Huge container ships' biggest problem is emissions

The Ever Given drama in the Suez Canal momentarily turned the world's attention to container shipping. It will require a more sustained focus to address the dangers these crucial ships pose to the climate. Shipping accounts for three per cent of the world's carbon emissions. If it were a country, the sector would be the world's sixth-largest emitter.

Container shipping has drastically reduced shipping costs and, over the past 50 years, has arguably played a larger role in global commerce than all trade agreements put together. The ships, however, run on cheap 'bunker fuel,' which when burned emits a large amount of carbon dioxide as well as black carbon, a fine particulate that can absorb a million times the energy of CO2 and may represent the second-largest contributor to climate change.

The International Maritime Organisation has set a goal of reducing carbon emissions from ships to 50 per cent below 2008 levels by 2050, and the Getting to Zero Coalition has brought together more than 150 companies and organisations across the maritime sector. Many shipping companies have adopted their own ambitious goals for their operations. Even so, decarbonizing shipping will be difficult, and its share of overall emissions will probably continue to rise for some years as other sectors reduce their carbon footprints more rapidly.

Cutting emissions is particularly challenging because of the long distances the ships travel and the massive cargo they carry. And because the energy density of bunker fuel is so great, cleaner alternative fuels are either much more expensive or would take up so much room on board as to be impractical. Bill Gates estimates that green alternatives to bunker fuel are currently 300 per cent to 600 per cent more expensive, and notes that the "best conventional container ships can carry 200 times more cargo than either of the two electric ships now in operation, and they can run routes that are 400 times longer."

Despite these difficulties, there are many ways to lower emissions, and the industry is not waiting for a magic bullet. One strategy is slow steaming, which means running at speeds below a ship's maximum engine capability. By one estimate, a 10 per cent reduction in ship speed can cut emissions by 19 per cent, after taking into account the extra ships needed to deliver the same amount of goods in the same amount of time.

But the big advances will come from alternatives to bunker fuel. In addition to the fuel-cell powered ships that Gates mentioned, container ships powered by liquid natural gas have already been launched. Carbon-neutral ships fuelled by methanol are rapidly being developed, even if those ships are intended for shorter distances.

Hydrogen could also potentially play a key role in greener container shipping. But because it is much less energy-dense than bunker fuel, the space required to store hydrogen fuel onboard for long voyages could be prohibitive. One idea is to build a series of liquid-hydrogen refuelling stations, so that ships would not need to store as much - though at the cost of longer voyages because of the refuelling stops. Some are instead betting on using hydrogen to make green ammonia, by combining the hydrogen with nitrogen, but the ammonia also has much lower energy density than bunker fuel.

The most radical and controversial proposal comes from Gates. "We should also be exploring nuclear-powered container ships," he writes in his new book on climate change. "The risks here are real (for example, you have to make sure the nuclear fuel doesn't get released if the ship sinks), but many of the technical challenges have already been solved. After all, military submarines and aircraft carriers run on nuclear power already."

Container ships have been crucial to the expansion of supply chains and the growth of global trade. Even with added costs from going green, they will still represent by far the least expensive method of moving goods over long distances. In the future, and long after the Suez Canal traffic is back to normal, they will also be crucial in the shift to net-zero emissions. (Bloomberg)