Guest Blog by S. A. Shelley: For almost all of human history, trade has been facilitated by water borne craft. Mesopotamia? They had boats on the rivers and in the gulf. Egypt? Boats on the river. Rome? Boats hauling grain from Egypt to Rome. China?  The Chinese were sailing and trading along East Asia for thousands of years.  By the time of the Clipper ships, naval architects had mastered wind power such that a clipper ship could make a transatlantic voyage in about 12 days . A modern fossil-fueled container ship can make the same voyage in about 8 days.  By 2018 goods carried on ships amounted to nearly 11 billion tonnes with some economists estimating that between 80% to 90% of all goods produced globally travel by ships across some water at some stage of production.

Ships today tend to be powered by fossil fuels, and when looking at the amount of CO2 emitted per tonne of cargo moved per kilometer, ships are by far the most efficient way to move goods (Fig. 1).