one of the odd paradoxes of the solubility of carbon dioxide in water (and all dissolved gases) is that cold water dissolves more gas (and under higher pressure, also) when cold. when boiling, all gas is driven out.
you can see this in action by making two separate ice cubes. one you make with regular tap water, the other, you boil the water first, before putting it in the freezer (obviously, let it cool a bit).
if you ever wondered how ritzy bars have those fancy translucent clear ice, that's what it is. the fog of bubbles inside non-boiled water frozen to ice is the air, separated from the water but trapped inside the ice.
