I was curious what the data sources for that are... unfortunately, I only vaguely understand phrases like
Stable oxygen isotope (d18O) measurements of two speleothems, collected from Huagapo Cave in the central Peruvian Andes and with overlapping age from 1.1 to 1.4 ka, characterize tropical South American climate variability over the last 7150 years.
It is interesting though. There have been a lot of theories including that the depopulation of the Americas as a result of massive die-off due to introduction of European diseases resulted in massive reforestation and carbon sequestration. AFAIK the current opinion is that that is not a cause or not a significant cause.