Part 3 of 10: Realizing a Hydrogen Economy Series International seaborne transportation is a primary driver of international trade and the global economy, with approximately 80 percent of global trade by volume carried by ships at sea. The shipping sector has experienced steady growth for decades, although carbon dioxide (CO 2) is the primary greenhouse gas (GHG) emitted from marine shipping. In 2012, CO 2 and GHG emissions from international shipping were estimated to be around 2.1 percent and 2.2 percent of global emissions, respectively. The International Maritime Organization (IMO) has since developed an initial GHG strategy that sets goals that international shipping should reduce total annual GHG emissions by at least 50 percent by 2050 with zero emissions