Editing IPCC:AR6/WGIII/Chapter-3 (section)

=== 3.4.4 Transport ===

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Reference scenarios show growth in transport demand, particularly in aviation and freight ( [[#Yeh--2017|Yeh et al. 2017]] ; [[#Sharmina--2020|Sharmina et al. 2020]] ; [[#Müller-Casseres--2021b|Müller-Casseres et al. 2021b]] ). Energy consumption continues to be dominated by fossil fuels in reference scenarios, with some increases in electrification ( [[#Yeh--2017|Yeh et al. 2017]] ; [[#Edelenbosch--2020|Edelenbosch et al. 2020]] ; [[#Yeh--2017|Yeh et al. 2017]] ). CO 2 emissions from transport increase for most models in reference scenarios ( [[#Yeh--2017|Yeh et al. 2017]] ; [[#Edelenbosch--2020|Edelenbosch et al. 2020]] ).

The relative contribution of demand-side reduction, energy- efficiency improvements, fuel switching, and decarbonisation of fuels, varyies by model, level of mitigation, mitigation options available, and underlying socio-economic pathway ( [[#Longden--2014|Longden 2014]] ; [[#Wise--2017|Wise et al. 2017]] ; [[#Yeh--2017|Yeh et al. 2017]] ; [[#Luderer--2018|Luderer et al. 2018]] ; [[#Yeh--2017|Yeh et al. 2017]] ; [[#Edelenbosch--2020|Edelenbosch et al. 2020]] ; [[#Müller-Casseres--2021a|Müller-Casseres et al. 2021a]] ,b). IAMs typically rely on technology-focused measures like energy- efficiency improvements and fuel switching to reduce carbon emissions ( [[#Pietzcker--2014|Pietzcker et al. 2014]] ; [[#Edelenbosch--2017a|Edelenbosch et al. 2017a]] ; [[#Yeh--2017|Yeh et al. 2017]] ; [[#Zhang--2018a|Zhang et al. 2018a]] ,b; [[#Rogelj--2018|Rogelj et al. 2018]] b; [[#Zhang--2018a|Zhang et al. 2018a]] ,b; [[#Sharmina--2020|Sharmina et al. 2020]] ). Many mitigation pathways show electrification of the transport system ( [[#Luderer--2018|Luderer et al. 2018]] ; [[#Pietzcker--2014|Pietzcker et al. 2014]] ; [[#Longden--2014|Longden 2014]] ; [[#Luderer--2018|Luderer et al. 2018]] ; [[#Zhang--2018a|Zhang et al. 2018a]] ); however, without decarboniszation of the electricity system, transport electrification can increase total energy system emissions ( [[#Zhang--2020|Zhang and Fujimori 2020]] ). A small number of pathways include demand-side mitigation measures in the transport sector; these studies show reduced carbon prices and reduced dependence on CDR ( [[#Grubler--2018|Grubler et al. 2018]] ; [[#Méjean--2019|Méjean et al. 2019]] ; [[#van%20de%20Ven--2018|van de Ven et al. 2018]] ; Zhang et al. 2018c; [[#Méjean--2019|Méjean et al. 2019]] ) ( [[#3.4.1|Section 3.4.1]] ). [[#footnote-006|14]]

Across all IAM scenarios assessed, final energy demand for transport continues to grow, including in many stringent mitigation pathways (Figure 3.25). The carbon intensity of energy declines substantially by 2100 in ''likely'' 2°C (&gt;67%) and below scenarios, leading to substantial declines in transport sector CO 2 emissions with increased electrification of the transport system (Figure 3.23).

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[[File:87344fffd1ca49bcfd1633cdecaf99fc IPCC_AR6_WGIII_Figure_3_25.png]]

'''Figure 3.25 | Transport finalenergy (a),CO''' 2 '''emissions (b), carbon intensity (cand share of final energy from electricity (d), hydrogen (e), and biofuels (f).''' See [[IPCC:Wg3:Chapter:Chapter-10|Chapter 10]] for a discussion of energy intensity. Carbon intensity is CO 2 emissions per EJ of final energy. The first three indicators are indexed to 2019, 13 , where values less than 1 indicate a reduction.

The transport sector has more detail than other sectors in many IAMs ( [[#Edelenbosch--2020|Edelenbosch et al. 2020]] ); however, there is considerable variation across models. Some models (e.g., GCAM, IMAGE, MESSAGE-GLOBIOM) represent different transport modes with endogenous shifts across modes as a function of income, price, and modal speed ( [[#Edelenbosch--2020|Edelenbosch et al. 2020]] ). [[#footnote-005|15]] However, IAMs, including those with detailed transport, exclude several supply-side (e.g., synthetic fuels) and demand-side (e.g., behaviour change, reduced shipping, telework and automation) mitigation options ( [[#Pietzcker--2014|Pietzcker et al. 2014]] ; [[#Creutzig--2016|Creutzig et al. 2016]] ; [[#Mittal--2017|Mittal et al. 2017]] ; [[#Davis--2018|Davis et al. 2018]] ; [[#Köhler--2020|Köhler et al. 2020]] ; [[#Mittal--2017|Mittal et al. 2017]] ; [[#Gota--2019|Gota et al. 2019]] ; [[#Wilson--2019|Wilson et al. 2019]] ; [[#Creutzig--2016|Creutzig et al. 2016]] ; [[#Köhler--2020|Köhler et al. 2020]] ; [[#Sharmina--2020|Sharmina et al. 2020]] ; [[#Pietzcker--2014|Pietzcker et al. 2014]] ; [[#Lefèvre--2021|Lefèvre et al. 2021]] ; [[#Müller-Casseres--2021a|Müller-Casseres et al. 2021a]] ,b).

As a result of these missing options and differences in how mitigation is implemented, IAMs tend to show less mitigation than the potential from national transport/energy models ( [[#Wachsmuth--2019|Wachsmuth and Duscha 2019]] ; [[#Gota--2019|Gota et al. 2019]] ; [[#Yeh--2017|Yeh et al. 2017]] ; [[#Gota--2019|Gota et al. 2019]] ; [[#Wachsmuth--2019|Wachsmuth and Duscha 2019]] ; [[#Edelenbosch--2020|Edelenbosch et al. 2020]] ). For the transport sector as a whole, studies suggest a mitigation potential of 4–-5 GtCO 2 per year in 2030 ( [[#Edelenbosch--2020|Edelenbosch et al. 2020]] ) with complete decarbonization decarbonisation possible by 2050 ( [[#Gota--2019|Gota et al. 2019]] ; [[#Wachsmuth--2019|Wachsmuth and Duscha 2019]] ). However, in the scenarios assessed in this chapter that limit warming to below 1.5°C (&gt;50%) with no or limited overshoot, transport sector CO 2 emissions are reduced by only 59% (28–% to 81%) in 2050 compared to 2015. IAM pathways also show less electrification than the potential from other studies; pathways that limit warming to 1.5°C with no or limited overshoot show a median of 25% (7– to 43%) of final energy from electricity in 2050, while the IEA NZE scenario includes 45% ( [[#IEA--2021a|]] [[#IEA--2021|IEA 2021]] a ).

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