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

=== 10.7.1 Transport Scenario Modelling ===

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This section reviews the results of three types of models that systemically combine options to assess different approaches to generating decarbonisation pathways for the transport system: (i) integrated assessment models (IAM); (ii) global transport energy models (GTEM); and (iii) national transport-energy models (NTEM) ( [[#Edelenbosch--2017|Edelenbosch et al. 2017]] ; [[#Yeh--2017|Yeh et al. 2017]] ). Common assumptions across the three model types include trajectories of socioeconomic development, technological development, resource availability, policy, and behavioural change. The key differences underlying these models are their depth of technological and behavioural detail versus scope in terms of sectoral and regional coverage. In very general terms, the narrower the scope in terms of sectors and regions, the more depth on spatial, technological, and behavioural detail. A large set of scenarios from these models were collected in a joint effort led by [[IPCC:Wg3:Chapter:Chapter-3|Chapter 3]] and supported by [https://www.ipcc.ch/report/ar6/wg3/chapter/chapter-10 Chapter 10] and others. The outcomes from over 100 models have been analysed for this chapter with the methodologies set out in Annex III for the whole report.

GHG emissions from transport are a function of travel demand, travel mode, transport technology, GHG intensity of fuels, and energy efficiency. These drivers can be organised around a group of levers that can advance the decarbonisation of the transport system. The levers thus include reducing travel activity, increasing use of lower-carbon modes, and reducing modal energy intensity and fuel carbon content. This section explores each lever’s contributions to the decarbonisation of the transport sector by reviewing the results from the three model types IAM, GTEM, and NTEM.

IAMs integrate factors from other sectors that interact with the transport system endogenously, such as fuel availability and costs. IAMs minimise mitigation costs to achieve a temperature goal ''across all sectors of the economy'' over a long time horizon (typically to 2100). IAMs typically capture mitigation options for energy and carbon intensity changes with greater technology/fuel details and endogeneity linked to the other sectors. In the scenarios with very large-scale electrification of the transport sector, the coupling with the other sectors in fuel production, storage, and utilisation becomes more important. G-/NTEMs and related regional transport sectoral models have more details on transport demand, technology, behaviours, and policies than IAMs, but treat the interactions with the other sectors exogenously, potentially missing some critical interactions, such as the fuel prices and carbon intensity of electricity. National models have detailed representation of national policies related to transport and energy, sometimes with greater spatial resolution. Compared with IAMs, G-/NTEMs typically have greater detailed representation to explore mitigation options along the activity and mode dimensions where spatial, cultural, and behavioural details can be more explicitly represented. Section 5 in Annex III provides more details about these types of models. Scenarios for shipping and aviation are handled in more detail in sections 10.5 and 10.6, respectively.

This section applies the following categorisation of scenarios (see Table 3.1 for more details):

• C1 (scenarios that limit warming to 1.5°C (&gt;50%) during the 21st century with no or limited overshoot)

'''•''' C2 (scenarios that return warming to 1.5°C (&gt;50%) during the 21st century after a high overshoot)

'''•''' C3 (scenarios that limit warming to 2°C (&gt;67%) throughout the 21st century)

'''•''' C4 (scenarios that limit warming to 2°C (&gt;50%) throughout the 21st century)

'''•''' C5 (scenarios that limit warming to 2.5°C (&gt;50%) throughout the 21st century)

'''•''' C6 (scenarios that limit warming to 3°C (&gt;50%) throughout the 21st century)

'''•''' C7 (scenarios that limit warming to 4°C (&gt;50%) throughout the 21st century)

• C8 (scenarios that exceed warming of 4°C (≥50%) during the 21st century)

A large share of the scenarios was developed prior to 2020. Results from such scenarios are indexed to a modelled (non-COVID) year 2020, referred to as 2020Mod.

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