Well yeah, I just took the time interlude since the carboniferous and projected it into the future. But what's the real answer to how soon it would naturally get troublesomely hot, when worked out properly, and why is it still not very soon at all?

Heat into space: I was thinking of "PDRC":

https://en.wikipedia.org/wiki/Passive_daytime_radiative_cool...

> If only 1%–2% of the Earth’s surface were instead made to radiate at [~100 W/m2] rather than its current average value, the total heat fluxes into and away from the entire Earth would be balanced and warming would cease.

Which is, you know, a nice fantasy and theoretically works. Like a solar shield, but terrestrial.

Edit for those thinking that even 1% is an unfeasibly large area: yes. It's about 5 million km², which is about one-fifth of North America. Maybe scatter the panels around the ocean?