In October 2016 the International Maritime Organization issued new rules for reducing sulfur in the heavy ship fuel called bunker oil. Sulfur emissions figure heavily in both greenhouse gases and acid rain. Sulfur content in diesel fuel for on-road and off-road engines have already been in place for years, so the marine bunker mandate is not a surprise. The timing however, was a major shock. The new low level, 0.5 parts per million (ppm), takes effect in 2020. Most ship owners and refiners expected the date to be 2025.
The mandate has a provision for ships to burn conventional bunker with sulfur, if a scrubber is installed. At present that is not simply like replacing a muffler on a car. Rather, it is heavy engineering on the ship in the engine room, including storage for the resulting sour water to be discharged at port.
Ship owners could also convert to marine diesels, either direct or electric drive, or to compressed or liquefied natural gas. Enforcement is also going to be a challenge. The oceans are vast, and there are hundreds of ports without a regulatory presence.