A century turned, bringing back familiar ghosts. They haunted our newspapers. Millions of Africans beginning the desperate and long walk from their croplands and pastures turned to scrub by drought. The bleaching bones of their dead cattle receding behind them.

According to the Red Cross, 2000 and 2001 were the two worst years for natural disasters ever recorded. As the engine of global warming gets going, floods and droughts will increase – both threatening our ability to grow food. For Africa the forecast is mainly dry.

At the end of last year the UN’s World Food Programme sent out an alert that nearly 40 million people were at risk of hunger in the Horn of Africa and in the South. Whereas poverty and inequality, conflict, political ineptitude and the toll of aids on farm workers all contributed to the looming famine in some countries, drought was the cracking whip.

Rainfall has been declining year on year in the Saharan region. The only zone of safety has been the humid tropical belt of Central and West Africa. But even here population pressures and climate stress are predicted to transform abundance into vulnerability (see graph).

If nothing is done to counter climate change the biggest losers in terms of water shortages and subsequent food deficits are predicted to be northern Africa, the Middle East and the densely populated Indian subcontinent. The arid and semi-arid regions of southern Africa where food production is a challenge at the best of times are especially at risk. Warmer temperatures could trigger steep declines in crop yields and unpredictable rainfall could damage the hydrological cycle.

Climate models have come up with percentages of people at increased risk of hunger in Africa by 2050 – and they aren’t small percentages either. But the human faces of the tragedy are visible already, with the poorest people at the back of the water queue.