Human activity contributed to climate change long before the Industrial Revolution, according to new research. Scientists analyzing ice core samples from Greenland found a spike in emissions of the greenhouse gas methane during a 200-year period around 2,000 years ago, when the ancient Roman and Chinese empires were at their peak, reports the Los Angeles Times. Researchers believe the rise was caused by the widespread use of charcoal as fuel and the burning of large areas of forest to clear farmland.
The amount of the heat-trapping gas emitted by human activity was only about a 70th of today's levels, but still accounted for a significant proportion of methane emissions, researchers say. Methane is also emitted from natural sources including wetlands and wildfires. "The pre-industrial time was not a natural time for the climate—it was already influenced by human activity," the lead researcher says. "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."