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

=== 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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