When the grey first came, people said, “Not to worry. It will pass.” But the greenhouse gases built up, temperate climates hit 43˚C midwinter, and the sea-levels rose, gobbling up all the coastal resorts.
Those people who survived, congregated on high ground and walked around naked, gasping and wheezing.
It had all started with microscopic weather manipulation devices placed inside the lids of waste-disposal bins around the world: so much more effective than pumping silver oxide into the atmosphere from above. The aliens were time-travellers, which meant they could wipe us out and colonise our planet in under five minutes.