From a size of 6,400 square kilometres (3,968 square miles) in 1965, Bhola island near the mouth of the Bay of Bengal is now only half its original size.

If the erosion continues at the same rate, it will completely disappear over the next four decades, said Mohammad Shamsuddoha, who carried out the research for the Dhaka-based non-governmental organisation The Coast Trust.

River erosion is a perennial problem in Bangladesh which is criss-crossed by a network of 230 rivers.

But Shamsuddoha said rising sea levels were responsible for the erosion of coastal islands such as Bhola that were not previously vulnerable to the problem.

"The erosion of Bhola island only started in the 1960s. Before that the size was stable and only a small amount of erosion took place on one side," he told AFP.

"But from the mid-1960s the erosion began and the rate has accelerated over the years," he said.

The government estimates that six million people out of the country's 140 million population, are displaced each year due to river erosion.

The study, entitled "Climate Change, Disaster and the Bangladesh Coastline", used satellite images and archive maps dating back to the 1950s to assess the loss of land.

It concludes that rising sea levels caused the Bhola erosion by creating stronger currents in the rivers surrounding the island.

"As a result (of the rise in sea levels), river currents have become fiercer at the mouth of the sea, continuously undercutting the land masses of the isles situated on estuaries," he said.

Bhola, one of six southern islands, is home to 1.6 million people. It is bordered on one side by the Meghna river and on the other by the Tetulia river.

Last year scientists in neighbouring India warned that the country's coastal areas could see a rise in sea levels of about half to one metreto 3.3 feet) by 2020.

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