Frozen Archives of the Atmosphere
Deep within the Antarctic ice sheet, tiny air bubbles trapped hundreds of thousands of years ago preserve pristine samples of ancient atmospheres. The EPICA Dome C ice core — drilled to 3,270 meters depth — provides a continuous CO₂ record spanning 800,000 years and eight glacial cycles. This is the longest direct measurement of atmospheric composition, and it reveals a remarkably regular pattern: CO₂ oscillates between ~180 ppm during ice ages and ~280 ppm during warm interglacials.
From Snow to Signal
Converting ice-core bubbles into a CO₂ time series requires careful science. Snow accumulates layer by layer, compressing under its own weight until pores close off at the firn-ice transition (~50-100 m depth). The trapped gas is younger than the surrounding ice — a gas age-ice age offset that must be modeled. This simulation includes a smoothing parameter representing the firn diffusion process, which acts as a natural low-pass filter on the atmospheric record.
The Glacial-Interglacial Rhythm
The CO₂ record's dominant periodicity matches Milankovitch orbital cycles — roughly 100,000 years. But CO₂ is not merely a passive follower of orbital forcing; it actively amplifies climate change through the greenhouse effect. During deglaciations, rising CO₂ contributed roughly one-third of the total warming, with ocean circulation changes and ice-albedo feedback providing the rest. This tight coupling makes CO₂ both a proxy for and a driver of past climate change.
Unprecedented Modern Levels
The ice-core record provides sobering context for modern CO₂ levels. At ~420 ppm, today's concentration is roughly 50% higher than any value in 800,000 years. The rate of increase — about 2.5 ppm per year — is at least 10 times faster than the fastest natural changes recorded in ice cores. Adjust the time window and amplitude to see how the natural CO₂ envelope compares to the modern spike that would tower off the top of any ice-core graph.