The Blind Spot in Net Zero: Global Shipping’s Fossil Fuel Dependency

For all the momentum behind net zero commitments, one of the most critical parts of the global economy remains largely underexamined: maritime shipping. 

Shipping is often framed as a “hard-to-abate” sector, and rightly so. But that framing undersells the scale of the challenge. The issue is not just that ships are difficult to decarbonise, but that the entire system they support is fundamentally built on fossil fuels. 

Today, approximately 40% of global maritime shipping by volume is dedicated to transporting fossil fuels themselves, coal, oil and gas. At the same time, around 99% of the international shipping fleet runs on oil-based fuels. In other words, shipping is not only a major consumer of fossil fuels; it is one of the primary enablers of their continued global use. 

This dual dependency creates a structural challenge for decarbonisation. Even as industries and governments commit to reducing emissions, the logistics systems underpinning global trade remain tightly coupled to fossil fuel demand. It is a feedback loop: fossil fuels drive shipping demand, and shipping sustains fossil fuel markets. 

The emissions impact is significant. Maritime transport accounts for close to 3% of global greenhouse gas emissions, roughly equivalent to a major industrialised nation. Yet unlike power generation or road transport, where viable alternatives are rapidly scaling, shipping faces a more complex transition pathway. 

Heavy fuel oil (HFO), the dominant marine fuel, is not only carbon-intensive but also produces high levels of sulphur oxides and nitrogen oxides, with well-documented impacts on air quality and human health. Transitional alternatives such as liquefied natural gas (LNG) have been positioned as a step forward, but they introduce their own challenges. Methane leakage across the LNG supply chain can significantly erode, and in some cases outweigh, the perceived climate benefits.

Recent geopolitical events are already demonstrating how fragile this system is. The ongoing conflict involving Iran has disrupted shipping through the Strait of Hormuz, one of the world’s most critical energy chokepoints, responsible for around one-fifth of global oil flows.  

As tanker movements slow and risks to vessels increase, the consequences are immediate: constrained supply, rising fuel costs, and ripple effects across global trade. In some regions, marine fuel prices have surged dramatically, with knock-on impacts for everything from freight rates to food prices.  

What this highlights is not geopolitical risk, but structural exposure. Shipping is not just carbon-intensive; it is deeply vulnerable to disruptions in the very fuels it depends on. 

This raises an uncomfortable question: are we underestimating the extent to which global decarbonisation depends on reducing, not just replacing, fossil fuel flows? 

Much of the current discourse focuses on future fuels, green ammonia, hydrogen, methanol, and the infrastructure required to support them. These are critical developments, but they address only one side of the equation. Without a corresponding shift in demand, particularly for fossil fuel commodities, the scale of transition required in shipping becomes exponentially more difficult. 

From a systems perspective, shipping is not an isolated sector. It is a reflection of upstream production and downstream consumption patterns. As such, decarbonisation strategies that focus narrowly on vessel technology risk missing the broader opportunity, and necessity, to reshape the flows of materials themselves. 

This is where circular economy thinking becomes increasingly relevant. Reducing reliance on virgin materials, improving resource efficiency, and localising supply chains where possible can all contribute to lowering demand for long-distance bulk transport. In doing so, they also reduce the emissions burden placed on the shipping sector. 

The challenge is not simply technical; it is structural. And while shipping is often described as a laggard in the transition, the reality is more nuanced. It is a sector carrying the weight of a global economy that is still, in large part, fossil fuel-dependent. 

Until that changes, shipping will remain one of the most difficult pieces of the net zero puzzle to solve.