Coupled climate-carbon simulations indicate minor global effects of wars and epidemics on atmospheric CO2 between ad 800 and 1850

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 (similar to 1200 to similar to 1380), the Black Death (similar to 1347 to similar to 1400), the conquest of the Americas (similar to 1519 to similar to 1700), and the fall of the Ming Dynasty (similar to 1600 to similar 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.