Around 1.4 billion people could be climate refugees by 2060, driven from low-lying coastal cities due to rising sea levels, says a new study.

By 2100, the global population may reach 11 billion and there could be 2 billion climate refugees, it says.

To feed those 9 to 11 billion people expected in the second half of the century, farmers will have to grow as much food in 40 years as they have grown in the last 8,000 years or so.

"The colliding forces of human fertility, submerging coastal zones, residential retreat, and impediments to inland resettlement are a huge problem," Charles Geisler, professor emeritus of Development Sociology at Cornell University in New York, was quoted as saying.

In any concerted attempts to contain the climate change and limit global warming, climate scientists have to consider two major aspects -- how to reduce use of fossil fuel drastically and how to ensure most efficient use of the land surface so it consumes atmospheric carbon dioxide.

Professor Geisler and his co-author Ben Currens, an earth and environmental scientist at the University of Kentucky, stressed the need for viewing the larger picture of land use in the long term.

In their report in the journal “Land Use Policy”, they considered the implications of an ever faster rate of global sea level rise, as atmospheric temperatures rise and glaciers melt.

A study in Nature Climate Change has just confirmed that the seas that were rising by on average 2.2 millimetres a year in the last century, are now rising by 3.3 millimetres a year.

"Although reclaiming land from oceans has been an important human project for millennia," write Geisler and Currens in their study, "it seems that oceans are now 'reclaiming' the land."