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

=== 10.7.3 Transport Activity Trajectories ===

<div id="h2-30-siblings" class="h2-siblings"></div>

Growth in passenger and freight travel demand is strongly dependent on population growth and GDP. In 2015, transport activities were estimated at around 35–50 trillion pkm, or 5,000–7,000 pkm per person per year, with significant variations among studies ( [[#IEA--2017b|IEA 2017b]] ; [[#ITF--2019|ITF 2019]] ). The number of passenger cars in use has grown 45% globally between 2005–2015, with the most significant growth occurring in the developing countries of Asia and the Middle East (119%), Africa (79%), and South and Central America (80%), while growth in Europe and North America is the slowest (21% and 4% respectively) ( [[#IOMVM--2021|IOMVM 2021]] ). On the other hand, car ownership levels in terms of vehicles per 1000 people in 2015 were low in developing countries of Asia and the Middle East (141), Africa (42), South and Central America (176), while in Europe and North America they are relatively high (581 and 670 respectively) ( [[#IOMVM--2021|IOMVM 2021]] ). The growth rate in commercial vehicles (freight and passenger) was 41% between 2005 and 2015, with a somewhat more even growth across developed and developing countries ( [[#IOMVM--2021|IOMVM 2021]] ).

Figure 10.18 shows activity trajectories for both freight and passenger transport based on the AR6 database for IAMs. According to demand projections from the IAMs, global passenger and freight transport demand could increase relative to a modelled year 2020 across temperature goals. The median transport demand from IAMs for all the scenarios in line with warming levels below 2.5°C (C1–C5) suggests that global passenger transport demand could grow by 1.14–1.3 times in 2030 and by 1.5–1.8 times in 2050 (1.27–2.33 for the 5–95th percentile across C1–C5 scenarios) relative to modelled 2020 level. Developed regions including North America and Europe exhibit lower growth in passenger demand in 2050 compared to developing countries across all the scenarios. In 2030, most of the global passenger demand growth happens in Africa (44% growth relative to 2020), and Asia and Pacific (57% growth in China and 59% growth in India relative to 2020) in the scenarios that limit warming below 2.5°C (&gt;50%) throughout the 21st century (C5). These regions start from a low level of per capita demand. For example, in India, demand may grow by 84%. However, the per capita demand in 2010 was under 7000 km per person per year ( [[#Dhar--2015|Dhar and Shukla 2015]] ). Similarly, in China, demand may grow by 52%, starting from per capita demand of 8000 km per person per year in 2010 ( [[#Pan--2018|Pan et al. 2018]] ). The per capita passenger demand in these regions was lower than in developed countries in 2010, but it converges towards the per capita passenger transport demand of advanced economies in less stringent climate scenarios (C6–C7). Demand for passenger travel would grow at a slower rate in the stricter temperature stabilisation scenarios (&lt;2.5°C and 1.5°C scenarios, C1–C5) compared to the scenarios with higher warming levels (C7–C8). The median global passenger demand in the scenarios that limit or return warming to 1.5°C during the 21st century (C1–C2) is 27% lower in 2050 relative to C8.

<div id="_idContainer055" class="Basic-Text-Frame"></div>

[[File:affb394906fc1525550c233b677c191d IPCC_AR6_WGIII_Figure_10_18.png]]

'''Figure 10.18 | Transport activity trajectories for passenger (bottom panel) and freight (top panel) in 2030, 2050, and 2100 indexed to 2020 modelled year across R6 Regions and World.''' Plots show 5–95th percentile, 25–75th percentile, and median. Numbers above thebars indicate the number of scenarios. Data from the AR6 scenario database.

Due to limited data availability, globally consistent freight data is difficult to obtain. In 2015, global freight demand was estimated to be 108 trillion tkm, most of which was transported by sea ( [[#ITF--2019|ITF 2019]] ). The growth rates of freight service demand vary dramatically among different regions: over the 1975–2015 period, road freight activity in India increased more than 9-fold, 30-fold in China, and 2.5-fold in the US ( [[#Mulholland--2018|Mulholland et al. 2018]] ). Global freight demand continues to grow but at a slower rate compared to passenger demand across all the scenarios in 2050 compared to modelled 2020 values. Global median freight demand could increase by 1.17–1.28 times in 2030 and 1.18–1.7 times in 2050 in all the scenarios with warming below 2.5°C (C1–C5). Like passenger transport, the models suggest that a large share of growth occurs in Africa and Asian regions (59% growth in India and 50% growth in China in 2030 relative to a modelled year 2020) in the C5 scenarios that limit warming below 2.5°C (&gt;50%) throughout the 21st century. Global median freight demand grows more slowly in the stringent temperature stabilisation scenarios, and is 40% and 22% lower in 2050 in the scenarios that limit or return warming to 1.5°C (&gt;50%) during the 21st century (C1–C2) and below 2.5°C scenarios (C3–C4), respectively, compared to scenarios with warming levels of above 4°C (C8).

GTEMs show broad ranges for future travel demand, particularly for the freight sector. These results show more dependency on models than on baseline or policy scenarios. According to ITF Transport Outlook ( [[#ITF--2019|ITF 2019]] ), global passenger transport and freight demand could more than double by 2050 in a business-as-usual scenario. [[#Mulholland--2018|Mulholland et al. (2018)]] suggest the freight sector could grow 2.4-fold over 2015–2050 in the reference scenario, with the majority of growth attributable to developing countries. The IEA suggests a more modest increase in passenger transport, from 51 trillion pkm in 2014 to 110 trillion pkm in 2060, in a reference scenario without climate policies and a climate scenario that would limit emissions below 2°C. The demand for land-based freight transport in 2060 is, however, slightly lower in the climate scenario (116 trillion tkm) compared to the reference scenario (130 trillion tkm) ( [[#IEA--2017b|IEA 2017b]] ). The ITF, however, suggests that ambitious decarbonisation policies could reduce global demand for passenger transport by 13–20% in 2050, compared to the business-as-usual scenario ( [[#ITF--2019|ITF 2019]] ; [[#ITF--2021|ITF 2021]] ). The reduction in vehicle travel through shared mobility could reduce emissions from urban passenger transport by 30% compared to the business-as-usual scenario. Others suggest that reductions larger than 25%, on average, for both passenger and freight in 2030 and 2050 may be needed to achieve very low carbon emissions pathways ( [[#Fisch-Romito--2019|Fisch-Romito and Guivarch 2019]] ). In the absence of large-scale carbon dioxide removal, few global studies highlight the need for significant demand reduction in critical sectors (aviation, shipping and road freight) in well below 2°C scenarios ( [[#van%20Vuuren--2018|van Vuuren et al. 2018]] ; [[#Grant--2021|Grant et al. 2021]] ; [[#Sharmina--2021|Sharmina et al. 2021]] ).

Many models find small differences in passenger transport demand across temperature goals because IAM models rely on historical relationships between population, GDP, and demand for services to estimate future demand. This assumption poses a limitation to the modelling efforts, as mitigation efforts would likely increase travel costs that could result in lower transport demand ( [[#Zhang--2018|Zhang et al. 2018]] ). In most models, demand is typically an exogenous input. These models often assume mode shifts of activities from the most carbon-intensive modes (driving and flying for passenger travel and trucking for freight) to less carbon-intensive modes (public transit and passenger rail, and freight rail) to reduce emissions.

Traditionally there is a disconnection between IAM models and bottom-up sectoral or city-based models due to the different scale (both spatial and temporal) and focus (climate mitigation vs urban pollution, safety ( [[#Creutzig--2016|Creutzig 2016]] )). The proliferation of shared and on-demand mobility solutions is leading to rebound effects for travel demand ( [[#Chen--2016|Chen and Kockelman 2016]] ; [[#Coulombel--2019|Coulombel et al. 2019]] ) and this is a new challenge for modelling. Some IAM studies have recently begun to explore demand-side solutions for reducing transport demand to achieve very low-carbon scenarios through a combination of culture and low-carbon lifestyle ( [[#Creutzig--2018|Creutzig et al. 2018]] ; [[#van%20Vuuren--2018|van Vuuren et al. 2018]] ); urban development ( [[#Creutzig--2015a|Creutzig et al. 2015a]] ); increased vehicle occupancy ( [[#Grubler--2018|Grubler et al. 2018]] ); improved logistics and streamlined supply chains for the freight sector ( [[#Mulholland--2018|Mulholland et al. 2018]] ); and disruptive low-carbon innovation, described as technological and business model innovations offering ‘novel value propositions to consumers and which can reduce GHG emissions if adopted at scale’ ( [[#Wilson--2019|Wilson et al. 2019]] ). In the literature from national models, demand has been differentiated between conventional and sustainable development scenarios through narratives built around policies, projects, and programmes envisaged at the national level ( [[#Dhar--2015|Dhar and Shukla 2015]] ; [[#Shukla--2015|Shukla et al. 2015]] ) and price elasticities of travel demand ( [[#Dhar--2018|Dhar et al. 2018]] ). However, a greater understanding of the mechanisms underlying energy-relevant decisions and behaviours ( [[#Brosch--2016|Brosch et al. 2016]] ), and the motivations for sustainable behaviour ( [[#Steg--2015|Steg et al. 2015]] ), are critically needed to realise these solutions.

Overall, passenger and freight activity are likely to continue to grow rapidly under the C7 (&gt;3.0°C) scenarios, but most growth would occur in developing countries. Most models treat travel demand exogenously following the growth of population and GDP, but they have limited representation of responses to price changes, policy incentives, behavioural shifts, nor innovative mobility solutions that can be expected to occur in more stringent mitigation scenarios. [[IPCC:Wg3:Chapter:Chapter-5|Chapter 5]] provides a more detailed discussion of the opportunities for demand changes that may result from social and behavioural interventions.

<div id="10.7.4" class="h2-container"></div>

<span id="transport-modes-trajectories"></span>