The way ordinary weather turns into a scientific record is one of the more genuinely elegant things Antarctica does. Snow falls on a particular corner of the East Antarctic plateau, roughly a thousand kilometres from the nearest coastline, in an area called Dome C. It’s cold enough there, all year round, that the snow doesn’t melt. It compresses under the weight of the next winter’s snow above it. That snow, in turn, is compressed by the winter after.
Over a couple of centuries the layers below the surface transition from soft snow into a granular substance called firn, and then, deeper still, into solid ice. At which point something quietly extraordinary happens. As the firn crystallises, tiny pockets of the surrounding atmosphere get sealed inside the ice as bubbles. Whatever the air was on the day that snow first fell, that’s what’s now trapped inside those bubbles. And once the bubbles are sealed, they stay sealed. For as long as the ice itself lasts.
Which, as it turns out, is a long time. Because East Antarctica has been continuously cold enough to hold ice at Dome C for at least the last eight hundred thousand years, the ice at the surface today sits above ice from every intervening winter going back that far. And every one of those older layers, provided you can get to it without melting or damaging it, still contains bubbles of the air from the day its parent snow first fell.
How the record was actually recovered
According to the peer-reviewed collection of research on the European Project for Ice Coring in Antarctica maintained by the journal Nature, which hosts the primary scientific papers describing the project’s findings and methodology, the effort to physically retrieve the record began in 1996. A consortium of ten European countries formed a research collaboration called EPICA, which stands for the European Project for Ice Coring in Antarctica, and set up two drilling stations on the East Antarctic plateau. The primary station, Concordia Research Station at Dome C, was chosen because the ice there was known to be one of the thickest continuous ice sheets anywhere on the continent, at roughly 3,270 metres from surface to bedrock.
The drill itself is a cylindrical instrument, roughly ten centimetres in diameter, that works by cutting a circular hole through the ice and preserving the central column intact. Every metre or so, the drill is pulled back to the surface, the extracted core is carefully removed, catalogued, packed into insulated containers, and shipped by icebreaker to European laboratories. Then the drill goes back down and cuts another metre. Then another. Over eight consecutive Antarctic summers between 1996 and 2004, the EPICA team drilled through the entire depth of the ice at Dome C. The final core, when all its sections were laid end to end back in the laboratories that received it, was 3,270 metres long and covered the last approximately eight hundred thousand years of terrestrial climate history.
Where the record gets more complicated, and where the popular framing sometimes slightly overreaches, is at the deeper sections of the core. Near the surface, meaning ice that fell as snow in the past twenty or thirty thousand years, the annual layers remain distinct enough that scientists can often count individual winters in the ice, the same way you can count tree rings. Deeper down, the weight of the overlying ice compresses everything below it. Layers that once represented a single year get squeezed together into thinner and thinner bands. By the time the drill reached the deepest ice at Dome C, meaning ice that fell as snow closer to eight hundred thousand years ago, the annual resolution had disappeared. What remained was a continuous record of the composition of the atmosphere across every one of those years, blended together over centuries or millennia depending on the depth. Which means the record isn’t strictly a diary of every winter. It’s more like a set of long, overlapping paragraphs describing what was in the air across successive stretches of time, each one increasingly compressed as you go further back.
What the ice has revealed, and what comes next
Once the extracted cores reached European laboratories, the actual work of reading them began. According to ScienceDaily’s reporting on the follow-on Beyond EPICA project, drawing on interviews with Hubertus Fischer of the Oeschger Center for Climate Change Research at the University of Bern about what the original EPICA data had established, the ice cores allowed researchers to reconstruct atmospheric carbon dioxide concentrations across the full eight hundred thousand year period. The pattern the data revealed was striking. Ice ages, meaning long cold periods during which the Northern Hemisphere was substantially glaciated, had alternated with shorter warm periods, called interglacials, on a fairly regular cycle of roughly one hundred thousand years. And carbon dioxide concentrations had swung between roughly 180 parts per million during ice ages and roughly 280 parts per million during interglacial warm periods. Never once, on the entire eight hundred thousand year record, had atmospheric CO2 exceeded that upper figure through natural variation.
The reason that specific finding mattered to atmospheric science is that CO2 concentrations in the modern atmosphere passed 280 parts per million in the nineteenth century and have continued climbing steadily since. As of 2025, the figure sits above 420 parts per million. Which meant the EPICA record established, on peer-reviewed measurement, that the current levels of atmospheric CO2 are the highest they have been at any point during the entire eight hundred thousand year window the ice covered. Not by a small margin. By a factor that puts the modern atmosphere considerably outside the range of anything humans have ever previously lived through.
The record is currently being extended. According to the Alfred-Wegener-Institut’s January 2025 press release on the Beyond EPICA follow-on project, drawing on field reports from chief scientist Julien Westhoff and the drilling team at Little Dome C, a new consortium of European researchers has now completed drilling a second, deeper core about thirty kilometres from the original Dome C site. This new core reached bedrock at a depth of about 2,800 metres. The team’s preliminary dating suggests the ice at the bottom of the new core is around 1.2 million years old. Which means the atmospheric record now extends by another four hundred thousand years beyond the original EPICA record, into a period nobody had previously been able to sample directly. At the deepest sections of the new core, the same compression problem that limited the original record’s resolution at depth returns in an even more extreme form. Westhoff’s field team estimates that up to thirteen thousand years of ice are compressed into a single metre of ice at those depths.
None of which is intuitively easy to imagine. A cylindrical column of ice, roughly two miles long, sitting in sections on refrigerated shelves in European laboratories at temperatures cold enough to keep the ancient air inside its bubbles intact. Each section is currently being cut into subsamples, ground under laboratory conditions to release the trapped gases, and analysed for its composition. What’s being released from those bubbles is, quite literally, the actual air of ancient winters. Not a reconstruction. Not a simulation. The physical gas that was in the atmosphere of Earth on days that occurred before human beings existed. Now measured. Now catalogued. Now sitting on refrigerated shelves in Bern, in Bremerhaven, in Grenoble, and in a handful of other European climate research laboratories, waiting for the next round of experiments that will read a few more years’ worth of what our planet used to breathe.
