Gloom abounds. James Lovelock, an environmental guru, posits a collapse in human population, in part related to migration, with a few “lifeboat” regions surviving. Then there is the pace of social change. The number of “megacities” — with populations in the tens of millions - may grow to several hundred by the middle of the 21st century. Most are poorly planned.

Would a migrant from a collapsed city receive aid? “We’ve not experienced anything of this kind, where whole regions, whole countries, may well become unviable,” says Jeffrey Sachs, head of Columbia University’s Earth Institute.

No wonder strategists see vast new security risks, and a big expansion in the world’s “ungoverned spaces”. But much can be done before the exodus turns biblical. In West Africa subsistence farming is badly irrigated. Improve that, throw in some seeds and fertiliser, scrap tariffs, build warehouses and roads, and the region may beat the worst of climate change.

Geographers at UN Habitat, a city-planning agency, say conurbations must adapt to the needs of climate-change migrants. “You can’t just stockpile people,” says Alex de Sherbinin of Columbia University. The pressure is tangible in Addis Ababa, which already has teeming slums. The price of teff, a staple, has surged after a famine that is still pushing people to the city. Mr Meles is not alone in his wrath.

© The Economist Newspaper Limited 2009