10. The Mongol Depredations Reduced the Amount of Cultivated Land Enough to Register on the Planet’s Carbon Balance
The Holocene study demonstrated that the depopulation and disruptions caused by the Mongol invasions were so massive that they led to a significant drop in the amount of cleared land under cultivation. Then as now, people chopped down forests to clear land for agriculture. That automatically increased the amount of carbon in the atmosphere, because vegetation stores carbon. Trees and shrubs are what scientists call “carbon sinks”, defined as things that absorb more carbon from the atmosphere than they release.
The mass of vegetation produced by agriculture in cleared land that had once been forested is significantly less than the mass of the trees that had once occupied that land. So acre for acre, the cultivated lands store less carbon than had been stored in the forests they replaced. Not only that, but human activity on those cleared lands transforms them from the carbon sinks they had once been when forested, and into carbon sources that increase rather than decrease atmospheric CO2.