This is really weird, New World Post-pandemic Reforestation Helped Start Little Ice Age, Say Scientists:
Stanford University researchers have conducted a comprehensive analysis of data detailing the amount of charcoal contained in soils and lake sediments at the sites of both pre-Columbian population centers in the Americas and in sparsely populated surrounding regions. They concluded that reforestation of agricultural lands–abandoned as the population collapsed–pulled so much carbon out of the atmosphere that it helped trigger a period of global cooling, at its most intense from approximately 1500 to 1750, known as the Little Ice Age.
The same researchers published a paper on this last spring, Effects of syn-pandemic fire reduction and reforestation in the tropical Americas on atmospheric CO2 during European conquest:
A new reconstruction of Late Holocene biomass burning in the tropical Americas is consistent with the expansion of fire use by Mesoamerican and Amazonian agriculturalists and a subsequent period of fire reduction beginning 500 years BP. The marked reduction of biomass burning after 500 years BP, a unique feature of the fire history of the tropical Americas relative to other regions of the globe, is synchronous with the collapse of the American indigenous population during pandemics accompanying European conquest. We predict that fire reduction contemporaneous with pandemics in the tropical Americas was associated with massive forest regeneration on 5 × 105 km2 of land and sequestration of 5-10 Gt C into the terrestrial biosphere, which contributed to the 2% global reduction in atmospheric CO2 levels and the 0.1‰ increase in δ13C of atmospheric CO2 from 1500 to 1750 A.D. This study 1) builds upon prior fire history reconstructions by synthesizing a substantially greater number of stratigraphic charcoal accumulation records and soil charcoal 14C dates to resolve features of the Late Holocene biomass burning record in the tropical Americas; and 2) corroborates the hypothesis advanced by Ruddiman [Ruddiman, W.F., 2003. The Anthropogenic Era began thousands of years ago. Climatic Change 61, 261-293, Ruddiman, W.F., 2005. Plows, Plagues, and Petroleum. Princeton University Press, Princeton, New Jersey] that biospheric carbon sequestration via reforestation of cropland abandoned during pandemics contributed to changes in atmospheric CO2 concentration during the past millennium.