By Amitabha Bhattasali
BBC News, Calcutta
A Greenpeace report on climate change says that if greenhouse gas emissions grow at their present rate, South Asia could face a major human crisis.
The Indian coastline is 'extremely vulnerable'
"More than 120 million people from India and Bangladesh alone will become homeless by the end of this century," the report says.
It estimates that 75 million people from Bangladesh will lose their homes.
It predicts that about 45 million people in India will also become "climate migrants".
The report says that the number of people who could be affected by climate change is almost 10 times greater than the number of people who migrated during and after the partition of India in 1947.
Around 130 million people now live in India, Pakistan and Bangladesh in what are called low elevation coastal zones, which comprise coastal regions that are less than 10m above average sea level.
"There is already plenty of evidence to suggest that the average global temperature rise we have already experienced is associated with substantial changes in weather patterns over recent decades," the Greenpeace report says.
"Droughts have become more common since the 1970s. The frequency of intense tropical cyclones has also increased and there has been widespread retreat of mountain glaciers."
It is argued that India's weather is becoming less predictable
The study says that "if global temperatures rise by about 4-5C in the course of the century - as they are projected to - the South Asian region could face a wave of migrants displaced by the impact of climate change".
"Most of these people will be forced to leave their homes because of the sea-level rise and drought associated with shrinking water supplies and monsoon variability. The bulk of them will come from Bangladesh as most of the parts of that country will be inundated," Dr Sudhir Chella Rajan, a climate expert and author of the study, told the BBC.
"And Bangladesh is already experiencing the migration," says an activist from Bangladesh, Mohon Kumar Mondol.
"Though Bangladesh is hardly responsible for the global warming and climate change, the Bangladeshi people are paying the price for it - they have never heard of these terms but are suffering from them."
The report says the Indian coastline is also extremely vulnerable.
Greenpeace has long campaigned in India
Several large cities within the low elevation coastal zone like Bombay (Mumbai) and Madras will go under the sea if the present growth rate of greenhouse emissions continue.
The report says that while huge investment is being made along the coast line of India, most of these projects are in the danger zone.
"This isn't going to happen gradually. What we are going to see is a series of coastal surges, you will see inundation, salt water intrusion - which will cause lots of harm and devastate a lot of these infrastructures," said Dr Rajan.
According to the Greenpeace report, major population movement from the coastal cities to other large urban centres like Delhi, Bangalore and Ahmedabad will take place.
"These cities will have serious resource constraints of their own by the middle of the century, but will have to be prepared to accommodate enormous numbers of migrants from the coasts."