Protocols are: The Helsinki Sulphur Protocol (1985), the Sofia NO_x Protocol (1988), the Geneva VOC Protocol (1991), the Oslo Sulphur Protocol (1994) and the Aarhus Protocols on Heavy Metal and on Persistent Organic Pollutants (POPs). Parties are required to submit annual national emissions of SO₂, NO_x, NMVOC, CH₄, CO and NH₃ and various heavy metals and POPs to UNECE (United Nations Economic Commission for Europe). Concerning aviation, UNECE request only data for emissions from the Landing and Take Off (LTO) phase of the flight for all other emissions species than CO₂. Only emissions of CO₂ are to be reported for the entire LTO and cruise phase [CORINAIR 2001]. This is different from the reporting requirements of the UNFCCC where Parties should report emissions through all stages of the flight, not only LTO emissions.

7.1.2 United Nations Framework Convention on Climate Change

United Nations Framework Convention on Climate Change aims at stabilising atmospheric greenhouse gas concentrations at a safe level within an acceptable time frame. All Parties to the Convention shall report national inventories of anthropogenic emissions by sources and removals by sinks of all greenhouse gases not controlled by the Montreal Protocol. Parties are required to report CO₂, CH₄, N₂O, PFCs, HFCs and SF₆ and should also provide information on emissions of CO, NO_x and NMVOCs and are encouraged to provide information on emissions of SO₂. Concerning aviation, unlike UNECE, UNFCCC requests reporting of emissions for the entire LTO and cruise phase [IPCC 2000].

7.1.2.1 IPCC reporting guidelines

UNFCCC requires Parties to use the "Revised 1996 IPCC Guidelines for National Greenhouse Gas Inventories" [IPCC 1996b, 1996c, 1996d]. IPCC has developed reporting guidelines that are described in the guidance document "Good Practice Guidance and Uncertainty Management in National Greenhouse Gas Inventories" [IPCC 2000].

According to the IPCC guidelines, generally national inventories should include greenhouse gas emissions and removals taking place within national (including administered) territories and offshore areas over which the country has jurisdiction. Thus, emissions from domestic air transport are to be included in national inventories. However, emissions based upon fuel sold to aircraft engaged in international transport should not be included in national totals but reported separately under international bunker emissions [IPCC 2000]. The main methodological problem related to this reporting is that national energy statistics often contain inaccurate estimates of the split between fuel sold for domestic and international activities [Velzen 2000] [Olivier 1999].

According to the current IPCC definition, civil aviation includes emissions from all civil commercial use of airplanes (international and domestic) consisting of scheduled and charter traffic for passengers and freight, including air taxiing, as well as general aviation (e.g. agricultural airplanes, private jets or helicopters). IPCC methods can also be used to estimate emissions from military aviation, but these emissions should be reported under the IPCC category 'Other'. Stationary combustion and ground transport at airports are to be included in other appropriate categories [IPCC 2000].

The IPPC definition of the split between domestic and international flights can be seen from Table 1. These definitions should be applied irrespective of the nationality of the carrier.

The IPCC guidelines note that fuel use data distinguished between domestic and international aviation may be obtained in different ways. What is feasible will depend on national circumstances, but some data sources (e.g. energy statistics or surveys) will give more accurate results than others. The following data sources should be evaluated:

1. Bottom-up data can be obtained from surveys of airline companies for fuel used, or estimates from aircraft movement data and standard tables of fuel consumed or both.
     
2. Top-down data can be obtained from national energy statistics or surveys of:

	Airports for data covering the delivery of aviation kerosene and aviation gasoline
	Fuel suppliers (quantity of aviation fuel delivered)
	Refineries (production of aviation fuels), to be corrected for import and export

3. Fuel consumption factors for aircraft (fuel used per LTO and per nautical mile cruised) can be used for estimates and may be obtained from the airline companies.

Table 1:
IPCC distinction between domestic and international flights [IPCC 2000]

Aircraft emit carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O), as well as carbon monoxide (CO), non-methane volatile organic compounds (NMVOCs), sulfur dioxide (SO₂), particulate matter (PM) and nitrogen oxides (NO_x). The IPCC methodology focuses on estimating the direct greenhouse gases CO₂, CH₄ and N₂O.

The IPCC guidelines for calculating aircraft emissions operate with three methods of varying accuracy, detail and complexity (this is in line with the CORINAIR and ANCAT/EMCAL reporting guidelines used by some EU Member States as discussed further in sections 8.1 and 8.2). These methodologies are dubbed Tier 1, Tier 2a and Tier 2b.

The simple Tier 1 method is based on an aggregate figure of fuel consumption for civil aviation multiplied by average emissions factors. For Tier 1 emission inventories only data on fuel consumption are needed. Emissions are estimated on the basis of the quantities of fuel consumed and average emission factors based on fleet average values, based on the assumption that 10% of the fuel is used in the LTO (landing/take off) phase of the flight.

In the Tier 2 methods emissions are separated into emissions below and above 3000 feet (914 m) to harmonise the methodology with other methods (such as the CORINAIR Methodology, see section 8.1). This distinction is made to increase the accuracy of the estimates as emission factors and fuel use factors vary between phases of the flight. In the Tier 2 methods the emission estimates are furthermore based on actual composition of the aircraft fleet and movement data. Tier 2a uses more aggregate aircraft data than Tier 2b, Tier 2a corresponding the CORINAIR Simple Methodology (see section 8.1) while Tier 2b resembles the CORINAIR Detailed Methodology (see section 8.1), but is less detailed in the number of aircraft categories and emission factors. Similar to the CORINAIR and ANCAT/EMCAL guidelines (see sections 8.1 and 8.2) the IPCC guidelines allow Parties to use national approaches if they are well documented and have been peer reviewed. A more detailed description of guidelines for estimating emission inventories is given in section 8.1 describing the CORINAIR guidelines.

7.1.3 Other reporting obligations

The European Community has adopted a monitoring mechanism on CO₂ and other greenhouse gas emissions. Member States shall report to the Commission their national inventory data on emissions and removal by sinks of the six Kyoto Greenhouse gases on an annual basis. Inventories are established in accordance with the methodologies accepted by IPCC and agreed upon by the Conference of Parties [CORINAIR 2001].

7.2 Aviation greenhouse gas emissions

This section gives a brief overview of different data sources for aviation greenhouse gas emissions. Section 7.2.1 presents the data on emissions from domestic and international aviation reported by Annex I Parties to the UNFCCC. Sections 7.2.2 and 7.2.3 presents data that are currently reported to the IEA for Annex 1 and Annex 2 countries using them as a basis for giving an overview of global aviation emissions. Section 7.2.2 describes CO₂ emissions from domestic and international aviation while section 7.2.3 focuses on CO₂ emissions from international aviation. Section 7.2.4 compares the data on CO₂ emissions from international aviation bunkers reported to the IEA and UNFCCC by Annex I countries.

7.2.1 Emissions from domestic and international aviation reported by Annex I Parties to the UNFCCC

This section briefly describes the data reported in 2001 from those Annex I countries that have used the Common Reporting Format (CRF). Appendix K to this report contains the full reporting on emissions of the three greenhouse gases CO₂, CH₄, N₂O, as well as the three indirect greenhouse gases CO, NO_x and NMVOCs and for SO₂ for the years 1990-1999. The data shown in Appendix K are published in a Working Paper that was recently submitted to ICAO by the UNFCCC Secretariat [UNFCCC 2002c]. The UNFCCC Working Paper illustrates that, in the 2001 reporting, of the 32 Annex I Parties, 12 Parties report CO₂ emissions from domestic aviation in all the years from 1990-1999 while 16 Parties report CO₂ emissions from international aviation in all the years from 1990-1999. Fewer Parties report the other emissions species from aviation for the whole period 1990-1999. Thus, currently there seems to be an inadequate geographical coverage of the data reported to the UNFCCC by Annex I Parties.

7.2.2 Global CO₂ emissions from domestic and international aviation - IEA data

To give a brief overview of global CO₂ emissions from domestic and international aviation activities we use the statistics provided by the International Energy Agency (IEA). We note that statistics on emissions from international aviation bunkers are known to be relatively weak, especially in the distinction between fuel used for domestic and international purposes [UNFCCC 1999f] [Olivier 1999] [Velzen 2000]. For example, the IEA notes that some countries (in both Annex I and non-Annex I countries) have incorrectly defined international bunkers as fuel used abroad by their own aircraft or have included international bunkers in their national totals [IEA 2001, p. I.4]. Furthermore, the IEA uses another definition of domestic aviation including the military use of aviation fuels, which, under the UNFCCC guidelines, are to be reported under the Source/sink category 1A5, "Other" [IEA 2001, p. I.5]. Furthermore, the IEA data on CO₂ emissions from aviation may be based on other units for calculating emissions from fuels than those used by individual Parties in their reporting to the UNFCCC [IEA 2001, p. I.6]. Therefore, the IEA data shown for emissions from domestic and international aviation in this section should be used with care, especially in comparisons to UNFCCC data.

Figure 8:
Global CO₂ emissions from domestic and international aviation 1971-1999. Source: [IEA 2002].

Figure 8 illustrates the growth in global emissions of CO₂ from domestic and international aviation based on data reported by countries to the IEA. According to these data aviation emitted around 635 million tonnes of CO₂ in 1999, corresponding about 3% of the 22.148 million tonnes of CO₂ emitted from fuel combustion globally in 1999 [IEA 2001]. In 1999, domestic aviation emit around 300 million tonnes while international aviation emit around 335 million tonnes. In the period between 1971 and 2000 global CO₂ emissions from aviation activities approximately doubled thereby growing faster than the total emissions of CO₂ from fuel combustion that grew by 50% in the period [IEA 2002].

Figure 9 illustrates that the top 20 emitters of CO₂ represent around 82% of the CO₂ emissions from domestic and international aviation activities. The United States alone represents 39% of CO₂ emissions and is by far the biggest consumer.

Figure 9:
Top 20 emitters of CO₂ emissions from domestic and international aviation 1999. Source: [IEA 2002].

Figure 10 illustrates the top 20 per capita emitters of CO₂ from domestic and international aviation activities. In terms of CO₂ per capita a range of smaller countries are major sellers of aviation fuel.

Figure 10:
Top 20 per capita emitters of CO₂ from domestic and international aviation 1999. Source: [IEA 2002].

It should be noted that the IEA data described in this section merely illustrates where the fuel used for domestic and international aviation is sold. The data do not show which nationalities are using the aviation services. Because of the truly international nature of aviation, airlines registered in one country can lift fuel from another country while transporting passengers and freight originating from a third country.

7.2.3 CO₂ emissions from international aviation bunkers for Annex I and Annex II countries - IEA data

Figure 11 plots data for the emissions of CO₂ from international aviation bunkers in 1971 and 1999 as collected by the IEA. Figure 11 suggests that CO₂ emissions from fuel sold for international aviation activities have doubled in the period. In 1971 non-OECD countries reported the main part of the CO₂ emissions from international aviation bunkers, whereas in 1999 the OECD countries represent the major part. Furthermore, as it is explained in the later chapter that discusses the allocation issue, the major share of the fuel sold for international air transport in non-OECD countries may most likely be attributable to passenger air travel performed by people living in OECD countries. Thus, Figure 11 merely illustrates where the fuel used for international aviation is sold, it does not show which nationalities that uses these services.

Figure 11:
IEA data on CO₂ emissions from international aviation bunkers 1971 and 1999. Source: [IEA 2001].

Statistics on emissions from international aviation bunkers are known to be relatively weak, especially in the distinction between fuel used for domestic and international purposes [Velzen 1999]. Therefore, the data shown for emissions from international aviation bunkers in this section should be used with care.

In 1999, according to the IEA statistics, the global emissions of CO₂ from fuel combustion add up to around 22.148 million tonnes excluding emissions from international aviation and marine bunkers. Emissions of CO₂ from international aviation bunkers equal 335 million tonnes and international marine bunkers equal 423 million tonnes, or about 1,5% and 1,9% of the total respectively.

Note that the figures discussed in this section do not include CO₂ emissions from fuel consumed for domestic aviation. In some of the large industrialised OECD countries rather large shares of the jet fuel is sold for domestic purposes (see Table 17, Appendix G) and the related CO₂ emissions are thereby already included in national reduction targets for greenhouse gases under the Climate Convention. Some examples of countries in which domestic air transport represents a rather significant share of the total air transport activities are summarised in Table 3 (in section 7.2.4).

Note also, that little less than one third of the CO₂ emissions from international aviation bunkers in 1999 relate to fuel sold in non-annex I countries that have not yet agreed to emission reduction targets under the Climate Convention. Furthermore, Annex I Parties that have not yet decided upon rectifying the Kyoto Protocol represent a rather significant share of the jet fuel sold (for domestic and international purposes) in Annex I countries¹⁹.

Figure 12 illustrates that around 80% of the total CO₂ emissions from international aviation bunkers are emitted by the 25 countries that have the largest sales of jet kerosene for international purposes. The United States is by far the biggest consumer.

Figure 12:
Top-25 consumers of international aviation bunkers. Source: [IEA 2001].

While Figure 12 illustrates the biggest consumers of jet fuel for international aviation activities, Figure 13 illustrate the top-25 consumers per capita. Again, as also noted in section 7.2.1, dealing with both domestic and international aviation, some relatively small countries have relatively high per capita sales of jet fuel.

Figure 13:
Top-25 consumers of international aviation bunkers per capita. Source: [IEA 2001].

Figure 14 illustrates the 25 countries where CO₂ emissions from international bunkers constitute the highest shares of national emissions of CO₂.

Figure 14:
The 25 Parties where international aviation bunkers constitute the largest share of total national CO₂ emissions. Source: [IEA 2001].

It should be noted that such a comparison is to some extent biased by the fact that national CO₂ emissions does not only depend on the use of energy services within a country, but also on the fuel intensity, that is for example the amount of fuel consumed per vehicle kilometre driven, and the types of primary energy used in each country's energy production system (countries that utilize CO₂ neutral energy sources such as hydro and wind or nuclear have lower CO₂ emissions per energy unit produced than countries using primarily fossil fuels). The differences between the rankings in Figure 13 and Figure 14 can thus be explained by differences between countries in the CO₂ intensity (fuel mix).

Figure 15 illustrates the significance of CO₂ emissions from international aviation bunkers for Annex I countries. The figure basically illustrates the same elements as those shown in Figure 13 and Figure 14, but this time only for Annex I countries. It goes beyond the scope of this report to describe in more detail the differences in activity, energy intensity and fuel mix that are underlying factors behind the figure. The data shown can however be used to exemplify the how different Annnex I countries could be affected if emissions of CO₂ from international aviation were to be allocated to Parties according to where the fuel is sold. We note that other allocation options are also possible that could involve other ways of distributing emissions between countries. This is discussed further in chapter 10.

Figure 15:
Significance of CO₂ emissions from international aviation bunkers for Annex I countries. Source: [IEA 2001].

7.2.4 Comparison of international aviation bunker emission statistics from IEA and UNFCCC - Annex I countries

This section continues by comparing the IEA data discussed in sections 7.2.2 and 7.2.3 to data reported by Parties to the UNFCCC.

A recent synthesis and assessment report from the UNFCCC describing the greenhouse gas inventories submitted by Annex 1 countries in 2001 contains a section wherein the data on aviation fuel consumption submitted to the UNFCCC are compared to similar data submitted to the International Energy Agency (IEA). This comparison shows that there is rather good agreement between the overall figures for total aviation fuel consumption but that for some Parties there are major discrepancies in the way the split between domestic and international uses are reported to the UNFCCC and the IEA [UNFCCC 2002b], see Table 17, Appendix G. Table 2 shows the deviation between data from the UNFCCC and the IEA for CO₂ emissions from international aviation bunkers for Annex I countries. As can be seen, for some countries there are quite big variations up to above 50%.

Table 2:
Comparison of data from IEA and UNFCCC for international aviation bunkers. See Table 17, Appendix G for more information on differences between UNFCCC and IEA data. Sources: [UNFCCC 2002b] and [IEA 2001].

Table 3 shows the deviation between data reported by Parties to the UNFCCC and the IEA for shares of fuel sold for domestic aviation in selected countries. Table 3 suggests that these large countries use significant shares of their total aviation fuel consumption for domestic purposes. The United States alone generate somewhere between 154-198 million tonnes of CO₂ from domestic aviation alone. For comparison, this corresponds to about 50% of the total emissions from international aviation bunkers globally. It should be noted that some of the difference between the shares of fuel sold for domestic and international aviation shown in Table 3 may be attributable to the before mentioned fact that the UNFCCC guidelines requires that Parties report fuel consumption for military aviation under the Source/sink category 1A5, "Other" while this is included under domestic aviation under IEA reporting guidelines [IEA 2001].

Table 3:
Shares of fuel sold for domestic aviation, selected countries. Source: [UNFCCC 2002b, p. 50]. See Table 17, Appendix G for more countries.

7.3 Discussion on statistics on fuel consumption and emissions

A few studies have been conducted aimed at describing the methods used to collect data and estimate and report emissions from aviation bunker fuels²⁰. These studies report that aviation emissions are complicated to estimate because the statistical basis is relatively weak. Especially the distinction between fuel used for domestic and international purposes is difficult [IEA 2001] [Velzen 1999] [UNFCCC 1999b and 1999f]. Another problem is the separation of fuel consumed by military aircraft from fuel consumed by civil aircraft. According to the UNFCCC guidelines Parties should report fuel consumption for military aviation under the Source/sink category 1A5, "Other" while this is included under domestic aviation under IEA reporting guidelines [IEA 2001].

Of the 32 Annex I Parties, 12 Parties report CO₂ emissions from domestic aviation in all the years from 1990-1999 while 16 Parties report CO₂ emissions from international aviation in all the years from 1990-1999. Fewer Parties report the other emissions species from aviation for the whole period 1990-1999 [UNFCCC 2002c]. Thus, currently there seems to be an inadequate geographical coverage of the data reported to the UNFCCC by Annex I Parties.

The UNFCCC Secretariat has requested CAEP to explore opportunities to examine and improve the quality of data reporting and comparability of aviation bunker fuel data [UNFCCC 2002a]. CAEPs Steering Group Meeting in September 2002 agreed that the ICAO Secretariat should take the necessary steps to organize a "scoping meeting", involving the UNFCCC Secretariat, the rapporteurs of some of CAEPs working groups and experts on emissions inventory and data reporting [CAEP 2002a]. This initiative may bring new insights of relevance to this report, but the deadline of work lies beyond the deadline of this report, and the initiative is therefore not described further here.

Eurostat and the International Energy Agency are preparing a joint manual on annual energy statistics to help Member States' statistical authorities in filling in the energy statistics questionnaires. Eurostat also organises training workshops for officials from these authorities to discuss problems in data collection and.

In a recent ECAC initiative European countries that participate in ECAC are encouraged to begin using the Detailed Corinair Methodology for calculating aircraft emissions (see section 8.2). This may improve the ability of European countries to separate better emissions for international air transport from emissions for domestic air transport.

Another recent European initiative has been launched in a cooperation between the European Environment Agency, Eurocontrol and Eurostat to improve the data availability involving the use of a database supplied by Eurocontrol on actual flights performed in Europe and the use of the detailed Corinair emission calculation methodology. This effort may offer the opportunity to compare the data reported by European countries to the data calculated by EEA, Eurocontrol and Eurostat (see section 8.3). At the time of writing this report the final results of the work has not been published.

Eurostat finances specific projects in the Member States which aim to eliminate differences in energy data reported to Eurostat and those used for the calculation of CO₂ emissions reported to the UNFCCC). This work will also improve reporting of marine and aviation bunker fuels. The projects will examinine the energy data used in the two submissions for the years 1990, 1995 and 2000, identifying and explaining the differences. The projects furthermore aim at establishing a procedure at national level that will eliminate diversions of the two reporting mechanisms in the future and also aim at providing the updated energy data in the form of annual questionnaires for the period 1990-2000, ensuring comparable data under the two reporting mechanisms.

Besides the need to improve the methodologies for separating emissions from international aviation from emissions from domestic aviation there is another related question that is applicable to the reporting of aviation emissions in the European Union: Since the European Union has ratified the Kyoto Protocol the question arises whether the EU inventory should merely represent the sum of national inventories or if international intra-EU flights should be regarded as "domestic" in the EU inventory. If it is decided that the EU inventory should include international intra-EU flights as domestic these emissions have to be separated from the emissions reported as international by EU Member States. The emission calculation work currently under way in the cooperation between the European Environment Agency, Eurostat and Eurocontrol may be used to produce the data needed for that process (see section 8.3 for further details).

Another problem that may remain in Europe is whether countries that have overseas territories should include flights to these areas in their national inventories or if these emissions should be reported as domestic emissions. Table 4 gives an overview of the territories in question. According to the IPCC/UNFCCC reporting guidelines, administered territories should be included in national inventories, but for many countries they are not at present.

Table 4:
Overview over EU Member States’ overseas territories. Source: [Lock 2002]

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