Humanity's carbon footprint was first impressed on the Earth during the era of the Roman and Chinese Empires, according to a study recently published in the journal Nature.
Researchers found that the burnt plant matter used for food, agriculture and smelting released "significant methane emissions" per person.
However, Celia Sapart, an atmospheric chemist in the Netherlands, concedes that "the quantities are much smaller [than now], because there were fewer people on Earth."
Specifically, "the results show that between 100 BC and AD 1600, human activity may have been responsible for roughly 20-30% of the total pyrogenic methane emissions," reads the report. The scientists were able to measure three periods of methane production through their studies: one spanning from AD 1 to 300, another from AD 800 to 1200, and the last from AD 1300 to 1600.
Sapart and her team used a mass spectrometer to analyze trapped methane in 2,000 year old ice core samples from Greenland. The Los Angeles Times clarifies that the scientists "were able to determine the ratio of methane produced by burning and by decomposition."
The chemist adds, "To date, we do not know how natural methane sources will evolve together with human-induced climate change, but it is likely those natural sources will increase."
Methane expert Ed Dlugokencky of the National Oceanic and Atmospheric Administration's Earth System Research Laboratory, notes that "the study give further evidence for a contribution to the global methane burden from anthropogenic sources."
Prior to this discovery, scientists believed that humans had no sizable impact on greenhouse emissions prior to 1750.