An ice core from Antarctica is a time machine that recorded the climate for 130,000 years straight, year after year, with no gaps. Air bubbles trapped in the ice preserve the carbon dioxide of those ancient eras. By comparing its concentration with the temperature that the ice also remembers, scientists have seen how the two talk to each other.
First, the gas calls the shots on temperature: if CO₂ in the air doubles, the planet warms by 13 degrees. But heat doesn't stay in debt: it makes the ocean and soil release extra gas: roughly 6 CO₂ particles for every degree of warming. This response doesn't come at once but over several centuries, like an echo in the mountains.
The key finding: the link between gas and heat is not instantaneous but stretched over time. First, the gas warms; then, the heat releases gas, and so on in a loop. The ice record shows this loop has been running steadily for tens of thousands of years. So, knowing today's CO₂ level, we can look into the climate's future with more confidence.
Ice cores preserve not only gas but also dust, volcanic ash, and even traces of ancient wildfires — revealing how life on Earth has changed.