In the refrigerated library, ancestral ice for a better understanding of climate

What kind of air did Caesar, Mohammed or Christopher Columbus breathe? In the suburbs of Copenhagen, a giant refrigerator with its ice cores has been hiding atmospheric secrets for millennia and allowing scientists to better understand the ups and downs of the climate.

“What we have in these archives is climate change since prehistoric times, we have a record of human activity in the last 10,000 years,” Jørgen Peder Steffensen, professor of glaciology at the University of Copenhagen.

Ice cores have been his passion for 43 years. While drilling an iceberg, he met his wife Dorthe Dahl-Jensen, also a leading authority on paleoclimatology.

Often between Greenland and Copenhagen, Mr. Steffensen has managed the island-continent’s ice library since 1991, which with its 25 kilometers of cumulative samples is among the most important in the world.

These ice fragments are all the more remarkable because they are not frozen water but compressed snow.

“The air between the snowflakes is trapped as bubbles, and that air is the same age as the ice,” he says.

In the hall or reading room it is -18°C, which is a mild temperature compared to -30°C in the main room, where about 40,000 blocks of ice are stored in boxes.

This is where researchers study samples – never too long to avoid the cold – under a microscope.

Mr. Steffensen takes a special carrot out of the box, the air bubbles of which are visible to the naked eye: snow that fell in year zero.

“So we have Christmas snow, real Christmas snow,” smiles the lively sixty-year-old man under his thick hat.

mother of Stone

In this unusual library, where works can be viewed exclusively on site, the oldest fragments were brought in the 1960s from Camp Century, the then secret US military base in Greenland.

The last ones were this summer, when scientists reached the substrate in the east of the island, more than 2.6 kilometers deep.

This latest arrival contains extracts from more than 120,000 years ago, during the last interglacial period, when the atmospheric temperature in Greenland was 5°C higher than today.

“The planet was much warmer than today. But that was before the arrival of man,” emphasizes the glaciologist.

The “new” blocks of ice should provide a better understanding of sea level rise, which can only be partially explained by the melting of the ice cap.

Another part of the explanation comes from “ice flows,” these glaciers shrinking like nothing else.

“If we understand the ice flows better, we will be able to have a better idea of ​​the future contribution of Greenland and Antarctica” to sea-level rise, Mr. Steffensen says.

“We hope to be able to help determine the sea level in a hundred years” with a margin of error of 15 centimeters, much smaller than the current limit (70 centimeters), the scientist says.


Ice cores are the only direct sources of knowledge about the state of the atmosphere in the past, before anthropogenic pollution.

“Using ice cores, we were able to determine how the greenhouse gases carbon dioxide and methane change over time. We can also look at the impact of fossil fuels in modern times,” emphasizes Mr. Steffensen.

This project is different from the Ice Memory Foundation project which aims to collect ice cores from twenty locations around the world to preserve them at the Franco-Italian Concordia Station in Antarctica for future researchers, before these resources disappear due to climate change.

“Preserving the glacial memory of Greenland is very good,” says the president of the foundation, Jérôme Chappellaz.

But, he worries, this storage in an industrial freezer may be subject to dangers that could erase this memory: technical failures, funding problems, attacks, war, etc.

In 2017, a freezer malfunction exposed 13% of precious millennium-old ice samples stored by Canada’s University of Alberta to unwanted heat.

On the Concordia Plateau, far from human chaos, the average annual temperature is -55°C, which provides optimal preservation conditions for centuries to come.

“They have a treasure,” emphasizes Mr. Chappellaz in his appeal to the Danes. “We must protect this treasure and, as far as possible, ensure that it joins the world heritage of humanity.”

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