Fields of seaweed expand to the ocean’s horizons. During the day the kelp draws carbon from the air. At night the drones to which it is tethered lower it below the surface to absorb nutrients. When the drones sense a field is ready for harvesting it is towed to processing plants where bioethanol fuel is extracted. Carbon produced during the process is captured and stored underground.
Further inland cattle graze on open plains, with no farming machinery in sight. Herds till the earth with their hooves and move on. Seeds are planted in the rich soil they leave. When the fields are farmed the crop residues, saturated with the carbon the land has absorbed, are gathered and combusted to make biochar, a kind of charcoal that can be taken to cement plants to be mixed with aggregates to make carbon absorbent concrete. The carbon emitted by the cities of the past becomes building material for the cities of the future.
Is this geoengineering? Both of these systems are designed to alter the Earth’s climate, to draw carbon from the atmosphere and to cultivate new sources of fuel at scales capable of powering advanced economies. But they seem far from the popular images climate intervention conjures: sunshades in space, planes spraying particles into the stratosphere, tankers dumping iron into the ocean to fertilise algae blooms.