Decarbonization of the Maritime Sector

Since we last discussed Liquid Natural Gas (LNG) as a maritime fuel in our April 2014 blog on Methane Slip and the Marine Industry there has been much research and development in the LNG industry, particularly as it relates to ship powering, methane slip, and GHG emissions. Recently, articles and research point to LNG as the fuel of the future, and the cost-effective option for vessel owners to meet IMO regulations and goals; yet LNG may not be the answer.

Cons of LNG

Disturbingly few published articles provide counter-arguments to LNG. These articles, such as from the International Council on Clean Transportation and SINTEF Ocean, posit that the global warming potential (GWP) of LNG is greater than that of HFO or MGO, calculated for 20 or 100-year time horizons.

Dr. Lindstad of SINTEF notes that un-combusted “Methane gives a GHG impact 28-34 times higher per gram emitted than CO2 in a one hundred-year perspective… the warming impact of methane is 85 time (sic) larger per gram than CO2” over a 20-year period. Both studies note that only high injection pressure, dual-fuel, 2-stroke engines have low enough methane slip emissions to be considered a viable engine option for LNG-powered ships, which can be seen in the figure below. This is particularly concerning when considering that LNG-powered four-stroke engines are the LNG fueling systems of choice in the marine industry today.

Methane slip and green house gas emissions of two-stroke and four-stroke LNG engines.


As in 2014, when we discussed bio-ethanol as a fuel source that was doomed from the start as a result of poor research and those who capitalized on the flaws in the research for their personal gain, we can see how LNG will potentially follow in these footsteps. Although the research contradicting the viability of LNG as a marine fuel source is still in its infancy, many LNG-producers and corporations with stakes in the LNG industry will inevitably perpetuate false claims for their own benefit.

Regardless of its GWP, it is time to recognize that LNG as a ship fuel is not necessarily a sustainable solution; it is just a sexier substitution for other hydrocarbon fuels and at best a temporary transition until we engineer truly reliable solutions.

Is Hydrogen the Future?

In the 2014 blog, and in many other blog posts, we noted that hydrogen fuel cells or using hydrogen (H2) in internal combustion engines seems to be the most promising fuel option for the future of transport, with the U.S. Energy Department’s Sandia National Laboratories providing corroborating research. Companies like Damen currently develop and construct hydrogen-powered ships as well.

Hydrogen Fuel Powered Vessel


Combustion of hydrogen may not be attractive either, as a 2006 UK study noted that hydrogen is an indirect greenhouse gas. However, its GWP is only a factor of 5.8 over a 100-year period: approximately five times less potent over the same time period as LNG. The same study also concluded that even with current inefficiencies in the extraction and storage processes of H2, “If a global hydrogen economy replaced the current fossil fuel-based energy system and exhibited a leakage rate of 1% then it would produce a climate impact of 0.6% of the current fossil fuel based system.”

Hydrogen poses a problem because its presence in the atmosphere perturbs the global distribution of greenhouse gases and may influence the ozone levels in the troposphere. However, even if hydrogen leakage is upwards of the study’s estimate, it is clear that converting from a fossil fuel-based energy economy to one based on hydrogen would have a significant positive environmental impact and reduction in GWP. Since hydrogen extraction and internal combustion of hydrogen will probably have similar slip problems as methane, it appears that hydrogen fuel cells are the answer if this route is taken.

The Rise of Green Ammonia

In August 2020, the IMO released their final report of the Fourth IMO Greenhouse Gas Study, which discusses the marine industry’s progress in reducing greenhouse gas emissions. Their findings were eye-opening. Not only was the global marine industry not on track to reduce its carbon footprint by 2030 or even 2050 as the IMO targeted, they noted that carbon emissions from ships and other marine sources increased about 10% from 2012 to 2018, and emissions from super pollutants increased 150% over that same period.

As with anything, people started to point fingers. Some blamed the growth of LNG and the resulting methane slip, and noted, as we have, its futility as a marine fuel source. Some blamed scrubbers for not effectively reducing black carbon emissions while also releasing harmful waste water back into the oceans. In the meantime, discussions arose on regulating methane and fuel efficiency.

What emerged as the bickering continued is increased research in to the viability of ammonia as a marine fuel. Yet, we have known the viability of ammonia as a maritime fuel since 2017! Even then we noted that issues like methane slip would be detrimental to the adoption of LNG, and that there is a significant reduction in greenhouse gas emissions when using ammonia even when mixed with existing hydrocarbon fuels. However, global extraction of ammonia in 2017 was almost wholly dependent on fossil fuels. Today, new developments in water, solar, and wind power allow for production of ammonia with near-zero carbon emissions, called “green ammonia”.

Adopting Ammonia as a Marine Fuel

In an Environmental Defense Fund (EDF) May 2019 article, they note that what is paramount in the adoption of a zero emission fuel source, like green ammonia, is the infrastructure to produce, transport, store, manage, and use it. As ammonia is already widely used in the agriculture industry and is used in concert with IMO Tier III engines as the catalyst for selective catalytic reduction, most of the infrastructure and technology is already established for green ammonia to be a primary fuel source in the marine sector. This includes the fact that there are storage and safety measures in place on ships to regulate the secure handling of ammonia. Furthermore, MAN B&W and Wartsila are both in the process of developing ammonia-powered engines.

Ammonia-powered ship


Unfortunately, nothing is as easy as it seems. The same EDF paper also notes that a total investment value of approximately 6 trillion dollars would be necessary for green ammonia plants and renewable energy plants worldwide to decarbonize approximately 40% of the international shipping fleet over the next 30 years. This investment will hopefully drive economic growth and job creation. However, the path of adoption is unclear, and this investment is a great economic, legislative, and even cultural hurdle in considering green ammonia’s potential to assist the decarbonization of the marine industry. Nonetheless, as we noted then, it is another potential option in the search for a fuel to achieve the IMO’s decarbonization targets.

What Next?

Only after many years of screaming into the storm by engineers and scientists willing to take a principled stand did it become apparent to the public at large that bio-ethanol is folly. As engineers and scientists, we must fight to distinguish the good from the bad. The future of energy may be LNG (unlikely), hydrogen, green ammonia, or another carbon-neutral fuel. Yet, we must continue to ask questions and pose hypotheses until our data, research, and experiments can answer the most daunting questions in the marine industry.

Martin & Ottaway