story identification - Looking for a novel about extreme climate variations

I am guessing you are hearkening back to the Helliconia Trilogy: Helliconia Spring, Helliconia Summer and Helliconia Winter. Per Wikipedia:

The Helliconia Trilogy is a series of science fiction books by Brian Aldiss, set on the Earth-like planet Helliconia. It is an epic chronicling the rise and fall of a civilisation over more than a thousand years as the planet progresses through its incredibly long seasons, which last for centuries.

Although perhaps the geography indicates otherwise:

Helliconia is 1.28 Earth masses in size, making it somewhat larger than Earth and with a bigger axial tilt of 35 degrees. This means that small year seasons are harsher but the planet still has huge polar ice caps, capable of surviving even the great summer, and the human-habitable surface area is comparable to that of Earth.

There are three continents, a tropical continent (Campannlat), a northern continent (Sibornal) and a southern continent (Hespagorat). "Helliconia Spring" and "Helliconia Summer" mainly take place in Campannlat, with its rich vitality, and "Helliconia Winter" focuses on Sibornal, where the harsher environment encourages technological progress. The southern continent features only briefly in the books.