The first
GURPS campaign I ran was science fiction/space which was centered in a galaxy I created for science fiction stories. I worked to design worlds realistically--which proved very difficult, even though
GURPS Space helped a great deal.
Axial tilt is an important factor in climate, but there are many others. There's the planet's atmosphere, its rotation rate (how many times does it rotate in one of its years), how eccentric is its orbit, etc.
NASA has an article that might help at
https://www.nasa.gov/audience/foredu...t_Seasons.html