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

=== 10.7.4 Transport Modes Trajectories ===

<div id="h2-31-siblings" class="h2-siblings"></div>

Globally over the last century, shares of faster transport modes have generally increased with increasing passenger travel demand ( [[#Schäfer--2017|Schäfer 2017]] ; [[#Schafer--2000|Schafer and Victor 2000]] ). For short- to medium-distance travel, private cars have displaced public transit, particularly in OECD countries, due to a variety of factors, including faster travel times in many circumstances ( [[#Liao--2020|Liao et al. 2020]] ); consumers increasingly valuing time and convenience with GDP growth; and broader transport policies, such as provision of road versus public transit infrastructure ( [[#Mattioli--2020|Mattioli et al. 2020]] ). For long-distance travel, travel via aviation for leisure and business has increased ( [[#Lee--2021|Lee et al. 2021]] ). These trends do not hold in all countries and cities, as many now have rail transit that is faster than driving ( [[#Newman--2015|Newman et al. 2015]] ). For instance, public transport demand rose from 1990 through to 2016 in France, Denmark, and Finland ( [[#eurostat--2019|eurostat 2019]] ). In general, smaller and denser countries and cities with higher or increasing urbanisation rates tend to have greater success in increasing public transport share. However, other factors, like privatisation of public transit ( [[#Bayliss--2018|Bayliss and Mattioli 2018]] ) and urban form ( [[#ITF--2021|ITF 2021]] ), also play a role. Different transport modes can provide passenger and freight services, affecting the emissions trajectories for the sector.

Figure 10.19 shows activity trajectories for freight and passenger transport through 2100 relative to a modelled year 2020 across different modes, based on the AR6 database for IAMs and global transport models. Globally, climate scenarios from IAMs, and policy and reference scenarios from global transport models, indicate increasing demand for freight and passenger transport via most modes through 2100 ( [[#Yeh--2017|Yeh et al. 2017]] ; [[#Mulholland--2018|Mulholland et al. 2018]] ; [[#Zhang--2018|Zhang et al. 2018]] ; [[#Khalili--2019|Khalili et al. 2019]] ). Road passenger transport exhibits a similar increase (roughly tripling) through 2100 across scenarios. For road passenger transport, scenarios that limit or return warming to 1.5°C during the 21st century (C1–C2) have a smaller increase from modelled 2020 levels (median increase of 2.4 times modelled 2020 levels) than do scenarios with higher warming levels (C3–C8) (median increase of 2.7–2.8 times modelled 2020 levels). There are similar patterns for passenger road transport via light-duty vehicle, for which median increases from modelled 2020 levels are smaller for C1–C2 (3 times larger) than for C3–C5 (3.1 times larger) or C6–C7 (3.2 times larger). Passenger transport via aviation exhibits a 2.2 times median increase relative to modelled 2020 levels under C1–C2 and C3–C5 scenarios but exhibits a 6.2 times increase under C6–C8. The only passenger travel mode that exhibits a decline in its median value through 2100 according to IAMs is walking/bicycling, in C3–C5 and C6–C8 scenarios. However, in C1–C2 scenarios, walking/bicycling increases by 1.4 times relative to modelled 2020 levels. At the 5th percentile of IAM solutions (lower edge of bands in Figure 10.19), buses and walking/bicycling for passenger travel both exhibit significant declines.

<div id="_idContainer057" class="Basic-Text-Frame"></div>

[[File:fc918ecc73b0a1b98684a4346fd2b207 IPCC_AR6_WGIII_Figure_10_14.png]]

'''Figure 10.19 | Transport activity trajectories for passenger and freight across different modes.''' Global passenger (billion pkm per year) and freight (billion tkm per year) demand projections relative to a modelled year 2020 index. Results for IAM are for selected stabilisation temperatures by 2100. Also included are global transport models Reference and Policy scenarios. Data from the AR6 scenario database. Trajectories span the 5th to 95th percentiles across models, with a solid line indicating the median value across models.

For freight, Figure 10.19 shows that the largest growth occurs in transport via road ( [[#Mulholland--2018|Mulholland et al. 2018]] ). By 2100, global transport models suggest a roughly four-fold increase in median-heavy-duty trucking levels relative to modelled 2020 levels, while IAMs suggest a two- to four-fold increase in freight transport by road by 2100. Notably, the 95th percentile of IAM solutions see road transport by up to 4.7 times through 2100 relative to modelled 2020 levels, regardless of warming level. Other freight transport modes – aviation, international shipping, navigation, and railways – exhibit less growth than road transport. In scenarios that limit or return warming to 1.5°C (&gt;50%) during the 21st century (C1–C2), navigation and rail transport remain largely unchanged and international shipping roughly doubles by 2100. Scenarios with higher warming (i.e., moving from C1–C2 to C6–C8) generally lead to more freight by rail and less freight by international shipping.

Relative to global trajectories, upper-income regions – including North America, Europe, and the Pacific OECD – generally see less growth in passenger road via light-duty vehicle and passenger aviation, given more saturated demand for both. Other regions like China exhibit similar modal trends as the global average, whereas regions such as the African continent and Indian subcontinent exhibit significantly larger shifts, proportionally, in modal transport than the globe. In particular, the African continent represents the starkest departure from global results. Freight and passenger transport modes exhibit significantly greater growth across Africa than globally in all available scenarios. Across Africa, median freight and passenger transport via road from IAMs increases by 5 to 16 times and 4 to 28 times, respectively, across warming levels by 2100 relative to modelled 2020 levels. Even C1 has considerable growth in Africa via both modes (3 to 16 times increase for freight and 4 to 29 times increase for passenger travel at 5th and 95th percentiles of IAM solutions by 2100).

As noted in [[#10.2|Section 10.2]] , commonly explored mitigation options related to mode change include a shift to public transit, shared mobility, and demand reductions through various means, including improved urban form, teleconferences that replace passenger travel ( [[#Creutzig--2018|Creutzig et al. 2018]] ; [[#Grubler--2018|Grubler et al. 2018]] ; [[#Wilson--2019|Wilson et al. 2019]] ), improved logistics efficiency, green logistics, and streamlined supply chains for the freight sector ( [[#Mulholland--2018|Mulholland et al. 2018]] ). NDCs often prioritise options like bus improvements and enhanced mobility that yield pollution, congestion, and urban development co-benefits, especially in medium- and lower-income countries ( [[#Fulton--2017|Fulton et al. 2017]] ). Conversely, high-income countries, most of which have saturated and entrenched private vehicle ownership, typically focus more on technology options, such as electrification and fuel efficiency standards ( [[#Gota--2016|Gota et al. 2016]] ). Available IAM and regional models are limited in their ability to represent modal shift strategies. As a result, mode shifts alone do not differentiate climate scenarios. While this lack of representation is a limitation of the models, it is unlikely that such interventions would completely negate the increases in demand the models suggest. Therefore, transport via light-duty vehicle and aviation, freight transport via road, and other modes will likely continue to increase through to the end of the century. Consequently, fuel and carbon efficiency and fuel energy and technology will probably play crucial roles in differentiating climate scenarios, as discussed in the following sub-sections.

<div id="10.7.5" class="h2-container"></div>

<span id="energy-and-carbon-efficiency-trajectories"></span>