It's the year 3052. Human numbers have dwindled since the runaway global warming that eventually triggered the water crisis. The biggest cities are now barren

It's the year 3052. Human numbers have dwindled since the runaway global warming that eventually triggered the water crisis. The biggest cities are now barren ruins. Humanity survives in tribal pockets near the poles, making do with scavenged old tech from the past. A breakthrough! Someone discovers an old harddrive that contains information on why we didn't fix this when it was still possible... An extraterrestrial event? Nuclear war? An incurable disease? Technological limitation? "It was too expensive."