2. Killing Enough People to Cool the Planet
Vegetation mass 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. Additionally, 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. The Mongols killed a whole lot of people and depopulated vast regions. Without people to keep cultivated areas clear, nature took over and those lands reverted to forests. Enough forest cover to absorb 700 million tons of carbon dioxide from the atmosphere. That is the equivalent of what people today – twenty times more numerous than in the days of Genghis Khan – pump into the atmosphere from gasoline in a year.
