Climate History Isn’t Debatable When It’s Drilled Out of Bedrock

With their metal frames quivering in winds capable of sandblasting exposed skin in a matter of minutes, the drill rigs appear almost delicate against the vast white silence of Antarctica. But what they extract from beneath the ice feels heavier than anything that can be explained by machinery: cylinders of frozen time, layered with ash, dust, trapped air, and tiny pieces of extinct worlds. Once debated in abstract graphs, climate history now rests in the palm of the hand like a glass rod.

Drilling ice cores from Greenland and Antarctica, cutting them into meter-long segments, and keeping them in specialized freezers at -36°C has taken scientists decades. Tiny air bubbles—ancient atmosphere sealed like glass messages—are contained within those cylinders. They contain methane and carbon dioxide, as well as remnants of volcanic eruptions and smoke from wildfires. The intimacy of it is difficult to ignore: air that no human has ever breathed, preserved for hundreds of thousands of years, and now thawing under lab lights.

As it happens, Snowfall works as an archivist. The weight of the seasons causes each winter layer to compress into firn and then dense ice by trapping dust, pollen, soot, and sea salt. Temperature changes are revealed by the chemistry of these layers through oxygen isotopes; heavier isotopes condense sooner, while lighter isotopes evaporate more readily. Colder weather is indicated when there is a shortage of heavy oxygen in polar ice. It is a sophisticated thermometer that silently records every change in climate. It is constructed without glass or mercury.

The scars of disaster are also present in ice cores. One Antarctic sample has a brushstroke-like dark streak of volcanic ash from 21,000 years ago. While underwater eruptions occasionally warmed the planet, sulfur-rich eruptions frequently cooled it by obstructing sunlight. Pollen reveals long-lost ecosystems, smoke residues indicate wildfire cycles that rose and fell with climate shifts, and dust layers hint at ancient droughts. The layers have the feel of episodes rather than data.

Ice records dating back 800,000 years seemed incredible for decades. Then, scientists discovered 2.7 million-year-old ice in wind-blown blue ice fields close to Antarctica’s Allan Hills. They focused on regions where ancient ice is pushed upward by glacier flow rather than drilling down through orderly layers. Older samples might be concealed under bedrock or ice sheets, awaiting new methods to bring them to light.

At the Crary Ice Rise in West Antarctica, a multinational team recently drilled through 523 meters of ice to retrieve a 228-meter sediment core that contained microscopic fossils, mud, gravel, and marine shells. The layers imply that during the last 23 million years, the ice sheet has repeatedly receded, revealing an open ocean where solid ice currently rests. Scientists were said to have felt both relief and anxiety as they watched the first cores emerge from the borehole—evidence of a shifting ice sheet suggests a shifting future.

The numbers themselves seem uninspiring. The amount of carbon dioxide in the atmosphere varied from 180 to 300 parts per million for at least 800,000 years. It is over 420 ppm now. In addition to increasing CO₂, ice cores also reveal decreasing carbon-14 ratios, which are a sign of fossil fuels containing diluted ancient carbon. Geologically, the change occurs instantly. When civilization first began, the climate was remarkably stable; the current spike is outside of that limited comfort zone.

Beyond ice, paleoclimate records exist. The chemistry of fossilized plankton changes with temperature and is preserved in ocean sediments. Tree rings record cycles of drought and precipitation. Ancient precipitation isotopic signals are stored in cave formations. When comparing these records, they all point to the same conclusion: temperatures rise in response to increases in carbon dioxide. Although the precise rate of ice sheet response this century is still unknown, historical data indicates that they are capable of a dramatic retreat.

At deep time, there’s a propensity to shrug. The Earth was much warmer and devoid of ice at the poles 50 million years ago. However, there were no global food systems that relied on predictable seasons or coastal megacities. The development of human civilization took place during a period of exceptionally stable weather. Given that the West Antarctic Ice Sheet alone has the potential to raise sea levels by several meters, even a small hint of stability raises adaptation-related concerns that seem less hypothetical.

The layers, which are dotted with dust from deserts that may have bloomed and disappeared long ago, resemble faint tree rings that alternate between clear and cloudy bands when standing next to a recently cut core. The past is not quiet. It is quantifiable, compressed, and layered. There is no debate about climate history on TV panels. It is measured molecule by molecule, melted under microscopes, and drilled out of bedrock. How quickly society reacts to what the ice is already saying is still up in the air.