With the numbers of visitors arriving in Greece increasing every year, and new hotels being built on the Greek islands at an accelerating rate, the dangers of over-tourism, with its pressures on infrastructure, water supply and drainage, traffic congestion etc, are beginning to cause concern. At the same time cruise ships are arriving in ever-increasing numbers at Chania and elsewhere, and are unthinkingly welcomed by local businesses and administrators.

While the impact of thousands of cruise passengers descending daily on a small city such as Chania is immediately apparent, less obvious, and less considered at a local level at least, is the environmental impact of the monster cruise ships themselves. Giannis Vourdobas, a mechanical engineer and regular contributor to Haniotika Nea has this week published an article which lays out the challenges presented by big ship pollution and the approaches needed to counter them. What follows is an edited version of his comments.

While cruising for many represents the height of luxury, Mr Vourdoubas says, the attractions of travelling from port to port in a floating hotel with unlimited facilities conceal a serious environmental challenge. He considers the problem under a number of different headings.

The energy consumption of cruise ships
A large cruise ship will carry a complement of several thousand passengers and crew, and its propulsion systems and the operation of ancillary services require the constant consumption of fuel. Most cruise ships use Heavy Fuel Oil (HFO), which is one of the most polluting fuels in existence. A single cruise ship can consume over 150 tons of fuel per day, releasing enormous quantities of carbon dioxide (CO2) into the atmosphere. HFO produces emissions of CO2, nitrogen oxide (NO), sulphur oxides (SO) and suspended particles, with serious consequences for the atmosphere and the health of the residents of coastal areas.

In the past few years, as a result of more stringent international regulations, many cruise ships have turned to low sulphur or Marine Diesel Oil (MDO), while many more recently constructed ships use liquefied natural gas (LNG), which emits fewer nitrogen oxides and almost no sulphur, reducing pollution in port cities. However, the use of LNG in marine engines risks leaks of methane – a particularly powerful greenhouse gas.

Some cruise ships are also now using anti-pollution technologies such as scrubbers, which clean the exhaust gases of sulphur, but this often produces liquid waste which is disposed of in the sea. Clearly these alternative technologies have their downsides, and they can only mitigate to some degree the continuing use of fossil fuels.

Comparison of cruise ships with other means of travel
According to data produced by international organisations, the carbon footprint of cruise ships per passenger kilometre is often greater than that of an aeroplane. Moreover ancillary activities such as catering, entertainment and maintenance can multiply the emissions per passenger. This makes cruising one of the most polluting forms of tourism, with negative consequences which are often not visible to the passengers. Generally speaking, it is estimated that the CO2 emissions per passenger day of a cruise are eight times those of a land-based holiday.

Environmental effects on coastal cities
The ports which accommodate cruise ships are subject to particular pressures. In addition to CO2, the ships emit nitrogen oxide, particles and other pollutants which have a direct effect on air quality. Ports such as Barcelona, Venice, Santorini and Naples have registered serious problems of atmospheric pollution due to the presence of large ships.

Economic dimensions and the “green” picture
The cruise companies often promote the positive economic effects which tourism can bring to local communities, but it is debatable whether the advantages can outweigh the environmental damage caused. The tourist who lands for a few hours and spends a limited amount cannot compensate for thousands of tons of CO2 emissions.

Some companies have cultivated a “green” image through their use of scrubbers to clean exhaust emissions, or of LNG for fuel. However, although these measures reduce some pollution, the basic issue of carbon emissions remains to a large extent unsolved.

International regulations and restrictions
The International Maritime Organization has adopted certain measures for the reduction of emissions in the shipping sector. One of the most important, in force since 2020, is the regulation restricting the permissible amount of sulphur in marine fuels. At the same time targets are under discussion for the gradual reduction of total emissions from shipping to 50% of 2008 levels by the year 2050. Despite this ambitious framework, progress is slow and many environmental organisations consider that the commitments do not correspond to the scale of the climate crisis.

Technological solutions and alternative fuels
Research into the use of “cleaner” forms of energy in shipping has intensified. LNG is being adopted as a temporary solution as it emits less CO2 than fuel oil, but it is still a fossil fuel with a considerable environmental footprint. Considered more hopeful are the technologies based on hydrogen (H2), biofuels, synthetic fuels or ammonia (NH3), which have no carbon emissions if they are produced by renewable energy sources.

At the same time, improving the design of ships, with more efficient lines and advanced propulsion systems, can contribute to reductions in fuel consumption. Some cruise ships are adopting renewable energy techniques such as solar panels, sails, and batteries to reduce power consumption while in port.

Altogether, Mr Vourdoubas says, the transition to alternative fuels and energies is not only a technological challenge, but a strategic necessity for the sustainability of cruising, the protection of the environment and conformity with international emissions regulations.

Climate neutral ports
The concept of climate-neutral ports which will have a zero carbon footprint in terms of energy use is beginning to occupy some port administrations. Among the solutions being considered are the provision of shore power so that ships do not have to operate their engines while they are berthed. [Although the impact on local grids of suddenly adding the equivalent of a small town of 5,000 people to daily consumption needs will have to be taken into consideration.]

In Greece this goal could be achieved with the use of renewable energy from solar-voltaic systems, wind turbines (assuming the average wind speed in ports is sufficient), electrical energy storage but also wave energy from devices which could be installed on harbour jetties. Already in Crete, the port of Heraklion has announced its intention of becoming a climate neutral port.

Public awareness
As environmental awareness increases, many travellers are now looking at their holidays’ carbon footprint. Some cruise companies have begun to offer emissions compensation programmes, but these remain few. However, the pressure of public opinion can act as a catalyst in speeding up more sustainable practices. As has happened in other sectors, from air travel to agriculture, public demand for “greener” choices can significantly influence business strategies.

Conclusions
The big cruise ships now represent one of the most polluting forms of tourism, with significant carbon emissions and multiple environmental effects. The current course is not sustainable, because it goes against global targets for the reduction of emissions and the limiting of climate change. The solution cannot be a simple one: it requires a combination of international regulations, technological innovation, significant investment in alternative fuels and changes in the mindset of both companies and passengers.

The transition towards a more “environmentally clean” form of cruising, Mr Vourdoubas says, is difficult but necessary. In the final analysis, journeys by sea cannot be truly enjoyable if they are accompanied by the destruction of the very planet which we all share.
(Haniotika Nea, 22/08/25)