Seminar

Reforestation and forest restoration are a commonly seen as one of the prime options for decreasing atmospheric CO2 concentrations. Are there any potential analogues in humanity’s past where such widespread vegetation regrowth led to an drop in CO2 recorded in ice cores? The dramatic consequences of the European arrival in the Americas may represent such an event. 

In this talk I investigate whether the decline in global atmospheric CO2 concentration by 7–10 ppm in the late 1500s and early 1600s which coincides with globally lowered surface air temperatures by 0.15 °C, was generated by natural forcing or was a result of the large-scale depopulation of the Americas after European arrival, subsequent land use change and secondary succession. I quantitatively review the evidence for (i) the pre-Columbian population size, (ii) their per capita land use, (iii) the post-1492 population loss, (iv) the resulting carbon uptake of the abandoned anthropogenic landscapes, and then compare these to potential natural drivers of global carbon declines of 7–10 ppm. I show that the global carbon budget of the 1500s cannot be balanced unless large-scale vegetation regrowth in the Americas is included.