Ice cores drilled from southern Greenland have revealed the first evidence of a surprisingly lush forest that existed in the region within the past million years. The findings from an international study published today in the journal Science suggest that the southern Greenland ice sheet may be much more stable against rising temperatures than previously thought.

Researchers analysed ice cores from a number of locations in Greenland, including Dye 3 in the south of the country. From the base of the 2km deep Dye 3 core, they were able to extract what they believe is likely to be the oldest authenticated DNA obtained to date.

By analysing these DNA samples, the researchers identified a surprising variety of plant and insect life, including species of trees such as alder, spruce, pine and members of the yew family, as well as invertebrates related to beetles, flies, spiders, butterflies and moths. The researchers believe that the samples date back to between 450,000 and 800,000 years ago.

"We have shown for the first time that southern Greenland, which is currently hidden under more than 2km of ice, was once very different to the Greenland we see today," explains Professor Eske Willerslev, a Wellcome Trust Bioarchaeology Fellow from the University of Copenhagen, who led the study."Back then, it was inhabited by a diverse array of conifer trees and insects."

The research implies that ancient forests covered southern Greenland during a period of increased global temperatures, known as an interglacial period. When temperatures fell again, the area became covered in ice. This ice sheet appears to have remained during the last interglacial period (116,000-130,000 years ago) when the temperature was 5degC warmer than today, contrary to the view currently held by scientists. Professor Dorthe Dahl-Jensen, also at the University of Copenhagen, has shown that in fact, even during this interglacial period, the ice thickness at Dye 3 would have been reduced to between 1 km to 1.5km.

"If our data is correct, then this means that the southern Greenland ice cap is more stable than previously thought," says Professor Willerslev. "This may have implications for how the ice sheets respond to global warming."

However, Professor Willerslev was keen to dismiss the idea that this meant sea levels would not rise to the levels predicted by scientific models.

"We know that during the last interglacial, sea levels rose by 5-6m, but this must have come from other sources additional to the Greenland ice cap, such as Antarctic ice. I would anticipate that as the Earth warms from man-made climate change, these sources would still contribute to a rise in sea levels."

The results also show conclusively that ancient biomolecules from the base of ice cores can be used by scientists to reconstruct the environments hidden underneath ice-covered areas and can yield insights into the climate and the ecology of communities from the distant past.

"Analysing ancient biomolecules from beneath glaciers and ice sheets is challenging due to the very low concentrations, but the information is worth the effort," says Dr Enrico Cappellini, a member of the University of York's new PALAEO Group and another of the paper's co-authors, whose work is supported by the European Commission. "Our study suggests a solution to this problem. Given that ten per cent of the Earth's terrestrial surface is covered by thick ice sheets, it could open up a world of new discoveries."