Every report, paper or study I have read from over the past decade, references shipping’s contribution to global greenhouse gas (GHG) emissions hovering stubbornly around 3%, despite the widespread adoption of efficiency measures over this same period. Efficiency gains through optimisation of operations alone has driven increased competition and lower costs in the shipping industry, which even without the ideals of GHG emissions behind them have resulted in less fuel used, and lower costs, for the same voyage patterns. More recently everything from wind assisted propulsion and air lubrication systems to advanced route optimisation software have reportedly begun to enhance and improve those efficiency gains. But, recent studies, including the IMO’s Fourth GHG Study, suggest that emissions have actually increased, rather than declined. The industry’s assumption has been that efficiency gains equate to emissions reductions, yet this assumption is increasingly being challenged. So what’s going on?
This contradiction may stem from a fundamental but overlooked paradox: instead of driving the industry forward, many green technologies are merely restoring lost efficiency, bringing aging vessels back to their original design performance rather than pushing them beyond it. The maritime sector, rather than making step change efficiency improvements, appears caught in a cycle of reclaiming efficiency that was already assumed in the vessel’s Energy Efficiency Design Index (EEDI) at launch.
New vessels are designed with an efficiency margin beyond their required EEDI compliance. This margin erodes over time due to operational realities, hull roughness, fouling, mechanical wear, engine degradation, and changing loading conditions. Efficiency retrofits, whether air lubrication, hull coatings, or wind propulsion, are frequently installed on vessels that have already lost some of their original performance. Instead of pushing beyond the original benchmark, they may merely bring the ship back to its sea trial efficiency. This effect is even more pronounced in the application of the Energy Efficiency Existing Ship Index (EEXI), which uses EEDI as a benchmark and reference point. Compliance driven retrofits may not create genuinely new efficiencies; instead they might only restore older ships to their initial standard, allowing them to continue operating without real technological step change.
This has led to a counterintuitive reality: efficiency measures may be delaying fleet renewal, extending the operational lifespan of aging tonnage, and inadvertently increasing total emissions. Shipowners often pursue retrofits not to exceed efficiency expectations but to avoid early obsolescence, ensuring that vessels remain viable within compliance frameworks while deferring investment in next generation zero emission ships.
The key issue is that this reclaimed efficiency is often framed as a net reduction in emissions, when in reality, it is a reset. We are replacing lost performance rather than advancing beyond it. Meanwhile, the Jevons Paradox tells us that efficiency gains often increase demand, counteracting expected reductions in emissions. A more efficient fleet should, in theory, reduce emissions, but if that efficiency simply enables increased trade volume and extended vessel lifetimes, the net result is higher total emissions from the sector.
This raises a crucial question: Should we formally recognize this effect as a distinct paradox within maritime decarbonization? The industry operates under the assumption that investments in air lubrication, wind propulsion, and hybrid propulsion systems are inherently beneficial for reducing emissions. But if these retrofits only return a vessel to its design margin rather than improving upon it, are we really decarbonising at all?
We could propose framing this as The Legacy Asset Efficiency Paradox, a scenario in which efficiency retrofits restore, rather than advance, a vessel’s performance, leading to a false perception of emissions reductions. This paradox highlights that older vessels, retrofitted with marginal gains, continue to dominate the fleet instead of being replaced by vessels that genuinely redefine fuel efficiency.
If the industry is serious about achieving net zero, we need to move beyond compliance driven retrofits and toward genuine, future proofed investments. Instead of designing regulatory mechanisms that reward marginal efficiency gains, we need to adopt a lifecycle based perspective, measuring decarbonisation efforts based on a vessel’s entire operational lifespan rather than snapshots of restored efficiency. Otherwise, shipping will remain in a holding pattern, where each new retrofit offers an illusion of progress but ultimately delays the transition to genuinely zero emission operations.
However, we must also acknowledge the economic realities of stranded assets. The pressure to comply with emissions regulations without prematurely scrapping vessels has created a strong financial incentive to retrofit rather than replace. This dynamic, while extending asset life, reinforces the paradox: it sustains outdated designs at the expense of technological progress. If shipowners are forced to choose between writing off valuable assets or applying incremental efficiency measures, their decisions will be shaped solely by financial, rather than environmental, when what we need is a healthy blend of both imperatives.
It’s important to recognise that retrofitting also plays a crucial role in testing and validating emission reduction technologies. Continued investment in wind assisted propulsion, air lubrication, and other measures ensures that these innovations are optimised and proven before integration into new vessel designs. If the industry abandoned retrofits entirely, we would risk losing the opportunity to refine these technologies before they are incorporated into the next generation of ships.
The solution lies in aligning regulation, financing mechanisms, and fleet transition strategies to ensure that efficiency retrofits do not become a crutch for avoiding fleet renewal. The conversation must shift from compliance based incentives to investment driven transformation, an approach that recognises both the realities of shipowner balance sheets and the urgency of deep emissions reductions. Without this shift, the industry risks perpetuating an endless cycle of reclaimed efficiency rather than realising true decarbonisation.
Charlie de Carbon 
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