An analysis suggests that spreading crushed silicate rocks on agricultural fields could remove up to 1.1 billion tonnes of carbon dioxide from the atmosphere each year by 2100, while boosting crop yields. The method, known as enhanced rock weathering, accelerates natural processes to lock away CO2. However, researchers highlight uncertainties about its scalability and potential side effects.
Enhanced rock weathering involves applying crushed silicate rocks, such as basalt, to farmland to speed up the chemical reactions that draw carbon dioxide from the air. Rainwater forms carbonic acid that reacts with the rocks, converting CO2 into bicarbonate ions, which then flow into rivers and oceans for long-term storage. This process mimics natural weathering that has helped regulate Earth's climate over millions of years. Farmers have long used ground limestone on fields to enhance nutrient uptake, and this technique offers similar soil benefits by adding elements like magnesium and calcium.
Chuan Liao at Cornell University in New York explains, “The main benefit is through sort of solving atmospheric CO2 through chemical reactions. And there are also some side benefits, such as adding… magnesium, calcium potentially, to supplement soil nutrients.” As global emissions rise, the United Nations climate body states that carbon removal methods are essential to cap warming at 1.5°C above pre-industrial levels. Countries including Brazil promote the approach to reduce emissions and fertilizer expenses. Last year, India's Mati Carbon secured a $50 million prize in Elon Musk’s XPRIZE for its carbon removal potential.
Liao's team assessed realistic adoption rates, factoring in farmer uptake similar to irrigation innovations and regional weathering efficiency. Their models predict 350 million to 750 million tonnes of CO2 removal annually by 2050, rising to 700 million to 1.1 billion tonnes by 2100. For context, global fossil fuel emissions are projected at around 38 billion tonnes in 2025. Initially, Europe and North America would lead, but Asia, Latin America, and sub-Saharan Africa could dominate later due to faster weathering in warmer, wetter climates. Liao notes, “[For] farmers in the Global South, there will be less barriers for them to do it decades from now.”
Critics question these projections. Marcus Schiedung at the Thünen Institute of Climate-Smart Agriculture in Germany points to risks like dry soils slowing removal by up to 25 times, or high-pH conditions leading to no net CO2 capture. He warns, “I’m a sceptic. We need to be sure that the CO2 is taken up. Otherwise, we get into the risk that we measure something [removing carbon], but somewhere else it’s released again.” Mining and transport emissions could also offset gains. David Manning at Newcastle University, UK, adds that removing one gigatonne of CO2 requires five gigatonnes of rock annually, posing a supply challenge: “That’s a major obstacle to growth.” Concerns include heavy metals like nickel and chromium in rocks such as olivine potentially contaminating food, and the need for new quarries.