The key to staying warm when ice climbing is to dress in layers. You need to be able to start out the day wearing just your baselayer or midlayer for the approach, then continue to add and remove layers throughout the day as you climb and belay. This is my current ice climbing apparel setup for the season. While the individual pieces may change from year to year, the general layering concept remains the same.
Over the years, I have a developed a pretty good personal layering system for ice climbing. My bottom half layers remain the same throughout the day, made up of my current favorite climbing pants and some sort of baselayer whose thickness depends on the weather. My top half usually consists of 4-6 layers, again depending on the temperature. These layers will be taken on and off at various stages throughout the day.
