Environmental impact of shipping
The environmental impact of shipping include air pollution, water pollution, acoustic, and oil pollution. Ships are responsible for more than 18% of nitrogen oxides pollution, and 3% of greenhouse gas emissions.
Although maritime transport is the most energy-efficient method to move a given mass of cargo a given distance, the sheer size of the industry means that it has a significant effect on the environment. The annual increasing amount of shipping overwhelms gains in efficiency, such as from slow-steaming. The growth in tonne-kilometers of sea shipment has averaged 4 percent yearly since the 1990s, and it has grown by a factor of 5 since the 1970s.
The fact that shipping enjoys substantial tax privileges has contributed to the growing emissions.
Ballast water
discharges by ships can have a negative impact on the marine environment. Cruise ships, large tankers, and bulk cargo carriers use a huge amount of ballast water, which is often taken on in the coastal waters in one region after ships discharge wastewater or unload cargo, and discharged at the next port of call, wherever more cargo is loaded. Ballast water discharge typically contains a variety of biological materials, including plants, animals, viruses, and bacteria. These materials often include non-native, nuisance, invasive, exotic species that can cause extensive ecological and economic damage to aquatic ecosystems along with serious human health problems.Sound pollution
Noise pollution caused by shipping and other human enterprises has increased in recent history. The noise produced by ships can travel long distances, and marine species who may rely on sound for their orientation, communication, and feeding, can be harmed by this sound pollution.The Convention on the Conservation of Migratory Species has identified ocean noise as a potential threat to marine life. The disruption of whales' ability to communicate with one another is an extreme threat and is affecting their ability to survive. According to a Discovery Channel article on Sonic Sea Journeys Deep into the Ocean over the last century, extremely loud noise from commercial ships, oil and gas exploration, naval sonar exercises and other sources has transformed the ocean's delicate acoustic habitat, challenging the ability of whales and other marine life to prosper and ultimately to survive. Whales are starting to react to this in ways that are life-threatening. Despite sonar's military and civilian applications, it is destroying marine life. According to IFAW Animal Rescue Program Director Katie Moore, "There's different ways that sounds can affect animals. There's that underlying ambient noise level that's rising, and rising, and rising that interferes with communication and their movement patterns. And then there's the more acute kind of traumatic impact of sound, that's causing physical damage or a really strong behavioral response. It's fight or flight".
Wildlife collisions
s, such as whales and manatees, risk being struck by ships, causing injury and death. For example, a collision with a ship traveling at only 15 knots has a 79% chance of being lethal to a whale. Ship collisions may be one of the leading causes of population decline for whale sharks.One notable example of the impact of ship collisions is the endangered North Atlantic right whale, of which 400 or fewer remain. The greatest danger to the North Atlantic right whale is injury sustained from ship strikes. Between 1970 and 1999, 35.5% of recorded deaths were attributed to collisions. From 1999 to 2003, incidents of mortality and serious injury attributed to ship strikes averaged one per year. From 2004 to 2006, that number increased to 2.6. Deaths from collisions has become an extinction threat. The United States' National Marine Fisheries Service and National Oceanic and Atmospheric Administration introduced vessel speed restrictions to reduce ship collisions with North Atlantic right whales in 2008, which expired in 2013. However, in 2017 an unprecedented mortality event occurred, resulting in the deaths of 17 North Atlantic right whales caused primarily from ship-strikes and entanglement in fishing gear.
Atmospheric pollution
es from ships are a significant source of air pollution, both for conventional pollutants and greenhouse gases.Conventional pollutants
from ships is generated by diesel engines that burn high sulfur content fuel oil, also known as bunker oil, producing sulfur dioxide, nitrogen oxide and particulate, in addition to carbon monoxide, carbon dioxide, and hydrocarbons which again leads to the formation of aerosols and secondary chemicals reactions including formations of HCHO and ozone in the atmosphere. Diesel exhaust has been classified by the U.S. Environmental Protection Agency as a likely human carcinogen. The agency recognizes that these emissions from marine diesel engines contribute to ozone and carbon monoxide nonattainment, as well as adverse health effects associated with ambient concentrations of particulate matter and visibility, haze, acid deposition, and eutrophication and nitrification of water. EPA estimates that large marine diesel engines accounted for about 1.6 percent of mobile source nitrogen oxide emissions and 2.8 percent of mobile source particulate emissions in the United States in 2000. Contributions of marine diesel engines can be higher on a port-specific basis. Ultra-low-sulfur diesel is a standard for defining diesel fuel with substantially lowered sulfur contents. As of 2006, almost all of the petroleum-based diesel fuel available in Europe and North America is of a ULSD type. However, bunker oil is still available, and large marine engines are able to switch between the two types simply by opening and closing the respective valves from two different on-board fuel tanks.In 2016, the IMO adopted new sulfur-emissions regulations for implementation by larger ships beginning in January 2020.
Of total global air emissions, marine shipping accounts for 18 to 30 percent of the nitrogen oxides and 9% of the sulfur oxides. Sulfur in the air creates acid rain which damages crops and buildings. When inhaled, sulfur is known to cause respiratory problems and even increases the risk of a heart attack. According to Irene Blooming, a spokeswoman for the European environmental coalition Seas at Risk, the fuel used in oil tankers and container ships is high in sulfur and cheaper to buy compared to the fuel used for domestic land use. "A ship lets out around 50 times more sulfur than a lorry per tonne of cargo carried."
Cities in the United States like Long Beach, Los Angeles, Houston, Galveston, and Pittsburgh see some of the heaviest shipping traffic, which has left local officials desperately trying to clean up the air. Increasing trade between the United States and China is helping to increase the number of vessels navigating the Pacific and is exacerbating multiple environmental problems. To maintain the level of growth China is experiencing, large amounts of grain are being shipped to China. The numbers of shipments are expected to continue increasing.
In contrast to sulfur emissions, nitrous oxide emissions are primarily a function of combustion temperature. As air contains over 70% nitrogen by volume, some of it will react with oxygen during combustion. Given that those reactions are endothermic, a higher amount of nitrous oxides will be produced at higher combustion temperatures. However, other pollutants, particularly unburned or partially burnt hydrocarbons, will be more common at lower combustion temperatures, so there is a trade-off between nitrogen oxides and soot.
Other than replacing ambient air with pure oxygen or some other oxidizing agent, the only ways to significantly reduce the nitrogen oxide emissions are via passing flue gasses through a catalytic converter and/or diesel exhaust fluid treatment, whereby an aqueous solution of urea reacts with the nitrous oxides in the flue gas to produce nitrogen, carbon dioxide and water. However, both those options add cost and weight. Furthermore, the urea in diesel exhaust fluid is usually derived from fossil fuels, and therefore it is not carbon neutral.
A third option entails the use of wet scrubbers that essentially spray seawater through the exhaust column as it is pumped through a chamber. Depending on the detailed engineering-design attributes of the wet scrubber, these devices can wash out the sulfur oxides, soot and nitrogen oxides from the engine exhaust, thus leaving a sludge that contains soot and various acidic compounds. This material can then be either treated via an on-board device, or it can simply be dumped overboard. The discharged material has been shown to harm marine life, especially in nearshore settings.
In a recent study, the future of ship emissions has been investigated and reported that the growth of carbon dioxide emissions do not change with most common alternatives such as ultra-low-sulfur diesel or liquefied natural gas as well as growing volume of methane emission due to methane slip through the LNG supply-chain. Methane is a much more powerful greenhouse gas than carbon dioxide per unit volume, and is only slowly broken down in the environment by various chemical, photochemical and
biological processes.
In inland-waters-based applications where sulfur cannot be removed from the fuel before combustion, flue gas scrubbing is commonly employed. However, this would add weight and cost on ships and produce a further waste stream which would have to be disposed of, adding yet further cost. In addition, calcium hydroxide commonly being produced by calcination of calcium carbonate releases yet more carbon dioxide into the atmosphere. While this stream is comparatively small in relation to carbon-dioxide emissions caused by combustion of fossil fuels, it needs to be taken into account as well, as part of a complete life-cycle assessment.