External costs of maritime transport have been studied very little, notwithstanding the public concerns towards the impacts of shipping and the growing scientific production on physical and biological impacts (concentrated on marine pollution). The need to valuate the external costs of shipping originates mainly from the high and growing emissions of ships, as compared to land transport modes. While road transport is under EU environmental legislation since the eighties, only in 2005 the first international regulation on shipping air emission control has entered into force (Marpol Annex VI) and only in 2006 a first European directive introduced limits to the sulphur content of all marine fuels (before the 33/2005/EC, directive 32/99/EC limited only marine gas oil sulphur content, when used by ships, with the result that most of ships abandoned the environmentally sound use of marine gasoil in port in favour of heavy fuel oils).
The CAFE study promoted by European Commission within its air quality control strategy, esteem that in the UE25 the emissions produced from navigation will exceed those deriving from all land sources in 2017 for SO2 and in 2020 for NOx (in 2005 shipping contribution is 45% and 43% respectively). This projection is due either to the emission reduction EU legislation in the industrial and other non transport sectors, either to the increasing trend marine emissions (3.5% per year). Since emission abatement technologies for ships are available and IMO new standard decision making is too slow and weak, it’s easy to expect that new community legislation will be introduced in the next decade.
The main external costs categories of maritime transport are those associates to:
Air pollution: emissions in atmosphere of harmful pollutants, due to combustion in the main and auxiliary engines, to on board incinerators and heaters, or to evaporation of volatile products (evaporative emissions). Air emissions may be distinguished in pollutants with effects on a global scale (CO2 and other gases to effect greenhouse) and pollutants with effects on a local and regional scale (the main ones are CO, NOx, NMCOV, SO2 and PM10). Shipping emissions are correlated to the ship fuels consumption. Marine fuels used by a single ship may be different (two, three or even four type in certain cases) due to the Annex VI environmental regulation and to fuel prices driving forces. Marine fuels consumption accountability at the ship level is already compulsory, while emission monitoring it is not.
Accidents: damages associated to shipping accidents (collision, fire, outbreak, etc.). Accident consequences may be distinguished in health effects (crew and passengers) and environmental pollution damages. Oil spills external cost are associated not only to oil tankers accident risk but to the general set of ships accident risk, since cargo and passenger ships may have on board (and spill, in case of accident) hundreds or thousands tonnes of marine fuels.
Operational (non accidental) discharges into the marine environment of liquid or solid harmful substances: the main impact factors in this category are: “treated” and “legally allowed non treated” black waters discharges (from ship toilettes), oily water discharges with oil content under 15 ppm (from bilge oil separator), dirty waters from the cleaning of cargo spaces, legally allowed release into the sea of solid wastes produced on board, ballast water containing alien species, antifouling paints releasing toxic chemicals. Other operational discharges may be linked to the possible installation on board of emission abatement devices (washing water from sulphur scrubber, etc.).
Solid and liquid wastes: some ships may generate huge amounts of solid waste (for examples cruise ships) that, even if correctly collected on board and delivered to land facilities, generate waste management external costs to the extent they cannot be recycled. Also liquid wastes are significantly produced on board and compulsory delivered to land waste management facilities (bilge oil, oil sludge, sludge from black water treatment system, etc.).