I think that its quite ironic that scientists call this issue global warming when it leads to an ice age so shouldn't it be called global freezing as thats whats going to happen?
Here is how it works, as the earth heats up, the polar ice caps melt, as they melt they expose more and more of the deep blue arctic ocean to the sun and absorbs more energy and heat which causes further ice melting, the ice from the ice caps cool the oceans which in turn cools our atmosphere leading to an ice age. Global warming is the correct term.
It doesn't lead directly to an ice age. The ice age would follow far in the future, not immediately.