The Environmental Impact of Cargo Ships

The vast majority of goods that we use and enjoy have spent at least some time traveling on a cargo ship. In fact, such ships facilitate over 80% of global trade. Unfortunately, they require quite a lot of fossil fuel to do so; Large cargo ships can burn up to 100 tons of oil every day. If these behemoths were a country, they would rank 6th in terms of CO2 emissions (higher than South Korea, Iran, and Canada).

In addition to releasing copious amounts of carbon into the atmosphere, cargo ships have several other negative effects on the environment. Also emanating from their exhaust pipes are fine particles, and compounds containing sulfur and nitrogen. All of these substances can impair the health of humans and other organisms.

As if the emissions weren’t bad enough, cargo ships also run into whales at an alarming frequency. At the moment, ship strikes are one of the leading causes of death for many of the world’s remaining whale species.

Bad as all this sounds, these massive ships actually have quite a lot going for them from an environmental and economic perspective. According to this article in Vox “A big ship will emit about 10 grams (0.4 ounces) of carbon dioxide to transport 1 metric ton of cargo 1 kilometer (2 tons of cargo 1 mile). That’s roughly half as much as a train, one-fifth as much as a truck and nearly a fiftieth of what an airplane would emit to accomplish the same task.”

In other words, if you want to get something from point A to point B, transporting it in a cargo ship is a very efficient way of doing so.

Still, the problems outlined above are very large, and well worth attempting to address. Scientists and engineers have been hard at work for decades trying to optimize the fuel economy and environmental friendliness of cargo ships. Though there is still much improvement to be made, this work has not been entirely fruitless.

One of the simplest solutions devised to address the fuel economy issue, is the use of cleaner fuel. Traditionally, cargo ships have used a substance called bunker fuel to power their massive engines. This relatively unrefined liquid contains massive amounts of sulfur, and several other compounds that create a very dirty exhaust when combusted. These days however, cargo ships are transitioning to more refined fuels with lower sulfur content that burn more cleanly. In some instances, they have even been retrofitted to burn liquified natural gas. The combustion of this gas releases methane, which does contribute to the greenhouse effect. However, methane is far less detrimental to human and environmental health than the combustion byproducts of most traditional ship fuels.

Another interesting option for the greening of cargo ships is the installation of exhaust scrubbers. These devices spray exhaust gases with a fine mist of water, that serves to remove pollutants, before the gases can make their way into the atmosphere. Scrubbers are not without their issues though. They require energy to run, which leads to more fuel being burned. Also, the waste water they generate is sometimes dumped into the ocean, which has negative ramifications for aquatic life.

Some organizations are attempting to decarbonize container ships altogether. Plans are on the table for hydrogen-powered cargo ships, and the first electrically propelled cargo ship is nearing completion. This 260 foot long vessel, named Yara Birkeland, will carry chemicals and fertilizer on a relatively short 30 mile route.

In addition to these innovation based solutions, the cargo ships currently on the water can reduce their per mile emissions by implementing a practice called “slow steaming.” As the name would suggest, ships employing this strategy travel as slower speeds than usual, and burn less fuel by doing so.

Though engineers are making progress, cargo shipping is likely to continue releasing large amounts of pollutants into the atmosphere for the time being. Though battery powered ships like Yara Birkeland are finally moving off the drawing board and into the water, their range is simply too limited to allow for mass replacement of the existing cargo fleet. The energy density of batteries will need to increase by a factor of around 30 before such replacements can begin taking place en masse.

That being the case, buying local is probably the average citizen’s best option for reducing shipping based emissions.