The coastal Nigerian community of Ayetoro was founded decades ago and nicknamed “Happy City,” meant to be a Christian utopia that would be sinless and classless. But now its remaining residents can do little against the rising sea.

Buildings have sunk into the Atlantic Ocean, an increasingly common image along the vulnerable West African coast. Old timber pokes from the waves like rotten teeth. Shattered foundations line the shore. Waves break against abandoned electrical poles.

For years,…