Waving ‘Bon Voyage’ to Cruise Ships: Are These Luxury Trips Worth the Environmental Impact?
- Kate Pugnoli
- Jun 15
- 7 min read
Updated: 19 hours ago
Whether on a honeymoon or family get-together, a cruise can be an idyllic way to spend a few days, a week, or longer enjoying a variety of cuisines, entertainment, informative lectures, and activities for young and old. While in port, one can enjoy excursions featuring picturesque sites, local culture, nature tours and unique shops.
Globally, there are now 350 cruise ships in operation, 70% of which are small or mid-sized, according to the Cruise Lines International Association (CLIA).
The trade group has announced that its member cruise lines will pursue net-zero emissions by 2050, but there still are environmental concerns involving both air and water that need to be addressed.
Cruise Ships—Lucrative and Popular
According to the 2024 State of the Cruising Report published by the CLIA, there were 31.7 million passengers globally in 2023, up 6.8% from 29.7 million in 2019. Just over half (16.9 million) were from the United States. COVID-19 impacted cruising resulting in fewer sailings, but the post-pandemic number of passengers is projected to increase to 39.7 million in 2027.
According to the report, 12% of cruise travelers cruise twice a year, 10% of cruise travelers take three to five cruises a year, 82% of those who have cruised will cruise again, and 71% of international travelers are considering taking their first cruise.
Amid their popularity, cruise ships create a spectrum of impacts to the environment including emissions, water pollution, and potential damage to environmentally sensitive marine areas. These negative impacts are not limited to the ocean, air, and marine life, but affect residents and local businesses in ports.
Carbon and Greenhouse Gas Emissions
Climate TRACE, a nonprofit coalition of organizations that monitors worldwide greenhouse gas emissions, stated that carbon dioxide emissions from cruise ships plummeted in March 2020—due to COVID-19 travel restrictions—but then rebounded to about 30% below pre-pandemic levels. By December 2022, however, these emissions reached new heights at “almost 6% higher than pre-pandemic levels.”
Carbon dioxide emissions from cruise ships plummeted in March 2020—due to COVID-19 travel restrictions—but then rebounded to about 30% below pre-pandemic levels. By December 2022, however, these emissions reached new heights at “almost 6% higher than pre-pandemic levels.”
European regulations require cruise ships that stop in Europe to report carbon dioxide emissions through the European Maritime Safety Agency’s (EMSA’s) THETIS MRV (The Hybrid European Targeting and Inspection System Monitoring, Reporting and Verification). According to data from EMSA’s THETIS MRV, for example, MSC Cruises’ ships had emissions ranging from 189 grams of CO2 per passenger per nautical mile (g CO2 / pax-n miles) for its Euribia line to 500.8 g CO2 / pax-n miles for its Orchestra line. Emissions in this regard were generally higher for Norwegian Cruise Line Holding’s ships’ emissions, ranging from 364.9 g CO2 / pax-n miles (Norwegian Breakaway) to 644.5 g CO2 / pax-n miles (Norwegian Sun).
Data from four cruise lines are provided below from their respective most recent environmental reports for 2023.
| Royal Caribbean Group | MSC Cruises (2023 report) | Carnival Corporation (2023 report) | Norwegian Cruise Line Holdings Ltd (2023 report) |
Passengers | 7,646,203 | 4,089,573 (guests) | 12.5 million | 2,716,546 |
Total GHG Emissions | 11.38 MT CO2e | 2.64 MT CO2 | 17.21 MT CO2e | 5.81 MT CO2e |
Scope 1 | 5.37 MT CO2e | 2.64 MT CO2 | 9.61 MT CO2e | 3.16 MT CO2e |
Scope 2 | 10,219 metric tons CO2e | 370 metric tons CO2e | 38,000 metric tons CO2e | 5,675 metric tons CO2e |
Scope 3 | 5.99 MT CO2e | - | 7.56 MT CO2e | 2.65 MT CO2e |
Sulfur oxides (SOx) | 275,717 metric tons | 2,373 metric tons | 7,000 metric tons | - |
Nitrogen oxides (NOx) | 73,271 metric tons | 38,597 metric tons | 165,000 metric tons | - |
Particulate Matter | 8,014 metric tons | - | 6,000 metric tons | - |
Discharged Water | 13.33 MT | 6.23 MT | 23.69 MT | - |
Treated discharged water | 10.47 MT (79%) | 3.71 MT (60%) | - | - |
Untreated discharged water | 2.86 MT (21%) | 72,869 metric tons (1%) | - | - |
Table 1. Emissions and pollutants based on cruise lines’ environmental reports. MT = million tons; CO2e = carbon dioxide-equivalent. Note that MSC Cruises’ greenhouse gas emissions do not include Scope 3 emissions.
Sulfur and Ship Scrubbers
Sulfur emissions are also a concern, so the International Maritime Organization set the sulfur limit to 0.5% mass to mass ratio for ship fuel in 2020 and reduced it to 0.1% in the Mediterranean as of May 2025. To work around using low-sulfur fuel, ships use “scrubbers” on their smokestacks that “scrub” some of the sulfur out of the exhaust air with seawater instead.
Unfortunately, the product of this process (washwater) is often discharged into the ocean (in an open loop system) without prior treatment. In contrast, in a closed-loop system, washwater is collected on board, treated, and disposed of in the next port. There are also hybrid systems with open- and closed-loop system modes.
However, according to the International Council on Clean Transportation (ICCT), about 80% of all ships in 2020 had open-loop systems, while 17% had hybrid systems, and less than 2% had closed-loop systems.
In a 2024 report by Pacific Environment, a nonprofit that provides funding and technical skills to environmental grassroots movements, scrubbers and their environmental impacts were explained through a review of various studies. Scrubber washwater is acidic (from sulfuric acid) and contains heavy metals, polycyclic aromatic hydrocarbons (PAHs), suspended particulate matter, and nitrates. For example, scrubber discharge has led to higher mortality rates for copepods and microplanktonic species, and accumulation of carcinogenic PAHs in residential killer whales.
Sewage and Wastewater
Cruise ships have other waste streams, including bilge water (containing oil, grease, and other contaminants), sewage, greywater (from showers, sinks, laundries, and kitchens), ballast water (used to stabilize ships), and solid waste. Ballast water can carry invasive species, such as the Asian kelp, cholera, and European green crab, that can disrupt ecosystems, but it has to be treated based on the Ballast Water Management Convention enforced since 2017.
Ballast water can carry invasive species, such as the Asian kelp, cholera, and European green crab, that can disrupt ecosystems, but it has to be treated based on the Ballast Water Management Convention enforced from 2017.
Although ships are required to treat sewage on board, the International Maritime Organization (IMO) states treated sewage can be discharged at a distance more than 3 nautical miles from shore. This extends to 12 nautical miles for raw sewage. In the US, however, treated sewage can be discharged within 3 miles, excluding no-discharge zones and freshwater sources.
Threats to Marine Life and Coral Reefs
Ships also generate noise that can disrupt marine life, such as in the Arctic. According to the Port of Vancouver, most underwater noise comes from ships’ propellers, and this noise can negatively affect marine animals’ ability to find prey, mate and reproduce, and navigate. The IMO also has guidelines to reduce underwater noise for ships.
There is also the threat of physical injury to whales, dolphins, and sea turtles due to collisions with large vessels.
Cruise ships can also cause significant damage to coral reefs because of the size of the vessels and weight of the chain and anchors needed to hold them. In 2020, for example, cruise ships stopping in Barbados caused “thousands of square meters of structural damage to the island’s valuable coral reefs.” In Cozumel, cruise ships have contributed to coral damage through their propellers stirring up sediment, which settles on the coral and effectively blocks their photosynthesis and starves them to death. Ballast water also introduced stony coral tissue loss disease to Cozumel’s coral in 2018, resulting in the death of over 60% of its coral.
In Cozumel, cruise ships have contributed to coral damage through their propellers stirring up sediment, which settles on the coral and effectively blocks their photosynthesis and starves them to death.
Alternatives and Flying
With a heightened environmental awareness among potential cruisers, cruise lines are being challenged to improve their practices. Greener alternatives for travel may include smaller cruise ships with sustainable practices.
For example, Hurtigruten is in the research and development stage of its “Sea Zero” project, a proposed “zero-emission propulsion” ship with a potential 60 megawatt-hour battery bank and retractable wind and solar sails. As a smaller ship with a capacity for 500 passengers, the company hopes it can begin sailing in 2030. However, battery and charging capacities at destinations is a concern, as “for ships that sail to the Galápagos, or the Arctic, batteries would be too heavy,” said Sönke Diesener, of Germany-based NGO the Nature And Biodiversity Conservation Union, to The Guardian.
Friends of the Earth, an international federation of autonomous environmental advocacy organizations, also has a Cruise Report Card that graded 243 cruise ships from 21 major cruise lines based on their sewage treatment, air pollution reduction, water quality or scrubber use, and transparency. Hurtigruten ranked highest overall for 2024.
Alternatively, travelers can directly fly to desirable destinations and take part in local hotels, restaurants, museums, shops, and activities. The ICCT stated in a blog that CO2 emissions from flying are generally lower than that of cruise ships, at about 10 g CO2/pax-km to 130 g CO2/pax-km versus 250 g CO2/pax-km for cruise ships, although calculations would change if other pollutants were taken into account.
*Kate Pugnoli is an Arizona-based freelance journalist and former educator who works with nonprofit organizations. Her area of interest is in addressing environmental issues impacting marine biodiversity and conservation.
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