Lots to unpack here. First, I don't believe any scientist has predicted a "runaway" greenhouse effect. CO2 has been rising in the atmosphere for quite some time. It's become so predictable you could almost set your watch to it.

Yes, "the loop" is self correcting, would take decades, but only after the reduction of greenhouse gas released.

What isn't known is the climate turbulence effects. The problem isn't nominal heat or cold. It's spikes in weather. Just like we believe humans could survive on Mars most of the time. In the middle of a Martian storm? Or on Venus, in the kinds of storms there?

How many more-violent droughts, storms and wars can our farmland withstand?

Yes, very low levels of CO2 would be "forbidding to life", but again, no scientist would dispute that. We have a choice about creating more CO2, do we have the same choice about more, considering current lifestyle? It's a fine literary argument, and suitable for any "scientist" in a science fiction novel...but...:)

As for the glaciers. They're still around? ;)