There's little doubt that slashing shipping's greenhouse gas emissions over the decades will require development of low-carbon and zero-carbon fuel technologies, not to mention a build-out of a supply chain to feed the vessels that use them.

But there are concerns that the focus on fuel is overshadowing the role that other technologies and operational measures will play in decarbonising the maritime sector.

As world leaders prepare to meet for the COP26 climate conference in Glasgow, transition to zero-carbon fuels is at the heart of calls urging the International Maritime Organization to adopt more ambitious targets.