The Greenland Ice Sheet more fragile than expected: Greenland was predominantly green only 416,000 years ago

Published 13-09-2023

A large part of Greenland was covered by tundra and possibly forest in recent geological times, specifically an interglacial period 416,000 years ago. This is revealed in a new study published in Science. The study provides new insights into what we can expect from sea level rises as a result of the melting of the Greenland Ice Sheet due to global warming.

A mostly green and brownish landscape with a lake and a winding river is seen. It is slightly hilly. A stream winds through a mostly green Greenlandic landscape characterized by tundra. (Photo: Joshua Brown, University of Vermont)

In the research article ’Deglaciation of northwestern Greenland during Marine Isotope Stage 11’ published 21 July 2023 in the journal Science, a number of researchers, including Research Professor Paul Knutz, Senior Researcher Tonny Bernt Thomsen and Senior Researcher Nynke Keulen, all GEUS, share a study that contributes new insights into the age of the Greenland Ice Sheet.

The study shows that Greenland was significantly more ice-free during an earlier interglacial than we have so far assumed. The Greenland Ice Sheet was smaller, and the global sea level was therefore higher than today.

“Actually, model calculations from the study show that the sea level was at least 1.4 meters higher at one point. A greater loss of ice mass and thus an even higher sea level cannot be ruled out, but this requires further research.”
- Paul Knutz, Research Professor at GEUS.

Old drill cores from the Cold War

The researchers have analysed deposits from the bottom of the Camp Century ice core drilling, which was carried out in 1966. Camp Century is best known as an underground US military base that was established in northwest Greenland in the 1960s. The cores, which contain frozen sediments and constitute a geological climate archive, lay dormant for decades until they were rediscovered in 2017.

When the researchers first started examining the cores, they were found to contain organic material, including parts of leaves and moss, which could indicate that there has been tundra and even forests not unlike those in the Nordic countries. The new study can now determine the period for the ice-free conditions in northwest Greenland to 416,000 years ago.

Reduced inland ice

The core samples from Camp Century originate from an interglacial period that took place 424,000-374,000 years ago known as ‘Marine Isotope Stage 11’ (MIS11). The period was characterised by a moderate albeit prolonged warming as a result of increased solar radiation. Compared to the climate we have today, however, the significant difference is that the atmospheric levels of heat-trapping carbon dioxide back then were far below the levels of today; 280 parts per million (ppm) versus 480 ppm. Despite that, the ice sheet was significantly reduced compared to today.

The researchers behind the study emphasise that the findings may indicate that the ice sheet is more sensitive to climate change than we previously assumed. One of the leaders of the study points out that this study proves the connection between global warming and the melting of the Greenland Ice Sheet:

“It's the first rock solid evidence we have that a large part of the Greenland Ice Sheet disappeared when it got warmer,” says Paul Bierman, professor at the University of Vermont, who co-led the study.

GEUS contributed to the study by establishing the geologic origin of the Camp Century core material; knowledge that is essential to be able to interpret the depositional history.

“We have determined the composition and origin of the sediment layers at the bottom of the Camp Century ice core, especially the formation ages of mineral grains and their relationship to the North Greenland geology,” says Paul Knutz.

“The result from the Camp Century ice core raises new questions and is therefore ideally timed with a scientific expedition to Baffin Bay in 2023. Here, we will carry out a series of deep core drilling off northwest Greenland as a part of the International Ocean Discovery Program (IODP). They are supposed to shed light on the ice sheet’s evolution and past reaction to climate warming. The common interest of the studies revolves around obtaining a continuous and detailed chronology of marine temperature conditions and ice melting that can clarify whether MIS11 was unique or just one of several ‘super-interglaciations’ over the past 2.5 million years,” says Paul Knutz.

Paul Knutz says that the researchers will also collect climate archives that go back 15-20 million years and can shed light on the effect of CO-induced warming on the dynamics of the ice sheet.

The study published in Science is the result of an international collaboration involving a number of American and European research institutions, including the Niels Bohr Institute, University of Copenhagen. GEUS's participation in this collaboration, which focuses on unraveling a climate history that has been hidden in a deep freezer for decades, primarily rests on GEUS's isotope-geochemical analysis facilities as well as on extensive knowledge of the geology of Greenland and the Arctic. The work has been carried out with support from Geocenter Danmark through the project ’Evolution of Icehouse Greenland – integrating Models and Archives’ (ENIGMA).

Expedition to Baffin Bay

In August-September 2023 there is an expedition to Baffin Bay. The expedition is a part of the International Ocean Discovery Program (IODP).

You can find more information about the expedition here (in Danish)

Camp Century: below the ice

You can find more information about the examination of sediments from Camp Century and find interesting pictures of the research here.

Camp Century: below the ice

Monitoring of the Greenland Ice Sheet

We are keeping a close eye on the Greenland Ice Sheet and the climate in Greenland.

You can see the current status of the Greenland Ice Sheet at

Scientific articles

You can read the Scientific article 'Deglaciation of northwestern Greenland during Marine Isotope Stage 11' here:
DOI 10.1126/science.ade4248
Released in Science the 21. juli 2023.

Paul Knutz
Research Professor
Near Surface Land and Marine Geology
Tonny Bernt Thomsen
Senior Researcher
Mapping and Mineral Resources
Nynke Keulen
Senior Researcher
Mapping and Mineral Resources
Malene David Jensen-Juul
Communications Officer
Press and Communication