Similar to tree rings, ice cores contain distinct layers representing each year’s snowfall. These annual layers act as a natural archive, not just of Earth’s past climate, but also of the history of humanity.
Jørgen Peder Steffensen, Professor of ice-core-related research at the Centre for Ice and Climate at the Niels Bohr Institute at the University of Copenhagen (Denmark), has been researching Greenland’s ice sheet for over 40 years.
Why are you extracting and analysing ice cores?
Jørgen Peder Steffensen: It was my former boss, Prof Willi Dansgaard, who discovered that by measuring the isotopic composition of oxygen in glacier ice you can tell the temperature of the cloud that the ice came from, and thus, gain insights into past climate.
The top of Greenland’s ice sheet doesn’t melt. All the snowflakes stay put and get buried by subsequent snow falls. The ice sheet doesn’t grow upwards as snow piles up because it moves slowly under its own weight towards the coast. Over the course of thousands of years, the ice caps have reached an equilibrium whereby the annual sink rate of the ice cap matches the snow fall on top. That means that the layers of snow become thinner as they get buried and participate in the flow. Sixty centimetres of snow, typically gets squashed to around 20 cm of glacier ice. Because there is no mixing of layers, when you drill a rod in the central part of an ice sheet, you can analyse each one and get a record of climate back in time.
The key thing is to establish the age of the ice. Every time there is a volcanic eruption in neighboring Iceland or a major one far away we can detect a layer of sulfuric acid in the ice cores, because these eruptions are irregular, we can use them as a time stamp or barcode. By analysing the chemical and physical properties of the layers within ice cores, we have created an accurate, high-resolution timeline of Greenland’s atmospheric conditions that extends back 60,000 years. That is half way into the last ice age!
Our analyses of Greenland’s ice core records have contributed to define the transition from the last glacial period (Pleistocene) to the current interglacial period (Holocene). The boundary is marked by an abrupt warming in the Greenland ice cores 11,729 years ago.
The absence of air bubbles in ice core layers is indicative of ice-sheet-wide surface melt events. There was only one such event between the year 1,000 AD and 2,000 AD, in 1889. However, since the year 2000 we have seen five. These findings confirm meteorological measurements collected around Greenland and are compelling evidence of global warming.
How is your research contributing to predicting the future climate?
Jørgen Peder Steffensen: We are collecting data about the past that can be feed into climate models and make them more accurate. We challenge these models by running them in the past to see if they can mimic what we see in the ice cores. We are helping to verify their predictions.
We don’t really know precisely what is going to happen in the future, we can only create a set of odds based on model predictions. These odds can quickly become hard currency.
The Intergovernmental Panel on Climate Change (IPCC) estimates that by 2100, sea levels will rise by 90 cm, plus or minus one metre. We are trying to reduce that uncertainty. If we can produce reliable results to be able to say that by 2100 the sea level will rise 80 cm with a possible variation of plus or minus 10 cm, that will immediately lead to meaningful actions to protect coastal communities.
What has been one of the most surprising findings to date?
Jørgen Peder Steffensen: In 2019 we found that by measuring lead in the ice cores we could to trace the economy of the Roman empire. Lead vapour was a significant by-product of Roman silver production and in the ice cores we can see how lead levels correlate with peaks and troughs of economic activity. This finding highlights how our research has direct links to history and archaeology.
How did your collaboration with Lucasz come about? Has it helped bring your work to new audiences?
Jørgen Peder Steffensen: Lucasz reached out to us and joined our camp in 2022. We are always on the lookout for collaborations with artists and keen to participate in outreach activities to communicate our work to wider audiences.
Someone who has no knowledge about what we are doing, will just see a cylindrical piece of clear ice. However, if you tell them that a particular fragment of ice contains snowflakes that fell between 1 BC and 1 AD, their perception changes, it becomes a tangible link to an ancient world.
Lukasz has captured the aesthetics of ice coring. Through clever use of light, Lukasz has managed to change people’s perception of ice cores. His ice portraits help convey that ice core research is not just about understanding climate but also the history of human civilisation.
As the East Greenland Ice-core Project (EastGRIP) is coming to an end, what are you working on next?
Jørgen Peder Steffensen: We are now embarking on the Green2Ice project, which will collect ice cores near the bedrock – the solid, consolidated rock layer beneath the Earth’s surface layers – and samples of the bedrock itself to understand how hot it needs to get for the ice sheet to disappear. As well as using the samples to determine the age and stability of Greenland’s ice sheet, we are planning to retrieve DNA samples to gain insights into ancient ecosystems.