[cbkeller]

That certainly doesn't help either! To some extent though, anthropogenic emissions are dangerous more for their rate than their absolute magnitude; in the long run, once we stop emitting, silicate weathering will take back over "soon enough" -- it's just that "soon enough" in this case means ~5 myr and probably a mass extinction later.

The other one I forgot to mention is that the sun is a bit brighter now than it was 700 Myr ago (by perhaps a few percent). Go back another two or three billion years to the Archean and the difference would have been bigger -- to the point that we have some trouble explaining why there weren't a lot more snowballs back then [1]

[1] https://en.wikipedia.org/wiki/Faint_young_Sun_paradox

[_0w8t]

Is it possible from geological evidence to confirm that Sun was dimmer billions years ago? I am asking as stability of Earth orbit cannot be taken for granted for such periods. For example, we could underestimate the effects of solar wind in past that could have pushed Earth, or the could be an interaction with passing close stars.

[cbkeller]

Ah, so there are many things that it is hard to be absolutely certain of in geology, but changing Earth's orbit is at least very very hard; even the kinetic energy from things like the Chixulub impact are far too small to have a significant effect. The "moon-forming impact" in the most common model of the origin of the moon might be more on the right order of magnitude, but there don't seem to have been any of those more recently than about 4.51 Ga. An astronomer could say more, but solar luminosity is also relatively well understood from studying other main-sequence stars of various ages.

The most common solutions involve high concentrations of organic greenhouse gases like methane as well as high CO2, but it's always possible there are other possibilities that have not yet been considered.

[_0w8t]

We do not have good models of the rate Sun has been losing hydrogen especially on scale of billions of years. So from that we do not have a precise answer how heavier was Sun in past. But heavier Sun implies that Earth was closer compensating for the dimmer younger Sun.

As I understand according to the current estimates this not enough to avoid the cold Earth problem, but there are way too much uncertainty. But if we do not have way to read the brightness from geology alone, that can be an answer.

[User23]

I have to say I was thinking to myself this person identified as a geologist, so an event that started 200 years ago probably isn’t a major concern. In the sense of geologic timescales I mean.

[vba616]

I perceive this as a little patronizing.

Up thread, there seems to be a question about human civilizations being erased by the ice.

A billion years ago.

And there was a polite reply, from said geologist, not a comment about timescales.