How shipping can become greener
At the international level, the International Maritime Organization (IMO) adopted measures to address projected rising emissions. In 2018, member countries agreed to reduce greenhouse gas emissions by 50% by 2050. They were unable to agree on more far-reaching measures that would be consistent with the goals of the 2015 Paris Climate Agreement by the end of 2021. Requests to achieve zero-emission or carbon-neutral shipping by 2050 were rejected by a small group of countries (Russia, Saudi Arabia, United Emirates, China and Argentina). The next revision of the targets will not occur again until 2023. At the European level, shipping has been included in the Fit for 55 legislative package, for example, by being included in the EU Emissions Trading Scheme (ETS). On June 23, 2022, the European Parliament voted to give the shipping sector a separate ETS (ETS II) along with the transport and buildings sectors. The measures have yet to be agreed with EU member states.
How can shipping become more climate-friendly?
While drives of smaller passenger ferries, motor boats and inland waterway vessels can also be electrified, this is not readily possible for ships of greater power or range. These ships include ocean-going vessels such as tankers, cruise ships and container ships, as well as coasters and RoPax ferries.
Quickly implementing "slow steaming" or efficiency improvements through technologies is not enough. Marine diesel and heavy fuel oils must be replaced with climate-friendly alternatives. Using conventional liquefied natural gas (LNG) and methanol can only reduce emissions by 15 to 25 percent and 10 percent, respectively.
Power-to-X products will therefore be indispensable as fuels in the future. These include hydrogen (pressurized, liquid, stored in carrier oils (so-called Liquid Organic Hydrogen Carriers, LOHC)), ammonia, methanol, synthetic diesel and synthetic natural gas (SNG). In addition to internal combustion engines, fuel cells combined with electric motors are also possible as propulsion engines.
The technologies still differ greatly in their degree of maturity. Hydrogen is already used in dual-fuel combustion engines and in fuel cells, especially on private and work boats or smaller ferries. Methanol-fueled internal combustion engines have been on the market for years. Methanol fuel cells are also currently being tested in demonstration projects. Numerous projects are currently being carried out by prominent marine engine manufacturers to develop combustion engines for ammonia, which is widely regarded as a promising propulsion medium. Ammonia fuel cells are also under development. SNG can already be used in marine engines. However, the development need here is for methane slip reduction. Unburned SNG escapes from the engine and enters the atmosphere, where it is 28 times more harmful to the climate than CO2.
One of the challenges already emerges from the multitude of possibilities mentioned above. Each of these hydrogen derivatives has advantages and disadvantages, so none has yet emerged as a clear favorite. Not all of them are suitable in the same way for powering the various types of ships with their differing deployment profiles, travel distances and sizes.
This is due to the energy density of the media and how they can be stored in tanks on board. To give an example, a cubic meter of hydrogen compressed to 700 bar carries about only one-third the energy as the same amount of ammonia. Accordingly, pressurized hydrogen takes up much more space on the ship. For passenger ferries or inland vessels that have regular access to a refueling infrastructure, this is not a knockout criterion. For seagoing container ships, however, it is.
Low availability of hydrogen derivatives and high prices
The development of engines and fuel cells as well as the consideration of which medium finds its place on which ship are not the only challenges. The market ramp-up of sustainable shipping is currently being held back primarily by the low availability of PtX products as fuels and their high prices. There is also the fact that ships have a service life of several decades and construction involves high investment costs. The decision for a technology is therefore a long-term one. Converting to a different type of propulsion is sometimes technically difficult and often not economical. To get around this, the subsequent use of alternative fuels should already be taken into account when designing and building ships.
There are also still open regulatory issues. Since the individual substances vary greatly in their aggregate state and hazard potential, there are no uniform rules and standards. For some derivatives, they have yet to be developed. Safe handling also requires training and further education of the ship's crew and port personnel.
Use in international maritime transport presents further challenges. The fuels must be available in all destination ports. The lower energy density of hydrogen, ammonia and methanol also reduces the range of the ships if the tank size remains the same, and larger fuel tanks in turn reduce the cargo volume. For climate-friendly shipping, it is therefore becoming increasingly important to adapt ships to their routes.
One possible solution would be to establish key trade routes as Green Corridors. Through stakeholder collaboration, zero-emission shipping along these routes can succeed. Key stakeholders include shipping companies, fuel producers, cargo owners, regulatory and port authorities, and classification societies. The first Green Corridors could then have positive carry-over effects on the rest of the transport sector.  At the UN Climate Change Conference in Glasgow, 22 nations, including Germany, already signed a declaration to establish at least six corridors by 2025.
As it turns out, shipping is only at the beginning of its transformation. How fast the development progresses also depends on the political objectives of the EU and IMO and binding laws.
By Junior Consultant Verena Hertzsch
 Beispiele für Projekte/Akteure: Methanol: Stena Germanica, Pa-X-ell2, Hydrogen One, Maersk im Bereich grüner Ammoniak: ShipFC, Demo 2000, MAN, Wärtsilä im Bereich LOHC: HyNjord, im Bereich CH2: Sea Change, ELEKTRA, HY-NOVA 40, im Bereich LH2: MF Hydra.
 Maritime Wertschöpfung und Beschäftigung in Deutschland
 Beispielsweise der Betrieb der Stena Germanica mit Methanol: https://www.dvz.de/rubriken/test-technik/alternative-antriebe/detail/news/methanol-lohnt-sich-wirtschaftlich-nicht.html
 Das wird unter anderem in der Studie vom DLR behandelt: https://www.dlr.de/content/de/downloads/publikationen/broschueren/2022/kurzstudie-maritime-treibstoffe.pdf?__blob=publicationFile&v=4