Well I must admit that I find that somewhat odd though. Yes, it tends to be cold underwater..... But if Heat decreases income in the water, then the justification for that is actually totally backwards, IMO. It should be that Cold is worse underwater, because you're making it FROSTY down there, deep ocean can drop well below freezing without becoming ice because of the huge pressures involved. And on the flip side of the coin, added Heat would not make it HOT underwater, merely not extremely cold. If the original assertion is true, then I would argue that all aquatics should at least have a +1 Cold affinity. Otherwise for some reason we are saying they are perfectly at home with frigid living conditions underwater, yet suddenly when they go on land, the cold has detrimental effects.
It would probably be a complicated mechanic to code, but it would be interesting to see some Heat increase income underwater, but severely affect aquatics on land. By the same token, the aquatic races that are attenuated to living in frigid waters would find moving onto land easier in cold climes, but would be harmed by excess cold in their already naturally cold underwater homes.
The plot thickens!
Okay, I ran a test, it took some turns to get my nations to 3 Cold and 3 Heat with no unrest from events (I shoulda tossed in Luck to speed that up
), and here's what I found-
Oceania - 3 Cold - 28240 pop - 705 supplies - 338 income = 83.5 pop/gold
R'lyeh - Even scale - 29700 pop - 884 supplies - 326 income = 91.1 pop/gold
Atlantis - 3 Heat - 29540 pop - 643 supplies - 324 income = 91.1 pop/gold
So at first glance, Cold actually looks like it's giving a 9% income boost (3% per scale?) while reducing supplies slightly. Heat on the other hand is not affecting income, but has a rather huge effect on supplies.
I might check it again later, but this is really weird results so far.