More Words, Deeper Hole

You'd think that a passing star that made all latitudes between (say) 50° north and south too hot to inhabit would also make enough changes to the climate of the polar places so that agriculture would stop working there, too. So even if the civilized polar people kept the barbarians out, their own civilization would collapse into hunter-gatherer as soon as their own food stores ran out.

Still, I haven't read the book, so Anderson might have finessed this objection of mine.