The landmark deal – for a polluting industry that has traditionally been resistant to change – includes a standout pledge to reduce its emissions to net zero “by or about 2050.”

The International Maritime Organization (IMO) had earlier pledged to reduce its emissions by half by 2050, so Friday’s agreement is a clear advance.

More importantly, the world’s shipping nations also agreed to interim goals to cut greenhouse gas emissions by at least 20%, aiming for 30 percent by 2030. And by 2040 they aim to cut at least 70%, aiming for 80%.

These targets are below what the Biden administration and other “high-ambition” nations were pushing for.

But the targets announced Friday signal how even the most resistant sectors are being pushed and pulled to help the planet hold future warming to 2.7 Fahrenheit to stave off dramatic sea-level rise and extreme weather events.

Ocean transport contributes about 3% of human greenhouse gas emissions. While that number might not seem like much, if the shipping sector was a country, it would be Germany – among the top 10 global polluters.

Other sectors that are difficult to decarbonize – like cement, steel, and aviation – will probably come under growing pressure to do so now that shipping is getting in line with goals set at U.N. climate conferences in Paris and Glasgow, Scotland.

Environmentalists characterized Friday’s agreement as positive but far from what was needed.

Whit Sheard, an expert in shipping emissions at the environmental group Ocean Conservancy, said the IMO has sent “a strong signal by historically committing to fully decarbonizing the shipping sector but has missed an enormous opportunity to cut emissions immediately.”

The United States and other countries were pushing for deeper cuts in shipping emissions much sooner.

“Caving to fossil fuel interests in the short term leaves a lot of work for industry and individual countries in the face of a global climate crisis,” Sheard said.

While the United States set high goals for those reductions, other countries have been more resistant, including Saudi Arabia, Russia, China, and Brazil.

Almost every import in an American home and garage arrives by ship – cars, appliances, furniture, clothes – and, increasingly, a lot of the food in the kitchen, such as steak from Argentina or bananas from Colombia.

About 90% of the world’s trade travels by ship, a ceaseless movement of 60,000 vessels plying their routes and moving 11 billion tons of goods each year.

The shipping industry – vital for trade but fiscally conservative, and international but greatly influenced by a small number of magnates in a handful of countries – plays a large role in climate change. It is traditionally a dirty sector, as most ships still burn heavy fuel oil.

IMO secretary-general Kitack Lim called the new targets “a monumental development” that “opens a new chapter toward maritime decarbonization.”

But he acknowledged the disappointment that more wasn’t promised. “It is not the end goal,” he said. “It is in many ways a starting point for the work that needs to intensify even more over the years and decades ahead of us.”

John Maggs, president of the Clean Shipping Coalition, representing environmental groups pushing for greater reductions in emissions, said: “There is no excuse for this wish-and-a-prayer agreement. The level of ambition agreed is far short of what is needed to be sure of keeping global heating below 1.5 Celsius, and the language seemingly contrived to be vague and noncommittal.”

Observers at the meeting said the officials from small nations were crucial in making the case for higher ambition.

“We fought tooth and nail for these numbers. They aren’t perfect, but they give us a shot at staying within 1.5°C. And that’s what we came here to do,” said Carlos Fuller, permanent representative of Belize to the United Nations.

The IMO described the deal as “historic” and said the “carbon intensity” of ships is expected to decline over time with new technologies.

One possible solution would be to outfit cargo vessels with “sails” mounted on their decks. These wouldn’t be traditional canvas managed by ropes but could wind up as giant kites, spinning rotors, or telescoping hard sails – like a folding airplane wing – that harness wind power to propel the vessel.

Another way for ships to immediately reduce emissions would be to slow down – essentially adhering to new voluntary “speed limits” in the ocean. Modern cargo vessels are capable of doing 25 knots. Soon, they may be “slow-steaming” at half that speed.

To meet the 2040 and 2050 goals, the industry will need to transition to alternative shipping fuels, such as ammonia and green hydrogen. Changing fuels requires a massive investment – new engines, new port infrastructure, and a steady supply of fuels.

Some companies are already beginning the transition. The A.P. Moller-Maersk shipping company recently announced it is deploying its first methanol-enabled container vessel. A company in Norway is retrofitting a pair of tugboats in a pilot test to run the ships on ammonia. In Scotland, the government has committed to running some regional ferries on green hydrogen that would be created with energy supplied by offshore wind power.