Cruise liners might look white and pristine from the surface, but they are leaving a dark dirty trail wherever they go. We know our oceans are now a thick soup of plastic materials soaking up toxic waste and harming sea life, and that during disasters such as oil spills quantities of sea creatures die, yet one of the major polluters of our waters is slipping under our radar.

When the world talks about sustainable tourism and responsible travel, travel by land or air comes under closer scrutiny every day for its impact on the health of the planet and its people. But what about at sea? Some travellers choose to cruise in the belief that it is an environmentally friendly option, when in fact, according to Climate Care, the carbon footprint of a cruise holiday could be around double that of flying abroad to stay in a hotel.

If we are to move beyond eco friendly travel to a far more sustainable world, we can’t continue to ignore cruise liners, especially as it’s a sector of the travel industry that is growing steadily, with regulations that some say are not strict enough. Around 26 million passengers went on a cruise in 2018, according to Cruise Market Watch, which is a 3.3% increase over 2017. Imagine the amount of food and drink consumed by those travellers and the resulting sewage, grey water (from sinks, showers, and laundries), chemicals, and oily bilge water (from the base of the engine room).

Where does all this waste go? Incredibly, international law allows disinfected sewage to be dumped up to three miles from our shores. Filthy bilge water too can simply flow back into the sea. And this waste, combined with disintegrating plastics (which can contain lead, cadmium and mercury – metals which are dangerous to humans) and other materials, not only infiltrate every step of the food chain, but studies show that the concentration of toxins measured in the tissues of animals are not just accumulative but actually magnified.

There are laws in place for when a cruise ship comes into port or drops anchor in a bay. Yet these are not always adhered to, making life around a cruise ship unhealthy for people on the land because of the subsequent water and air pollution. Waste is also offloaded onto the land as the cruise progresses, leaving the country in question to dispose of the rubbish, which not all of them by any means do responsibly.

When it comes to energy consumption, a cruise ship, of course, does not sail with the wind. ‘Many large ocean liners run on giant diesel engines, which can stand at more than three stories tall and span the length of two school buses. This equipment, along with smaller auxiliary engines, can emit dangerous levels of sulfur dioxide,’ writes Alison Moody in The Guardian.

What’s concerning is that the luxury cruising trend shows no sign of abating. Demand for cruise holidays has grown 68% in the last ten years, according to the CLIA (Cruise Line International Association). And there’s a new generation of mega-liners that are like floating cities. Harmony of the Seas owned by Royal Carribean, for example, can carry up to 5479 passengers and 2100 staff, and burns hundreds of tonnes of fuel a day.

The CLIA’s latest yearly report states that cruise companies have ‘invested significantly over the last decade to develop new technologies to help reduce air emissions’. But many scientists and experts in the field don’t think it’s enough. If the liners don’t have a conscience about how they treat the earth, then it’s up to responsible travellers like us to think carefully before making the decision to cruise. The 2016 Cruise Ship Report Card lets travellers decide which cruise to take based on a cruise ship or cruise line’s environmental and human health impacts, while some responsible tour operators have a few small cruise liners they approve, including Responsible Travel.

‘For our small ship cruises a connection with local people and places is a key part of the experience,’ says Sarah at Responsible Travel. ‘In Croatia, for example, the ships are run and owned by local families, evenings are spent enjoying the culture and food of the small port towns the ship visits and most of the produce served on board is sourced locally. These cruises take the focus away from simply ticking off destination after destination and instead become a journey into the local heart and soul of a region or country.’ Sounds good to us.

However, Carnival Corporation – the largest cruise ship company in the world – has not only ignored cries from climate change defenders asking them to acknowledge the damage that their ships are causing – but their carbon pollution has actually increased by 20% in the last decade. Stand.Earth has been running a campaign against Carnival, asking them to shift to ditch the pollution and instead become leaders in clean ships.

Of course it will take more than stopping cruise trips to solve the serious issues affecting our troubled seas, which include rising temperatures caused by green house gas emissions that are killing our coral and sea life. Be aware that taking a cruise is more harmful to the environment and human health than many other forms of travel, so use the power of your wallet to only support responsible cruise liner companies that seriously commit to sustainability and are accountable and transparent. Don’t let your holiday ruin the destination. As travellers, we can be part of the solution to inspire change on all counts.