Wizards who are cold specialists focus on arcane cold of all schools, rather than studying one school of magic as most wizards do.
Whenever you cast a spell that deals cold damage, add 1/2 your wizard level to the damage (minimum +1). This bonus only applies once to a spell, not once per missile or ray, and cannot be split between multiple missiles or rays. At 20th level, whenever you cast a spell with the [cold] descriptor you can roll twice to penetrate a creature’s spell resistance and take the better result.
At 6th level, anytime you are within 30 feet of a creature of the [cold] subtype, as a free action you can make a Knowledge (arcana) check to learn its type (and all subtypes) and any information usually gained from a Knowledge check appropriate to its type. The DC of this check is 10 + the creature’s CR.
You also make a Knowledge (arcana) check as a free action whenever anyone within your line of sight casts a spell with the [cold] descriptor. The DC of this check is 15 + the spell’s level. On a successful check you know the name, level, and general effect of the spell being cast.
Any time a spellcaster casts a spell with the [cold] or [fire] descriptors, and you have identified the spell being cast, you may use any prepared spell of the same or higher level in an attempt to counterspell the [cold] or [fire] spell.