The environmental cost of XXL ships

Much of what surrounds us at any given moment – whether a product, a commodity or a raw material – was once on a ship. To travel from their place of origin to their point of use or consumption, these goods embark on seaborne journeys around the globe. This occurs thousands of times a day on tens of thousands of vessels moving from port to port. Ships manage approximately 90 percent of global trade, transporting nearly 11 billion tons of goods each year.
This happens because oceans, which cover the majority of the Earth’s surface, offer relatively unobstructed pathways for both passengers and cargo ships traveling between continents. Sea routes are strategically chosen for their economic efficiency in linking lands and one of the most significant sea routes is the North Atlantic Ocean route, which Energy Observer is currently covering. This route has the highest traffic among all ocean routes: nearly two thirds of the global number of ships and cargo volume navigate this route, linking ports of Western Europe with those on the east coast of North America since its opening in 1840.

Whether the importance of such a sector is evident and widely known, its impacts are often poorly understood.

To keep pace with the expanding global economy, the total loading capacity of ships nearly quadrupled between 1996 and 2020. Newer, bigger, and faster vessels have been added to the fleet and this trend shows no sign of slowing down. Unfortunately, bigger ships mean bigger impacts. With faster ships comes higher underwater noise: according to scientists, noise levels in the oceans are doubling roughly each decade.
Today, a cargo ship emits about 190 decibels, exceeding the noise of a jet engine at take-off. Most of this acoustic pollution comes from propellers’ cavitation, a phenomenon that, in addition to noise, results in a loss of energy efficiency. In addition, sound travels much faster in water than in air – around four times faster – which means it can travel great distances and impact a large portion of the ocean.

Now, sound is the very lifeline of the ocean. From whales to dolphins, countless marine species rely on sound for survival: they use it to communicate, to find food or avoid predators, to reproduce or to orient themselves. Like ships’ sonars, some animals can use sounds to detect, locate and characterise objects. Anytime ship noise drowns out natural sounds, marine animals are forced to adapt: some flee their habitat, others struggle to feed and nurse their babies, and most experience high levels of stress.
The good news is that this impact can be easily reduced. Changes can be made to the design of the ship’s propellers and hull, but there is an even simpler solution: slowing down. Every knot of speed reduction translates into a 1 decibel decrease in noise.

Much is said about the shipping sector’s greenhouse gas emissions, which account for around 3% of global emissions. This figure gives us a clear order of magnitude, however it only includes direct emissions from fuel combustion for propulsion and does not seize the full picture. To fully grasp the fleet’s environmental impact, we should also take into account all indirect emissions throughout the whole vessels’ lifecycle, from construction to decommissioning.

Although the focus often falls on operational emissions, a ship's environmental impact starts even before it sets sail. Steel, the primary material used in shipbuilding, makes a significant contribution to a vessel's embodied carbon footprint. Steel production is highly energy-intensive and accounts for a whopping 11% of global CO2 emissions. On top of that, the mining and processing of iron ore (used to make steel) adds to the emissions burden. At present, despite ships being made of 75-85% steel by weight, their construction currently makes up only about 3% of the emissions produced during a vessel’s lifetime. Nevertheless, this share is poised to rise as cleaner technologies and regulations drive down operational emissions. Here’s the challenge: improve the traceability and transparency of materials throughout a ship's lifecycle, which today remain a blind spot hindering efforts to minimize the environmental impact of steel in shipbuilding.

Oil spills, although more and more sporadic, rank among the most serious threats to marine ecosystems, as they are hard to clean up and can last for extended periods of time. These large spills account for roughly 10 - 15% of all oil entering the ocean globally each year. Lost cargos add to the problem. Even with precautions, containers tumble overboard and pose a double threat: they represent lost goods, but also and above all a long-term environmental hazard. As they decompose on the seabed, they release harmful chemicals and toxic substances threatening marine life. While a single lost container may be a blip, when thousands of them litter the seabed, the impact can be devastating.

Besides, ships waste poses an additional risk to the marine environment. Cargo ships routinely release various types of wastewaters, including bilge water (containing oil residue), black water (sewage), and greywater (from sinks, showers, and galleys). These discharges can decrease water quality, harm marine ecosystems, and even pose health risks. Finally, ballast water. Ships rely on ballast water, held in special tanks, to maintain stability during voyages. This water, taken on in one port and released in another, acts as an unwelcome taxi service for marine life : microscopic organisms, plants, and even small animals can be scooped up in these waters. When released at the next destination, these "exotic species" can establish themselves in new environments, disrupting the local ecosystem. Thankfully, regulations exist to minimize these impacts.

The ocean may seem boundless, but the reality is, ships and whales are increasingly competing for the same space. Images of whales found dead, lodged on tanker’s bows or with propeller wounds remind us of that. Whale feeding grounds and shipping lanes often overlap and the ever-growing number of ships on the oceans intensifies the risk of collisions. Furthermore, constant exposure to heavy traffic may be making marine mammals less responsive to approaching dangers. Result: every year, cargo ships, cruise liners and fishing boats kill around 20,000 whales.

Here too, speed is key. Slower vessels have more time to react, potentially preventing collisions entirely or minimizing the damage. But benefits extend far beyond whale safety. Whales play a vital role in our fight against climate change: they act as carbon sinks, capturing and storing carbon throughout their lives and even after death, their bodies continue to lock this carbon deep in the ocean. Moreover, their feeding and waste patterns act as a natural fertilizer, stimulating the proliferation of phytoplankton – tiny ocean plants that absorb even more carbon dioxide from the atmosphere. Needless to say, we need to protect whales.

The evidence of these impacts is dramatic, we cannot afford to ignore it any longer. Fortunately, solutions exist, and awareness is growing. International regulations are mandating emissions cuts, ballast water discharge controls and speed limits in certain areas: for example, from November to the end of April, along the East Coast of the United States, speed is restricted to reduce the risk of collisions with whales on their migration route. Technological advancements in cleaner fuels and quieter ship designs offer hope for improvement too. However, to truly make a difference, maritime organisations need to step up their efforts to establish stricter enforcement and create marine protected areas and we, as consumers, should reflect about what we buy and how quickly we need it.