"We're in a hurry trying to identify which fuels shipping must use to become climate neutral by 2050."
So says Anders Erlandsson, a maritime professor at DTU Construct and affiliated with DTU Maritime Center.
Even after many years of global research into green alternatives, there is still no convincing candidate ready to replace shipping fossil fuels, explains Anders Erlandsson.
Nor does it help in the green transition of shipping that it currently lacks broad international support. In the autumn of 2025, a majority in the UN's shipping agency, the International Maritime Organization (IMO), voted to pause negotiations on the 2050 target for a year.
Must be ready by 2030
But it's urgent to find solutions that can lower shipping's carbon emissions, because if the entire global fleet is to be converted to climate neutrality by 2050, the shipping companies must know which solutions to invest in no later than in four years, says Anders Erlandsson, who elaborates:
"If you convert five per cent of the fleet annually, it will take 20 years to convert the entire fleet. This means that the ships that leave the shipyards already in 2030 must, in principle, be ready for green propulsion if shipping is to be climate neutral by 2050."
But the question remains what the shipping companies should invest in—ammonia engines, methanol, or electricity, to name just some of the many possible solutions. The right solution depends on multiple factors, including the size of the vessel and whether it is an ocean-going vessel or just a ferry that sails in inland waters, says the professor.
"Small vessels can be electrified, but the large ocean-going container vessels cannot, because it requires so many batteries that there will be no room for the containers," says Anders Erlandsson.
Dilemma of biofuels
There is a low-hanging fruit, namely biofuels—i.e. fuels produced from biomass. Biofuels are attractive because they fit the standard fuel specifications, which means they can be used without significant adjustments to, e.g., engines, fuelling, or storage. But biofuels put us in a dilemma, Anders Erlandsson points out:
"If there's insufficient biomass to produce biofuels for the global fleet, then the question is whether it is sustainable for our planet to use land for growing biomass to get enough for fuel. Areas that we may or may not need for food production because they are covered by rainforest. Biomass should therefore be regarded as a limited resource and is probably not suitable to meet shipping demand for energy."
Unrealistic climate targets
Anders Erlandsson predicts that we will see combinations of solutions in the attempt to achieve climate-neutral shipping.
Some will combine green technologies such as sails or power to reduce fossil fuel consumption. Others will combine conventional fuels with fuels that have lower carbon emissions such as bio-based LNG (liquefied natural gas) or biofuels.
Some will exploit carbon capture, and others may again use nuclear power if smaller reactors are developed for this purpose. Either way, we still have a long way to go before we can achieve 100% CO2-neutral shipping, says Anders Erlandsson:
"As things stand, I think it's unrealistic to believe that shipping by 2050 will be 100% climate neutral. My optimistic guess is that by 2050 the ships may be 80 per cent climate neutral."
