The global shipping industry will still need to ratchet up its efforts to decarbonize to keep the goals of the Paris Agreement alive.

(Illustration: Kevin Budnik)

An agreement reached by 170 countries on Friday mandates that the shipping industry halve emissions by 2050.

The International Maritime Organization's announcement, which follows weeks of negotiations in London, said the industry must reduce carbon dioxide emissions by at least 50 percent of 2008 levels.

"Today the IMO has made history. While it may not be enough to give my country the certainty it wanted, it makes it clear that international shipping will now urgently reduce emissions and play its part in giving my country a pathway to survival," Hilda Heine, president of the Republic of the Marshall Islands, an IMO member, said in a statement. "This deal helps make every country a little safer, but even with a landmark sectoral cap and clear targets to reduce emissions consistent with the Paris Agreement, we will need to improve it over time in line with the latest science."

Climate advocates note that a 50 percent emissions reduction falls short of the goals of the Paris Agreement, which would require full decarbonization by 2050 in order to keep warming below 1.5 degrees Celsius. Still, the directive marks a critical turning point for the industry, which, as we reported in 2016, was not included in the the Paris Agreement. (That was a major omission: If the industry were a country, it would be the sixth-largest emitter in the world; until now, its emissions were only expected to grow.)

Friday's agreement calls for the shipping industry to pursue strategies for full decarbonization by mid-century. Exactly how the industry will meet these emissions reductions goals is still unclear.

Industry leaders will now face the arduous task of delegating responsibility among the world's countries. International climate negotiations are guided by the principle of "common but differentiated responsibility": Richer, more industrialized nations—which have historically contributed more to climate change—should take a greater lead in combating global warming. That principle is tricky to implement in the shipping industry.

For one thing, shipping emissions are hard to attribute to a single country due to "open registries," in which some countries allow foreign-owned and -operated ships to fly their flags. To use the same example we gave in 2016, "let's say a German ship, flying Panama's flag, with a British captain and a multinational crew, transports goods from China to the U.S. Which country should take responsibility for those emissions?"

For another, the IMO typically applies regulations equally across flag states, but the majority of the global fleet is registered in developing countries. Shipowners have historically used "flags of convenience" to skirt the strictest laws and regulations, and they would likely do the same to avoid tougher emissions standards.

Negotiators have until 2023 to hammer out the details.