The Dark Side Of Tankers: Understanding Their Pollution Impact

Tankers and other ships have a significant environmental impact, contributing to air, water, acoustic, and oil pollution. While shipping is the most energy-efficient method to transport a given mass of cargo, the large volume of goods being shipped means that the industry has a considerable effect on the environment. For example, ships are responsible for more than 18% of nitrogen oxide pollution and 3% of greenhouse gas emissions. The fuel used in tankers and container ships is high in sulfur, and a ship emits around 50 times more sulfur than a lorry per tonne of cargo carried.

Shipping's contribution to air pollution

Shipping contributes significantly to air pollution, with marine shipping accounting for 18 to 30% of global nitrogen oxide emissions and 9% of sulfur oxide emissions. The fuel used in oil tankers and container ships is high in sulfur and cheaper than fuel used for domestic land use. This results in ships emitting around 50 times more sulfur than lorries per tonne of cargo carried. The high sulfur content in ship fuel creates acid rain, damaging crops and buildings and causing respiratory issues and an increased risk of heart attacks when inhaled.

While shipping is the most energy-efficient method for moving cargo over long distances, the scale of the industry means it has a significant environmental impact. The annual increase in shipping volume outpaces efficiency gains from innovations like slow-steaming. The growth in tonne-kilometers of sea shipments has averaged 4% yearly since the 1990s and expanded fivefold since the 1970s. Shipping's substantial tax privileges have also contributed to rising emissions.

Ballast water discharges from ships negatively impact the marine environment, and cruise ships, large tankers, and bulk cargo carriers are significant contributors. Oil spills from tankers are another environmental concern, with incidents like the Exxon Valdez spill in 1989 leading to stricter regulations and the requirement for double-hulled tankers in US ports. The International Convention for the Prevention of Pollution from Ships (MARPOL73/78) is the primary legal instrument for preventing ship pollution, and it includes measures such as tanker equipment inspections, oil pollution discharge requirements, and the phase-out of single-hull tankers.

Despite these efforts, regulations have often been inadequate, focusing on technical aspects of safety and pollution control rather than addressing the root causes of sub-standard shipping practices. The IMO, for instance, has long allowed ships to burn bunker fuel, a highly sulfuric byproduct of crude oil refinement, resulting in ship pollution comparable to that of cars. While claims that 15 or 16 large ships produce as much pollution as all the world's cars have been disputed, they highlight the significant environmental impact of shipping and the need for stricter regulations and cleaner fuels.

Regulations and their effectiveness

The International Maritime Organization (IMO) has implemented several regulations to address the environmental impact of tankers and shipping more broadly. These regulations aim to reduce air and water pollution, as well as prevent accidents that can lead to oil spills.

One key regulation is the International Convention for the Prevention of Pollution from Ships (MARPOL 73/78), which includes rules for subdivision and stability to ensure ships can withstand collisions or strandings. MARPOL 73/78 also introduced the concept of protective segregated ballast tanks, which are positioned to minimise the impact of collisions. The 1983 MARPOL convention introduced a requirement for new oil tankers to be fitted with segregated ballast tanks, and from 1996 onwards, to be fitted with double hulls, significantly enhancing the protection of the marine environment. The revised MARPOL Annex I Regulations for the prevention of oil pollution by oil, which entered into force on 1 January 2007, incorporated amendments to phase out single-hull tankers and introduce double-hull requirements.

In addition to MARPOL, the International Convention for the Safety of Life at Sea (SOLAS74) and the International Convention on Maritime Search and Rescue (SAR) contain preventative measures. These include institutional measures such as tanker equipment inspections, oil pollution discharge requirements, and a ship reporting system, as well as technical measures like top loading, the inert gas system, crude oil tank cleaning, and a stability meter.

To address air pollution, the IMO has implemented regulations to reduce sulfur emissions from ships. In 2020, the upper limit on the sulfur content of ships' fuel oil was reduced to 0.50% outside of designated Emission Control Areas, where the limit is 0.10%. These regulations are expected to significantly reduce the amount of sulfur oxides emitted by ships, which contribute to acid rain and respiratory problems. The IMO is also developing regulations to reduce the greenhouse gas intensity of ship fuel and plans to implement a global, mandatory charge on greenhouse gas emissions by 2027.

While these regulations have been successful in reducing pollution and improving safety, some challenges remain. For example, ballast water discharge can contain invasive species and other biological materials that can cause ecological, economic, and human health issues. Additionally, plastic pollution continues to be a problem, with some vessels violating international regulations by discharging plastic waste directly into the sea.

Water, acoustic, and oil pollution

Tankers and the shipping industry have a significant environmental impact. While they are the most energy-efficient method to move a given mass of cargo over a given distance, the industry's sheer size means that it has a substantial effect on the environment. This includes water, acoustic, and oil pollution.

Water pollution from tankers is primarily caused by oil spills, which can have disastrous consequences for marine life, the environment, and related industries such as fisheries and tourism. Oil spills can be caused by tanker accidents, collisions, groundings, and leakage. While the number of accidental spills has decreased over the last few decades, oil pollution from shipping remains an environmental risk. In addition to accidental spills, operational pollution from routine tank cleaning operations also contributes to water pollution.

One of the most well-known oil spills occurred in 1989 when the Exxon Valdez grounding substantially harmed the marine environment off the coast of Alaska. More recently, the Sanchi oil spill in 2018 was described as "the most serious and most polluting oil tanker accident in the 21st century." To address the risk of oil spills, various regulations and preventative measures have been implemented, including the International Convention for the Prevention of Pollution from Ships (MARPOL 73/78) and its amendments. These regulations include requirements for segregated ballast tanks and the phasing out of single-hull tankers in favor of double-hull structures, which reduce the amount of cargo spilled in the event of a collision.

Acoustic pollution, or noise pollution, caused by shipping activities is another concern. The noise produced by ships can travel long distances and negatively impact marine species that rely on sound for orientation, communication, and feeding. The Convention on the Conservation of Migratory Species has identified ocean noise as a potential threat to marine life, particularly whales, whose ability to communicate is disrupted by the loud noise from commercial ships.

Overall, while the industry has taken steps to mitigate the environmental impact of tankers, water, acoustic, and oil pollution remain significant issues that require continued attention and efforts to reduce their harmful effects on the marine environment.

The impact of sulphur in the air

Sulphur dioxide (SO2) is a gaseous air pollutant that is formed when sulphur-containing fuels such as coal, petroleum oil, or diesel are burned. Coal-fired power plants are one of the biggest sources of SO2, along with ports and smelters. When released into the atmosphere, SO2 can have detrimental effects on both human health and the environment.

Short-term exposure to SO2 can harm the human respiratory system, causing wheezing, shortness of breath, and chest tightness. People with asthma, especially children, are particularly vulnerable to these effects. Long-term exposure to high levels of SO2 increases respiratory symptoms and impairs lung function. Additionally, SO2 can react with other compounds in the atmosphere to form small particles that contribute to particulate matter (PM) pollution. These particles can penetrate deeply into the lungs and, in sufficient quantities, can lead to health issues.

SO2 and other sulphur oxides (SOx) can also contribute to acid rain, which can harm sensitive ecosystems. Acid rain occurs when SO2 and SOx react with other compounds in the atmosphere, forming fine particles that reduce visibility in certain areas, such as national parks. High concentrations of gaseous SOx can damage foliage and decrease the growth of trees and plants.

To mitigate the impact of sulphur in the air, governments and organisations have implemented various measures. The US Environmental Protection Agency (EPA), for example, has established national ambient air quality standards for SO2 and SOx to protect human health and the environment. The EPA works with state, local, and tribal governments to identify areas with poor air quality and develop plans to reduce SO2 levels. Additionally, policies promoting cleaner fuels and pollution controls on power plants have helped reduce SO2 emissions over time, leading to improvements in air quality.

Greenhouse gas emissions

The burning of fossil fuels by tankers is a major source of greenhouse gas emissions. Tankers typically use heavy fuel oil (HFO), which is a highly polluting and carbon-intensive fuel. The combustion of HFO

Frequently asked questions