Right now, most shipping (i.e., ocean vessels) relies on fossil fuels. And, shipping is the primary engine behind the world’s economy. (There are more than 100,000 ships weighing more than 100 tons plying our oceans every year.) And, fossil fuels will remain the fuel of choice for a while, since the International Maritime Organization (IMO), a United Nations agency that governs international shipping, relies on countries like Saudi Arabia to fund its green ships initiative.