This raises the horrors of a "wholesale relocation of populations" which in turn will raise fundamental questions about citizenhood and nationality. Once land has been lost, will a residual nationality be able to continue, or will we have to create a new category of "world citizens"if many lands are lost permanently?

The concept of the world citizen would also acknowledge the fact that climate change is a collective problem and requires a collective solution. Again, in the event of full-scale national evacuation, what happens to an abandoned country's exclusive economic zone, its territorial waters and nationhood?

Few things could be more sensitive than carving out new territory to create space for a nation.

Also, in such a scenario, what about the "waves of environmental refugees that spill across borders with destabilizing effects" on domestic order and international relations?

Population movement can have significant negative impacts on the natural environment. Refugee crises in Burundi, Rwanda and Somalia have highlighted the devastating impact large-scale population displacement can have on the environment and resources in neighboring countries of refuge.

The Impact of Dying cities
Another issue is that of cities no longer proving sustainable. For example, Quetta In Pakistan was originally designed for just 50,000 people. Today, it has 1 million plus inhabitants. All of whom depend on 2,000 wells pumping water deep from underground, depleting what is believed to be a fossil or nonreplenishable aquifer. Experts say that Quetta may have enough water for say a decade. After that, in the words of a water assessment study, Quetta will be "a dead city."

With most of the nearly 3 billion people to be added to the world's population by 2050 living in countries where water tables are already falling and where population growth swells the ranks of those sinking into hydrological poverty, water refugees are likely to become commonplace.

They will be most common in arid regions where populations are outgrowing water supply. Even Indian villages have been abandoned because overpumping had depleted the local aquifers and villagers could no longer reach water. Millions in China and in parts of Mexico may have to move because of a lack of water.

Relocating Squatter Cities
When a city is dying, the first to be hit could be the squatter cities. In Bangkok, rising sea levels would cost an additional $ 20 million per year in pumping costs alone. Costs for relocating displaced squatter communities would be astronomical. In Shanghai, up to a third of the city's 17 million inhabitants would be flooded, displacing up to 6 million people. Singapore, one city with a comprehensive planning culture, has nothing in its latest 50-year master plan to deal with a one-metre sea-level rise.

The Spreading of deserts
Spreading deserts are also displacing people. In China, where the Gobi Desert is growing by 10,400 square kilometers a year, the refugee stream is swelling. An Asian Development Bank assessment in Gansu province identified 4,000 villages that face abandonment.

As the desert takes over, farmers and herdsmen are forced to move, squeezed into the shrinking area of habitable land or forced into cities.

The refugee flows from falling water tables and expanding deserts are just beginning.

All these factors taken together do not augur well and the environmental refugees of tomorrow could be both from villages and cities.