Getting ships into shape: Decarbonisation of shipping

2nd November 2020

Web p22 credit richard gleed

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  • sea ice loss ,
  • Fossil fuels ,
  • Air


Nicole Linney

Simon Bullock assesses the possible decarbonisation of the shipping industry

Our prospects on climate change seem to get both better and worse with every passing year. The impacts get worse: Australian and Californian wildfires, disintegrating ice sheets, flooding, drought. However, in some areas, we are starting to see real progress after decades of inaction. Wind and solar are now the cheapest power sources worldwide, and coal power is almost completely off the grid in the UK – unthinkable just 10 years ago.

Nevertheless, we need much more rapid action, and in every sector: the IPCC's Global Warming of 1.5°C report states that we should be aiming for global zero CO2 emissions by 2050. That might be doable for electricity, but for some other sectors, such as shipping, it will be a challenge.

Shipping is pivotal to the world's economy – it transports more than 80% of the world's goods by volume. It's also a big polluter: if it were a country, it would be the sixth biggest CO2 emitter, between Japan and Germany. Getting shipping to zero-emissions is therefore a big deal.

Existing ships

A lot of the current debate in shipping is over how to get to zero-carbon ships. The global Getting to Zero Coalition is working on how to ensure such ships are operating on our oceans by 2030. There are many options for low or very low-carbon propulsion systems, such as hydrogen, ammonia, batteries, methanol and even wind. All have their difficulties, and different parts of the sector will likely use different systems. Ports and fuelling infrastructures will also need to change.

While a zero-emission target date helps focus attention on the need for these new technologies, it's not the end date that matters from a climate perspective. CO2 stays in the atmosphere and warms the planet for hundreds of years; it is the amount of cumulative emissions up to the point of zero emissions that determines the level of warming.

How much carbon will the sector emit before the zero-emission target date? To answer this, we need to turn our attention to existing ships. One difficulty is that ships are so long-lived compared with cars or TVs or lightbulbs – each ship is in use for, on average, 27 years. That means that the existing global fleet of around 90,000 ships will keep churning out pollution for many years to come.

Researchers from the Tyndall Centre at the University of Manchester published a new paper on this challenge, 'Shipping and the Paris climate agreement: a focus on committed emissions' (, this summer. First, they calculated how much carbon dioxide the shipping sector can emit before it exceeds its fair share of the Paris 1.5°C temperature limit. Then they calculated the 'committed emissions' from the future operations of today's ships. The findings are bad news for the climate: without action focusing on the ships operating today, the existing fleet on its own will take up more than the entire carbon budget for shipping.

So, while zero-carbon propulsion systems for new ships are important, it is not the only part of the answer – there has to be a focus on cutting emissions from existing ships as well. The University of Manchester team investigated multiple measures. For example, cutting speeds saves a lot of fuel. There are multiple operational efficiencies that could be utilised, such as fitting sails like Flettner rotors, or using paints that reduce drag. Blending zero-carbon biofuels into the fuel is an option if other sustainability concerns can be overcome. Ships could plug into electricity grids when in port, rather than using their auxiliary engines. Hybrid engines could be retrofitted in the coming decade, and whole ships retrofitted to use zero-carbon fuels such as ammonia as these fuels become available from 2030.

The good news is that if all of these options are taken up, and quickly, it is still possible for shipping to stay within a 1.5°C-compatible carbon budget – so the research has a message of both urgency and hope. Solutions exist, but there is not a lot of time. Any delay in action makes the challenge harder in the future. The research illustrates that there must be a focus on existing ships, not just on developing zero-carbon fuels for new ships in 10 years' time.

Stepping up

Will this happen? Shipping is a global sector, and its environmental governance is handled primarily at the global level by the International Maritime Organisation (IMO). In recent years the IMO has set a greenhouse gas target to cut emissions by 50% by 2050 compared to 2008. This is far stronger than the targets set in aviation, but it is not sufficient – zero emissions of CO2 by 2040 would be Paris-compatible – and there are not yet adequate policies to meet this target. Moreover, the IMO's recent Fourth Greenhouse Gas Study showed worrying signs that emissions are rising. The IMO plans to have stronger policies on both existing and new ships by 2023, but the pace of policy development is glacially slow, and progress on critical issues such as carbon pricing has stalled – international marine fuel, like aviation kerosene, continues to be exempt from all taxation. The IMO can enact policies – this year saw global regulation to limit sulphur dioxide pollution – but it seems prudent to assume at the moment that it will not act with sufficient speed on climate.

This means that national and regional governments, and the shipping sector itself, will need to step up. The EU is leading the way – its frustration with the speed of IMO talks led it to vote for shipping to become part of the EU Emissions Trading Scheme (EUETS). This is a welcome move from a climate perspective, but the EUETS is also not aligned with Paris 1.5°C.

Decarbonising shipping is complex. It needs multiple solutions at multiple levels, which will require multiple actors and multiple policies. There is a clear role not just for international and regional entities such as the IMO and the EU, or big shipping companies such as Maersk and Carnival, but also national governments. Last year the UK published its Clean Maritime Plan – a world-first document, with high ambition. But this high-level plan now needs stronger policies to make turn its ambition into a reality.

There's a strong case for the government's spending review this autumn to include a major infrastructure fund for shipping and port decarbonisation. One mechanism could be the provision of grants for ports to provide 'shore-power' for ships to plug into while at berth; this would also help cut local air pollution in urban areas. Along with battery storage, renewable power generation and the electrification of cranes, gantries and trucks, shore-power is one element of a future 'smart port' electricity strategy. There are similar opportunities for the development of hydrogen and ammonia infrastructures, using increasingly abundant and cheap North Sea offshore renewables. And the North Sea and English Channel short-sea passenger and freight routes are the perfect test-bed for deployment of hybrid and then fully electric ships, as battery costs continue to plummet. However, progress on all of these will require UK government policy and leadership.

80% of the world's goods by volume are transported via ship

6thIf shipping was a country, it would be the world's 6th biggest CO2 emitter

90,000 The existing global fleet includes 90,000 ships

2050 The IMO has targeted a 50% emissions reduction by 2050

Simon Bullock is a PhD reseacher at the Tyndall Centre for Climate Change Research, University of Manchester.

Picture credit: Richard Gleed


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