[Edi]

Have you checked the units' encumbrance in provinces with Heat 2? They could have increased encumbrance, and will certainly have in Heat 3 provinces.

As for the weakened abilities etc, some nations have units whose armor is affected by the heat/cold scale so that their armor has its nominal value in heat/cold 0 and improves by X for each cold scale and decreases by X for each heat scale. This property of a unit is known as icearmor. Niefel Giants and Niefel Jarls and many Caelian and late era Atlantis units have it, making them substantially tougher in cold provinces.

Some units also have increased other abilities depending on heat/cold. The Abysian lava warriors are one example, iirc, and the Abysian hero Rago the Rage Lord has increased attack and defense in hot provinces.

Edi