When the tide comes in, sea water laps at the top of a mud embankment that towers 6 metres (20 feet) above Alauddin's adjacent house and is all that keeps it from being washed away.

After a 10-year study in and around the Bay of Bengal, oceanographers say the sea is rising at 3.14 millimetres a year in the Sunderbans against a global average of 2 mm, threatening low-lying areas of India and Bangladesh.

"At least 15 islands have been affected but erosion is widespread in other islands as well," said Sugato Hazra, an oceanographer at Jadavpur University in Kolkata, the capital of West Bengal.

A United Nations climate panel, which grouped 2,500 scientists from 130 countries, concluded last month that human activity was causing global warming and predicted more droughts, heatwaves and rising seas.

But for the Sunderbans, made up of hundreds of islands and criss-crossed by narrow water channels and home to many of India's dwindling tiger population, the threat is more immediate.

"The crops have failed due to scanty rainfall but where do we go?" says Alauddin as his family of twelve stares at their parched farmland.

A combination of drought and then heavy rainfall this year and increasing soil salinity have made it impossible to grow enough food to survive on traditional agriculture alone.

"We now depend on fishing in the high seas and sometimes even eat leaves from different plants to survive," a frail-looking Jameel Mullick said.

At least 4 million people live in the islands spread across 9,630 sq. km (3,700 sq. miles) of mangrove swamps.

TIGERS THREATENED

Top climate experts on the UN panel predicted that temperatures would increase by between 1.8 and 4 Celsius (3.2 and 7.8 Fahrenheit), and sea levels would rise by between 7 and 23 inches (18 and 59 centimetres) to submerge islands in the 21st century.

The impact could be even greater if ice sheets in Antarctica and Greenland thaw.

The 400 or so families living on tiny Moushuni know what is coming.

Two nearby islands disappeared beneath the sea after residents were forced to leave, and the sea has swallowed about 100 sq. km of mangrove forest in three decades in the Sunderbans.

"Global warming and rising sea levels are already having a telling effect on the tiger's habitat," said Pronobes Sanyal of the National Coastal Zone Management Authority.

Rapid erosion over the last five years has destroyed mangrove cover up to 15 metres inland on several islands, environment experts say.

SALT AND SORROW

For centuries, the mangroves fed on both saline and fresh water -- tides brought sea water upstream and mixed it with water from the Ganga and Brahmaputra rivers.

But now rising sea levels are pushing salt water inland.

Sixty year old Ayesha Khatoon stood on top of a mud embankment in Moushuni that has been breached at least seven times in the past 10 years.

"There was a lovely mud road surrounded by trees beyond this embankment and we had 3 acres (1.2 hectares) of farmland which the sea swallowed in the last few years," recalled Ayesha.

"No one visits us now and they have left us all to die," she said, tears welling in her eyes as she hugs her young grandson.

Rapid felling of trees on the islands -- in part to fuel two small power plants -- is adding to erosion woes.

Dilip Maity, a farmer, lamented how he had erred in hacking down several rows of trees, an act which weakened and led to sea water flooding his small farm.

Alarmed, West Bengal's minister for the Sunderbans, Kanti Ganguly, said the islands had to be protected.

"We have realised it now and have taken a decision to raise heights of the mud embankments and increase mangrove cover in Sunderbans," he said.