[CalRobert]

People had moved on from mud huts by the 1600's, and yet had a pretty small (though non-zero) carbon footprint.

I do agree that population, especially the population of people living a carbon-intense lifestyle, is a serious concern. Many people point a finger at poor nations with high population growth rates while failing to acknowledge that people in those countries tend to emit very little.

[dredmorbius]

Human civilisation had burned through (or been climate-changed out of) several ecosystems by 1600. Europe was reaching the point of overexploiting its fuelwood resources. India and China were peaking as civilisations, reaching levels they'd not return to until the late 19th or 20th centuries in absolute level, and reaching relative standings among other nations and civilisations not since exceeded.

I'm currently reading Vaclav Smil's Energy in World History and the two volumes of Manfred Weissenbacher's Sources of Power: How energy forges human history. They're impressive and sobering.

While there are a range of estimates, there are a substantial group of population theorists, largely grounded in ecology, who see the population levels of 1650, roughly 500 million worldwide, as a likely long-term maximum.

(The broader range runs from as few as 50 million, which still exceeds virtually all large land mammals, to several trillion. I find the lower bound potentially plausible, though pessimistic, the higher range delusional.)