Maritime transport has traditionally been seen as an environmentally friendly mode of transport and has thus avoided the strict environmental regulation of other modes of transport. However, the situation changed rapidly after the 1990s, and in the 2010s, many new environmental controls have been introduced globally.
The biggest local environmental impact from maritime transport is due to accidents. A ship might leak fuel or other important substances, or the tank of the ship might leak dangerous chemicals such as crude oil. 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 solid 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 can be added.
In this text, I will focus on sulphur and carbon dioxide emissions from combustion engines. I will write more about other harmful effects of shipping later.
Environmental views on shipping: sulphur dioxide (SO2)
There are two exhaust gases that have been discussed recently 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, although 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 the 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 has been limited globally 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. Scrubbers also take space in the ship and thus reduce the total cargo capacity. It is also possible to reduce sulphur emissions by using alternative sources of energy, such as electricity, liquefied natural gas (LNG), or synthetic biofuels.
Environmental views on shipping: carbon dioxide (CO2)
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 from breathing.
The proportion of all globally emitted greenhouse gases from maritime transport 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 best way to reduce emissions is by reducing fuel consumption in relation to the amount of cargo transported, or to switch to other energy sources.