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On a tributary of the Hudson River, a tugboat powered by ammonia eased away from the shipyard dock and sailed for the first time to show how the maritime industry can slash planet-warming carbon dioxide emissions.

The tugboat used to run on diesel fuel. The New York-based startup company Amogy bought the 67-year-old ship to switch it to cleanly-made ammonia, a new, carbon-free fuel.

The tugboat's first sail on Sunday night is a milestone in a race to develop zero-emissions propulsion using renewable fuel. Emissions from shipping have increased over the last decade—to about 3% of the global total according to the United Nations—as vessels have gotten much bigger, delivering more cargo per trip and using immense amounts of fuel oil.

CEO Seonghoon Woo said he launched Amogy with three friends to help the world solve a huge, pressing concern: This backbone of the global economy has not started to transition to clean energy yet.

"Without solving the problem, it's not going to be possible to make the planet sustainable," he said. "I don't think this is the problem of the next generation. This is a really big problem for our generation."

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