Coupled climate–carbon simulations indicate minor global effects of wars and epidemics on atmospheric CO 2 between ad 800 and 1850

Abstract

Historic events such as wars and epidemics have been suggested as explanation for decreases in atmospheric CO₂ reconstructed from ice cores because of their potential to take up carbon in forests regrowing on abandoned agricultural land. Here, we use a coupled climate–carbon cycle model to assess the carbon and climate effects of the Mongol invasion (~1200 to ~1380), the Black Death (~1347 to ~1400), the conquest of the Americas (~1519 to ~1700), and the fall of the Ming Dynasty (~1600 to ~1650). We calculate their impact on atmospheric CO₂ including the response of the global land and ocean carbon pools. It has been hypothesized that these events have contributed to significant increases in land carbon stocks. However, we find that slow regrowth and delayed emissions from past land cover change allow for small increases of the land biosphere carbon storage only during long-lasting events. The effect of these small increases in land biosphere storage on global CO₂ is reduced by the response of the global carbon pools and largely offset by concurrent emissions from the rest of the world. None of these events would therefore have affected the atmospheric CO₂ concentration by more than 1 ppm. Only the Mongol invasion could have lowered global CO₂, but by an amount too small to be resolved by ice cores.