Visitors from Earth show up just as the northern hemisphere is warming, causing its indigenous sentient Ishtarians to begin migrating south yet again, threatening another of the periodic collapses of their civilization. Despite being more advanced than humans--for the libertarian conservative Anderson that meant having no states (p. 64)--Istarians could not prevent their societies from succumbing to the climate emergency. "Always civilization had gone under, in flood, storm, famine, breakdown, and the onset of wild peoples driven out of countries still more ruined." (p.48) (Perhaps they needed to develop states capable of dealing successfully with such crises.)
A similar climate emergency - civilizational collapse cycle takes place in Brian J. Aldiss's Heliconia trilogy, which was published in 1982, 1983 and 1985.