OSLO (Reuters) - A 200-year period covering the heyday of both the Roman Empire and China's Han dynasty saw a big rise in greenhouse gases, according to a study that challenges the U.N. view that man-made climate change only began around 1800.
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.
