Lead author, Julia Pongratz, and Ken Caldeira of the Carnegie Institution and colleagues at the Max Planck Institute for Meteorology in Germany analyzed historical records of land use and compared those with a global climate/ carbon cycle model to track how land use and historical events altered carbon dioxide levels.
The longer the duration of the human catastrophe, the more carbon was absorbed by new forests, Pongrantz found. The depopulation of the Americas after invasion by the Spanish, English and other European powers had a similar atmospheric impact to the Mongol conquests. But other shorter-term mass deaths didn't slow agriculture down enough to affect the atmosphere.
"We found that during the short events such as the Black Death and the Ming Dynasty collapse, the forest re-growth wasn't enough to overcome the emissions from decaying material in the soil," says Pongratz. "But during the longer-lasting ones like the Mongol invasion and the conquest of the Americas there was enough time for the forests to re-grow and absorb significant amounts of carbon."
"Today about a quarter of the net primary production on the Earth's land surface is used by humans in some way, mostly through agriculture," Pograntz said. "So there is a large potential for our land-use choices to alter the global carbon cycle."
"In the past we have had a substantial impact on global climate and the carbon cycle, but it was all unintentional," Pograntz said. "Based on the knowledge we have gained from the past, we are now in a position to make land-use decisions that will diminish our impact on climate and the carbon cycle. We cannot ignore the knowledge we have gained."
The current rate and scale of climate change are unprecedented in human history, and another study point out that if humanity does not heed the fate of the Greenland Vikings and the Roman Empire, civilization may be doomed to repeat the chaos of collapse.
Rome rose and prospered during a stable, warm, moist period in climate history, but collapsed during colder, drier, more variable times, according to research by a team of researchers led by Ulf Buntgen of the Swiss Federal Research Institute for Forest, Snow and Landscape, which Emily Sohn of Discovery News wrote about recently.