The airstrip at Lokichoggio, in the scorched wastes of north Kenya, was once ground zero for food aid. During Sudan’s civil war, flights from here kept millions of people alive. The warehouses are quieter now, but NGOs keep a toehold, in case war restarts — and to deal with what pundits call the “permanent emergency” of “environmentally induced” migration.

Take the local Turkana people. Their numbers have surged in recent decades, and will double again before 2040. But as the area gets hotter and drier, it has less water, grazing and firewood. The drought cycle in northern Kenya has gone from once every eight years to every three years and may contract further. That means no recovery time for the Turkana and their livestock; the result is an increasingly frantic drift from one dry place to another.

A local crisis with local causes? Only partly. Scientists think it is part of a global phenomenon: people across the world on the move as a result of environmental degradation. Just how many are moving, or about to move, is maddeningly unclear.

The International Organisation for Migration thinks there will be 200m climate-change migrants by 2050, when the world’s population is set to peak at 9 billion. Others put the total at 700m.

These startling numbers may conjure up a picture of huge, desperate masses, trekking long distances and if necessary overrunning border defences because their homelands have dried up or been submerged. But at least initially, the situation in Kenya and other parts of east Africa is likely to be more typical: an already poor population whose perpetual search for adequate pasture and shelter grows harder and harder. In such conditions, local disputes — even relatively petty ones between clans and extended families — can easily worsen, and become embroiled in broader religious or political fights. And that in turn makes it harder for everybody in the area to survive, and more desperate to find new places to live, even if they are not far away.

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