Earth system impacts of the European arrival and Great Dying in the Americas after 1492

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• We estimate that 55 million indigenous people died following the European conquest of the Americas beginning in 1492. This led to the abandonment and secondary succession of 56 million hectares of land

• This was a change from the 1400s of 9.9 Pg C (5 ppm CO2). Including feedback processes this contributed between 47% and 67% of the 15–22 Pg C (7–10 ppm CO2) decline in atmospheric CO2 between 1520 CE and 1610 CE seen in Antarctic ice core records.

• These changes show that human actions had global impacts on the Earth system in the centuries prior to the Industrial Revolution.

• Using indigenous population decline estimates and their per capita land use we can estimate the extent to which vegetation succession in the Americas occurred following the Great Dying in the first century after European arrival, and how this may have impacted resulting carbon sequestration.

• However, in almost all cases an increase in plant biomass occurs over time, increasing the carbon stored on the land

• The median carbon uptake is 7.4 Pg C (IQR 4.9–10.8 Pg C, 1 Pg = 1 × 1015 g) from the abandonment of 55.8 million ha of land in the Americas over the 100 years after 1517 CE (date of first documented mainland epidemic).

• Large population reduction led to reforestation of 55.8 Mha and 7.4 Pg C uptake.

• Humans contributed to Earth System changes before the Industrial Revolution.

• The uptake of carbon on the abandoned anthropogenic lands after European contact may have been large enough to impact the atmospheric CO2 record

• Furthermore, at the same time high-resolution Antarctic ice-core records of atmospheric CO2 concentration show an anomalously large decline of ∼7–10 ppm

• Isotope analysis shows that the anomaly was driven by an increase in the terrestrial carbon sink

• This study finds that the decline in atmospheric CO2 contributed to the observed cooling, which is consistent with uptake following secondary succession in the Americas.

• We therefore test the hypothesis that human actions impacted CO2 levels and global surface air temperatures in the 16th and 17th centuries, just before the Industrial Revolution

• The strength of our approach is the absence of such covariance as all available combinations are evaluated, and suggests substantial LUC – the recovery of 56 million ha of land – followed the arrival of the Europeans in the Americas after 1492 CE.

• The abandonment of 56 million ha of land in the 1500s following the deaths of 55 million people would have resulted in widespread vegetation succession coupled with a decrease in human driven fire activity.