Romans, Han Dynasty, kick-started climate change

Anthropogenic climate change may not be a recent phenomenon, with researchers reporting ice cores from the first two centuries AD show big spikes in methane prevalence.

Those two centuries, the researchers note, co-incide with the most prosperous periods for the Roman Empire and Han Dynasty.

A Nature paper, Natural and anthropogenic variations in methane sources during the past two millennia, speculates that deforestation and use of charcoal as a fuel made for increases in methane emissions.

The methane was detected in ice cores from Greelanand. The cores also show methane levels tailed off around 200 AD, a time at which deforestation slowed as Rome declined and the Han Dynasty collapsed.

Lead author Celia Sapart of Utrecht University told Reuters the team behind the paper say they have spotted a spike in methane emissions that corresponds roughly to the end of the dark ages, and a dip not longer after the Black Death.

One possible fly in the ointment is a rise in methane prevalence before the Little Ice Age.

Sapart feels the results mean climate scientists need to rethink what is a "normal" state for Earth's climate.

"The pre-industrial time was not a natural time for the climate - it was already influenced by human activity," she told Reuters, adding that "When we do future climate predictions we have to think about what is natural and what did we add." &reg