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

=== 10.7.6 Fuel Energy and Technology Trajectories ===

<div id="h2-33-siblings" class="h2-siblings"></div>

Two mechanisms for reducing carbon emissions from the transport sector are fuel switching for current vehicle technologies and transitioning to low-carbon vehicle technologies. Figure 10.21 combines data from IAMs and GTEMs on shares of transport final energy by fuel. These shares account for fuel uses across modes – road, aviation, rail, and shipping – and both passenger and freight transport. Since the technologies have different conversion efficiencies, these shares of final energy by fuel are necessarily different from the shares by service (passenger-km or tonne-km) by fuel and shares of vehicle stock by fuel. For example, a current battery electric LDV powertrain is roughly three times more energy-efficient than a comparable ICE powertrain ( [[#10.3|Section 10.3]] , Table 10.9 in Appendix 10.1); thus, fuel shares of 0.25 for electricity and 0.75 for oil could correspond to vehicle stock shares of 0.5 and 0.5, respectively. In general, while models may project that EVs constitute a greater share of road vehicle stock, and provide a greater share of road passenger-kilometres, their share of transport final energy (Figure 10.21) can still remain lower than the final energy share of fuels used in less-efficient (e.g., ICE) vehicles. Thus, the shares of transport final energy by fuel presented in Figure 10.21 should be interpreted with care.

<div id="_idContainer061" class="Basic-Text-Frame"></div>

[[File:862a87fe74c2e1e94e15f5de13c89425 IPCC_AR6_WGIII_Figure_10_16.png]]

'''Figure 10.21 | Global shares of final fuel energy in the transport sector in 2030, 2050, and 2100 for freight and passenger vehicles.''' Plots show 10th/90th percentile, 25th–75th percentile, and median. Data from the AR6 scenario database.

IAM and GTEM scenarios indicate that fuel and technology shifts are crucial to reduce carbon emissions to achieve lower levels of warming ( [[#Edelenbosch--2017|Edelenbosch et al. 2017]] ; [[#IEA--2017b|IEA 2017b]] ). Across the transport sector, a technology shift towards advanced fuel vehicles is the dominant driver of decarbonisation in model projections. This trend is consistent across climate scenarios, with larger decreases in the final energy share of oil in scenarios that achieve progressively lower levels of warming. Due to efficiency improvements, the higher efficiency of advanced fuel vehicles, and slower progress in the freight sector, the final energy share of oil decreases more rapidly after 2030. By 2050, the final energy shares of electricity, biofuels, and alternative gaseous fuels increase, with shares from electricity generally about twice as high (median values from 10–30% across warming levels) as the shares from biofuels and gases (median values from 5–10%). While IAMs suggest that the final energy share of hydrogen will remain low in 2050, by 2100 the median projections include 5–10% hydrogen in transport final energy.

While few IAMs report final energy shares by transport mode or passenger/freight, several relevant studies provide insights into fuel share trends in passenger LDVs and freight vehicles. The IEA suggests that full LDV electrification would be the most promising low-carbon pathway to meet a 1.75°C goal ( [[#IEA--2017b|IEA 2017b]] ). The MIT Economic Projection and Policy Analysis model focuses on the future deployment of gasoline versus EV technologies in the global LDV stock ( [[#Ghandi--2019|Ghandi and Paltsev 2019]] ). These authors estimate that the global stock of vehicles could increase from 1.1 billion vehicles in 2015 up to 1.8 billion by 2050, with a growth in EVs from about 1 million vehicles in 2015 up to 500 million in 2050. These changes are driven primarily by cost projections (mostly battery cost reductions). Similarly, the International Council on Clean Transport (ICCT) indicates that EV technology adoption in the light-duty sector can lead to considerable climate benefits. Their scenarios reach nearly 100% electrification of LDVs globally, leading to global GHG emissions from LDVs ranging from 0% to 50% of 2010 levels in 2050 ( [[#Lutsey--2015|Lutsey 2015]] ). Khalili et al.(2019) estimate transport stocks through 2050 under aggressive climate mitigation scenarios that nearly eliminate road transport emissions. They find the demand for passenger transport could triple through 2050, but emissions targets could be met through widespread adoption of BEVs (80% of LDVs) and, to a lesser extent, fuel cell and plug-in hybrid electric vehicles. Contrary to these estimates, the US Energy Information Administration finds small adoption of electrification for LDVs and instead identifies diffusion of natural gas-fuelled LDVs in OECD and, to a greater extent, non-OECD countries through 2040. This trend occurs in a reference and a ‘low liquids’ case, which lowers LDV ownership growth rates and increases preferences for alternative fuel vehicles. A comprehensive overview of regional technology adoption models across many methodological approaches can be found in [[#Jochem--2018|Jochem et al. (2018)]] .

In freight transport, studies indicate a shift toward alternative fuels would need to be supplemented by efficiency improvements. The IEA suggests efficiency improvements would be essential for decarbonisation of trucks, aviation, and shipping in the short-to-medium term. At the same time, the IEA suggests that fuel switching to advanced biofuels would be needed to decarbonise freight in the long term ( [[#IEA--2019d|IEA 2019d]] ). [[#Mulholland--2018|Mulholland et al. (2018)]] investigated the impacts of decarbonising road freight in two scenarios: countries complying with COP21 pledges and a second more ambitious reduction scenario in line with limiting global temperature rise to 1.75°C. Despite the deployment of logistics improvements, high-efficiency technologies, and low-carbon fuels, activity growth leads to a 47% increase in energy demand for road freight while overall GHG emissions from freight increase by 55% (4.8 GtCO 2- eq) in 2050 (relative to 2015) in the COP21 scenario. In the 1.75°C scenario, decarbonisation happens primarily through a switch to alternative fuels (hybrid electric and full battery electric trucks), which leads to a 60% reduction in GHG emissions from freight in 2050 relative to 2015. [[#Khalili--2019|Khalili et al. (2019)]] also find substantial shifts to alternative fuels in HDVs under aggressive climate mitigation scenarios. Battery electric, hydrogen fuel cell, and plug-in hybrid electric vehicles constitute 50%, 30%, and 15% of heavy-duty vehicles respectively in 2050. They also find 90% of buses would be electrified by 2050.

<div id="box-10.4" class="h2-container box-container"></div>

<span id="box-10.4-three-illustrative-mitigation-pathways"></span>