Big-ship cruising, by virtue of its very nature, is not the most environmentally friendly way to vacation.

In addition to the airborne pollution created by the engines of a cruise ship, there is the matter of disposing of a variety of waste created by crew and passengers. When a cruise line operates dozens of vessels visiting hundreds of ports each year, managing sustainability is a major challenge.

The world’s biggest cruise companies, however, have become more active in reporting on their sustainability efforts and setting goals to decrease the environmental impact.

Carnival Corp. this month released its 2015 sustainability report, showing progress toward the company’s stated goal of incremental sustainability improvements by 2020.

The report gives an update on the company’s most ambitious sustainability initiative, which involves switching to liquid natural gas as fuel for a new generation of Carnival ships that will be more energy efficient and emit less greenhouse gas.

The company has four ships on order that will run on liquid natural gas, but faces challenges in deploying the ships. Liquid natural gas is less dense than traditional fuel, which means that the tanks holding the liquid have to be larger than traditional fuel tanks. This affects the design of the cruise ship and the need to be refueled when in port.

“We have a specific mission; the reason why this is so important to us is that even though liquid natural gas is available worldwide, the quantity needed is not everywhere in the world,” said Elene Heldewier, sustainability director at Carnival Corp., in an interview with Skift. “There is a lot of work that needs to be done in terms of infrastructure. We need to design the ships and work in parallel with the infrastructure so it’s available in the quantity we need. It’s a huge game changer for the maritime industry because it has less CO2.”

Not everyone, however, thinks major cruise lines focus as much as they should on sustainability.

“They do innovative, progressive things and feature them; the problem is that it’s like a shell game,” said Ross A. Klein, editor of Cruise Junkie, a site detailing the more controversial aspects of the cruise industry. “Let’s look at the new things we’re putting on the hull, the engines, waste water systems, but don’t look at the other 70 or 80 ships that don’t have them… what are they doing to clean up their act where they don’t have to? Presently what we’re seeing is positive moves, but they’re either motivated by regulation, legislation, or economic benefit.”

In particular, Klein points to the financial value for cruise lines to switch to less expensive liquid natural gas as the real incentive behind the new technology. He also notes that the waste sequestered by emission scrubbers still has to be disposed of eventually, despite decreasing airborne pollution to a certain extent.

Overall, Carnival Corp. is set to meet many of its sustainability goals by 2020. Across its 99 ships and 10 cruise brands, the company is on track to reduce the company’s carbon footprint by 25 percent from its 2005 baseline.

Some goals, like a five percent reduction in water usage by 2020, are lagging.

Carnival executives pointed out that CEO Arnold Donald is giving them the ability to take a long-term approach, looking past its current 2020 goals, to developing the company’s sustainability practice.

“In our most recent executive management meeting, the dialogue about greenhouse gases is happening, but 30 years out is top of mind,” said John Haeflinger, vice president of maritime policy and analysis at Carnival Corp. “We know we’re building much more efficient ships, and we know we will continue that with our liquid natural gas strategy. Since 2011 our greenhouse gas emissions have been flat to down through last year, and that’s going to be a challenge to sustain. We’d like to do better than that… there’s a lot of internal discussion, to think beyond building four-plus liquid natural gas ships. What does our fleet look like 10, 20 years from now?”

Some changes may prove more difficult to implement, especially when it comes to sustainability when in port and disposing of waste. There is also the problem of phasing out old ships with less efficient technology.

“Here we have a challenge of infrastructure, where worldwide not everywhere is at the same level,” said Heldewier. “In some places you can recycle everything, and in other ports you can only recycle one thing, usually the metals, or none. In the U.S. we’re able to recycle most of our waste that is recyclable, that’s not the case in most of the Caribbean islands. We can, based on itineraries, hold onto the recyclables and land it in specific locations where it can be recycled. As we move forward in our sustainability journey, we want to focus on how we can enhance our partnerships with different destinations. How can we be of a positive impact?”

The company is also discharging more water waste than in previous years. Here is a breakdown of Carnival’s emissions, energy usage, and waste disposal since 2010.

(Gray water is waste from showers, sinks, and washing machines. Black water is waste water from toilets.)

201020112012201320142015
Total Greenhouse Gas Emissions (metric tonnes CO2e)10,748,63611,003,07210,877,39910,617,43610,385,72110,374,922
Total Energy Consumption (Gigajoules)136,071,929139,240,147137,615,148134,007,500131,221,157131,964,513
Gray Water Discharged (Metric Tonnes)16,280,43816,539,34716,657,68017,430,80218,096,24517,494,817
Black Water Discharged (Metric Tonnes)7,075,8017,776,0897,783,5947,370,5267,098,1697,692,427
Total Waste (Metric Tonnes)489,075493,926469,990498,190477,570486,451
Photo Credit: Cruise lines, for all their talk about improving sustainability, encounter systemic challenges to reducing their impact on the environment. Carnival Inspiration is pictured here, along with some California wildlife. greg lilly / Flickr