What air did Caesar, Muhammad, or Christopher Columbus breathe? The answer lies in a giant refrigerated library in Copenhagen, where ancient ice samples are stored that hide the secrets of the atmosphere of other times.
“What we have in these archives are climate changes since prehistoric times. We have a list of human activities over the last 10,000 years,” Jørgen Peder Steffensen, professor at the University of Copenhagen, tells AFP.
Ice blocks have been his passion for four decades. He met his wife, Dorthe Dahl-Jensen, also an authority on paleoclimatology, drilling on the Greenland ice floe.
Since 1991, Steffensen has managed the library of 25 kilometers of samples, most from Greenland, that help scientists understand changes in the climate. These fragments are exceptional because they are not frozen water but compressed snow.
“The air between the snowflakes is trapped in the form of bubbles, and this air is as old as ice,” he explains.
In the anteroom, or reading room, the temperature is -18°C, an almost mild temperature compared to the -30°C in the main room, where around 40,000 blocks are stored in boxes.
It is in this space that researchers study samples under a microscope, but not for long to avoid changing temperatures.
Steffensen takes a special sample from a box, whose air bubbles can be seen with the naked eye: it is the snow from year zero.
“We have Christmas snow, real Christmas snow,” he says, smiling.
In the unusual library, the oldest samples were brought in the 1960s from Camp Century, a secret US military base in Greenland.
The most recent arrived this summer (winter in Brazil), after scientists reached the mother rock in the east of the island, more than 2.6 km deep.
These latest samples include extracts from more than 120,000 years ago, during the last interglacial period, a time when the atmospheric temperature in Greenland was 5°C higher than today.
Ice cores are the only direct sources for knowing the state of the atmosphere in the past, before human-made pollution.
“Thanks to ‘ice witnesses’, we are able to determine how greenhouse gases carbon dioxide and methane change over time. We can also observe the impact of fossil fuels in modern times,” explains Steffensen.
This project is different from that of the Ice Memory Foundation, which is trying to collect ice samples in 20 places around the world to preserve them at the French-Italian Concordia station in Antarctica for future researchers, before these resources disappear with climate change.
“Storing Greenland’s glacial memory is very good,” says the foundation’s president, Jérôme Chappellaz.
He is concerned, however, about the risks of using an industrial freezer, which range from technical problems, financial difficulties, or the possibility of attack or war.
In 2017, a freezer malfunction exposed 13% of ancient ice samples preserved at the University of Alberta, in Canada, to too high a temperature.
At the base of Concordia, far from human activity, the average annual temperature is -55°C.
“They have a treasure trove,” Chappellaz says of the Danish scientists. “This treasure must be protected and, as far as possible, added to the world heritage of humanity.”