The challenge is particularly acute because the choices shipping companies make now will play out over the next 30 years. "We're building the ships today which will be in operation over the next three decades," Dr. Tristan Smith, an expert in shipping and energy at University College London's (UCL) Energy Institute, said in an interview with CNN Business. To stand any chance of meeting the IMO target, zero emissions vessels need to enter the fleet by 2030 at the latest, he added.

Little headway

But sailing more slowly is only a short-term fix that won't do enough to hit the IMO target, according to CDP. Success requires new ships, new engines and new fuels. Major financial, regulatory and technical barriers have to be overcome, and so far much of the shipping industry is dragging its feet when it comes to innovation. "Shipping companies are failing to push for the critical technologies required to reduce their carbon footprint," according to CDP. Just three of the 18 companies CDP ranked have a committee at board level responsible for tackling the climate emergency.

_{The Mette Maersk, powered by an oil and biofuel blend, arrives in Hong Kong — Credit: Maersk}

It's an approach CMB has already adopted. The company, which has won multiple sustainability awards since it was bought by the Saverys family in 2015, recently announced a partnership with Japan's Tsuneishi Facilities and Craft to build the world's first ferry that can run on hydrogen and diesel by 2021. CMB's strategy is about testing low-carbon technologies on smaller ships, such as the Hydroville, and then scaling them up. "The Hydroville is a small project which aims 10 years ahead of its time," Roy Campe, CMB's research and development manager, told CNN Business.

Cleaner cruising?

Norwegian cruise liner Hurtigruten is pursuing different technology. It has just launched the world's first hybrid cruise ship. Powered by a combination of batteries and marine gas oil, the Roald Amundsen sailed from Tromso to Hamburg in July, producing 20% fewer emissions than other ships of the same size, according to Daniel Skjeldam, Hurtigruten's CEO.

"To operate sustainably, you have to invest in new technology. This is a new green revolution that's coming," said Skjeldam, adding that the cruise sector has been lagging other industries when it comes to cutting emissions.

The cruise industry grew by almost 50% between 2010-2018 and the number of passengers increases by 4-6% each year, according to Cruise Lines International Association.

Despite the trials of new technology by companies such as Maersk, Hurtigruten and CMB, industry-wide progress is too slow. Big companies are hesitant to invest billions of dollars in new technology and there are few financial incentives and regulations in place to push them to do so. But experts say it is crucial that the industry does not wait to be forced to act.

"The cruise industry should be front runners in introducing new technology and reducing emissions. We simply cannot wait for regulations," Skjeldam said.

Burning dead fish

The biggest challenge for the shipping industry is moving away from heavy fuel oil, a type of diesel used by most of the world's tankers and cargo ships. Battery technology is powering the clean vehicle revolution on land. But fully electric ships are unlikely to be sailing the seas by 2050. Electric batteries cannot store enough energy to propel deep sea vessels traveling long distances, experts say. Low carbon fuel may be the answer, UCL's Smith said.

Many companies are focusing on liquified natural gas (LNG) and biofuels as alternatives. By 2021, Hurtigruten aims to operate a fully hybrid fleet, retrofitting all its 16 ships with a combination of LNG, batteries and biogas. "Almost half our fleet will be literally powered by nature, as we will replace engines with batteries, natural gas and biogas — made from organic waste such as dead fish," Skjeldam said.

The batteries on board the Roald Amundsen kick in whenever there is a surge in energy demand, Skjeldam explained. "We use the batteries to take care of these peaks. When the engines produce excess energy, this is transferred into the batteries. This secures smooth and optimal running of the engines at all time, significantly reducing fuel consumption and emissions," he said. "LNG is substantially less polluting than conventional diesel fuel and utilizing LNG as a component in different hybrid set-ups is a major step towards achieving Hurtigruten's ultimate ambition of sailing emission free," he added.

Biofuel is a better alternative as far as Maersk is concerned. The company recently used a blend of fuels produced from plant waste to help power a container ship traveling from Rotterdam to Shanghai. By using the fuel mix — 20% biofuels and 80% fuel oil — Maersk reduced the vessel's CO2 emissions by 85% or 1,500 tons, the equivalent of what 200 households produce each year. "It's the only option for now," Kornerup told CNN Business.

The challenge of hydrogen

Hydrogen is one of the most promising solutions for companies looking to meet the IMO target as it is clean and suitable for all ship sizes. But this fuel also presents challenges. "The storage of hydrogen is probably the biggest stumbling block. Compressed hydrogen takes 15 times more space compared to diesel for the same amount of energy," CMB CEO Saverys said.

Experts say companies should make the huge leap towards decarbonization by investing in dual combustion systems, which use a combination of diesel and low-carbon fuels, such as hydrogen, or batteries. "At the moment the cheapest way to operate is to continue using an internal combustion engine [which runs on diesel] and liquid fuel like hydrogen or ammonia that you have produced using renewable energy," according to Smith.

Blending fuel is at the heart of CMB's strategy. "Our diesel-hydrogen engines are a natural transition towards hydrogen. Diesel can still be burnt as principal fuel (in case no hydrogen is available), which gives users peace of mind to adopt this new technology," Saverys said.

More companies should adopt transitional solutions, according to CDP. In its report, Carole Ferguson, head of investment research, said companies should focus on "step change innovations." "There are no zero carbon technologies that you can apply on ships today that are viable," said Kornerup. "But we simply need to speed up [innovation] because we only have 11 years."

The biggest barrier to achieving low-carbon shipping is cost. Hydrogen and other low-carbon fuels are much more expensive than diesel. A hydrogen-powered ship costs around $10-$15 million more to build than a diesel vessel, and the investment is hard to justify given the lack of incentives or regulation, according to Saverys.

"The technology is already here," said Smith. "What's lacking is the impetus."