According to the United Nations, human induced climate change has started in the 1800s. Researchers at Utrecht University (The Netherlands), however, are convinced that emissions of greenhouse gas date way back to the times of the Roman Empire and China’s Han dynasty.
The high levels of heat-trapping methane in the atmosphere within the ice of Greenland were found to be nearly 2000 years old. As Celia Sapart, the lead author of the study, states, the release of this gas has taken place during deforestation and charcoal use.
The study published last week in Nature reveals that the Roman Empire and Han’s Dynasty have been emitting a substantial amount of greenhouse gasses. The decrease in these emissions happened around AD 200, mainly due to population declines in Europe and China following the fall of the two kingdoms.
Although the release of methane before the year 1800 account for only 10% of the current levels, the team of scientists at Utrecht challenge the U.N. panel and their view that climate change has begun with the use of fossil fuels during the Industrial Revolution.
Methane is a naturally occurring gas released through wetlands, wildfires and mud volcanoes, but it is also produced by human activities such as burning of forests and fossil fuels, landfills, livestock or rice paddies.
Scientific teams from the Netherlands, Switzerland, Denmark, The U.S and France report rise in methane levels in Medieval times, which coincides with the emerging of the European economy. This could be one of the explanations for the rise in temperatures between years 800 and 1200. Additionally, the increased population size of Europe and Asia might have led to higher rates of deforestation for farming. The researchers explain the following drop by the reduced population size due to the Black Death.
In the 1500s, the population started growing again after the plague, and so as the methane levels, with the beginning of the Little Ice Age
The challenge in front of the team of scientists is to find a method to distinguish between naturally occurring and man-made methane emissions. Observing the layers of compacted snow in the ice cores from Greenland, it was estimated that methane concentrations increased from about 600 parts per billion around 2,000 years ago to above 700 ppb by 1800. Currently, the concentrations are about 1,800 ppb.
According to the U.N, greenhouse gas emissions are the main cause for raising temperatures and sea level. China is leading greenhouse-gas emitter, followed by the U.S, the EU, India and Russia.