Since 2010 an estimated 1.5 million people have left sub-Saharan Africa for Europe and the US, according to a study released last year by the Pew Research Center. Pew also surveyed respondents in six countries about plans to migrate. Senegal ranked highest, with 44 per cent of those asked saying they planned to move to another country within five years. So many here have embarked on the often-perilous journey that there is a phrase for it: ‘Get to Europe or die trying.’

Ibra Ndaw, 32, was one of the young men to go in search of a new life. A struggling taxi driver in the city of Touba, in 2016 he decided to leave his wife of seven years, Fali Ndiaye, and two young children to travel to Europe and raise money for his family. Holding their wedding photograph in shaking hands, Fali Ndiaye describes how she received a phone call from one of his travelling companions, who said the boat to Italy her husband had been on had capsized in the ocean, and most of those on board – including Ibra – had drowned. ‘I will never forget the day of that phone call,’ she says. ‘I feel so lonely without him.’

Often they leave with no word of warning. Bamba Samb, a 29-year-old tailor from Dahra, a town an hour or so north of Touba, vanished in 2016 without telling his family. He too drowned in the Mediterranean en route to Italy. Like thousands of others his body has never been recovered. ‘I think about him every day,’ says his father, Abdou. ‘Every parent is worried their son will be next but what can we do? Climate change has really affected people here. That is why all our young people try and find jobs somewhere else.’

Will a tree ever stand in their way? Colonel Sarr is insistent that in time the Great Green Wall can do more than any barrier to dissuade his countrymen from fleeing. ‘There is a philosophy that says first there were trees, then there was man and then there was the desert,’ he says. ‘It depends on us now. But a tree can be a powerful thing.’

greatgreenwall.org

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