[Windchaser]

> 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.

[SV_BubbleTime]

So… the sun is hotter now than it was what… since the 1950s? The 1850s? The Jurassic period? What scale is do you need to make this claim reasonable?

Also, I see a lot of things presented as facts in your comment, you seem to have convinced yourself quite thoroughly.

[jemmyw]

10% every billion years. So negligible on our timescale, but it is significant if you talk about ancient climate conditions like this thread does.

[blueflow]

complex life on earth is half a billion years old (cambrian explosion 550ma ago), so the sun shouldn't be that much of an factor.