**4. E**ffi**ciency in Marine Transportation Sector**

International maritime shipping is the most used means to transport goods and people. In fact, global shipping is responsible of moving about 90% of the world trade, while cruise ships in 2017 allowed nearly 25 million of passenger to sail the oceans. Moreover, the availability, the low cost, and the fuel efficiency of the maritime transport made possible the growth of industrial production in emerging economies. These significant results were enabled by the ability of the shipbuilding industry to respond promptly to the market demands, despite the unfavourable economic scenario in recent years caused by the global economic crisis. In particular, at present ship designers and shipbuilders are spending a lot of effort in increasing the performance of ships, by introducing new technologies on board. Nevertheless, it is well known that shipbuilding industry is one of the hardest metal industries, characterized by high levels of raw materials and energy consumption, hazardous materials exposure, and potential risk of sea and air pollution [84]. In addition, shipping greatly contributes to the emission of air pollutants (PM, SOx, NOx), sea pollutants (noise, thermal, discharges), and greenhouse gases. In particular, the contribution of maritime transport to the latter is up to 3% of global emissions. However, maritime transport is still the most fuel-efficient means of shipping goods, as can be seen from Figure 2. As an example, its CO2 emissions are nearly 100 times lower than airplanes when considering the tons of goods transported over km, while presenting a similar operative range.

**Figure 2.** Comparison of typical CO2 emissions among goods transportation options.

The shipping and shipbuilding industries are governed by global international agreements, promoted by the International Maritime Organization (IMO). In order to face the future environmental challenges caused by the expected growth of world's population and global economy, the IMO decided to set technical and operational measures to reduce ships' emissions, to be applied worldwide. In particular, in July 2011 the IMO delivered a roadmap for the reduction of environmental footprint of ships (Figure 3), by adopting the International Convention for the Prevention of Pollutions from Ships (MARPOL), Annex VI, officially entered into force in January 2013 [85].



**Figure 3.** International Maritime Organization (IMO) roadmap for the reduction of ships' environmental footprint.

Such a decision was the result of studies about the mitigation of ship emissions started in 2005 by IMO. The resulting MARPOL annexes collect specific guidelines in this regard. In detail, MARPOL labels specific sea regions as "special areas", considering their oceanographic and ecologic importance, as well as sea traffic and risk of environment contamination. For these areas, MARPOL impose strict limits for air pollutant emissions, including volatile organic compounds (VOCs), nitrogen oxides (NOx), polychlorinated biphenyls (PCBs), sulphur oxides (SOx), chlorofluorocarbons (CFCs) and heavy metals. These substances are specifically addressed since they contribute to the creation of ozone at ground level (VOCs and NOx), rain acidification (NOx and SOx), eutrophication or oxygen depletion of inland and coastal waters (NOx), depletion of atmospheric ozone (CFCs), and the accumulation of PCBs and heavy metals in the food chain. While an emission limit is enforced all over the globe, in special areas stricter limits are imposed depending on their specific characteristics:

