Section 12 pages 145-156 q 5

It is hinted that there was a nuclear war. Images of a nuclear winter are included as well as the masses of burning bodies indicate a nuclear attack. 

It is possible that the disaster could be of a nuclear war or an attack. Seeing as how the effects is ash and soot, and the sun does not shine. It is unlikely that the disaster was natural. So the only possible global disaster is nuclear war or nuclear attack.