After decades of global warming, the new ice age left humanity gobsmacked. The oceans solidified, the forests and fields were scoured by blizzards, oil froze into black diamonds. The population halved within a year.
The penguins marched up from the south like iron filings towards a magnet. They had been shackled by hot, dry earth, but on ice they were transfigured into torpedoes, bullets.
They hunted in packs. Humans, who had held the evolutionary advantage for so long, were helpless. Their efforts to flee futile, they were knocked down and ripped apart by razor-like beaks.
It was quicker than freezing.