Heavy fuel oil (HFO) is the predominant marine fuel. It is viscous, dirty, inexpensive and widely available. Because of its high sulfur content, maritime shipping accounts for 8% of global emissions of sulfur dioxide (SO₂), making the industry an important source for acid rain as well as respiratory diseases.

IMO Secretary-General Kitack Lim welcomed the decision which he said reflected the Organization’s determination to ensure that international shipping remains the most environmentally sound mode of transport.

Further work to ensure effective implementation of the 2020 global sulfur cap will continue in the Sub-Committee on Pollution Prevention and Response (PPR).

Regulations governing sulfur oxide emissions from ships are included in Annex VI to the International Convention for the prevention of Pollution from ships (MARPOL Convention). Annex VI sets progressive stricter regulations in order to control emissions from ships, including sulfur oxides (SO_x) and nitrous oxides (NO_x)—which present major risks to both the environment and human health.

The date of 2020 was agreed in amendments adopted in 2008. When those amendments were adopted, it was also agreed that a review should be undertaken by 2018 in order to assess whether sufficient compliant fuel oil would be available to meet the 2020 date. If not, the date could be deferred to 2025. That review was completed in 2016 and submitted to MEPC 70. The review concluded that sufficient compliant fuel oil would be available to meet the fuel oil requirements.

Under the new global cap, ships will have to use fuel oil on board with a sulfur content of no more than 0.50% m/m, against the current limit of 3.50%, which has been in effect since 1 January 2012. The interpretation of “fuel oil used on board” includes use in main and auxiliary engines and boilers. Exemptions are provided for situations involving the safety of the ship or saving life at sea, or if a ship or its equipment is damaged.

Ships can meet the requirement by using low-sulfur compliant fuel oil. An increasing number of ships are also using gas as a fuel as when ignited it leads to negligible sulfur oxide emissions. This has been recognized in the development by IMO of the International Code for Ships using Gases and other Low Flashpoint Fuels (the IGF Code), which was adopted in 2015. Another alternative fuel is methanol which is being used on some short sea services.

Ships may also meet the SO_x emission requirements by using approved equivalent methods, such as exhaust gas cleaning systems or “scrubbers”, which “clean” the emissions before they are released into the atmosphere. In this case, the equivalent arrangement must be approved by the ship’s Administration (the flag State).

The new global cap will not change the limits in SO_x Emission Control Areas (ECAS) established by IMO, which since 1 January 2015 has been 0.10% m/m. The ECAs established under MARPOL Annex VI for SO_x are: the Baltic Sea area; the North Sea area; the North American area (covering designated coastal areas off the United States and Canada); and the United States Caribbean Sea area (around Puerto Rico and the United States Virgin Islands).