Across oceans, peatlands, forests and ancient woodlands, our planet quietly sequesters carbon dioxide from the air. Until the eighteenth century, the carbon cycle balanced CO₂ levels in the atmosphere and supported life for over 11,700 years: a period that researchers have named the Holocene.

In Hengill, a volcanic ridge east of Reykjavik, a white steam cloud blurs the outline of a metal power plant. Its four units each contain two metal boxes that whir with fans. These are sucking in the air to trap carbon dioxide, using a sponge-like filter called solid sorbent that binds with the carbon. Once the sponge is saturated, the interior is heated to 100 degrees Celsius, then the carbon is squeezed out and injected deep into an underground basalt rock formation. Within two years, it turns to stone.