“runaway glaciation”
Hmmm.
As water grows colder, its ability to hold carbon dioxide in solution INCREASES. Once water freezes, the carbon dioxide already in solution is, well, frozen in place.
Only when an external heat source is applied to the now frozen-down system, converting the solid form of ice to liquid water, does the water begin to give up its dissolved carbon dioxide, passing it into the atmosphere.
Carbon dioxide contributes VERY little to heat transference at any point of the phase change of ice to water to water vapor. But this phase change of water is a POWERFUL heat transfer system.