Can enhanced rock weathering deliver measurable climate impact at scale?

How much CO₂ can ERW actually remove at a global scale?

The most optimistic projections come from large-scale modeling studies. One study combined a reactive transport model with climate data across ~1,000 agricultural sites globally and found that applying 10 tons of basalt dust per hectare could sequester 64 gigatons of CO₂ over 75 years; when extrapolated to all agricultural land, that figure rises to 217 gigatons of CO₂ [2]. To put that in perspective, global CO₂ emissions in 2023 were about 37 gigatons, so 217 gigatons represents roughly six years of current emissions. A separate UK-focused model estimated that ERW on arable croplands could remove 6–30 million tons of CO₂ per year by 2050, which is up to 45% of the atmospheric carbon removal the UK needs to meet its net-zero target [1].

Another study using an integrated climate-energy-economy model found that applying basalt to forests could triple the carbon sequestration from ERW compared to using it only on croplands, because the phosphorus released by the rock also boosts tree growth and organic carbon storage [4]. That study estimated that leveraging this 'biotic' pathway could make ERW a much larger contributor to meeting Paris Agreement goals.

However, these are modeled projections, not measured results. The same global study [2] also noted that a significant fraction of the applied basalt does not fully weather even on a multidecadal timescale, meaning the actual CO₂ removal per ton of rock may be lower than the theoretical maximum. The key takeaway is that the potential is large, but realizing it depends on real-world conditions.

What happens when you actually test ERW in the field?

The strongest real-world evidence in this set comes from a four-year ERW-reforestation experiment in South Wales, UK, covering 11.5 hectares with 64 plots [5]. This study directly measured what happened when crushed metabasalt was added to soil in a forest setting. The inorganic carbon removal—the direct chemical weathering that captures CO₂—was detectable but small: only about 0.19 tons of CO₂ per hectare per year. More importantly, the rock weathering products mostly stayed in the soil rather than being exported as alkalinity, which is the form needed for permanent carbon storage.

Worse, the study found that the rock addition stimulated tree growth (which removed an extra 0.34 tons of CO₂ per hectare per year aboveground), but it also increased soil CO₂ efflux—microbes and roots respiring more carbon back into the atmosphere—by about 2.54 tons of CO₂ per hectare per year. When all these fluxes were added up, the net effect was a release of about 2 tons of CO₂ per hectare per year, meaning the site became a net carbon source rather than a sink over the four-year study [5]. The authors emphasize that organic pathways (plant and soil responses) dominated the system, and that these feedbacks must be better understood before large-scale deployment.

This doesn't mean ERW is a failure—it means that in some ecosystems, the side effects can overwhelm the intended carbon removal. The study was in a reforested area, not a cropland, and the results may differ in agricultural soils where tillage and crop management alter carbon dynamics. But it is a clear warning that models that ignore ecosystem responses may overestimate ERW's climate benefit.

What makes ERW work well in some places and poorly in others?

Several studies converge on the same key factors: climate, soil conditions, and rock particle size. The global modeling study [2] found that ERW becomes modestly more effective with global warming and that the 'payback period'—the time needed for the rock to weather and remove the CO₂ emitted during its production—is significantly shorter in hot and humid environments. These conditions happen to coincide with many low-income countries, suggesting that ERW could be both more effective and more equitable if deployed in the tropics.

A detailed reactive transport modeling study [6] using forsterite (a proxy for the mineral in basalt) showed that complete weathering within five years is possible under ideal conditions, removing about 2.3 kg of CO₂ per square meter per year. But the rate is 'highly variable' depending on site-specific conditions. The study found that the in-situ weathering rate is enhanced when CO₂ is readily available—either from well-drained soils that allow atmospheric CO₂ to penetrate, or from high biological activity (plants and microbes) that generates CO₂ in the soil. It also showed that grinding rock to finer particles only speeds up weathering if CO₂ supply is not limiting; otherwise, the energy cost of grinding may not be justified.

The cost and energy of grinding are themselves manageable. A geospatial analysis for the coterminous US [3] found that grinding 1 gigaton of rock would consume less than 2% of annual national electricity supply, and the CO₂ emissions from grinding are small (5–35 kg CO₂ per ton of rock) compared to the carbon removal potential. The cost of grinding ranges from about $1 to $8 per ton of rock depending on particle size and power source. So the energy and cost barriers are modest—the real challenge is ensuring that the rock actually weathers and that the carbon stays locked up.

About These Sources

This answer is built on 6 peer-reviewed studies — published from 2022 to 2026, 3 from 2024 or later, 4 in Q1 journals, collectively cited 215 times — selected as the most relevant from 9 studies that passed quality screening, drawn from 34 papers retrieved from a database of over 500 million.

Sources used in this answer

Related research questions