For centuries, it’s been treasured in kitchens in Asia and neglected almost everywhere else: those glistening ribbons of seaweed that bend and bloom in cold ocean waves.

Today, seaweed is suddenly a hot global commodity. It’s attracting new money and new purpose in all kinds of new places because of its potential to help tame some of the hazards of the modern age, not least climate change.

In London, a startup is making a plastic substitute out of seaweed. In Australia and Hawaii, others are racing to grow seaweed that, when fed to livestock, can cut methane from cow burps. Researchers are studying how much carbon dioxide can be sequestered by seaweed farms as investors see a new source of carbon credits for polluters to offset greenhouse gas emissions.

And in South Korea, one of the most established seaweed-growing countries in the world, farmers are struggling to keep up with growing export demand.

What was mainly a relatively small Asian industry is now coveted by the West. Far beyond South Korea, new farms have cropped up in Maine, the Faeroe Islands, Australia, even the North Sea. Globally, seaweed production has grown by nearly 75% in the past decade. The focus is moving far beyond its traditional use in cuisine.

But even as its champions see it as a miracle crop for a hotter planet, others worry that the zeal to farm the ocean could replicate some of the same damage to farming on land. Much is unknown about how seaweed farms, particularly those far offshore, can affect marine ecosystems.

Seaweed is itself feeling the impact of climate change, particularly in Asia.

“The water is way too hot,” said Sung-kil Shin, a third-generation seaweed farmer, as he pulled his boat into harbor one morning on Soando Island, just south of the South Korean mainland.

Shin, 44, grows a red kelp species called pyropia, which favors cold water during its growing season — but since 1968, the waters where he farms have warmed by 2.5 degrees, slightly higher than the global average. So he has been going further and further from shore in search of chilly waves.

By mid-April, Shin said, the water isn’t as cold as pyropia likes. His yield has suffered.

Steve Meller, an American businessman in Australia, grows seaweed in giant glass tanks on land — a red seaweed native to the waters around Australia called asparagopsis, which beef and dairy companies are eyeing as a way to meet their climate goals.

A sprinkle of asparagopsis in cattle feed can cut methane from their burps by between 82% and 98%, according to several independent studies. Cattle burps are a major source of methane.

Seaweed farms are a far cry from the rows of corn and wheat that make up monoculture farming on land. But even as they signify new opportunities, they present ecological risks.

They could block sunlight to creatures who need it below. They could scatter plastic buoys in the sea, which already suffers from too much plastic. They could leave their plant detritus on the seafloor, altering the marine ecosystem.

“It needs to be carried out with a great deal of care,” said Scott Pillias, a doctoral student in economics who studies marine systems at the University of Queensland. “We shouldn’t expect seaweed to save us.”