> but a runaway green house effect is certainly possible

Could you go into detail about how this could happen? My understanding is that this would require lots of greenhouse gasses getting pumped into the atmosphere somehow (Something like all the forests in the world burning down). I remember hearing one theory regarding methane calthrate [1] causing this effect, however I haven't read any studies going into the specifics of how large this effect could be.

[1]: https://en.wikipedia.org/wiki/Methane_clathrate#Methane_clat...