https://en.wikipedia.org/wiki/4.2_kiloyear_event
https://phys.org/news/2014-02-decline-bronze-age-megacities-... https://www.livescience.com/20614-collapse-mythical-river-ci...
https://en.wikipedia.org/wiki/Before_Present
Apparently, the "before present" time scale is commonly used in archaeology and geology, and uses an epoch date of Jan 1, 1950. And there're two reasons for this: radiocarbon dating was first standardized in the 1950s, using a reference sample from 1950; and after the 1950s, widespread nuclear testing made radiocarbon dating inaccurate.
It's actually less arbitrary and shortsighted than it seems. Future civilizations are going to face a discontinuity in the archaeological record, and it'll be roughly at the Before Present epoch date.
Nuclear bombs put energy and radioactive particulates into the atmosphere. The effects of the radioactive particulates are fairly well understood. The amount of energy from even the largest bombs is negligible at those scales.
https://en.wikipedia.org/wiki/Modernity
See also "modern humans".
Wait, I'm confused. Are you claiming that current climate change will lead to the collapse of civilization?
Essentially the IPCC and scientists in general have baked in the assumption to the models that we are smart enough to avoid collapse by changing our behavior. TBD.
Or to put it in P.G./HN jargon, (our current) civilization is "default dead" if we stay above 10Gt/year for the latter half of the century.
For the overview of the argument, I'd recommend a paper called "Deep Adaptation: A Map for Navigating Climate Tragedy". Direct link: http://www.lifeworth.com/deepadaptation.pdf
The reality will probably look a bit more rosy if we get our act together and do manage to reduce CO2 emissions, at least I hope this will happen.