No citations to hand but Antarctica used to be temperate rainforest and many of the conditions of present day tropical rainforests and savanna could be found much farther from the equator.

The paleocene–eocene thermal maximum makes for interesting related reading. https://en.wikipedia.org/wiki/Paleocene%E2%80%93Eocene_therm...

We can't say for sure that the current feedback loops will be identical to those that did or did not exist in the past. Differences in the initial state could result in different outcomes.

For example was there as much methane trapped in the arctics during the last time CO2 was high?

Does the rate of the increase of CO2 and temperature have an effect? Because it's currently getting hotter far faster (absurdly so) than any other period we have records for.

> Water vapor (clouds) also reflects sunlight. So it's complicated. We know the planet has had higher CO2 and higher temperatures in the past, and it did not "run away"

Yes. But stars like ours burn brighter as they move through their lifetimes, and the Sun is a bit brighter now than it was back when we had higher CO2 levels. That's why a runaway GHG didn't happen back then, but is basically guaranteed to happen within a billion years.

It might not run away to infinity, but it may well run away in the sense that the rate of change could continue to increase even if humans stop contributing to it.

It doesn't matter if the top of the curve flattens out, if we can't survive outside of the bottom part that looks exponential.