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2.2.5 Allocation of Transportation Emissions

Among the many human activities that produce GHGs, the use of energy, 80 % of which still comes from fossil fuels, represents by far the largest source of emissions. Within the energy sector, CO2 dominates total GHG emissions. In addition, the energy sector includes emissions from “fuel combustion” and “fugitive emissions”, which are intentional or unintentional releases of gases resulting from production, processes, transmission, storage and use of fuels (e.g. CH4 emissions from coal mining). Figure 2.4 shows direct GHG emissions of the transportation sector broken down by transportation mode for the period 1970–2010.

Fig. 2.4 Direct GHG emissions of the transportation sector (shown here by transportation mode) rose 250 % from 2.8 Gt CO2eq worldwide in 1970 to 7.0 Gt CO2eq in 2010. Source: IPCC AR5 report—IPCC (2014)

According to the 2014 highlights on CO2 emissions from fuel combustion, transportation is responsible for 23 % of global CO2 emissions. As for transportation, the fast emissions growth was driven by emissions from the road sector, which increased by 64 % since 1990 and accounted for about three quarters of transportation emissions in 2012. It is interesting to note that despite efforts to limit emissions from international transportation, emissions from marine and aviation bunkers, 65.8 % and 86.4 % higher in 2012 than in 1990 respectively, grew even faster than those from road. According to the IEA, international marine bunkers are responsible for 602.2 MtCO2 in 2012 and aviation bunkers for 477.86 MtCO2 of a total of 31,734.3 MtCO2 of emissions due to fuel combustion.

As discussed previously, the Kyoto Protocol addresses emissions from fuel used for international aviation and maritime transportation in its Article 2, paragraph 2. Article 2.2 of the Kyoto Protocol states that the Parties included in Annex I shall pursue limitation or reduction of emissions of greenhouse gas emissions not controlled by the Montreal Protocol from aviation and marine bunker fuels, working through the ICAO and the IMO, respectively. It is generally accepted that the emission estimates of transportation activities presented by the UNFCCC and IEA are reliable for most modes except aviation and shipping. Bunker emissions from these two sectors are reported by the respective UN agencies.

According to the Third IMO GHG study (Smith et al. (2014)), with year 2012 as base year, total international shipping emissions were approximately 949 million tonnes CO2 and 972 million tonnes CO2eq for all GHG gases. International shipping accounts for approximately 2.2 % (and 2.1 %) of global CO2 (and GHG) emissions on a CO2eq basis, respectively. In absolute numbers, international shipping emissions for 2012 are estimated to be 796 million tonnes CO2 and 816 million tonnes CO2eq for GHGs.

According to the same study, for the period 2007–2012, on average, international shipping accounted for approximately 3.1 % of annual global CO2 and approximately 2.8 % of annual GHGs on a CO2eq basis using 100-year global warming potential conversions from the AR5. This study estimates 2007–2012 average annual totals of 20.9 million and 11.3 million tonnes for NOx (as NO2) and SOx (as SO2) from all shipping, respectively, representing about 15 % and 13 % of global NOx and SOx from anthropogenic sources reported in the latest IPCC Assessment Report (AR5), respectively. This study uses also IEA data to estimate emissions based on fuel consumption (top-down method). International shipping fuel consumption ranged between approximately 200 million and 270 million tonnes per year, depending on whether consumption was defined as fuel allocated to international voyages (top-down) or fuel used by ships engaged in international shipping (bottom-up), respectively.

In general we should note that different studies produce different results. There is a large difference between the IEA estimates, the UNFCCC submissions and the 2014 IMO GHG study estimations. The need for a consensus because on this subject is due to the fact that if we do not know what is the level of emissions we cannot set any meaningful emissions reduction targets.

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