Emissions of the potent greenhouse gas methane began well before the Industrial Age, according to a study published Wednesday in the journal Nature, raising questions over the benchmark used to calculate global warming and adding urgency to addressing climate change.
The group of researchers studied Greenland's ice over the past two millennia to measure changes in methane in the atmosphere. Celia Sapart of Utrecht University, lead author of the study, said that people "were already emitting quite a lot in the Roman Empire and Han Dynasty."
The study cites methane-releasing human activities from before the Industrial Age, including deforestation and the use of charcoal as fuel.
"The pre-industrial time was not a natural time for the climate -- it was already influenced by human activity," Sapart told Reuters. "When we do future climate predictions we have to think about what is natural and what did we add. We have to define what is really natural," she said.
Sapart emphasized the "urgency" to use this information to act on climate change.
"This study shows the urgency of controlling greenhouse gas emissions as soon as possible, because it shows that the disequilibrium in the climate system caused by humans existed for much longer than we expected," she said in an email exchange with Agence France-Presse.