Using the world's oldest recovered DNA, a new study suggests Greenland was much warmer than previously thought during the last Ice Age and natural global warming trends may be as significant as human-induced warming.

The international study, published Thursday in the journal Science, was co-written by University of Alberta glaciologist Dr. Martin Sharp.

During their research, a team of international scientists retrieved ancient DNA found at the bottom of a two-kilometer ice sheet in Greenland.

The sample came from trees, plants, and insects of a boreal forest estimated to be between 450,000 and 900,000 years old.

The DNA samples suggest the temperature of the southern Greenland boreal forests was probably between 10 C in summer and -17 C in winter. By comparison, the temperatures at the ice surface in Greenland today are -8 C in summer and -30 C in winter.

"To have a forest at this location we would probably have had to melt at least the southern one-third of the Greenland ice sheet," Sharp wrote in an email to

"It provides further evidence that natural processes can and do produce climate change, and that this can be large enough to produce effects similar to those predicted to result from anthropogenic warming."

The reduced glacier cover in the region also meant the global ocean was probably between one and two metres 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," Sharp said in a release.

While the study does suggest a natural warming progression is significant, Sharp cautioned the 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.

"Both natural processes and human influences are involved in the climate changes that we have seen over the past 50 years."

Sharp explained the ice found beneath the glacier created a kind of natural "freezer" that preserved the ancient DNA.

In previous years, scientists had found older organic matter but none that were older than the uncontaminated Greenland samples.

Control samples from the Canadian Arctic helped researchers identify the age of the Greenland samples.

Sharp's also helped to determine the DNA samples were from an actual forest in Greenland and were not from plant matter carried on the wind from other parts of the world.