Calcutta, Oct. 29: Islands in the Sunderbans are disappearing, submerged by rising sea levels. A dozen will disappear within the next decade, scientists here forecast.

Two islands — Lohachara and Suparibhanga (also called Bedford) — have already vanished over the last three decades.

The rising sea levels are a result of increasing temperatures or climate change across the globe, scientists say.

Some 10,000 people fled their homes over the last decade as the two Sunderbans islands slowly sank into the sea. The islands form part of the UN world heritage site of the mangrove forests, famous for the Bengal tiger.

Sugata Hazra, head of the School of Oceanographic Studies at Jadavpur University, has reported the alarming trend in a study commissioned by the Union environment and forests ministry.

“The sea levels could go up by 3.5 mm a year over the next few decades. This could wash out 15 per cent of the islands, displacing a further 70,000 people,” he told The Telegraph.

The report has been sent as a national communication to the UN Framework Convention on Climate Change.

The inhabitants are likely to join the first wave of “envirogees” (environment refugees) on one of the largest islands, Sagar, which itself runs a high risk of sinking gradually. Other vulnerable islands include Dulibhasani, Namkhana, Ajmalmari and Dalhousie.

The influx is swamping the original inhabitants of Sagar, putting pressure on the island’s fragile resources. Sagar receives lakhs of people during the annual Gangasagar mela pilgrimage in January.

Hazra’s study, yet to be made public, shows that the islands also face the threat of large-scale land erosion because of increasing salt content in the soil. This is gradually depleting the soil-binding mangroves and could eventually flood the entire island conglomerate.

Officials of the Bengal government, however, say the study cannot directly be linked to climate change. Atanu Raha, director of Sundarban Biosphere Reserve, said the islands were getting eroded by oceanic currents, not by rising sea levels.

“Erosion and accretion are natural phenomena. Across the world islands submerge and new ones emerge. This is natural,” Raha said.

He argued that people displaced by rising sea levels — the envirogees — couldn’t be called refugees in the first place. According to him, most of them are illegal immigrants from Bangladesh who settled on these islands decades ago.

“However, since any benevolent government must have a policy for immigrants, we must improve agriculture and livelihood resources for them. But we must also keep in mind that any place has a carrying capacity beyond which it can’t accommodate.”