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

=== 10.6.4 Mitigation Potential of Fuels, Operations and Energy Efficiency ===

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A range of vessel mitigation options for the international fleet exist and are presented in this section. A variety of feedstocks and energy carriers can be considered for shipping. As feedstocks, fuels from biomass (advanced biofuels), fuels produced from renewable electricity and CO 2 capture from flue gas or the air (electro-, e-, or power-fuels), and fuels produced via thermochemical processes (solar fuels) can be considered. As energy carriers, synthetic fuels and the direct use of electricity (stored in batteries) are of relevance. The most prominent synthetic fuels discussed in the literature are hydrogen, ammonia, methane, methanol, and synthetic hydrocarbon diesel. Figure 10.15 shows the emissions reductions potential for alternative energy carriers that have been identified as having the highest potential to mitigate operational emissions from the sector ( [[#Chatzinikolaou--2014|Chatzinikolaou and Ventikos 2014]] ; [[#Brynolf--2014|Brynolf et al. 2014]] ; [[#Teeter--2014|Teeter and Cleary 2014]] ; [[#Traut--2014|Traut et al. 2014]] ; [[#Lindstad--2015|Lindstad et al. 2015]] ; Psaraftis 2015; [[#Seddiek--2015|Seddiek 2015]] ; [[#Tillig--2015|Tillig et al. 2015]] ; [[#Winkel--2016|Winkel et al. 2016]] ; [[#DNV%20GL--2017|DNV GL 2017]] ; [[#Bicer--2018a|Bicer and Dincer 2018a]] ; [[#Biernacki--2018|Biernacki et al. 2018]] ; [[#Bongartz--2018|Bongartz et al. 2018]] ; [[#Gilbert--2018|Gilbert et al. 2018]] ; [[#Hua--2018|Hua et al. 2018]] ; [[#ITF--2018b|ITF 2018b]] ; [[#Singh--2018|Singh et al. 2018]] ; [[#Balcombe--2019|Balcombe et al. 2019]] ; [[#Hansson--2019|Hansson et al. 2019]] ; [[#Sharafian--2019|Sharafian et al. 2019]] ; [[#Winebrake--2019|Winebrake et al. 2019]] ; [[#Czermański--2020|Czermański et al. 2020]] ; [[#Faber--2020|Faber et al. 2020]] ; [[#Hansson--2020|Hansson et al. 2020]] ; [[#Kim--2020|Kim et al. 2020]] ; [[#Liu--2020a|Liu et al. 2020a]] ; [[#Nguyen--2020|Nguyen et al. 2020]] ; [[#Perčić--2020|Perčić et al. 2020]] ; [[#Sadeghi--2020|Sadeghi et al. 2020]] ; [[#Seithe--2020|Seithe et al. 2020]] ; [[#Xing--2020|Xing et al. 2020]] ; [[#Valente--2021|Valente et al. 2021]] ; [[#Stolz--2021|Stolz et al. 2021]] ).

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[[File:7e88f275b9838e5ffcba305cb48ecd85 IPCC_AR6_WGIII_Figure_10_15.png]]

'''Figure 10.15 | Emissions reductions potential of alternative fuels compared to conventional fuels in the shipping sector.''' The x-axis is reported in %. Each individual marker represents a data point from the literature, where the brown square indicates a full LCA CO 2 -eq value; light blue triangles tank-to-wake CO 2 -eq; red triangles well-to-wake CO 2 -eq; yellow triangles well-to-wake CO 2 ; and dark blue circles tank-to-wake CO 2 emissions reduction potentials. The values in the Figure rely on the 100-year GWP value embedded in the source data, which may differ slightly with the updated 100-year GWP values from WGI. ‘n’ indicates the number of data points per sub-panel. Grey shaded boxes represent data where the energy comes from fossil resources, and blue from low-carbon renewable energy sources. ‘Advanced biofuels EMF33’ refers to emissions factors derived from simulation results from the integrated assessment models EMF33 scenarios (darkest coloured box in top left panel). Biofuels partial models CLC refers to partial models with constant land cover. Biofuels partial models NRG refers to partial models with natural regrowth. For ammonia and hydrogen, low-carbon fuel is produced via electrolysis using low-carbon electricity, and ‘fossil’ refers to fuels produced via steam methane reforming of natural gas.

Low-carbon hydrogen and ammonia are seen to have positive potential as a decarbonised shipping fuel. Hydrogen and ammonia, when produced from renewables or coupled to CCS as opposed to mainly by fossil fuels with high lifecycle emissions ( [[#Bhandari--2014|Bhandari et al. 2014]] ), may contribute to significant CO 2 -eq reductions of up to 70–80% compared to low-sulphur heavy fuel oil ( [[#Bicer--2018b|Bicer and Dincer 2018b]] ; [[#Gilbert--2018|Gilbert et al. 2018]] ). These fuels have their own unique transport and storage challenges as ammonia requires a pilot fuel due to difficulty in combustion, and ammonia combustion could lead to elevated levels of NO x , N 2 O, or NH 3 emissions depending on engine technology used ( [[#DNV%20GL--2020|DNV GL 2020]] ). There is a need for the further development of technology and procedures for safe storage and handling of fuels such as hydrogen and ammonia, both onboard and onshore, for faster uptake ( [[#Hoegh-Guldberg--2019|Hoegh-Guldberg et al. 2019]] ), but they remain an encouraging decarbonisation option for shipping in the next decade.

While methanol produced from fossil sources induces an emissions increase of +7.5% (+44%), e-methanol (via hydrogen from electrolysis based on renewable energy and carbon from direct air capture) reduces emissions by 80% (82%). In general, several synthetic fuels, such as synthetic diesel, methane, methanol, ethanol, and dimethyl ether could in principle be used for shipping ( [[#Horvath--2018|Horvath et al. 2018]] ). The mitigation potential of these is fully dependent on the sourcing of the hydrogen and carbon required for their synthesis.

As noted in [[#10.3|Section 10.3]] , LNG has been found to have a relatively limited mitigation potential and may not be viewed as a low-carbon alternative, but has a higher availability than other fuel options ( [[#Gilbert--2018|Gilbert et al. 2018]] ). Emissions reductions across the full fuel lifecycle are found in the order of 10%, with ranges reported from –30% (reduction) to +8% (increase), if switching from heavy fuel oil to LNG, as indicated in Figure 10.15 ( [[#Bengtsson--2011|Bengtsson et al. 2011]] ). Regardless of the production pathway, the literature points to the risk of methane slip (emissions of unburnt methane especially at low engine loads and from transport to ports) from LNG-fuelled vessels, with no current regulation on emissions caps ( [[#Anderson--2015|Anderson et al. 2015]] ; [[#Ushakov--2019|Ushakov et al. 2019]] ; [[#Peng--2020|Peng et al. 2020]] ). Leakage rates are a critical point for the total climate impact of LNG as a fuel, where high pressure engines remedy this more than low pressure ones. As discussed in [[#10.3|Section 10.3]] , some consider LNG as a transition fuel, while some literature points to the risk of stranded assets due to the increasing decarbonisation regulation from IMO and the challenge of meeting IMO’s 2030 emissions reductions targets using this fuel.

In addition to fossil and e-fuels, advanced biofuels might play a role to provide the energy demand for future shipping. Biomass is presently used to produce alcohol fuels (such as ethanol and methanol), liquid biogas, or biodiesel that can be used for shipping and could reduce CO 2 emissions from this segment. As explained in Box 10.2 and Chapter 7, the GHG footprint associated with biofuels is strongly dependent on the incurred land use and land-use change emissions. Advanced biofuels from processing cellulose rather than sugar are likely to be more attractive in terms of the quantities required but are not commercially available ( [[#10.3|Section 10.3]] ). The estimates of emissions reductions from biofuels shown in Figure 10.15 rely on data from the Integrated Assessment Models – Energy Modelling Forum 33 (IAM EMF33), partial models assuming constant land cover (CLC), and partial models using natural growth (NRG). Box 10.2 and [[#10.4|Section 10.4]] include a more detailed description of the assumptions underlying these models and their estimates. The results based on IAM EMF33 and CLC suggests median mitigation potential of around 73% for advanced biofuels in shipping, while the NRG-based results suggest increased emissions from biofuels. The EMF33 and CLC results rely on modelling approaches compatible with the scenarios in the AR6 database ( [[IPCC:Wg3:Chapter:Chapter-6|Chapter 6]] and Box 7.7).

In addition to fuels, there are other measures that may aid the transition to low-carbon shipping. The amounts and speed of uptake of alternative low- or zero-carbon fuels in ports depend upon investments in infrastructure – including bunkering infrastructure, refinery readiness, reliable supply of the fuels, as well as sustainable production. The ship lifetime and age also play a role; retrofitting ships to accommodate engines and fuel systems for new fuel types may not be an option for older vessels. As such, operational efficiency becomes more important ( [[#Bullock--2020|Bullock et al. 2020]] ). There is some potential to continue to improve the energy efficiency of vessels through operational changes ( [[#Traut--2018|Traut et al. 2018]] ), reducing the speed or ‘slow steaming’ ( [[#Bullock--2020|Bullock et al. 2020]] ), and improved efficiency in port operations ( [[#Viktorelius--2019|Viktorelius and Lundh 2019]] ; [[#Poulsen--2020|Poulsen and Sampson 2020]] ). There is also a growing interest in onboard technologies for capturing carbon, with prototype ships underway showing 65–90% potential reduction in CO 2 emissions ( [[#Luo--2017|Luo and Wang 2017]] ; [[#Awoyomi--2020|Awoyomi et al. 2020]] ; Japan Ship Technology Research Association et al. 2020). Challenges identified include CO 2 capture efficiency ( [[#Zhou--2014|Zhou and Wang 2014]] ), increased operating costs, and limited onboard power supply ( [[#Fang--2019|Fang et al. 2019]] ). Furthermore, designing CO 2 storage tanks for transport to shore may pose a challenge, as the volume and weight of captured CO 2 could be up to four times more than standard oil ( [[#Decarre--2010|Decarre et al. 2010]] ).

Changes in design and engineering provide potential for reducing emissions from shipping through a range of measures, for example by optimising hull design and vessel shape, power and propulsion systems that include wind- or solar-assisted propulsion, and through improved operations of vessels and ports. Figure 10.15 shows that such measures may decrease emissions by 5–40%, though with a broad range in potential ( [[#Bouman--2017|Bouman et al. 2017]] ). Nuclear propulsion could decrease emissions from individual vessels by 98%. Battery- or hybrid-electric ships have been identified as a means to reduce emissions in short-sea shipping such as ferries and inland waterways ( [[#Gagatsi--2016|Gagatsi et al. 2016]] ), which may also importantly reduce near-shore SLCF pollution ( [[#Nguyen--2020|Nguyen et al. 2020]] ). Figure 10.15 shows that the median emissions from electric ships can be about 40% lower than equivalent fossil-based vessels but can vary widely. The wide reduction potential of battery electric propulsion is due to different assumptions about the CO 2 intensity of the electricity used and the levels of CO 2 footprints associated with battery production.

Although projections indicate continued increase in freight demand in the future, demand-side reductions could contribute to mitigation. The development of autonomous systems may play a role ( [[#Colling--2020|Colling and Hekkenberg 2020]] ; [[#Liu--2021|Liu et al. 2021]] ) while 3-D printing can reduce all forms of freight as parts and products can be printed instead of shipped ( [[#UNCTAD--2018|UNCTAD 2018]] ). As more than 40% of transported freight is fossil fuels, a lessened demand for such products in low-emissions scenarios should contribute to reducing the overall maritime transport needs and hence emissions in the future ( [[#Sharmina--2017|Sharmina et al. 2017]] ). An increase in alternative fuels, on the other hand, may increase freight demand ( [[#Mander--2012|Mander et al. 2012]] ). Potentials for demand-side reduction in shipping emissions may arise from improving processes around logistics and packaging, and further taxes and charges could serve as leverage for reducing demand and emissions.

The coming decade is projected to be costly for the shipping sector, as it is preparing to meet the 2030 and 2050 emissions reduction targets set by the IMO ( [[#UNCTAD--2018|UNCTAD 2018]] ). With enough investments, incentives, and regulation, substantial reductions of CO 2 emissions from shipping could be achieved through alternative energy carriers. The literature suggests that their cost could be manyfold higher than for conventional fuels, which in itself could reduce demand for shipping, and hence its emissions, but could make the transition difficult. R&amp;D may help reduce these costs. The literature points to the need for developing technology roadmaps for enabling the maritime transport sector to get on to pathways for decarbonisation early enough to reach global goals ( [[#Kuramochi--2018|Kuramochi et al. 2018]] ). Accounting for the full lifecycle emissions of the vessels and the fuels is required to meet the overall long-term objectives of cutting GHG and SLCF emissions. The urgency of implementing measures for reducing emissions is considered to be high, considering the lifetime of vessels is typically 20 years, if not more.

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