Fossils show Greenland was once ice-free – and could be again

Ancient plants, seeds and insects preserved beneath Greenland’s ice sheet reveal that it once melted completely, raising concerns about sea level rise if it happens again.

Fossilised plants and insects extracted from beneath the centre of Greenland provide “smoking gun” evidence that the ice sheet has completely collapsed in the past – and could do so again.

A rocky landscape near the eastern coast of Greenland, similar to what the interior of the island may have looked like when its massive ice sheet melted away
Joshua Brown

The findings, taken from a sediment core drilled 30 years ago, reveal that the island was once an ice-free Arctic tundra complete with insects and plant life.

This landscape could return due to climate change, says Paul Bierman at the University of Vermont. “These small fossils are giving us a big warning that we could very likely lose the Greenland ice sheet if we continue on the path we’re doing right now.”

The Greenland ice sheet, which is more than 3 kilometres thick in some places, is already melting rapidly in response to climbing global temperatures. If it melts completely, which scientists estimate would take centuries, global sea levels would rise by 7.2 metres, submerging coastal cities around the world.

After proving last year that north-west Greenland was free of ice around 400,000 years ago, Bierman and his colleagues wanted to find out whether the very centre of Greenland has always been covered in ice.

They studied sediment from the base of an ice core drilled in the centre of the island in 1993, known as GISP2. Trapped in the sediment was evidence of biological material, including an insect eye, fungus spores, bud scales of a young willow tree and an Arctic poppy seed.

The findings prove that Greenland was once a very different Arctic landscape, says Bierman. “The fossil plants are the smoking gun. If you have plants where today you have ice, there was no ice.”

If the ice at the centre of the island was gone, 90 per cent of the rest had to be melted too, he says.

Willow bud scale, Arctic poppy seed, fungal bodies and rock spike-moss megaspores found in the GISP2 soil sample
Halley Mastro/University of Vermont

The last deglaciation of Greenland was probably caused by changes in Earth’s orbit. Previous analysis of rocks from GISP2 suggests the Greenland ice sheet is no more than 1.1 million years old, but more research is needed to identify exactly when the island was last free of ice, says Bierman. “Greenland was basically green, deglaciated, at some point in the past. The outstanding question now is when.”

Eric Wolff at the University of Cambridge says the findings are “really interesting” and demonstrate the value of preserving ice cores for the future. “We need data from underneath other areas of Greenland, and new ideas to establish exactly when, and under what climate, Greenland last deglaciated and reglaciated,” he says.

Journal reference:

Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.2407465121