A massive 125 million people may be displaced in India and Bangladesh by a rise in the sea level triggered by a projected four-five degrees Celsius increase in global temperature this century.

Painting the grim picture, a report released by independent environment watchdog Greenpeace on Tuesday said that Bangladesh, Pakistan and India have almost 130 million people living in the Low Elevation Coastal Zone who will be the most vulnerable to sea-level rise and coastal erosion as well as drought.

"We need to keep in mind as well that the bulk of the 75 million people from Bangladesh are very likely to seek refuge in India," the report, authored by S Chella Rajan, professor of humanities and social sciences at IIT, Chennai, said.

"Looking at India and Bangladesh alone, approximately 125 million migrants, comprising about 75 million from Bangladesh and remaining 50 million from densely-populated coastal regions and other vulnerable parts of India, could be rendered homeless by the end of this century," the report said.

To minimise the impact, the report suggested, "India should seek policy options that are proactive in terms of developing international strategies to reduce the risk of destructive climate change."

In the event of such a climate change, large coastal cities such as Mumbai and Kolkata will witness an average elevation sea level of 2-10 metres.

"Major population is likely to move from these cities as well as other coastal mega cities like Chennai to other large urban settlements."