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

== 10.1 Introduction and Overview ==

<div id="h1-2-siblings" class="h1-siblings"></div>

This chapter examines the transport sector’s role in climate change mitigation. It appraises the transport system’s interactions beyond the technology of vehicles and fuels to include the full lifecycle analysis of mitigation options, a review of enabling conditions, and metrics that can facilitate advancing transport decarbonisation goals. The chapter assesses developments in the systems of land-based transport and introduces, as a new feature since AR5, two separate sections focusing on the trends and challenges in aviation and shipping. The chapter assesses the future trajectories emerging from global, energy, and national scenarios and concludes with a discussion on enabling conditions for transformative change in the sector.

This section ( [[#10.1|Section 10.1]] ) discusses how transport relates to virtually all the Sustainable Development Goals (SDGs), the trends and drivers making transport a big contributor to greenhouse gas (GHG) emissions, the impacts climate change is having on transport that can be addressed as part of mitigation, and the overview of emerging transport disruptions with potential to shape a low-carbon transport pathway.

<div id="10.1.1" class="h2-container"></div>

<span id="transport-and-the-sustainable-development-goals"></span>
=== 10.1.1 Transport and the Sustainable Development Goals ===

<div id="h2-1-siblings" class="h2-siblings"></div>

The adoption of the 2030 Agenda for Sustainable Development by the United Nations (UN) has renewed international efforts to pursue and accurately measure global actions towards sustainable development ( [[#United%20Nations--2015|United Nations 2015]] ). The 17 SDGs set out the overall goals that are further specified by 169 targets and 232 SDG indicators, many of which relate to transport ( [[#United%20Nations--2017|United Nations 2017]] ; [[#Lisowski--2020|Lisowski et al. 2020]] ). A sustainable transport system provides safe, inclusive, affordable, and clean passenger and freight mobility for current and future generations ( [[#Williams--2017|Williams 2017]] ; [[#Litman--2021|Litman 2021]] ) so transport is particularly linked to SDGs 3, 7, 8, 9, 11, 12, and 13 ( [[#Move%20Humanity--2018|Move Humanity 2018]] ; [[#IRP--2019|IRP 2019]] ; [[#WBA--2019|WBA 2019]] ; [[#SLoCaT--2019|SLoCaT 2019]] ; [[#Yin--2019|Yin 2019]] ). Table 10.1 summarises transport-related topics for these SDGs and corresponding research. [[IPCC:Wg3:Chapter:Chapter-17#17.3.3.7|Section 17.3.3.7]] also provides a cross-sectoral overview of synergies and trade-offs between climate change mitigation and the SDGs.

'''Table 10.1 | Transport and the Sustainable Development Goals: Synergies and trade-offs.'''

{| class="wikitable"
|-
| rowspan="3"|
| colspan="5"| '''Sustainable Development Goals: Synergies and trade-offs'''

|-
| '''Basic human needs'''

| '''Earth preconditions'''

| '''Sustainable resource use'''

| '''Social and economic development'''

| '''Universal values'''

|-

|-
| '''Transport-related topics (low-carbon transport; active transport; electric vehicles)'''

'''Advances in vehicle technology; Improved public transport system'''

| – Lower air pollution contributes to positive health outcomes.

– Energy access can contribute to poverty alleviation.

– Transport planning is a major player in reducing poverty in cities.

– Access to healthcare.

– Diseases from air pollution.

– Injuries and deaths from traffic accidents.

– Reduced driving-induced stress.

– Links between active transport and good health with positive effects of walking and cycling.

– Improving road accessibility to disabled users.

– Reduce time spent on transport/mobility.

| – Reduction of GHG emissions along the entire value chain, e.g., Well-to-Wheel.

– Further development addressing minor GHG emissions and pollutants.

– Transport oriented to sustainable development.

– Circular economy principle applied to transport.

| – Share of renewable energy use.

– Energy efficiency of vehicles.

– Clean and affordable energy off-grid.

– Reduce material consumption during production, lifecycle analysis of vehicles and their operations including entire value chains.

– Closed loop carbon and nutrient cycle linked to circular economy.

| – Role of transport for economic and human development.

– Decarbonised public transport rather than private vehicle use.

– Transport oriented to sustainable development.

– Sustainable transport infrastructure and systems for cities and rural areas.

– Affordability of mobility services, this can also be covered under ‘universal access’ to public transport.

– Accessibility vs mobility: mobility to opportunities; transport equity; development as freedom.

– Positive economic growth (employment) outcomes due to resource efficiency and lower productive energy cost.

– Role of transport provision in accessing work, reconfiguration of social norms, as working from home.

– Transport manufacturers as key employers changing role of transport-related labour due to platform economy, and innovations in autonomous vehicles.

| – Gender equality in transport.

– Reduced inequalities.

– Enables access to quality education.

– Partnership for the goals.

|-
| '''References'''

| [[#Grant--2016|Grant et al. 2016]] ; [[#Haines--2017|Haines et al. 2017]] ; [[#Cheng--2018|Cheng et al. 2018]] ; [[#Nieuwenhuijsen--2018|Nieuwenhuijsen 2018]] ; [[#Smith--2018|Smith et al. 2018]] ; [[#Sofiev--2018|Sofiev et al. 2018]] ; [[#Peden--2019|Peden and Puvanachandra 2019]] ; [[#King--2020|King and Krizek 2020]] ; [[#Macmillan--2020|Macmillan et al. 2020]]

| [[#Farzaneh--2019|Farzaneh et al. 2019]] ; see particularly following chapters.

| [[#SLoCaT--2019|SLoCaT 2019]] ; see particularly following chapters.

| [[#Bruun--2015|Bruun and Givoni 2015]] ; [[#Pojani--2015|Pojani and Stead 2015]] ; [[#Hensher--2017|Hensher 2017]] ; [[#ATAG--2018|ATAG 2018]] ; [[#Grzelakowski--2018|Grzelakowski 2018]] ; [[#Weiss--2018|Weiss et al. 2018]] ; [[#Brussel--2019|Brussel et al. 2019]] ; [[#Gota--2019|Gota et al. 2019]] ; [[#Mohammadi--2019|Mohammadi et al. 2019]] ; [[#Peden--2019|Peden and Puvanachandra 2019]] ; [[#SLoCaT--2019|SLoCaT 2019]] ; [[#Xu--2019|Xu et al. 2019]]

| [[#Hernandez--2018|Hernandez 2018]] ; [[#Prati--2018|Prati 2018]] ; [[#Levin--2019|Levin and Faith-Ell 2019]] ; [[#Vecchio--2020|Vecchio et al. 2020]]

|}

<div id="10.1.2" class="h2-container"></div>

<span id="trends-drivers-and-the-critical-role-of-transport-in-ghg-growth"></span>
=== 10.1.2 Trends, Drivers and the Critical Role of Transport in GHG Growth ===

<div id="h2-2-siblings" class="h2-siblings"></div>

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]] ).

<div id="_idContainer015" class="Basic-Text-Frame"></div>

[[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]] ).

<div id="10.1.3" class="h2-container"></div>

<span id="climate-adaptation-on-the-transport-sector"></span>
=== 10.1.3 Climate Adaptation on the Transport Sector ===

<div id="h2-3-siblings" class="h2-siblings"></div>

Climate change impacts such as extremely high temperatures, intense rainfall leading to flooding, more intense winds and/or storms, and sea level rise can seriously impact transport infrastructure, operations, and mobility for road, rail, shipping, and aviation. Studies since AR5 confirm that serious challenges to all transport infrastructures are increasing, with consequent delays or derailing ( [[#Miao--2018|Miao et al. 2018]] ; [[#Moretti--2018|Moretti and Loprencipe 2018]] ; [[#Pérez-Morales--2019|Pérez-Morales et al. 2019]] ; [[#Palin--2021|Palin et al. 2021]] ). These impacts have been increasingly documented but, according to [[#Forzieri--2018|Forzieri et al. (2018)]] , little is known about the risks of multiple climate extremes on critical infrastructures at local to continental scales. All roads, bridges, rail systems, and ports are likely to be affected to some extent. Flexible pavements are particularly vulnerable to extreme high temperatures that can cause permanent deformation and crumbling of asphalt ( [[#Underwood--2017|Underwood et al. 2017]] ; [[#Qiao--2019|Qiao et al. 2019]] ). Rail systems are also vulnerable, with a variety of hazards, both meteorological and non-meteorological, affecting railway asset lifetimes. Severe impacts on railway infrastructure and operations can arise from the occurrence of temperatures below freezing, excess precipitation, storms and wildfires ( [[#Thaduri--2020|Thaduri et al. 2020]] ; [[#Palin--2021|Palin et al. 2021]] ) as can impacts on underground transport systems ( [[#Forero-Ortiz--2020|Forero-Ortiz et al. 2020]] ).

Most countries are examining opportunities for combined mitigation-adaptation efforts, using the need to mitigate climate change through transport-related GHG emissions reductions and reduction of pollutants as the basis for adaptation action ( [[#Thornbush--2013|Thornbush et al. 2013]] ; [[#Wang--2020|Wang et al. 2020]] ). For example, urban sprawl indirectly affects climate processes, increasing emissions and vulnerability, which worsens the potential to adapt ( [[#Congedo--2014|Congedo and Munafò 2014]] ; Macchi and Tiepolo 2014). Hence, using a range of forms of rapid transit as structuring elements for urban growth can mitigate climate change-related risks as well as emissions, reducing impacts on new infrastructure, often in more vulnerable areas ( [[#Newman--2017|Newman et al. 2017]] ). Such changes are increasingly seen as having economic benefit ( [[#Ha--2017|Ha et al. 2017]] ), especially in developing nations ( [[#Chang--2016|Chang 2016]] ; [[#Monioudi--2018|Monioudi et al. 2018]] ).

Since AR5 there has been a growing awareness of the potential and actual impacts from global sea level rise due to climate change on transport systems ( [[#Dawson--2016|Dawson et al. 2016]] ; [[#Rasmussen--2018|Rasmussen et al. 2018]] ; [[#IPCC--2019|IPCC 2019]] ; [[#Noland--2019|Noland et al. 2019]] ), particularly on port facilities ( [[#Stephenson--2018|Stephenson et al. 2018]] ; [[#Yang--2018b|Yang et al. 2018b]] ; [[#Pérez-Morales--2019|Pérez-Morales et al. 2019]] ). Similarly, recent studies suggest changes in global jet streams could affect the aviation sector ( [[#Staples--2018|Staples et al. 2018]] ; [[#Becken--2019|Becken and Shuker 2019]] ), and extreme weather conditions can affect runways (heat buckling) and aircraft lift. Combined, climate impacts on aviation could result in payload restrictions and disruptions ( [[#Coffel--2017|Coffel et al. 2017]] ; [[#Monioudi--2018|Monioudi et al. 2018]] ). According to [[#Williams--2017|Williams (2017)]] , studies have indicated that the amount of moderate-or-greater clear-air turbulence on transatlantic flight routes in winter will increase significantly in the future as the climate changes. More research is needed to fully understand climate-induced risks to transportation systems.

<div id="10.1.4" class="h2-container"></div>

<span id="transport-disruption-and-transformation"></span>
=== 10.1.4 Transport Disruption and Transformation ===

<div id="h2-4-siblings" class="h2-siblings"></div>

Available evidence suggests that transport-related CO 2 emissions would need to be restricted to about 2 to 3 Gt in 2050 (1.5°C scenario-1.5DS, B2DS), or about 70 to 80% below 2015 levels, to meet the goals set in the Paris Agreement. It also indicates that a balanced and inter-modal application of Avoid, Shift, and Improve measures is capable of yielding an estimated reduction in transport emissions of 2.39 GtCO 2 -equivalent by 2030 and 5.74 GtCO 2 -equivalent by 2050 ( [[#IPCC--2018|IPCC 2018]] ; [[#Gota--2019|Gota et al. 2019]] ). Such a transformative decarbonisation of the global transport system requires, in addition to technological changes, a paradigm shift that ensures prioritisation of high-accessibility transport solutions that minimise the amount of mobility required to meet people’s needs, and favours transit and active transport modes ( [[#Lee--2018|Lee and Handy 2018]] ; [[#SLoCaT--2021|SLoCaT 2021]] ). These changes are sometimes called disruptive as they are frequently surprising in how they accelerate through a technological system.

The assessment of transport innovations and their mitigation potentials is at the core of how this chapter examines the possibilities for changing transport-related GHG trajectories. The transport technology innovation literature analysed in this chapter emphasises how a mixture of mitigation technology options and social changes are now converging and how, in combination, they may have potential to accelerate trends toward a low-carbon transport transition. Such changes are considered disruptive or transformative ( [[#Sprei--2018|Sprei 2018]] ). Of the current transport trends covered in the literature, this chapter focuses on three key technology and policy areas: electro-mobility in land-based transport vehicles, new fuels for ships and planes, and overall demand reductions and efficiency. These strategies are seen as being necessary to integrate at all levels of governance and, in combination with the creation of fast, extensive, and affordable multimodal public transport networks, can help achieve multiple advantages in accordance with SDGs

Electrification of passenger transport in light-duty vehicles (LDVs) is well underway as a commercial process with socio-technical transformative potential and will be examined in detail in Sections 10.3 and 10.4. But the rapid mainstreaming of electric vehicles (EVs) will still need enabling conditions for land transport to achieve the shift away from petroleum fuels, as outlined in [[IPCC:Wg3:Chapter:Chapter-3|Chapter 3]] and detailed in [[#10.8|Section 10.8]] . The other mitigation options reviewed in this chapter are so far only incremental and are less commercial, especially shipping and aviation fuels, so stronger enabling conditions are likely , as detailed further in Sections 10.5 to 10.8. The enabling conditions that would be needed for the development of an emerging technological solution for such fuels are likely to be very different from those for electromobility, but nevertheless they both will need demand and efficiency changes to ensure they are equitable and inclusive.

[[#10.2|Section 10.2]] sets out the transformation of transport through examining systemic changes that affect demand for transport services and the efficiency of the system. [[#10.3|Section 10.3]] looks at the most promising technological innovations in vehicles and fuels. The next three sections (10.4, 10.5, and 10.6) examine mitigation options for land transport, aviation, and shipping. [[#10.7|Section 10.7]] describes the space of solutions assessed in a range of integrated modelling and sectoral transport scenarios. Finally, [[#10.8|Section 10.8]] sets out what would be needed for the most transformative scenario that can manage to achieve the broad goals set out in [[IPCC:Wg3:Chapter:Chapter-3|Chapter 3]] and the transport goals set out in [[#10.7|Section 10.7]] .

<div id="10.2" class="h1-container"></div>

<span id="systemic-changes-in-the-transport-sector"></span>