It is common sense nowadays that excessive carbon dioxide in the air caused by excessive lumbering leads to global greenhouse effects.

But a team of archaeologists from China and the United States is saying that the greenhouse effect started about 5,000 years ago, much earlier than people might expect.

This is the conclusion reached by a group of Chinese and US archaeologists based on research on the relics excavated from the ruins of a Neolithic site in Rizhao City, east China's Shandong Province, over the past ten years.

The joint archaeological team of experts from Shandong University and US scholars began its survey at the ruins of the ancient Liangcheng Town in suburban Rizhao in 1995, focusing on the relationship between plants and human activity.

They collected wood samples from the site and did research on 21 pieces of waterish logged timber and three pieces of charcoal. Archaeologists found that the wood excavated at the site were mostly the remains of burning or construction activities.

"Prehistoric human beings probably burned wood in cooking, lighting, molding pottery and even bronze smelting, while large quantities of relics of ancient housing facilities indicate that people of that time lumbered much to build houses," said Kuan Fengshi, head of the Archaeological Research Center of the Shandong University and a member of the excavation group.

The team also deduced that prehistoric human beings used plants for other purposes, such as curing diseases, making furniture or tools and feeding animals, but these plants were hardly preserved and found.

Luan concluded that the remains of plants and trees at the site showed that prehistoric humans had started lumbering and that the increase of carbon dioxide therefore probably started before the industrial age.

The traditional view was that human beings affected the environment little in ancient times and that it was not human beings but climate change or catastrophes that promoted or vanquished ancient cultures.

"What we have found has refuted the conception," said Luan.

(Xinhua News Agency November 1, 2005)