First a tractor sprays nearly 20 tonnes of gray crushed basalt over one field. Then the farmer makes several more passes ...

The proposal is a rather simple one: spreading crushed basalt over farm fields. If you’re unfamiliar with basalt, it’s just cooled lava, a rock that is rich in magnesium, iron and other minerals.

The technique, known as enhanced rock weathering, involves spreading finely crushed basalt, a natural volcanic rock, on fields to boost the soil’s ability to extract CO 2 from the air. In the first ...