Look at an ad for the cruise industry and what do you expect to see? Images of deep blue, crystal clear seas; cloudless skies; idyllic, untouched beaches or pristine icebergs; perhaps a happy fish or two.

The cruise industry depends on attractive environments to woo customers, and with nearly 20 million passengers a year, they’ve proved very good at enticing people on board. However, it’s unlikely many people embarking on a cruise know the impact the trip could have on the seas, skies, beaches, icebergs and fish depicted in those advertisements.

Given the size of today’s cruise liners, the list of environmental transgressions the ships can and often do make is vast. A cruise is a much more carbon-intensive form of travel than the much-derided long-haul flight: estimates from carbon offsetter Climate Care find cruise liners emit nearly twice as much CO2 per passenger mile as aeroplanes, while other estimates say it’s three times as much. Cruise ships also emit particularly pernicious air pollutants – both from unregulated onboard incinerators and through burning fuel. Though it is outlawed in certain areas, many ships (both recreational and industrial) regularly burn bottom-of-the-barrel bunker fuel – what remains once lighter fractions like petrol, diesel and so on have been removed from crude oil through distillation – and this has a sulfur content 2,000 times that of diesel. (Sulfur creates sulfur dioxide when burned, which is harmful to human health and is a precursor to acid rain.) Ocean campaigning group, Oceana, estimates air pollution from a cruise ship equates to that from 12,000 automobiles, though other estimates place the figure as high as 350,000.

And then there’s the impact ships have on local ecosystems through anchors and ballast water. According to the Smithsonian Institution in the US, a single cruise ship anchor dropped in a coral reef for one day can immediately destroy an area half the size of a football pitch, with half the same area again dying later. (Coral recovery takes 50 years.) The practice of using ballast water – to stabilise a vessel by maintaining its weight following disposal of wastewater or cargo – can have even more devastating effects. Water is taken on in one location and released in another, meaning the practice introduces non-native species (potentially including poisonous algae, cholera, bacteria, and invasive animal and plant species) to delicate ecosystems. The list goes on.

At the heart of the problem is the inefficacy of the International Maritime Organisation (IMO), a specialised agency of the United Nations overseeing international shipping regulations, notably the International Convention for the Prevention of Pollution from Ships (known as MARPOL).

Dr Ross A Klein, sociologist and founder of the International Centre for Cruise Research, explains some of the weaknesses in the system: “Conventions adopted by the IMO, which is a slow-moving and complex body, must be approved by 50 per cent of the registered [shipping] tonnage (meaning countries like Panama and Bahamas have considerable strength given the number of ships they have registered) before taking effect. Many conventions can take five to 10 years from approval by the IMO and taking effect given the number of ratifications. Countries not ratifying a convention are not obligated to enforce that convention. For example, the US has not ratified the convention on discharge of sewage and as a result has much less stringent requirements than MARPOL.”

What’s more, MARPOL does not have its own enforcement regime, but depends on enforcement by those states whose waters are affected or where a ship is registered (essentially meaning – especially when ships are in remote waters – no one’s looking). And some substances, including the aforementioned ballast water and grey water, are not regulated whatsoever.

Most waste streams generated by a cruise ship are controlled to some extent, but there are undeniable shortcomings to the system. Let’s start with black water. An average cruise ship generates over 30 litres of sewage per person per day (adding up to over a million litres for a one-week cruise on some of the bigger ships). While ships are required to be fitted with devices to clean black water, raw sewage can be dumped anywhere beyond three miles of the coast. Sewage contains harmful bacteria, pathogens and viruses (all of which can contaminate fisheries and shell fish beds), as well as nutrients like nitrogen and phosphorus, which promote algal growth, potentially depriving sea life of oxygen.

Cruise liners also produce up to 340 litres of grey water per person per day (which can add up to close to two million litres per day on some of the larger ships) from sources including sinks, showers, galleys and laundry. While MARPOL does not regulate grey water, the US recently introduced legislation to ban the discharge of untreated grey water – but only within one nautical mile of shore. This waste stream often contains contaminants like faecal coliform bacteria, food waste, detergents, oils, medical and dental waste, as well as nutrients and other oxygen-demanding materials.

And then there’s solid waste. While there’s no doubt the industry’s improving – thanks to waste reduction efforts, gone are the days when each passenger created 3.5 kilogrammes of waste a day – ships still produce a significant amount of waste, adding up to nearly 19 tonnes from a one-week cruise on the bigger ships. Under MARPOL, waste: cannot be discharged within three miles of the coast; can only be discharged between three and 12 miles if it is ground up and can pass through a one-inch screen; and can be discharged more than 12 miles from shore, so long as it is not plastic or hazardous.

In practice, many large ships have incinerators onboard for solid waste, the ash from which (classed as hazardous on land) is normally dumped overboard. As already mentioned, there are no standards limiting emissions from ship incineration, so the advanced pollution control systems fitted on incinerators on land have yet to reach the seas. What’s more, as much as 75 per cent of solid waste is incinerated, and so this inevitably includes recyclable items, though glass and aluminium at least are increasingly stored and recycled on shore.

Food waste, which can account for half of all solid waste due to cruise ships’ elaborate catering arrangements, is normally macerated and discharged at sea. The US Environmental Protection Agency’s recent ‘Cruise Ship Discharge Assessment Report’ notes that food waste discharged in large quantities ‘can contribute to increases in biological oxygen demand, chemical oxygen demand, and total organic carbon, diminish water and sediment quality, adversely effect marine biota, increase turbidity, and elevate nutrient levels’. It also points out that food waste can be detrimental to fish digestion and health, and can cause ‘ecological changes such as perturbations to species behavioral [sic] patterns and alternation to community species composition and diversity’.

Many cruise ships have waste management plans in place that claim they will reduce, reuse and recycle ‘where possible’ (Celebrity Cruises), ‘all that we can’ (Holland America) or ‘[Insert meaningless PR phrase here]’. As many cruises take place in far-flung, developing destinations, just how easy is it to recycle? Dr Klein says: “My understanding is ships use recycling when it is available and cost effective. Recycling is available in most ‘developed’ world ports, but is not an option in most small island states and parts of the developing world.” Klein also advises taking cruise lines’ promises with a pinch of salt, citing anecdotal evidence that Royal Caribbean hasn’t followed the ‘no waste overboard’ policy it set when it was on probation for discharge violations, and saying bluntly: “I would look at the cruise industry’s promises with scepticism. There is a history of claims being greater than accomplishments, and cases where branding
is directly contradicted
by behaviour.”

But the above only describes minimum requirements for the most part. And while the industry has sometimes found it difficult to meet even those low standards (resulting in fines exceeding US$55 million since 1998 – with many cases still pending), there are instances of best practice and commendable innovation, too. Many ships now use advanced wastewater treatment systems, which allegedly yield ‘drinking-water quality’ effluent; Holland America Cruises, like Royal Caribbean, claims to allow no waste to go overboard; Celebrity Cruises has included solar panels (though only enough to power the lights) in the aptly-named ship Solstice; Disney Cruise Lines (yes, the mouse has taken to the seas) has introduced innovations like utilising used cooking oil as fuel (for machinery on Disney’s private island, not the ship itself) as well as donating reusable furnishings to the disadvantaged in port communities; and Norwegian Cruise Lines has introduced an ‘eco-ballast system’ to prevent introducing toxins and invasive species to the waters it sails.

Of course, smaller cruise ships will naturally have less of an environmental impact. Lindblad Expeditions, which carry only around 150 passengers, are still trying to set an example, though – according to Director of Communications Patty Disken-Cahill, the company has introduced a dinner sign-up scheme to “help our chefs to anticipate the quantities [and to] significantly reduce food/packaging waste”. The company has also introduced a scheme in the Galapagos to help local artisans convert tourist waste into items like jewellery and glassware to sell back to tourists.

Despite these examples of improvement, the cruise industry in general has a long way to go before it can truly represent itself as steward of the world’s oceans and pristine environments. Klein explains: “I believe there is always progress being made, if for no other reason than new ships are better than the old ships. The problem is there are many older ships and these are essentially ignored as the industry promotes what it is doing on its newest ships. Again, there is progress but the problem is there are many older ships that have old technology and that are not being upgraded.”

Asked if it would be possible for the cruise industry to ever become sustainable, Klein responds: “The answer is ‘yes’. The problem is that sustainability has certain costs (e.g. better systems for treatment of all wastes) – costs that are inconsistent with offering a vacation at bargain basement prices – and the cruise industry has placed continued high profits above implementing the types of systems that would reflect their many claims.”

With a bit of pressure from the cruise-going public who so enjoy a pristine environment, that could all change, though. In future, before hopping on board, passengers might want to tell the cruise lines they ought to shape up or ship out.