Cold Spell Specialization( Frostburn, p. 47)
You do additional damage with cold spells.
In cold areas (temperature at or below 40Â° F), you gain a +1 bonus per die to any dice rolled to determine damage caused by cold spells you cast. For example, if an 11th-level wizard with this feat casts a cone of cold in a cold area, the spell does 11d6+11 points of damage. In areas of extreme cold (below-20Â° F), the damage bonus increases to +2 per die.