At geological time scales, what really controls the climate isn’t the atmosphere, it’s the ground. Most of Earth’s carbon dioxide is held underground, in reservoirs of natural gas and oil, but also in the rocks themselves. As the planet’s tectonic plates slide and churn against one another, they bury carbon deep beneath the surface while exposing fresh rock that will soak up more carbon over time.

That carbon can be liberated in large volcanic events, causing mass extinctions. But the pro