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Troubled Waters: Decarbonizing Marine Transportation

by Antonina Scheer

While the field of sustainable mobility continues to focus on electric vehicles, those interested in mitigating the climate impacts of transport might, for a moment, like to cast their gaze out to sea. The emissions from freight transport are notoriously difficult to reduce, but solutions are emerging as the largely invisible shipping industry slowly drifts into climate policy discussions. Three challenges make it a daunting sector to decarbonize. Firstly, the technologies available to move colossal vessels without fossil energy are varied and unproven. Secondly, the international governance of shipping emissions is complicated by the fact that no one has jurisdiction over the high seas. Thirdly, the ever-increasing demand for international shipping services will feed the ballooning of emissions. While technological and legal avenues for change must be taken, they should not preclude the reduction of demand as a method to lower shipping emissions.

The backbone of global trade

Shipping and global trade are profoundly intertwined, with industry representatives and scholars alike using anatomical metaphors to describe their symbiosis: “‘shipping is the life blood of the global economy”’, the “‘backbone of global trade”’. Approximately 90% of all traded goods travel by sea, but shipping has immense costs that are not included in the prices of seaborne products. The industry uses heavy bunker fuel, an inefficient byproduct from oil production that contains high concentrations of pollutants like sulphur and nitrogen oxides.

Although sea freight is the most energy efficient form of long-distance transportation, it currently accounts for nearly 3% of global carbon dioxide emissions. This may seem insignificant given that all transportation services accounted for about 20% of global emissions in 2014. However, the emissions from international shipping and aviation are growing at almost double the rate of emissions growth in other sectors. Projections for the shipping industry indicate a likely tripling of emissions by 2050 if current demand growth continues. By mid-century, it could account for up to 17% of global emissions. This is deeply concerning given that net global emissions must reach zero by then if the world is to honour its aspiration to limit global warming to well below 2°C.

A broad portfolio of technical decarbonization measures

As with most environmental problems, there is no technological panacea for reducing shipping emissions. A recent review by Norwegian scientists assessed various studies on possible means of reducing greenhouse gas emissions from ships. Their results suggest that a combination of technical and operational measures should be adopted. Biofuels, vessel size, and speed optimization offer the greatest potential, but none of them is sufficient alone. Meanwhile, wind energy could play an important role supplementing these initiatives.

Biofuels stretch far ahead of all other measures, showing immense decarbonization potential. However, in addition to competing for scarce land resources, biofuels are not always carbon neutral. Second-generation biofuels, which use waste biomass and therefore do not compete with food production, are potentially well-poised to become major players in decarbonizing freight transport.

Increasing ship size enables economies of scale that reduce the carbon footprint of each ton of shipment. But if these growing titans take to the seas carrying less than their maximum capacity, which is frequently the case, carbon gains can be minimal. Operational measures such as ‘slow steaming’, which simply means travelling at reduced speeds, can create significant fuel savings that do not require new technology. Unfortunately, pressures from international trade discourage slow steaming. Speed reductions tend to be adopted only during economic downturns due to depressed demand for shipping services.

Wind powered vessels may be more than just a nostalgic nod to the sails of the last centuries. Flettner rotors for instance can reduce fuel consumption by up to 15%. They can be installed on existing ships through retrofitting, avoiding the need to await fleet overhaul when ships reach their end of life.

According to the report, if the various measures shown in the graph above were all adopted carefully and rapidly, shipping emissions could sink by 75%. This estimate is purely statistical: no ship has yet been built that combines all the recommended measures, and it is not yet clear to what extent the shipping industry will be willing to adopt them. Nevertheless, low-carbon ships may soon emerge on the horizon.

The global governance of shipping emissions

Given the variety and complexity of the technical solutions to decarbonize ships, adequate governance to coordinate them is essential. The environmental regulation of marine transport is anything but straightforward: a shipping company from one country can register its ships with a “‘flag of convenience”’ state like Panama, Liberia, or the Marshall Islands. These states, which often cannot uphold environmental and labour standards, have registries open to non-domestic ships. This is not a marginal issue: nearly 75% of the world’s ships are registered in countries other than that of the shipowner. As a result, national responsibility for a given ship’s climate impact is ambiguous because its emissions are released in international waters.

The Secretariat of the UN Framework Convention on Climate Change has developed various proposals for allocating shipping emissions: to the country exporting or importing transported goods, or to the country where the ship is registered, or to the country of the shipping company. However, no specific allocation has been deemed adequate by the signatory states of the climate convention. The challenge of attributing ships’ emissions to individual states led negotiators of the 1997 Kyoto Protocol to delegate emissions reductions to the UN’s International Maritime Organization (IMO). The 2015 Paris Agreement makes no mention of shipping or aviation, implicitly casting them aside to be dealt with in future negotiations. In the context of global climate agreements, international transport has been left adrift.

As an active signatory of both climate agreements, the European Union (EU) attempted to include the emissions of ships entering their ports in the EU Emissions Trading System, a program to control and lower the region’s emissions. The shipping sector resisted the initiative. Like most globalized industries, it would prefer to operate on a level playing field, meaning that any environmental regulations affecting their operating costs should be imposed on all companies operating in all regions. This international level playing field can only be coordinated by a global body whose regulatory reach encompasses all the world’s oceans: the International Maritime Organization (IMO).

The IMO deals with environmental issues through the 1973 International Convention for the Prevention of Pollution from Ships, better known as MARPOL. In 2011, the IMO adopted an amendment establishing an Energy Efficiency Design Index. In 2018, the convention was again amended to establish an emissions reduction target of 50% by 2050. Despite the IMO’s relative ambition, its target is not enough. The Intergovernmental Panel on Climate Change has stated that emissions from all sectors must reach net zero by mid-century if we are to remain close to 1.5°C of warming. Maersk, the largest container shipper, is steaming ahead of the IMO with the lofty goal of carbon neutrality by 2050. But without specific pathways to reach these goals, the governance of shipping emissions is limited to efficiency standards and headline-catching targets.

Efficiency is insufficient

This brings us to a core issue in decarbonizing marine transport. In the context of strongly growing demand for shipping services, efficiency gains may simply enable companies to transport more goods more cheaply. This rebound effect would offset the climate benefits of efficiency by increasing overall sea traffic. The impressive reduction in emissions per unit of shipment achieved thus far by the industry has not lowered the sector’s emissions in absolute terms because demand has simply continued to grow. Of course, efficient ships are better, but they are insufficient for decarbonization without an absolute and shrinking cap on emissions.

Carbon trading systems are designed to establish such emissions caps. While the IMO has floated the idea of such market-based measures, it is languishing in the preliminary stage of merely reporting fuel consumption. Furthermore, trading schemes can offer fairly weak results in practice. Even committed policymakers in the EU have taken years to address the oversupply of emission allowances, which has led to a low carbon price. Demand-side policies, though unpopular, may be necessary to complement an eventual emissions trading system given the expected challenges.

The deeper solution of demand management

Directly restraining shipping and global trade would be ineffective and undesirable. However, investigating the most significant types of shipped goods could shed light on how the sector’s emissions might be encouraged to fall. This kind of demand-side solution is rarely discussed. Alice Larkin, a professor of climate science and energy policy at Manchester University, suggests that domestic programs to decarbonize energy can lower shipping demand, noting that 50% of imports in the United Kingdom in 2010 were fossil fuels. On a global scale, crude oil and coal together account for a third of maritime trade. Policies aimed at energy independence, electrification, and the mass deployment of renewable energy could thus indirectly cut shipping emissions by a massive amount.

Another bulk product travelling by ship is waste material: the United States’ two biggest shipped exports by weight are waste paper and scrap metal. The fact that this is surprising justifies a deeper critical questioning of what goods really need to be imported and exported. The emergence of circular economy principles focused on increasing product lifespan, reuse, repairability, and recycling could lower maritime exports from wasteful wealthy countries. Another surprisingly significant seaborne product is furniture, the biggest US import by weight. Many goods are manufactured through planned obsolescence, but things like furniture, clothing, and electronics should not be disposable. By rejecting excessive consumerism and regulating manufacturers, there is substantial room to lower demand for many products that are unnecessarily shipped across the globe.

Demand management is an expanding and promising option among decarbonization solutions, but it has not been applied to freight transport. Sustainable transport studies posit an avoid, shift, improve prioritization of solutions, which mirrors the reduce, reuse, recycle hierarchy of material waste reduction. Of these options, recycle and improve have enjoyed all the limelight because they do not threaten the economic imperative of growing consumption. Regarding freight transport, reducing emissions through the avoidance of certain services has not yet even surfaced in the policy debate, despite its significant potential.

This discussion of marine transport echoes many conversations on climate mitigation: emissions must be reduced through technological innovation and robust governance. But perhaps most centrally, the per capita consumption enjoyed in wealthy countries must be contracted. Climate policy in general relies on an integrated approach because nearly every part of the world economy contributes to climate change. The management of shipping emissions is no exception. A growing sense of sufficiency, which runs against the currents of consumerism, supported by strong policies mandating circular economy principles, along with the broad abandoning of fossil fuels, would contribute to reducing shipping emissions. Such demand side policies, which have clear co-benefits, should not be ignored.


Illustration by Julia Jones

Antonina Scheer is a graduate student at Oxford University pursuing the MSc in Environmental Change and Management. She received her BSc from McGill University in environmental sciences and economics. She is interested in climate change mitigation from the varying perspectives of research, policy design, and practical implementation. Specifically, her fascination lies in the realm of sustainable and just energy transitions. With experience working on several interdisciplinary research projects, including a study on hydroelectricity development in western Panama, she hopes to contribute to communications work at the interface of science and policy. She has experience managing an ecology research lab at McGill, and coordinating energy efficiency and sustainable waste management in student residence buildings. She has been involved with the fossil fuel divestment campaigns at both McGill and Oxford, and is the MCR Ethics, Environment, and Charity representative at Mansfield College.


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