Ninety percent of world trade is transported by ships at sea. Traditionally this has been considered a greener method of transport than road or air, but toxic pollution from ships kills tens of thousands of people every year.
The Port of Gothenburg, Scandinavia's busiest shipping hub, is pioneering a number of methods to mitigate the effects of pollution from ships.
From plugging ships into onshore green energy supplies so they do not have to burn fuel whilst in dock, to pioneering a new 'sniffer' technique which monitors passing ships' sulphur emissions.
Nick Clark travels to Sweden to see how the Port of Gothenburg is cleaning and greening its act and laying down the environmental gauntlet to other ports around the world to clean up our sea air.