LOS ANGELES, July 6 (Xinhua) -- A team of international researchers used oldest DNA to show that Greenland was much warmer at some point during the last Ice Age than most people have believed.

The DNA samples were collected by the scientists from the bottom of a two kilometer thick ice sheet and from the trees, plants and insects of a boreal forest estimated to be between 450,000 and 900,000 years-old.

Previously, the youngest evidence of a boreal forest in Greenland was from 2.4 million years ago.

The DNA samples suggest the temperature of the southern Greenland boreal forests 450,000 to 900,000 years ago was probably between 10 degrees Celsius in summer and -17 degrees Celsius in winter.

Also, the reduced glacier cover in that region means the global ocean was probably between 1 and 2 meters higher during that time compared to current levels.

"These findings allow us to make a more accurate environmental reconstruction of the time period from which these samples were taken, and what we've learned is that this part of the world was significantly warmer than most people thought," said Martin Sharp, a glaciologist at the University of Alberta and a co-author of the paper.

Sharp said the silty ice found underneath the huge Greenland glacier created a perfect, natural "freezer" to preserve the prehistoric DNA. Scientists have, in the past, found older organic matter, but they have not found any uncontaminated DNA that is as old or older than the Greenland samples.

Sharp and his PhD student Joel Barker contributed to the research by providing DNA samples from the silty ice of much younger glaciers (3,000 years old) on Ellesmere Island in Arctic Canada. The Canadian DNA samples offered a control sample for the researchers around the world who worked to estimate the age of the Greenland DNA samples.

Sharp, who has been a supporter of the idea that the current global warming trend is human induced, believes the new research offers evidence that climate warming on the current scale is possible through natural conditions.

However, he cautions that this research does not prove the current global warming trend is not human induced.

"It could mean that our current warming is the result of both natural processes and human influences, and we may be heading for even bigger temperature increases than we previously thought," Sharp said.

The results of the research were published in the latest issue of the Science Journal.