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

== 10.6 Decarbonisation of Shipping ==

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Maritime transport is considered one of the key cornerstones enabling globalisation ( [[#Kumar--2002|Kumar and Hoffmann 2002]] ). But as for aviation, shipping has its challenges in decarbonisation, with a strong dependency on fossil fuels without major changes since AR5. At the same time, the sector has a range of opportunities that could help reduce emissions through not only changing fuels, but also by increasing energy efficiency, optimising operations and ship design, reducing demand, improving regulations, as well as other options that will be reviewed in this section.

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=== 10.6.1 Historical and Current Emissions from Shipping ===

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Maritime transport volume has increased by 250% over the past 40 years, reaching an all-time high of 11 billion tonnes of transported goods in 2018 ( [[#UNCTAD--2019|UNCTAD 2019]] ). This growth in transport volumes has resulted in continued growth in GHG emissions from the shipping sector, despite an improvement in the carbon intensity of ship operations, especially since 2014. The estimated total emissions from maritime transport can vary depending on data set and calculation method, but range over 600–1100 MtCO 2 yr –1 over the past decade (Figure 10.14), corresponding to 2–3% of total anthropogenic emissions. The legend in Figure 10.14 refers to the following data sources: [[#Endresen--2003|Endresen et al. (2003)]] , [[#Eyring--2005|Eyring et al. (2005)]] , [[#Dalsøren--2009|Dalsøren et al. (2009)]] , DNV GL ( [[#DNV%20GL--2019|DNV GL 2019]] ), CAMS-GLOB-SHIP ( [[#Jalkanen--2014|Jalkanen et al. 2014]] ; [[#Granier--2019|Granier et al. 2019]] ), EDGAR ( [[#Crippa--2019|Crippa et al. 2019]] ), [[#Hoesly--2018|Hoesly et al. (2018)]] , [[#Johansson--2017|Johansson et al. (2017)]] , ICCT ( [[#Olmer--2017|Olmer et al. 2017]] ), the IMO GHG Studies; IMO 2nd ( [[#Buhaug--2009|Buhaug et al. 2009]] ), IMO 3rd ( [[#Smith--2014|Smith et al. 2014]] ), IMO 4th-vessel and IMO 4th-voyage ( [[#Faber--2020|Faber et al. 2020]] ), and [[#Kramel--2021|Kramel et al. (2021)]] .

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[[File:fc918ecc73b0a1b98684a4346fd2b207 IPCC_AR6_WGIII_Figure_10_14.png]]

'''Figure 10.14 | CO''' 2 '''emissions (Mt yr''' –1 ''') from shipping 2000–2018.''' Data from various inventories as shown in the label.

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=== 10.6.2 Short-lived Climate Forcers and Shipping ===

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Like aviation, shipping is also a source of emissions of SLCFs as described in [[#10.5|Section 10.5]] , including nitrogen oxides (NO x ), sulphur oxides (SO x , such as SO 2 and SO 4 ), carbon monoxide (CO), black carbon, and non-methane volatile organic compounds (NMVOCs) ( [[#Szopa--2021|Szopa et al. 2021]] ). Though SLCF have a shorter lifetime than the associated CO 2 emissions, these short-lived forcers can have both a cooling effect (e.g., SO x ) or a warming effect (e.g., ozone from NO x ). The cooling from the SLCF from a pulse emission will decay rapidly and diminish after a couple of decades, while the warming from the long-lived substances lasts for centuries ( [[#Szopa--2021|Szopa et al. 2021]] ).

Emissions of SLCF from shipping not only affect the climate, but also the environment, air quality, and human health. Maritime transport has been shown to be a major contributor to coastal air quality degradation ( [[#Zhao--2013|Zhao et al. 2013]] ; [[#Jalkanen--2014|Jalkanen et al. 2014]] ; [[#Viana--2014|Viana et al. 2014]] ; [[#Goldsworthy--2015|Goldsworthy and Goldsworthy 2015]] ; [[#Goldsworthy--2017|Goldsworthy 2017]] ). Sulphur emissions may contribute towards acidification of the ocean ( [[#Hassellöv--2013|Hassellöv et al. 2013]] ). Furthermore, increases in sulphur deposition on the oceans have also been shown to increase the flux of CO 2 from the oceans to the atmosphere ( [[#Hassellöv--2013|Hassellöv et al. 2013]] ). To address the risks of SO x emissions from shipping, there is now a cap on the on the sulphur content permissible in marine fuels ( [[#IMO--2013|IMO 2013]] ). There is also significant uncertainty about the impacts of pollutants emitted from ships on the marine environment ( [[#Blasco--2014|Blasco et al. 2014]] ).

Pollution control is implemented to varying degrees in the modelling of the SSP scenarios ( [[#Rao--2017|Rao et al. 2017]] ); for example, SSPs 1 and 5 assume that increasing concern for health and the environment result in more stringent air pollution policies than today ( [[#Szopa--2021|Szopa et al. 2021]] ). There is a downward trend in SO x and NO x emissions from shipping in all the SSPs, in compliance with regulations. The SLCF emissions reduction efforts, within the maritime sector, are also contributing towards achieving the UN SDGs. In essence, while long-lived GHGs are important for long-term mitigation targets, accounting for short-lived climate forcers is important both for current and near-term forcing levels as well as broader air pollution and SDG implications.

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=== 10.6.3 Shipping in the Arctic ===

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Shipping in the Arctic is a topic of increasing interest. The reduction of Arctic summer sea ice increases the access to the northern sea routes ( [[#Smith--2013|Smith and Stephenson 2013]] ; [[#Melia--2016|Melia et al. 2016]] ; [[#Aksenov--2017|Aksenov et al. 2017]] ; [[#Fox-Kemper--2021|Fox-Kemper et al. 2021]] ). Literature and public discourse has sometimes portrayed this trend as positive ( [[#Zhang--2016b|Zhang et al. 2016b]] ), as it allows for shorter shipping routes, for example between Asia and Europe, with estimated travel time savings of 25–40% ( [[#Aksenov--2017|Aksenov et al. 2017]] ). However, the acceleration of Arctic cryosphere melt and reduced sea ice that enable Arctic shipping reduce surface albedo and amplify climate warming ( [[#Eyring--2021|Eyring et al. 2021]] ). Furthermore, local air pollutants can play different roles in the Arctic. For example, black carbon emissions reduce albedo and absorb heat in air, on snow and ice ( [[#Browse--2013|Browse et al. 2013]] ; [[#Kang--2020|Kang et al. 2020]] ; [[#Messner--2020|Messner 2020]] ; [[#Eyring--2021|Eyring et al. 2021]] ). Finally, changing routing from Suez to the northern sea routes may reduce total emissions for a voyage, but also shifts emissions from low to high latitudes. Changing the location of the emissions adds complexity to the assessment of the climatic impacts of Arctic shipping, as the local conditions are different and the SLCF may have a different impact on clouds, precipitation, albedo and local environment ( [[#Dalsøren--2013|Dalsøren et al. 2013]] ; [[#Fuglestvedt--2014|Fuglestvedt et al. 2014]] ; [[#Marelle--2016|Marelle et al. 2016]] ). Observations have shown that 5–25% of air pollution in the Arctic stems from shipping activity within the Arctic itself ( [[#Aliabadi--2015|Aliabadi et al. 2015]] ). Emissions outside the Arctic can affect Arctic climate, and changes within the Arctic may have global climate impacts. Both modelling and observations have shown that aerosol emissions from shipping can have a significant effect on air pollution and shortwave radiative forcing ( [[#Ødemark--2012|Ødemark et al. 2012]] ; [[#Peters--2012|Peters et al. 2012]] ; [[#Dalsøren--2013|Dalsøren et al. 2013]] ; [[#Roiger--2014|Roiger et al. 2014]] ; [[#Righi--2015|Righi et al. 2015]] ; [[#Marelle--2016|Marelle et al. 2016]] ).

Increased Arctic shipping activity may also pose increased risks to local marine ecosystems and coastal communities from invasive species, underwater noise, and pollution ( [[#Halliday--2017|Halliday et al. 2017]] ; [[#IPCC--2019|IPCC 2019]] ). Greater levels of Arctic maritime transport and tourism have political, as well as socio-economic, implications for trade, and nations and economies reliant on the traditional shipping corridors. There has been an increase in activity from cargo, tankers, supply, and fishing vessels in particular ( [[#Winther--2014|Winther et al. 2014]] ; [[#Zhao--2015|Zhao et al. 2015]] ). Projections indicate more navigable Arctic waters in the coming decades ( [[#Smith--2013|Smith and Stephenson 2013]] ; [[#Melia--2016|Melia et al. 2016]] ) and continued increases in transport volumes through the northern sea routes ( [[#Corbett--2010|Corbett et al. 2010]] ; [[#Lasserre--2011|Lasserre and Pelletier 2011]] ; [[#Winther--2014|Winther et al. 2014]] ). Emission patterns and quantities, however, are also likely to change with future regulations from IMO, and depend on technology developments, and activity levels which may depend upon geopolitics, commodity pricing, trade, natural resource extraction, insurance costs, taxes, and tourism demand ( [[#Johnston--2017|Johnston et al. 2017]] ). The need to include indigenous peoples’ voices when shaping policies and governance of shipping activities in the high north is increasing ( [[#Dawson--2020|Dawson et al. 2020]] ).

The Arctic climate and environment pose unique hazards and challenges with regard to safe and efficient shipping operations: low temperature challenges, implications for vessel design, evacuation and rescue systems, communications, oil spills, variable sea ice, and meteorological conditions ( [[#Buixadé%20Farré--2014|Buixadé Farré et al. 2014]] ). To understand the total implications of shipping in the Arctic, including its climate impacts, a holistic view of synergies, trade-offs, and co-benefits is needed, with assessments of impacts on not only the physical climate, but also the local environment and ecosystems. To further ensure safe operations in the Arctic waters, close monitoring of activities may be valuable.

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=== 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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=== 10.6.5 Accountability and Governance Options ===

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Regulatory frameworks for the shipping sector have been developed over time and will continue to be through bodies such as the IMO, which was established by the UN to manage international shipping. The IMO strategy involves a 50% reduction in GHG emissions from international shipping by 2050 compared to 2008 ( [[#IMO--2018|IMO 2018]] ). The strategy includes a reduction in carbon intensity of international shipping by at least 40% by 2030, and 70% by 2050, compared to 2008. IMO furthermore aims for the sectoral phase-out of GHG emissions as soon as possible this century.

In 2020, the IMO approved the short-term goal-based measure to reduce the carbon intensity of existing international vessels. This measure addresses both technical and operational strategies. The operational element is represented by a Carbon Intensity Indicator (CII), and the technical element is represented by the Energy Efficiency Existing Ship Index (EEXI), which will apply to ships from 2023. The EEXI builds upon the Energy Efficiency Design Index (EEDI), which is a legally-binding mitigation regulation for newbuild ships, established as a series of baselines for the amount of fuel ships may burn for a particular cargo-carrying capacity. The EEDI differs per ship segment. For example, ships built in 2022 and beyond should be 50% more energy efficient than those built in 2013. This legislation aims to reduce GHG emissions in particular. Energy efficiency may be improved by several of the mitigation options outlined above. The Ship Energy Efficiency Management Plan (SEEMP) is seen as the international governance instrument to improve energy efficiency and hence emissions from ships. SEEMP is a measure to enable changes to operational measures and retrofits (see [[#Johnson--2013|Johnson et al. 2013]] ). The combination of EEXI, EEDI, and SEEMP may reduce emissions by 23% by 2030 compared to a ‘no policy’ scenario (Sims et al. 2014). With regards to accountability, it is mandatory for ships greater than or equal to 5000 gross tonnage to collect fuel consumption data, as well as specified data. Such as for transport work. Similarly, the EU Monitoring, Reporting and Verification Regulation requires mandatory reporting of a vessel’s fuel consumption when operating in European waters.

Policy choices may enable or hinder changes, and gaps in governance structures may, to some degree, hinder the objectives of mechanisms like SEEMP to improve energy efficiency and emissions. Policies may be developed to incentivise investments in necessary changes to the global fleet and related infrastructures. The literature argues that regulations and incentives that motivate mitigation through speed optimisation, ship efficiency improvements, and retrofits with lower-carbon technologies at a sub-global scale may contribute to immediate reductions in CO 2 emissions from the sector ( [[#Bows-Larkin--2015|Bows-Larkin 2015]] ). The role of the financial sector, through initiatives such as the Poseidon Principle, which limit lending to companies that fail to uphold environmental standards, could also become increasingly important ( [[#Sumaila--2021|Sumaila et al. 2021]] ).

It has been proposed to make shipping corporations accountable for their emissions by making it mandatory to disclose their vessels’ emissions reductions ( [[#Rahim--2016|Rahim et al. 2016]] ). Market-based mechanisms may increasingly encourage ship operators to comply with IMO GHG regulations. Development of policies such as carbon pricing or taxation to enable a business case for adopting low-carbon fuels could be a near-term priority for acceleration of transformation of the sector ( [[#Hoegh-Guldberg--2019|Hoegh-Guldberg et al. 2019]] ). The EU is considering including shipping in its carbon trading system, with the details still to be agreed upon but expected to come into force in 2023, along with the CII. The proposition is that shipowners who conduct voyages within Europe, or start or end at an EU port, will have to pay for carbon permits to cover the CO 2 emitted by their vessel.

Regulations exist also to limit emissions of air pollution from shipping with the aim to improve environment and health impacts from shipping in ports and coastal communities. In sulphur emission control areas (SECAs), the maximum permissible sulphur content in marine fuels is 0.10% mass/mass. These are further tightened by the IMO legislation on reducing marine fuel sulphur content to a maximum of 0.5% in 2020 outside SECAs, compared to 3.5% permissible since 2012 (MARPOL Convention). The MARPOL Annex VI also limits the emissions of ozone-depleting substances and ozone precursors, NO x , and volatile organic compounds from tankers ( [[#Mertens--2018|Mertens et al. 2018]] ). The implementation of the emission control areas have been shown to reduce the impacts on health and the environment ( [[#Viana--2015|Viana et al. 2015]] ).

While there are many governance and regulatory initiatives that help reduce emissions from the shipping sector, few are transformative on their own, unless zero-carbon fuels can become available at a reasonable cost as suggested in Sections 10.3 and below.

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=== 10.6.6 Transformation Trajectories for the Maritime Sector ===

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Figure 10.16 shows CO 2 emissions from shipping in scenarios from the AR6 database and the Fourth GHG study by the IMO ( [[#Faber--2020|Faber et al. 2020]] ). Panel (a) shows that CO 2 emissions from shipping go down by 33–70% (5–95th% percentile) by 2050 in the C1 and C2 scenarios, which limit warming to 1.5°C (&gt;50%) during the 21st century with no or limited overshoot or return warming to 1.5°C (&gt;50%) during the 21st century after a high overshoot. By 2080, median values for the same set of scenarios reach net zero CO 2 emissions. IAMs often do not report emissions pathways for shipping transport and the sector is underrepresented in most IAMs ( [[#Esmeijer--2020|Esmeijer et al. 2020]] ). Hence pathways established outside IAMs can be different for the sector. Indeed, the IMO projections for growth in transport demand ( [[#Faber--2020|Faber et al. 2020]] ) indicate increases of 40–100% by 2050 for the global fleet. Faber and et al. (2020), at the same time predict reductions in trade for fossil fuels dependent on decarbonisation trajectories. The energy efficiency improvements of the vessels in these scenarios are typically of 20–30%. This offsets some of the increases from higher demand in the future scenarios. Fuels assessed by the Fourth IMO GHG study were limited to heavy fuel oil, marine gasoil, LNG, and methanol, with a fuels mix ranging from 91–98% conventional fuel use and a small remainder of alternative fuels (primarily LNG and some methanol). Panel (b) shows average fleetwide emissions of CO 2 based on these aggregate growth and emissions trajectories from the IMO scenarios. In these scenarios, CO 2 emissions from shipping remain stable or grow compared to 2020 modelled levels. These results contrast with the low emissions trajectories in the C1–C2 bin in panel (a). It seems evident that the scenarios in the AR6 database explore a broader solutions space for the sector than the Fourth GHG study by the IMO. However, the 1.5°C–2°C warming goal has led to an IMO 2050 target of 40% reduction in carbon intensity by 2030, which would require emissions reduction efforts to begin immediately. Results from global models suggest the solutions space for deep emissions reductions in shipping is available.

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[[File:862a87fe74c2e1e94e15f5de13c89425 IPCC_AR6_WGIII_Figure_10_16.png]]

'''Figure 10.16''' | '''CO''' 2 '''emissions from shipping scenarios indexed to 2020 modelled year.''' Panel '''(a)''' scenarios from the AR6 database. Panel '''(b)''' scenarios from the Fourth IMO GHG Study ( [[#Faber--2020|Faber et al., 2020]] ). Figures show median, 5th and 95th percentile (shaded area) for each scenario group.

Combinations of measures are likely to be needed for transformative transitioning of the shipping sector to a low-carbon future, particularly if an expected increase in demand for shipping services is realised ( [[#Smith--2014|Smith et al. 2014]] ; [[#Faber--2020|Faber et al. 2020]] ). Both GHG and SLCF emissions decrease significantly in SSP1-1.9, where mitigation is achieved in the most sustainable way ( [[#Rao--2017|Rao et al. 2017]] ). Conversely, there are no emissions reductions in the scenarios presented by the IMO Fourth GHG study, even though these scenarios incorporate some efficiency improvements and a slight increase in the use of LNG.

Options outlined in this chapter suggest a combination of policies to reduce demand, increase investments by private actors and governments, and develop the technology readiness level of alternative fuels and related infrastructure (especially synthetic fuels). Some literature suggests that battery electric-powered short-distance sea shipping could yield emissions reductions given access to low-carbon electricity. For deep sea shipping, advanced biofuels, hydrogen, ammonia, and synthetic fuels hold potential for significant emissions reductions, depending on GHG characteristics of the fuel chain and resource base. Other options, such as optimisation of speed and hull design and wind-assisted ships, could also combine to make significant contributions by 2050 to further bring emissions down. In total a suite of mitigation options exists or is on the horizon for the maritime sector.

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