NEW DELHI — Global warming appears to have finally resolved a dispute that gunboats never could: An island located midway between India and Bangladesh that became a flashpoint for military threats in the 1980s is now submerged under the rising seas.

The Bay of Bengal island, which India called New Moore Island and Bangladesh referred to as South Talpatti, has ceased to exist, the Jadavpur University’s School of Oceanic Studies declared this week.

Sugata Hazra, the program director, said he started looking at satellite imagery recently after reading media claims that the island, which peaked at 1.3 miles long and 1.1 miles wide, was actually growing in size. Close examination failed to reveal anything. He then checked with local fishermen.

“They confirmed the island had gone sometime back,” he said. “We raised the alarm that we’d better take stock of how much loss is occurring.”

The tiny island was first noticed after a severe cyclone in the early 1970s. Both countries soon laid claim amid speculation there might be oil or natural gas beneath its sandy shores.

No permanent structures were ever built on it, but in 1981 India sent gunboats and its coast guard members planted a flag. As soon as India’s boats sailed away, security experts said, Bangladeshis would take the flag down.

The island actually began shrinking in the 1990s, part of an 81-square-mile reduction in land mass witnessed in the Bay of Bengal’s Sunderbans mudflats over the past 40 years, Hazra said. Another 27 square miles has been lost to erosion.

In the 1990s, the island was only about 6 feet above sea level, part of a low-lying delta extremely vulnerable to rising seas.

As for climate change and the future, a U.N. panel predicted that 17 percent of Bangladesh will vanish by 2050, displacing 20 million people, if water levels rise by 3.3 feet, as some predict.

“There’s a lesson here that the world should learn while negotiating over territory,” Hazra said. “It’s not whether some country makes a gain. It’s whether we all collectively win or lose given the impact we’re seeing on the global environment.”

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