"Worse things happen at sea, or so the saying goes. And it rings true in the context of emissions: while countries bring in bans on petrol and diesel on land, at sea, ships are still permitted to run around on heavy fuel oil, a tar-like substance that belches out toxic pollution as well as carbon dioxide.

According to the European Commission, the shipping industry accounts for around two per cent of global CO2 emissions, which is more than Germany’s contribution. With the industry hitherto not obliged to comply with the Paris agreement, concerns abound that shipping could be a drag on emissions targets."

https://www.positive.news/economics/a-new-dawn-for-wind-powered-shipping/