Establishing and expanding urban rail networks in existing and future large cities

A rich literature finds that the provision of reliable, convenient, and affordable public transit, and in the case of large cities, metro and light rail, not only reduces the per capita transport emissions in these cities, but can also contribute substantially to reducing levels of pollutants associated with road vehicles, and also enables reductions in the macroand micro-economic costs of providing urban mobility.

Other studies identify economic and equity benefits that come from urban rail systems.

International shipping

To put international shipping on the SDS trajectory, it is essential to switch to lowand zerocarbon fuels, as they barely figure in the maritime fuel mix.

Interest in using alternative fuels such as ammonia, hydrogen or advanced biodiesel and ammonia mounted significantly after the IMO adopted its initial strategy to reduce GHG emissions from ships by 2050. This agreement happened shortly before the implementation of Emission Control Areas (which limit sulphur oxide [SOx] and particulate matter [PM] emissions near ports) and tighter sulphur emission regulations, which will come into force in 2020.

Although advanced biofuels, hydrogen and ammonia are potential low-carbon options to replace conventional fuels, an important uptake barrier is their high cost compared with conventional fuels. In the cases of ammonia and hydrogen, another barrier is the lack of infrastructure.

Transitioning to low-carbon ammonia or hydrogen fuel

In addition to diversifying the sources of maritime fuel supplies, adopting alternative fuels would help meet the tighter sulphur standards coming into effect in 2020; alternatives to bunker fuel will also be needed to meet SOx and PM emissions limits near a growing number of the world's ports (Emission Control Areas). These near-term air pollution targets can generally be met by switching to low-sulphur diesel or investing in scrubbers, and liquefied natural gas (LNG) is also an option because it does not emit SOx.

Oil demand in this fast-growing sector is set to rise 20% (to 6 million barrels per day) by 2030 unless measures are taken to enforce the IMO’s long-term GHG emissions target. Ship owners must therefore make some important decisions very soon.

In the long term, GHG emissions from international shipping must be cut by at least 50% by 2050. A challenge to meeting this IMO target is that ship lifetimes generally span two to three decades. However, depending on eventual costs and incentives, using ammonia or hydrogen could be a solution.

Aviation

Aviation is likely to be the most difficult transport sector to decarbonise.

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