COPENHAGEN, Denmark, Oct. 3 (UPI) -- The Greenland ice sheet has yielded evidence of the level of emissions of the greenhouse gas methane going back to Roman times, climate researchers say.
Scientists from the Niels Bohr Institute at the University of Copenhagen say the ice sheet can show how much methane originates from natural sources and how much is due to human activity, with results going back thousands of years and up to the present, where more than half of the emissions are now man-made.
The difference can be traced through different isotopic composition in samples trapped for thousands of years in Greenland ice, researchers say.
"We have analyzed the methane composition more than 2,000 years back in time," researcher Thomas Blunier said. "We can see that already 2,100 years ago during Roman times, some cultures were spreading out and burning large amounts of wood for fuel in furnaces to work with metals that required intense heat to process. But the level was still low."
From around the year 1800 there were large increases that were man-made, the researchers said.
"Emissions of methane increased dramatically from around 1800, when the Industrial Revolution took off and where there occurred a large increase in population," Blunier said.
"The extent to which our ancestors were able to influence the emissions of methane with their activities is surprising."