The Elephant in the Room at the COP 27 Climate Conference

The agenda of the recent U.N. Climate Conference held in Egypt this past November leaves out a very big emissions source that could prevent meeting the 2050 deadline for a net “Carbon Zero” global economy, and that is transportation. 

The reason that transportation was left off the agenda is because there is seemingly no solution to a fossil fuel-based transportation sector when accounting for maritime shipping, rail transportation, commercial aviation and long-haul trucking. These four parts of the transportation sector simply cannot be electrified because electrical storage technologies are simply not energy dense enough for large-scale practical applications. Each of these industries comprise such a significant portion of global emissions that each one could be considered an elephant in their own right—perhaps even a mastodon.

It is one thing to electrify personal automobiles in developed countries where suitable infrastructure and reliable electric grids are well established, but electrifying the maritime industry is an entirely different story.

Considering the maritime industry alone represents a bumper crop of low-hanging fruit that needs approaches which are both environmentally sound and cost-effective. Such approaches, as of yet, though remain “technologiae incognita.” 

The range and speed that modern container ships or car carriers must be able to achieve represents a huge carbon footprint. A typical Panamax container ship operating at a standard cruising speed can consume 63,000 gallons of maritime fuel per day resulting in more than 750 metric tons of CO2, not to mention NOx, volatile organic compounds and particulate emissions. There are calculations that estimate just fifteen of the world’s largest container vessels exceed the emissions from the world’s 750 million vehicles annually.

Some more modern ship designs are “hybrid” types of propulsion plants, in the industry known as diesel electric propulsion. This really is not new to the maritime world since during World War II (and well beyond) all submarines were diesel electric. This configuration has been demonstrated to be more fuel efficient which reduces the carbon footprint, but by no means does it reach anything close to net “carbon zero” by 2050 as established by COP 27 simply because it remains based upon the internal combustion engine.

It has been proposed that the maritime industry should return to sail power, which is entirely inadequate to the point of absurdity. Others have proposed that the maritime industry convert to nuclear-powered propulsion. Yes, this would be a zero-carbon solution, but not without a significant down side. Trying to convert commercial shipping to nuclear-powered vessels is a bad idea since these shipboard reactors could potentially be used to produce weapons-grade nuclear material, e.g. 235uranium or 238plutonium, not to mention what is to be done with the spent fuel rods. 

Case in point, the Russian icebreaker LEPSE, long considered Russia’s most radioactive ship, was decommissioned in 1988, and is only now having the last of the spent fuel removed while undergoing decontamination. The only U.S. flagged nuclear maritime vessel to have ever been built was an economic failure; the n/s Savannah. It could not carry enough cargo nor passengers to be profitable and so it remains tied up in Charleston Harbor in South Carolina as a museum.

What is needed is an entirely new propulsion system that is neither based upon the internal combustion engine nor nuclear power. The maritime industry went through several conversion of propulsion systems in the twentieth century, first from coal-fired steam plants to diesel-fired steam plants, then on to diesel-powered plants, and ultimately diesel-electric plants. 

One more conversion to save on fuel while reducing emissions is the logical next step. But what would that conversion look like?

There is a technology that has been overlooked for decades that is only now being considered as an alternative propulsion system. A proven technology is in production by Saab Kockums AB, headquartered in Malmö, Sweden. This technology is a series hybrid-electric technology with a significant difference—it does not use an internal combustion engine, but rather an external combustion engine known as a Stirling Cycle engine. 

The Stirling engine was demonstrated by NASA to be more than twice as efficient as an internal combustion engine in a Department of Energy funded project conducted in the 1980s. At present the maritime application for this propulsion system is in the littoral class of submarines, but it is notable that the Stirling Cycle engine is completely scalable to the megawatt-size power plant with no significant difference in weight to horsepower ratio nor volumetric constraints as compared to existing ship board power plants.

Not only is the Stirling engine more fuel efficient, it has significantly lower emissions as well. Because combustion takes place at atmospheric pressure, oxides of nitrogen (NOx) are reduced by 90% and volatile organic compounds (VOCs) are reduced by more than 90%. Particulates are reduced to trace amounts and CO2 emissions are cut by more than half.

Given the fact that the International Maritime Organization has designated the waters off North America as Emissions Control Areas (ECAs) to reduce NOx emissions (as well as some coastlines in Europe and U.S. territories in the Pacific), this sort of low-emissions technology becomes more attractive. Currently the alternative is for ships to use Diesel Emissions Fluid (DEF) which results in more that 1200 gallons per day of DEF to mitigate NOx emissions while operating in the ECAs. Storage of that much DEF aboard ship is, to say the least, problematic, as well as having a negative impact on profit margins. Since the Stirling engine can burn any type of fuel with no mechanical modifications the ability to switch from low sulfur fuels to bunker C and back again is easy as turning a valve. The atmospheric pressure combustion results in near trace amounts of NOx emission, eliminating the need for DEF.

For those not familiar with the maritime industry, it might seem that swapping out engines in a huge container ship is an impossible task, but that is not the case. Modern ship designs are built with the idea that engines and reduction gear need to be overhauled and removed for repair. Swapping out a marine diesel engine for a Stirling Cycle series electric hybrid propulsion system is an easily doable engineering task. Conversion to this propulsion system is no more difficult than a normal shipyard overhaul.  

Make no mistake, the world is serious about reducing all emission including CO2. The clock is ticking and the maritime industry will be forced to do its part in reducing CO2 and other emissions. The time is now to get ahead of the curve to maintain profitability. Innovation is essential to survive lest the maritime industry as we know it go the way of the mastodon.   

Mac McDowell spent a career at sea and is now the CTO of Quantum Industrial Development Corp., a company that has developed a microgrid technology based upon the APEX Power system. His email is and his company’s website is