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The Environmental Impact of Maritime Transport (and How to Combat Emissions)

Cargo ship docked against sunset sky

Maritime transport has traditionally been seen as environmentally friendly and has thus avoided the strict environmental regulation of land transport. However, the situation changed rapidly after the 1990s, and in the 2010s many new environmental controls have been intro­duced globally.

The biggest cause of local environmental impact from maritime trans­port is accidents. The ship might leak its own fuel or other important substances, or the tank of the ship might leak dangerous chemicals such as crude oil.

On the other hand, a big share of environmental impacts related to maritime transport can be reduced by reducing other transport costs. Removing unnecessary trips, increasing the size of transport batches and decreasing cruising speed can reduce fuel consumption and thus also pollution.

The most commonly discussed environmental effects of maritime transport are the exhaust emissions carbon dioxide (CO2), sulphur dioxide (SO2), nitrogen oxides (NO2 and NO3) and particulates (PM or particulate matter). These are formed in the ship’s combustion engines and can be reduced simply by reducing fuel consumption, using sulphur scrubbers or catalysts or switching to a cleaner fuel.

Other environmental effects are waste, water pollution, noise and the risk of spreading foreign organisms to vulnerable ecosys­tems. In addition, the consumption of energy and natural resources, health and environmental effects from unload­ing cargo, the land taken up by ports and sea lanes and their barrier effect, and erosion.

Reducing Sulphur Dioxide (SO2) emissions

There are two exhaust gases that have been discussed lately in relation to maritime transport, namely sulphur and carbon dioxides. Sulphur dioxide (SO2) reduces air quality and affects public health. It dissolves easily into water, causing acidification of water systems and the ground. Crude oil pumped from the ground always contains sulphur, though the amount differs between oil drilling areas. Sulphur has been removed from fuel used in cars for decades now, but unpurified sulphur-rich fuel in sea traffic may still be used. The consumption of these unpurified fuels has made maritime transport the worst producer of sulphur emissions.

There are international regulations for reduction of sulphur emis­sions; for example, in 2015 in the Baltic Sea and Bay of Bothnia, the sulphur content of fuel was limited to 0.1%. The sulphur content of fuels was globally limited to 0.5% starting from 2020.

Sulphur can be removed from fuel either at the refinery before the fuel is used, or after the fuel has been burned in the engine, by remov­ing the sulphur from the exhaust fumes with a sulphur scrubber. Both options are expensive. In the latter case, there are further costs from buying the chemicals needed for the scrubber. The scrubbers also take space in the ship and thus reduce the total cargo capacity.

It’s also possible to reduce sulphur emissions by using alternative fuels, such as liquefied natural gas (LNG) or biofuels. Solar and wind energy have also been brought into use on ships, and they are suitable to support energy production. Additionally, emissions have been reduced by connecting ships to the electrical grid during their stay at ports (shore-side electricity).

Reducing Carbon Dioxide (CO2) emissions

Carbon dioxide (CO2) is the most significant greenhouse gas emitted through human activity. Greenhouse gases cause global warming, which increases the average temperature of the earth. CO2 is formed as a side product of burning - in all combustion engines - and also when breathing.

The proportion of maritime transport of all globally emitted greenhouse gases is 2.5%. Transportation consumes 33% of all energy in the EU, and of that, 13% is mari­time transport.

There is no technical equipment to reduce CO2 emis­sions of ships and currently, the only way to reduce the emissions is by reducing fuel consumption in relation to the amount of cargo transported. Some of the most effective methods are enhancing the fuel efficiency of engines and reducing the speed of the ship. It is also possible to reduce energy consumption per unit of cargo by increas­ing the size of the ship and using transport methods with the highest stowage rates, such as container ships instead of ro-ro ships.

Increasing fuel efficiency 

To increase the fuel efficiency of ship engines, the International Maritime Organization (IMO) has developed a tool called the Energy Efficiency Design Index (EEDI), which defines efficiency values for new ships. EEDI is calculated for each new ship in the designing phase. It depicts the relationship between the amount of fuel consumed by the ship and the amount of cargo transported. Because the stowage factor of a ship greatly affects the efficiency values, different indexes are used for different types of ships.

In 2018, IMO adopted an initial IMO strategy on reduction of GHG emissions from ships, setting out a vision which confirms IMO’s commitment to reducing GHG emissions from international shipping and to phasing them out as soon as possible. The initial GHG strategy envisages, in particular, a reduction in carbon intensity of international shipping; and that total annual GHG emissions from international shipping should be reduced by at least 50% by 2050 compared to 2008.

It is not known how the vision will be achieved. For example, France, supported by its domestic ship-owners, presented a proposal to reduce the speed limit for certain types of ships, with the intention of lowering greenhouse gas emissions.

In any case, these kinds of discussions will have a major effect on the design of future vessels. In particular, the effect will be on the biggest vessels that have the fastest cruising speed, namely ferries. This may have an effect on whole ro-ro business and passenger–car ferries and their transport flows. On effect that should be taken into account in strategies of ports and shipping companies.