Efficient new ships won’t be enough to meet the Paris Agreement’s goals

01 Jul 2020


The shipping sector has a low profile in discussions of energy and climate change, but, shipping is an integral part of a globalised economic system. Although efficient – per tonne of goods transported – in total international shipping emits more carbon dioxide than Germany – the sixth biggest emitting country. To date, the International Maritime Organisation (IMO) has focussed efforts on new efficient ships, but, our latest research shows that this won’t be enough to meet the Paris Agreement’s climate goals, and we should take swift action to reduce emissions from the current fleet.

Committed emissions

The concept of “committed emissions” is used to consider the climate impact of existing long-lived infrastructure, in comparison to anything we will build in the future. The concept has been particularly useful in the power sector, providing insights into existing coal-fired power stations. Ships are similarly long-lived, with those serving the EU having an average lifespan of 28 years, much longer than cars and lorries. In our recent paper, we used a new EU data set of 11,000 ships to estimate future emissions from the current fleet through the rest of their economic lives.

Paris-compatible carbon budgets

Having arrived at a total committed emissions value of approximately 2260 million tonnes of CO2 for EU shipping, we need to put that in context. The climate responds to the total quantity of carbon dioxide that accumulates through time, rather than the emissions in any given year. This is the scientific basis of the carbon budgets that underpin UK climate policy. The higher the cumulative emissions, the greater the chance of failing to hold the increase in temperature to ‘well below 2°C…and to pursue …1.5°C.’ We find that without action, committed emissions from ships are expected to be well over 100% of a pro-rata share of a carbon budget compatible with the Paris climate agreement.

Putting sails back on ships – amongst other things

So, is there anything that we can do with the current fleet? It turns out that there is reason for optimism, as unlike aviation, there are many measures that can be introduced without scrapping current ships and before new very-low or zero-emissions ships are introduced. For instance, travelling at slower speeds, fitting renewable propulsion such as wing sails and Flettner rotors, connecting to grid electricity while in port, switching to zero carbon fuels, and retrofitting other energy-saving measures can all make a substantial difference, up to 65% reduction in total. With these measures, time is of the essence, and we estimate that moving quickly to introduce these measures immediately will have a greater total impact than waiting and pushing harder at a later date.

The IMO target of a 50% reduction in emissions by 2050 is much stronger than anything proposed for international aviation, where the industry is relying on buying offset credits from other sectors. However, this needs to be tightened further to meet the Paris Agreement temperature goals. The ideal first step would be to establish regulations to reduce the speed of existing ships and follow this up with a programme to ensure new ships use zero-carbon fuels from 2030.

Dr John Broderick will be conducting a project on biofuels for shipping within Theme 5: Energy For Mobility: https://ukerc.ac.uk/project/low-carbon-aviation-and-shipping/