Editing IPCC:AR6/WGIII/Chapter-10 (section)

=== 10.1.2 Trends, Drivers and the Critical Role of Transport in GHG Growth ===

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The transport sector directly emitted around 8.9 Gtonnes (Gt) of carbon dioxide equivalent (CO 2 -eq) in 2019, up from 5.1 GtCO 2 -eq in 1990 (Figure 10.1). Global transport was the fourth largest source of GHG emissions in 2019 following the power, industry, and the agriculture, forestry and land use (AFOLU) sectors. In absolute terms, the transport sector accounts for roughly 15% of total GHG emissions and about 23% of global energy-related CO 2 emissions ( [[#IEA--2020a|IEA 2020a]] ). Transport-related GHG emissions have increased fast over the last two decades, and since 2010, the sector’s emissions have increased faster than for any other end-use sector, averaging +1.8% annual growth ( [[#10.7|Section 10.7]] ). Addressing emissions from transport is crucial for GHG mitigation strategies across many countries, as the sector represents the largest energy consuming sector in 40% of countries worldwide. In most remaining countries, transport is the second largest energy-consuming sector, reflecting different levels of urbanisation and land use patterns, speed of demographic changes and socio-economic development ( [[#IEA--2012|IEA 2012]] ; [[#Gota--2019|Gota et al. 2019]] ; [[#Hasan--2019|Hasan et al. 2019]] ; [[#Xie--2019|Xie et al. 2019]] ).

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[[File:8858bbe7686b673c11d0b8016f1111f0 IPCC_AR6_WGIII_Figure_10_1.png]]

'''Figure 10.1 | Global and regional transport greenhouse gas emissions trends.''' Indirect emissions from electricity and heat consumed in transport are shown in panel '''(a)''' and are primarily linked to the electrification of rail systems. These indirect emissions do not include the full lifecycle emissions of transportation systems (e.g., vehicle manufacturing and infrastructure), which are assessed in [[#10.4|Section 10.4]] . International aviation and shipping are included in panel (a) but excluded from panel (b). Indirect emissions from fuel production, vehicle manufacturing and infrastructure construction are not included in the sector total. Source: adapted from [[#Lamb--2021|Lamb et al. (2021)]] using data from [[#Minx--2021|Minx et al. (2021)]] .

As of 2019, the largest source of transport emissions is the movement of passengers and freight in road transport (6.1 GtCO 2 -eq, 69% of the sector’s total). International shipping is the second largest emission source, contributing 0.8 GtCO 2- eq (9% of the sector’s total), and international aviation is third with 0.6 GtCO 2 -eq (7% of the sector’s total). All other transport emissions sources, including rail, have been relatively trivial in comparison, totalling 1.4 GtCO 2- eq in 2019. Between 2010 and 2019, international aviation had among the fastest growing GHG emissions among all segments (+3.4% per year), while road transport remained one of the fastest growing (+1.7% per year) among all global energy-using sectors. Note that the COVID-19-induced economic lockdowns implemented since 2020 have had a very substantial impact on transport emissions – higher than any other sector (Chapter 2). Preliminary estimates from [[#Crippa--2021|Crippa et al. (2021)]] suggest that global transport CO 2 emissions declined to 7.6 GtCO 2 in 2020, a reduction of 11.6% compared to 2019 ( [[#Crippa--2021|Crippa et al. 2021]] ; [[#Minx--2021|Minx et al. 2021]] ). These lockdowns affected all transport segments, and particularly international aviation (estimated 45% reduction in 2020 global CO 2 emissions), road transport (–10%), and domestic aviation (–9.3%). By comparison, aggregate CO 2 emissions across all sectors are estimated to have declined by 5.1% as a result of the COVID-19 pandemic ( [[IPCC:Wg3:Chapter:Chapter-2#2.2.2|Section 2.2.2]] ).

Growth in transport-related GHG emissions has taken place across most world regions (see Figure 10.1b). Between 1990 and 2019, growth in emissions was relatively slow in Europe, Australia, Japan and New Zealand, Eurasia, and North America while it was unprecedently fast in other regions. Driven by economic and population growth, the annual growth rates in Eastern Asia, Southern Asia, South-East Asia and Pacific, and Africa were 6.1%, 5.2%, 4.7%, and 4.1%, respectively. Latin America and the Middle East have seen somewhat slower growth in transport-related GHG emissions (annual growth rates of 2.4% and 3.3%, respectively) ( [[#ITF--2019|ITF 2019]] ; [[#Minx--2021|Minx et al. 2021]] ). [[#10.7|Section 10.7]] provides a more detailed comparison of global transport emissions trends with those from regional and sub-sectoral studies.

The rapid growth in global transport emissions is primarily a result of the fast growth in global transport activity levels, which grew by 73% between 2000 and 2018. Passenger and freight activity growth have outpaced energy efficiency and fuel economy improvements in this period ( [[#ITF--2019|ITF 2019]] ). The global increase in passenger travel activities has taken place almost entirely in non-OECD countries, often starting from low motorisation rates ( [[#SLoCaT--2018a|SLoCaT 2018a]] ). Passenger cars, two- and three-wheelers, and mini buses contribute about 75% of passenger transport-related CO 2 emissions, while collective transport services (bus and railways) generate about 7% of the passenger transport-related CO 2 emissions despite covering a fifth of passenger transport globally (Rodrigue 2017; [[#Halim--2018|Halim et al. 2018]] ; [[#Sheng--2018|Sheng et al. 2018]] ; [[#SLoCaT--2018a|SLoCaT 2018a]] ; [[#Gota--2019|Gota et al. 2019]] ). While alternative lighter powertrains have great potential for mitigating GHG emissions from cars, the trend has been towards increasing vehicle size and engine power within all vehicle size classes, driven by consumer preferences towards larger sport utility vehicles (SUVs) ( [[#IEA--2020a|IEA 2020a]] ). On a global scale, SUV sales have been constantly growing in the last decade, with 40% of the vehicles sold in 2019 being SUVs ( [[#IEA--2020a|IEA 2020a]] ) ( [[#10.4|Section 10.4]] , Box 10.3).

Indirect emissions from electricity and heat shown in Figure 10.1 account for only a small fraction of current emissions from the transport sector (2%) and are associated with electrification of certain modes like rail or bus transport ( [[#Lamb--2021|Lamb et al. 2021]] ). Increasing transport electrification will affect indirect emissions, especially where carbon-intense electricity grids operate.

Global freight transport, measured in tonne-kilometres (tkm), grew by 68% between 2000 and 2015 and is projected to grow 3.3 times by 2050 ( [[#ITF--2019|ITF 2019]] ). If unchecked, this growth will make decarbonisation of freight transport very difficult ( [[#McKinnon--2018|McKinnon 2018]] ; [[#ITF--2019|ITF 2019]] ). International trade and global supply chains from industries frequently involving large geographical distances are responsible for the fast increase of CO 2 emissions from freight transport ( [[#Yeh--2017|Yeh et al. 2017]] ; [[#McKinnon--2018|McKinnon 2018]] ), which are growing faster than emissions from passenger transport ( [[#Lamb--2021|Lamb et al. 2021]] ). Heavy-duty vehicles (HDVs) make a disproportionate contribution to air pollution, relative to their global numbers, because of their substantial emissions of particulate matter and of black carbon with high short-term warming potentials ( [[#Anenberg--2019|Anenberg et al. 2019]] ).

On-road passenger and freight vehicles dominate global transport-related CO 2 emissions and offer the largest mitigation potential ( [[#Taptich--2016|Taptich et al. 2016]] ; [[#Halim--2018|Halim et al. 2018]] ). This chapter examines a wide range of possible transport emission reduction strategies. These strategies can be categorised under the ‘Avoid-Shift-Improve’ (ASI) framework described in [[IPCC:Wg3:Chapter:Chapter-5|Chapter 5]] ( [[#Taptich--2016|Taptich et al. 2016]] ). ‘Avoid’ strategies reduce total vehicle travel. They include compact communities and other policies that minimise travel distances and promote efficient transport through pricing and demand management programmes. ‘Shift’ strategies shift travel from higher-emitting to lower-emitting modes. These strategies include more multimodal planning that improves active and collective transport modes, complete streets roadway design, high occupant vehicle priority strategies that favour shared modes, Mobility as a Service (MaaS), and multimodal navigation and payment apps. ‘Improve’ strategies reduce per-kilometre emission rates. These strategies include hybrid and electric vehicle incentives, lower-carbon and cleaner fuels, high-emitting vehicle scrappage programmes, and efficient driving and anti-idling campaigns ( [[#Lutsey--2012|Lutsey and Sperling 2012]] ; [[#Gota--2015|Gota et al. 2015]] ). These topics are assessed within the rest of this chapter, including how combinations of ASI with new technologies can potentially lead from incremental interventions into low-carbon transformative transport improvements that include social and equity benefits ( [[#10.8|Section 10.8]] ).

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