DNA of trees, plants and insects including butterflies and spiders from beneath the southern Greenland glacier was estimated to date to 450,000 to 900,000 years ago, according to the remnants retrieved from this long-vanished boreal forest.

That contrasts sharply with the prevailing view that a lush forest of this kind could only have existed in Greenland as recently as 2.4 million years ago, according to a summary of the study, which is published Thursday in the journal Science.

The samples suggest the temperature probably reached 10 degrees C (50 degrees Fahrenheit) in the summer and -17 C (1 F) in the winter.

They also indicated that during the last period between ice ages, 116,000-130,000 years ago, when temperatures were on average 5 C (9 F) higher than now, the glaciers on Greenland did not completely melt away.

"These findings allow us to make a more accurate environmental reconstruction of the time period from which these samples were taken," said Martin Sharp, a glaciologist at the University of Alberta, Canada, and a co-author of the paper.

"What we've learned is that this part of the world was significantly warmer than most people thought."

In a separate paper, also published in Science, European experts said they had analysed the world's deepest ice core, enabling them to reconstruct patterns of warming and glaciation over the past 800,000 years.

The 3,260-metre (10,595-feet) core was drilled into the East Antarctica icesheet at the Franco-Italian base, Dome C. The drillers, gathered in a venture called the European Project for Ice Coring in Antarctica (EPICA) stopped just 15 metres (48.75 feet) short of the bedrock.

Using traces of the hydrogen isotope deuterium in air bubbles trapped in the ice layers, the scientists built a record of greenhouse-gas concentrations over the aeons, which in turn provides a record of temperature.

They found the temperature varied widely, by as much as 15 C (27 F) over the 800,000 years. In the last Ice Age, which ended around 11,000 years ago, the temperature was 10 C (18 F) lower than today.

The EPICA team had previously analysed the Dome C core to a depth equivalent to 650,000 years ago.