Every ice using metahuman in comics is different. Each performs their abilities in different ways so there is no easy way to best describe how their powers work, especially in relationship to the real world.
Bobby Drake, aka, Iceman affiliated most strongly with the X-men has the mutant ability to:
Freeze his own body to temperatures below -105 degrees Fahrenheit, nearly instantly. The source of this ability is unknown, but if we were to use mutants such as Cyclops (who draws his optic blast from an alternate dimension of pure kinetic energy) or Colossus (who replaces his cellular materials with a living form of Osmium steel, also believed to be from another dimension) as a base, he is shunting his heat into another dimension.
His second power is to draw heat away from the environment, gather moisture together and created ice constructs capable of being used as armor, weapons, shields, barriers or even ice slides.
Despite Marvel's insistence that he is using ambient water from the environment, unless his structures are incredibly strong, yet remarkably porous, there is rarely enough moisture in any environment for him to create the objects he creates.
In recent years, his control of his mutant power has expanded and supports my third supposition, that he is a portal (the same way Cyclops and Colossus are) to a dimension of water and his real mutant power is the manipulation of his water-formed or water-replaced body appearing as "ice manipulation".
He is able to merge his mutant water form with normal bodies of water and use them as a medium of movement, flowing with or even against the current, he is able to break off pieces of himself and by restoring them with water, rebuild his body; he has even had holes through his central ice form mass and survived as long as he remained in ice form.
In Iceman's case his mutant powers have grown so powerful, it is hard to describe the true nature of his mutation:
- Is he a man with control over heat or molecular energy?
- Is he a telekinetic who can affect water and molecular action, or
- Is he a being who is now composed completely of a water-like analogue who can draw more of his being from a parallel reality and use it to manipulate water/ice in his own?