THROUGH THE SOIL INTO THE OCEAN
Enhanced Rock Weathering (ERW)
The illustration explains Enhanced Rock Weathering from quarry to ocean. On the left, a rock mill grinds silicate rock rich in magnesium and calcium. Trucks deliver the fine material to farms, where a tractor spreads it across fields. Rain falls on the soil; CO2 from air dissolves in rainwater to form carbonic acid. In the soil, carbonic acid reacts with rock minerals and releases nutrients for plants; the carbon is converted mainly to dissolved bicarbonate. The inset shows roots in amended soil and a reaction chain from CO2 + H2O to bicarbonate with Mg/Ca. Bicarbonate remains dissolved in soil and groundwater, then travels via streams and rivers to the sea. In the ocean, it can stay stored for centuries to millennia and, over time, react with Ca/Mg to form solid carbonate minerals that accumulate on the seafloor. The diagram highlights co‑benefits (soil fertility, nutrient supply) and the stepwise pathway from field to river to ocean storage.
Certain rocks absorb CO₂ from the air as they weather. This process is accelerated when the rock is finely ground. When powdered rock is spread on agricultural soils or meadows, the CO₂ is bound in the soil as it weathers. Rivers then wash it into the oceans, where it is stored long-term in the water and ultimately in the ocean floor.
ERW is still in the research phase. Initial pilot trials are underway in the United Kingdom, the USA, Canada, Brazil and India.
ERW uses a natural process and relies on existing infrastructure: grinding mills in quarries and transport and distribution networks for rock powder are already in place in many locations.
However, before the method can be applied on a large scale, there are still key questions to be answered: How can we accurately measure how much CO₂ is permanently sequestered? Which soils are particularly suitable? And what effects does ERW have on soil fertility, plant growth and water quality in the soil? Also, how can we prevent heavy metals in the rock powder and ensure that it is not inhaled during application?
Finely ground basalt is spread over a field to remove CO₂ from the atmosphere through accelerated weathering. Photo: Fengchao Sun (Yale Centre for Natural Carbon Capture)