CHINGUETTI, Mauritania (AP) — For centuries, poets, scholars and theologians have flocked to Chinguetti, a trans-Saharan trading post home to more than a dozen libraries containing thousands of manuscripts. But it now stands on the brink of oblivion. Shifting sands have long covered the ancient city’s 8th-century core and are encroaching on neighborhoods at its current edge. Residents say the desert is their destiny. As the world’s climate gets hotter and drier, sandstorms are more frequently depositing inches and feet of dunes onto Chinguetti’s streets and in people’s homes, submerging some entirely. Tree-planting projects are trying to keep the invading...