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.’
Pity that brief bouts of killing don't have much of an impact. You need really intensive and long-lasting slaughter to have an effect.
Well, hey, maybe we'll get lucky again with these ultimate carbon offsets.
Nobody tell Al Gore. Imagine how many jet trips he could take and mansions he could build if he wipes out an entire country!
