SEATTLE (CBS SEATTLE) — A recent European study found that a record rise in greenhouse gases happened during two centuries in which the Roman Empire and Han Dynasty were ruling the region.

In a challenge to the United Nations’ view that man-made climate change only began around the year 1800, the study was conducted at Utrecht University in the Netherlands. A record of the atmosphere trapped in Greenland’s ice found the level of heat-trapping methane rose about 2,000 years ago and stayed at that higher level for about two centuries, according to Reuters.

“Per capita they were already emitting quite a lot in the Roman Empire and Han Dynasty,” said Celia Sapart of the findings by an international team of scientists in Thursday’s edition of the journal Nature.

Rates of deforestation “show a decrease around AD 200, which is related to drastic population declines in China and Europe following the fall of the Han Dynasty and the decline of the Roman Empire,” the scientists wrote.

However, mankind’s emissions 2,000 years ago, when the world population was an estimated 300 million, were discernible but tiny compared with current levels caused by a population of 7 billion.

Sapart estimated that methane emissions until 1800 were about 10 percent of the total for the past 2,000 years, with 90 percent since the Industrial Revolution. According to Reuters, methane is generated from human sources including burning of forests and fossil fuels, rice paddies, livestock or landfills. Natural sources include wetlands, wildfires or mud volcanoes.

“The pre-industrial time was not a natural time for the climate – it was already influenced by human activity,” Sapart wrote in the study. “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.”

The scientists, in the Netherlands, Switzerland, Denmark, the United States and France, noted a second rise in methane in Medieval times, coinciding with a warm period from 800 to 1200 that also saw Europe’s economy emerge from the Dark Ages. According to the authors, that spike might be because population growth in Asia and Europe led to more deforestation for farming.

A U.N. panel of climate scientists has said the build-up of greenhouse gases is pushing up temperatures and causing more droughts, floods, and rising sea levels. China is now the biggest greenhouse-gas emitter ahead of the United States, the European Union, India and Russia.


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