the effects of temperature?

[Saxon]

Well, if Caelum attacks you and you are at cold 3, their protection values will be higher than otherwise. Not only will you be easier to beat, but you will be a more tempting target. I can not remember if anyone else gains. I suspect Abysia would lose something, but forget what.

[Endoperez]

Every pick the Heat/Cold scale is off from your preferred, you get less resources, income and supply. In addition, units without cold resistance get more encumberance in Cold 2 or worse, and units without fire resistance get more encumberance in Heat 2 or worse. I'm not positive about Heat, but I remember that a Nataraja-pretender of Caelum tires down unless he can cast Resist Cold or Breath of Winter.

This also means that Abysia loses LOTS of money if their Heat 3 doesn't cover their entire empire, and that they make less money if their dominion doesn't spread farther than their own borders as the temperature can take half-dozen turns to adjust for the just-conquered provinces.