I'm no expert, but it seems one prominent theory on why CO2 dropped around 1600 is that it's a result of Europeans killing so many indigenous Americans. The red

I'm no expert, but it seems one prominent theory on why CO2 dropped around 1600 is that it's a result of Europeans killing so many indigenous Americans. The reduction in agriculture led to forests regrowing, giving a temporary boost to CO2 sequestration. The CO2 dip is referred to as the "Orbis Spike". This seems to be one of the better results on the subject: https://www.ucl.ac.uk/news/2015/mar/epoch-defining-study-pinpoints-when-humans-came-dominate-planet-earth https://www.ucl.ac.uk/news/2015/mar/epoch-defining-study-pin...