With today's trading merchant fleet now numbering 74,505 ships — according to the Bimco ICS Seafarer Workforce Report 2021 — the vast majority of emissions reductions needed to meet the International Maritime Organization's 40% cut in greenhouse gases by 2030 will have to come from improving the performance of existing vessels.

Often, more efficient fuel consumption and lower emissions are considered two sides of the same coin.

But even where "slow steaming" has appeared to show shipping economics and environmental objectives converging, going slow is no panacea: it also means steaming for longer, less efficient part load engine operation and, effectively, more emissions per rpm.