Maritime transport emits as much_CO2 as aviation, but the decarbonisation of this sector has long been neglected, with priority being given to health issues related to oil spills and air pollution. Wind, a free and renewable energy, could however blow on maritime freight to help it cope with climate issues.

In the public debate, there is a lot of talk about the impacts of aviation on the climate, much less about those of maritime transport.

In 2024, however, ships travelling the world (excluding military ships) released one billion tonnes (gigatonnes or Gt) of_CO2 into the atmosphere. This figure is equivalent to the emissions of civil aviation, with a comparable growth rate – with the exception of exceptional events such as the Covid-19 pandemic in 2020.

To mitigate global warming, the decarbonisation of maritime transport is therefore just as strategic as that of civil aviation. The use of wind – through sailing transport – should play a much more structuring role than we imagine.

Delays in the ignition of the International Maritime Organization

International routes generate just over 85% of the maritime sector’s emissions, with the rest coming from inland lines and fisheries. As a result, the regulations adopted by the International Maritime Organization (IMO) play a crucial role in decarbonization.

Climate issues were only belatedly integrated into the IMO’s environmental regulations. These were historically designed to limit the risk of oil spills, and then local air pollution caused by the use of heavy fuel oils in engines.

Until 2023, the reduction of greenhouse gas emissions was only targeted through regulations on energy efficiency, limiting the amount of fuel used to propel ships, with stricter rules for the discharge of sulphur oxides and other local pollutants (nitrogen oxides and fine particles mainly) than for CO₂.

These regulations have not been able to limit the climate footprint of maritime transport. The two main levers used by shipowners to improve energy efficiency have been to reduce the speed of ships and increase their size. These gains have made it possible to reduce the operating costs of maritime freight, but not CO₂ emissions, due to the growth in traffic.

The specific constraints on local pollutants have even increased the climate footprint of maritime transport.

The substitution of LNG for oil, for example, drastically reduces local pollutant emissions, but generates methane leaks whose impact on global warming most of the time exceeds the gains obtained by the_CO2 saving.

Above all, the reduction of SO₂ emissions from marine diesel carried out in 2020 to comply with IMO regulations, by around 80%, has abruptly reduced the amount of aerosols present in the atmosphere. Researchers see this as one of the major causes of the acceleration of global warming observed since 2020.

Late but ambitious climate regulations

However, the increase in_CO2 emissions from maritime transport is not inevitable. It reflects the past decisions of the IMO, which was so slow to integrate climate issues. But the tide is turning.

In July 2023, IMO members agreed on a decarbonization strategy aiming for neutrality by 2050, with ambitious interim targets in 2030 and 2040.

To achieve them, the IMO plans to introduce a CO₂ emissions pricing mechanism in 2028 that penalises shipowners who do not comply with these new requirements and pays those who decarbonise more quickly.

For its part, the European Union is gradually integrating maritime transport into its CO₂ allowance trading system.

In this new context, we can no longer count on incremental progress such as improving energy efficiency. Maritime transport will have to undergo a much more radical transformation, both technically and socio-economically.

With around 100,000 ships sailing the ocean, this transformation concerns both the existing fleet and the construction of the ships of the future. However, wind, a free and renewable energy, can be mobilized in both cases.

Ancestral know-how and technical innovations

To simplify, we can distinguish four main families of techniques for capturing wind energy to move ships:

• The first two are represented by huge cylindrical columns on the deck of ships: rotors or suction sails, as shown in the image of E-ship 1 above.

• The use of sails or wings carried by masts represents the third family, which is broken down according to their thickness, rigidity and the materials of which they are composed.

• Last family: kites attached to the ship capturing more regular and powerful winds at height. The latter have the advantage of not taking up space on the deck of the ships, but their effectiveness decreases as soon as you have to go upwind.

The use of wind to move ships combines low-tech, sometimes ancestral methods with cutting-edge engineering based on aerodynamics, numerical modelling, task automation, artificial intelligence, etc.

Wind as a booster

At the beginning of 2025, about fifty ships in operation already had sail assistance. Three-quarters of them were old “retrofitted” ships, mainly by adding rotors or suction sails. A tiny drop in the bucket, compared to the total number of ships on the oceans!

But the nascent market for sail assistance is accelerating strongly. The reference certification bodies, such as DNV or Lloyd’s Register, anticipate a change in the scale of the market, with an increasing proportion of operations involving new ships.

On older ships, retrofitting can reduce emissions by around 5 to 15% depending on the case. However, the gains are much higher on new ships. The Canopy, launched in 2022, makes it possible to transport the elements of Ariane rockets from Europe to French Guiana while saving around a third of the emissions compared to a standard cargo ship.

New business models boosted by carbon pricing

Wind is a flow energy found in nature. Unlike alternative fuels to oil such as methanol, ammonia or hydrogen, it does not need to be produced, it is simply captured.

This certainly generates an additional investment cost, which is still high due to the youth of the sailing industries, but which is all the more easily amortised as carbon pricing increases the price of the most emitting fuels. This advantage of the availability of wind comes into even greater play when it becomes the main source of energy.

In main sail propulsion, the ship’s engine is only used for manoeuvring in ports or for safety or punctuality reasons. The_CO2 reductions then change scale, reaching 80 to 90%. Neutrality can then be achieved if the auxiliary engine uses carbon-free energy.

Sail-powered propulsion makes the complete decarbonisation of maritime transport possible. Not to mention that it also reduces or eliminates other nuisances, such as underwater noise and damage caused by propeller movement. Its development can therefore contribute to a profound transformation of maritime transport, as will be analysed in a future article.

Christian de Perthuis, Professeur d’économie, fondateur de la chaire « Économie du climat », Université Paris Dauphine – PSL

Cet article est republié à partir de The Conversation sous licence Creative Commons. Lire l’article original.