Looking for pathways to decarbonise shipping
Alessandro Schönborn,
Assistant Professor, Maritime Energy Management (MEM),
The World Maritime University
As the World Meteorological Organization announced that the global mean temperature for 2020 was 1.2 ± 0.1 °C above the 1850–1900 baseline, while at the same time the International Energy Agency reported that in 2021 global carbon dioxide emissions are expected to rise by around 5%, the challenge which climate change poses to our current way of life is clear.
The Baltic Rim Economies are traditionally relying on their strong maritime industry, hosting many household names of the maritime industry. As this sector is looking to free itself from greenhouse gas emissions, companies and institutions in the Baltic Rim are looking to take the global lead in decarbonizing shipping.
Shipping is an important contributor to the world’s anthropogenic greenhouse gas emissions, at around 3%, and the International Maritime Organization (IMO) has already laid out ‘The Initial IMO Strategy on Reduction of GHG Emissions from Ships’. With discussions ongoing, and its revision planned for Spring 2023, is likely to become more ambitious rather than less. The recent 77th session of the IMO MEPC discussed proposals from several parties aiming to revise the GHG reduction strategy to reaching zero net greenhouse gas emissions from international shipping by 2050. Assuming that the life-time of a vessel is of the order of 25 years, this yields some indication about the technological actions needed by 2025.
The aim is clear, but we are still looking for suitable pathways to decarbonise shipping.
The prevalent source of energy in international shipping is chemical energy stored in fossil fuels such as fuel oils and liquefied natural gas. Phasing out greenhouse gas emissions from shipping consequently requires the reduction of energy needs, or replacing the fossil fuels with a climate neutral alternative.
The trivial solution of removing energy needs is impossible, assuming that we wish to move ships at some speed, but energy needs may be reduced. The simplest way is reducing sailing speeds. While this may be a smart option for commodities that can endure longer transit times, it may not be practical for others, such as fresh produce needing to reach their markets. Energy saving without reducing speed, is possible by reducing friction via hull air lubrication systems and optimized hull shapes, more efficient propellers and rudders. Increasing engine efficiency or replacing engines with fuel cells or electric drivetrains may help further, but overall efficiency improvements are inherently limited. Even if drivetrains approached 100% efficiency, the need for energy and the associated emission of greenhouse gas emissions would remain considerable, unless the source of energy ceases to be unabated fossil fuels.
Replacing the remaining fossil energy with renewable energy is thus necessary; assuming that safe and abundant nuclear energy is still some way out of reach.
Using renewable energy can be achieved in two ways: The first option is using renewable energy directly to propel ships in the form of sail power, or solar power captured onboard. This is the most direct and efficient option, since the problem is solved in situ. In the case of wind power, forces propelling the ship are applied directly to the ship, and thus they conveniently avoid the losses of the propeller. The second option is to harness renewable energy elsewhere, on land or at sea, and to store it either in the form of electricity (using batteries) or in the form of the energy contained in fuels, such as hydrogen, ammonia or synthetic natural gas (SNG) or methanol. Such chemically-stored energy needs to be converted back into propulsive energy on a ship using an engine or motor driving a propeller. This option has the advantage of being available on demand, but it inevitably transfers the problem from international shipping to the world’s renewable energy production, rather than solving it where it occurs. It is also associated with significant energy losses when converting renewable energy to fuels and then reconverting converted back into movement in the ship engine or fuel cell via a propeller. It is widely accepted that at the current state of development in battery design, storing energy in batteries is not yet a viable option for intercontinental shipping, because batteries cannot store enough energy.
Looking for pathways to decarbonise shipping also requires consideration of the social, and economic dimensions, and the challenge is thus significantly more complex than suggested above.
From an environmental perspective, however, even clean fossil fuels are a red herring. And although they are widely discussed and arguably necessary to some extent, zero-carbon renewable fuels, will apply further pressure on climate neutral energy production occurring ‘elsewhere’, rather than shipping taking responsibility for its renewable energy production. The most sustainable pathways to decarbonise shipping lead clearly to the production of renewable energy in situ, as much as possible.
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