Genghis Khan the GREEN: Invader killed so many people that carbon levels plummeted

Genghis Khan has been branded the greenest invader in history – after his murderous conquests killed so many people that huge swathes of cultivated land returned to forest. .. The 700 million tons of carbon absorbed as a result of the Mongol empire is about the same produced in a year from the global use of petrol.

Daily Mail | Science Daily | Carnegie Science | January 2011

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Genghis Khan has been branded the greenest invader in history – after his murderous conquests killed so many people that huge swathes of cultivated land returned to forest.

The Mongol leader, who established a vast empire between the 13th and 14th centuries, helped remove nearly 700 million tons of carbon from the atmosphere, claims a new study.

The deaths of 40 million people meant that large areas of cultivated land grew thick once again with trees, which absorb carbon dioxide from the atmosphere.

And, although his methods may be difficult for environmentalists to accept, ecologists believe it may be the first ever case of successful manmade global cooling.

‘It’s a common misconception that the human impact on climate began with the large-scale burning of coal and oil in the industrial era,’ said Julia Pongratz, who headed the research by the Carnegie Institution’s Department of Global Ecology.

‘Actually, humans started to influence the environment thousands of years ago by changing the vegetation cover of the Earth’s landscapes when we cleared forests for agriculture,’ she told Mongabay.com.

The 700 million tons of carbon absorbed as a result of the Mongol empire is about the same produced in a year from the global use of petrol.

The Carnegie study measured the carbon impact of a number of historical events that involved a large number of deaths.

Time periods also looked at included the Black Death in Europe, the fall of China’s Ming Dynasty and the conquest of the Americas.

All of these events share a widespread return of forests after a period of massive depopulation.

But the bloody Mongol invasion, which lasted a century and a half and led to an empire that spanned 22 per cent of the Earth’s surface, immediately stood out for its longevity.

And this is how Genghis Khan, who repeatedly wiped out entire settlements, was able to scrub more carbon from the atmosphere than any other despot.

‘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,’ explained Pongratz.

‘But during the longer-lasting ones like the Mongol invasion… there was enough time for the forests to re-grow and absorb significant amounts of carbon.’

Though the Khan will remain known as Genghis the Destroyer and not Genghis the Green, Dr Pongratz hopes that her research will lead to future historians examining environmental impact as well as the more traditional aspects of study.

‘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,’ she said.

‘We cannot ignore the knowledge we have gained.’

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War, Plague No Match for Deforestation in Driving CO2 Buildup

January 20, 2011 | Carnegie Science

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Carnegie: War, Plague No Match for Deforestation in Driving CO2 Buildup [03:18]

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Stanford, CA— Genghis Khan and his Mongol hordes had an impact on the global carbon cycle as big as today’s annual demand for gasoline. The Black Death, on the other hand, came and went too quickly for it to cause much of a blip in the global carbon budget. Dwarfing both of these events, however, has been the historical trend towards increasing deforestation, which over centuries has released vast amounts of carbon dioxide into the atmosphere, as crop and pasture lands expanded to feed growing human populations. Even Genghis Kahn couldn’t stop it for long.

“It’s a common misconception that the human impact on climate began with the large-scale burning of coal and oil in the industrial era,” says Julia Pongratz of the Carnegie Institution’s Department of Global Ecology, lead author of a new study on the impact of historical events on global climate published in the January 20, 2011, online issue of The Holocene. “Actually, humans started to influence the environment thousands of years ago by changing the vegetation cover of the Earth‘s landscapes when we cleared forests for agriculture.”

Clearing forests releases carbon dioxide into the atmosphere when the trees and other vegetation are burned or when they decay. The rise in atmospheric carbon dioxide resulting from deforestation is recognizable in ice cores from Greenland and Antarctica before the fossil-fuel era.

But human history has had its ups and downs. During high-mortality events, such as wars and plagues, large areas of croplands and pastures have been abandoned and forests have re-grown, absorbing carbon dioxide from the atmosphere.

Pongratz decided to see how much effect these events could have had on the overall trend of rising carbon dioxide levels. Working with colleagues at the Max Planck Institute for Meteorology in Germany and with global ecologist Ken Caldeira at Carnegie, she compiled a detailed reconstruction of global land cover over the time period from 800 AD to present and used a global climate-carbon cycle model to track the impact of land use changes on global climate. Pongratz was particularly interested in four major events in which large regions were depopulated: the Mongol invasions in Asia (1200-1380), the Black Death in Europe (1347-1400), the conquest of the Americas (1519-1700), and the Fall of the Ming Dynasty in China (1600-1650).

“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.”

The global impact of forest re-growth in even the long-lasting events was diminished by the continued clearing of forests elsewhere in the world. But in the case of the Mongol invasions, which had the biggest impact of the four events studied, re-growth on depopulated lands stockpiled nearly 700 million tons of carbon absorbed from the atmosphere. This is equivalent to the world’s total annual demand for gasoline today.

Pongratz points out the relevance of the study to current climate issues. “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,” she says. “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. 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.”

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The Department of Global Ecology was established in 2002 to help build the scientific foundations for a sustainable future. The department is located on the campus of Stanford University but is an independent research organization funded by the Carnegie Institution. Its scientists conduct basic research on a wide range of large-scale environmental issues, including climate change, ocean acidification, biological invasions, and changes in biodiversity.

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