Helena Joyce
The global shipping industry is facing increasing pressure to reduce the pollution caused by freight boats. Shipping is a vital part of the global economy, with sea freight representing 80% of global trades. However, freight boats contribute heavily to ocean oil pollution, noise pollution, and air pollution. They emit nitrous oxides, sulphur oxides, and CO2, which are highly toxic chemicals that cause acid rain and have detrimental effects on human health. For example, a study by the Danish government's environmental agency suggested that shipping emissions cost the Danish health service almost £5 billion a year, primarily for treating cancers and heart problems. Additionally, oil spills, sewage discharge, and ballast water release from freight boats can have disastrous impacts on ocean ecosystems and human health. While efforts are being made to reduce freight pollution, such as the development of green fuels, the industry remains one of the least regulated parts of the global transportation system.
| Characteristics | Values |
|---|---|
| Greenhouse gas emissions | 3% of global emissions |
| CO2 emissions | 10-40 grams of CO₂ per kilometer |
| NOx emissions | More than 18% of global nitrogen oxides pollution |
| SOx emissions | Bunker oil produces sulfur dioxide |
| Particulate matter | Produces carcinogens |
| Water pollution | 10 billion tons of wash water |
| Acoustic pollution | Noise travels long distances and affects marine life |
| Oil pollution | Oil spills |
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What You'll Learn
Greenhouse gas emissions
Shipping, or maritime transportation, accounts for approximately 3% of global greenhouse gas emissions. While shipping is the most energy-efficient method to move cargo over long distances, the vast size of the industry means it has a significant environmental impact. The annual increase in shipping volumes, averaging 4% since the 1990s, has overwhelmed efficiency gains. The growth in shipping has been fuelled by substantial tax privileges, which have further contributed to rising emissions.
The primary sources of greenhouse gas emissions from ships are their diesel engines. These engines burn high-sulfur fuel oil, also known as bunker oil, which produces sulfur dioxide, nitrogen oxide, and particulate matter, in addition to carbon monoxide, carbon dioxide, and hydrocarbons. The US Environmental Protection Agency (EPA) has classified diesel exhaust as a likely human carcinogen, and it contributes to adverse health effects and air quality issues.
To address the environmental impact of the shipping industry, the International Maritime Organization (IMO) has set ambitious targets for reducing emissions. The initial goal was to cut emissions by 40% in 2030 and 70% in 2050 compared to 2008 levels. However, member nations have agreed on even more aggressive "benchmark milestones," aiming for a 30% reduction by 2030 and 80% by 2040. The IMO's strategy includes initiatives to harness renewable energy sources, such as wind and solar power, and to transition to cleaner alternative fuels that emit fewer pollutants and greenhouse gases.
Additionally, the IMO is working to implement a global sulfur cap on marine fuels to reduce sulfur oxide and particulate emissions. The establishment of the Mediterranean Sea Emission Control Area (ECA) in December 2022 is a significant step in regulating emissions from busy maritime routes. These efforts demonstrate the growing recognition of the need to mitigate the environmental impact of the shipping industry and its contribution to global greenhouse gas emissions.
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Nitrogen and sulphur oxides
Nitrogen oxides (NOx) and sulphur oxides (SOx) are the two main pollutants emitted by ships. These gases are formed during the combustion of fossil fuels, such as marine gas oil and heavy fuel oil, in the presence of oxygen and nitrogen in the air. NOx and SOx emissions from shipping have been regulated internationally for over fifteen years, as they have adverse effects on the environment and human, animal, and plant health.
NOx emissions are primarily a function of combustion temperature. Higher combustion temperatures result in a higher amount of NOx produced. Marine diesel engines, which burn high-sulphur fuel oil, are a significant source of NOx. Ships are responsible for more than 18% of nitrogen oxides pollution globally.
International maritime regulations have been successful in reducing SOx emissions in certain regions, such as the North and Baltic Seas, and the Mediterranean Sea. However, these regulations have had limited success in reducing NOx emissions. This may be due to the fact that, while SOx emissions depend on the type of fuel used, reducing NOx emissions requires lowering combustion temperatures, which can lead to other pollutants, such as unburned or partially burnt hydrocarbons.
To further reduce NOx and SOx emissions from ships, various methods have been proposed, including passing flue gases through a catalytic converter or treating them with diesel exhaust fluid, in which an aqueous solution of urea reacts with the nitrous oxides to produce nitrogen, carbon dioxide, and water. The International Maritime Organization (IMO) has set ambitious targets for reducing greenhouse gas emissions from the maritime sector, including a goal of net-zero emissions by 2050.
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Oil spills
Intentional spills, though less studied and publicized, make up a larger proportion of marine pollution. Vessels routinely discharge oily wastewater illegally, creating spills kilometres long. Seafarers often bypass pollution safeguards and avoid detection by using different techniques. The impact of small oil discharges on marine life remains under-researched, but even minor oil spills can have lasting harmful effects on marine life when they occur frequently. Repeated spills create a form of chronic pollution that severely damages the environment. Oil spills harm sea creatures, make seafood unsafe to eat, and ruin beaches.
Several international conventions contain regulations aimed at preventing oil spills, including OILPOL54 and its successor, MARPOL73/78, which is the primary legal instrument for preventing pollution from ships. The International Convention for the Safety of Life at Sea (SOLAS74) and the International Convention on Maritime Search and Rescue (SAR) also contain preventative measures. The International Convention on Oil Pollution Preparedness, Response and Co-Operation (OPRC) by the IMO promotes oil spill emergency preparedness and international cooperation.
Cleanup methods for oil spills include the use of booms, which are floating physical barriers that help contain the oil and keep it away from sensitive areas. Skimmers can also be used to "skim" oil from the sea surface. In situ burning involves setting fire to an oil slick to burn the oil away at sea, and chemical dispersants can break up oil slicks from the surface. However, cleanup activities can never remove 100% of the spilled oil, and scientists must be careful not to cause additional harm.
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Noise pollution
The primary source of underwater noise emitted by freight boats is propeller cavitation, a design issue that causes a breakdown in water flow over the propeller blades. This can be addressed through design changes to the propeller and the hull of the ship, or by using new devices to smooth water flow into the propeller. In 2017, Maersk modified several of its ships by installing efficient propellers and reconfiguring hulls, resulting in a 75% reduction in noise energy emitted. Other sources of noise include the ship's engine, which can be mitigated by placing the engine on mounts so it does not touch and transfer noise through the hull.
The impact of noise pollution on marine life is significant. Marine mammals rely on underwater sounds for essential functions like searching for prey, avoiding predators, locating offspring, and finding a mate. Noise pollution disrupts these activities and can cause elevated stress in marine mammals, lowering their resilience to other challenges such as water pollution and climate change. Studies have shown that the population of cetaceans (whales and dolphins) has declined in areas prone to noise pollution from ships. The death of marine animals can occur hours after exposure to extreme underwater noise, and mass strandings have been observed in coastal areas of Spain between 2001 and 2003.
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Sewage and garbage
Freight boats produce a significant amount of sewage and garbage pollution. Sewage discharge from boats can degrade water quality, especially in marinas with high boat traffic. While on board, human waste and other solid waste should be collected in a U.S. Coast Guard-approved marine sanitation device (MSD). Upon returning to shore, these MSDs must be discharged at approved pump-out stations. Treated sewage effluent from ships can be pumped overboard, but only if certain conditions are met. For example, vessels with comminuting systems are prohibited from discharging treated sewage within three nautical miles of land and must store treated sewage in a holding tank.
The discharge of garbage into the sea is generally prohibited. Most cruise ship garbage is treated on board (incinerated, pulped, or ground up) before being discharged. However, when garbage must be offloaded (e.g., glass and aluminium), cruise ships can overwhelm port reception facilities. The global shipping industry is under increasing pressure to reduce emissions and pollution, including sewage and garbage pollution.
Cruise ships generate a substantial amount of solid waste. On average, each passenger produces at least two pounds of non-hazardous solid waste per day, resulting in about eight tons of solid waste on a large cruise ship during a one-week cruise. It is estimated that 24% of the solid waste generated by vessels worldwide comes from cruise ships.
In addition to sewage and garbage, freight boats contribute to water pollution through ballast water discharges, oil spills, and the release of biocides used in antifouling paints. Ballast water is often taken on in coastal waters and can disrupt the marine environment when discharged in other regions. Oil spills are challenging to clean up and have disastrous effects on marine life. The release of biocides and antifouling paints into the water can also be harmful. Overall, the environmental impact of the shipping industry is significant, and efforts to reduce emissions and pollution are ongoing.
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Frequently asked questions
Freight boats create a lot of pollution. In 2022, international shipping accounted for approximately 3% of the world's greenhouse gas emissions. Shipping containers produce more greenhouse gas emissions than some small countries.
Freight boats are responsible for air, water, acoustic, and oil pollution. They emit harmful gases such as carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), nitrogen oxide (NOx), sulfur dioxide, and sulfur oxide (SOx). They also produce waste, sewage, and oil spills.
There is increasing pressure on the global shipping industry to cut the pollution created by freight boats. The International Maritime Organization (IMO) has set targets to reduce emissions by 40% in 2030 and 70% in 2050 compared to 2008 levels. The IMO is also working on implementing a global sulfur cap on marine fuels. Some shipping companies are investing in new ships that will run on sustainably produced methanol.
