The Inside Scoop on Enhanced Rock Weathering

Permanent, nature-based carbon removal with co-benefits

Aug 28, 2024

Gigaton Potential

Enhanced rock weathering (ERW) has the potential to remove 1–5 gigatons of CO₂ per year once scaled. (1) It’s a wide range since the industry is only in its infancy, but experts tend to agree that ERW will play a key role in the annual 6–10 gigaton CO₂ removal capacity needed by 2050 to reach Paris climate goals (1.5 degrees Celsius target limit). (2)

For reference: in 2019, the world emitted 51 gigatons of CO₂-equivalent greenhouse gases. Project Drawdown estimates we need to cumulatively prevent and eliminate 1,000 GT from 2020-2050 to keep global warming below 2 degrees Celsius.

What You Should Know

Enhanced rock weathering is a method of carbon dioxide removal (CDR) that transfers carbon from the relatively fast organic cycle (largely involving plants and animals) to the slower geologic cycle, where carbon is locked away for 100,000+ years. Sounds fancy? It’s not!

The natural process of weathering already accounts for the removal of 1 gigaton of CO₂ from the atmosphere every year. (3) Enhanced weathering simply accelerates this process… ~50,000 times over.

How does it work?

As rainfall naturally erodes rock on mountains, in forests, and across grasslands, the CO₂ in rainwater reacts with the rock to form new, carbon-rich rock particles called ‘carbonates’, thereby capturing the atmospheric carbon in mineralized, stable geologic form. Over time, these carbonates sink through the soil into groundwater systems and rivers, eventually coming to rest in the ocean.

The rate at which this natural process occurs is dependent on a few variables:

Rock characteristics (e.g. Mg- and Ca-rich silicate rocks weather quickly)
The surface area of the rock (how much rock comes in contact with CO₂)
Climate (e.g., precipitation, humidity)
Soil (e.g., organic carbon levels, pH, soil temperature)
The length of time that passes before the carbonates reach the ocean

Using these principles, enhanced weathering project developers source silicate rock from existing quarries, grind it up into fine dust, and spread it onto soils in (typically, nearby) fields using existing agricultural networks and machinery. They then carefully track the capture of carbon over time and sell the resulting credits to interested buyers on the voluntary carbon market.

Why spread on agricultural land?

In addition to capturing carbon, rock-spreading offers co-benefits, which are essential to enhanced weathering’s value proposition to farmers—and the reason why they are willing to host spreading activities on their productive land. The application of rock dust such as basalt and wollastonite to agricultural soils releases micro- and macro- nutrients, increases soil pH (more alkaline), improves soil structure, and increases plant resilience to pests. In short, this means increased plant productivity and yields.

Another reason why ERW works well is that last-mile infrastructure already exists. Most farmers already work with contractor networks that routinely spread large amounts of limestone across vast tracts of land. This helps keep ERW relatively cheap and easy to scale. Rock is sourced (often as a byproduct) from nearby quarries. When accounting for all the emissions associated with the grinding, hauling, and spreading of rock in the final calculation of credits generated, you’ll often see carbon efficiencies of at least 90% in ERW processes. This means that 10% of the carbon captured by the process is used to offset the emissions from these operations, while the remaining 90% can be counted as net carbon sequestration and sold as carbon credits to third parties.

How can we verify the total carbon removed?

As with any method of carbon removal, the ability of developers to track and trace the amount and timing of carbon captured is integral to their ability to sell carbon credits. Developers must be able to prove a) how much carbon was captured, b) when it was captured, and c) for how long it will be stored. This is where the simple task of spreading rock on fields gets much more complicated.

Soil is naturally rich in both organic and inorganic carbon. Carbon cycles out when crops grow, and cycles back in as fertilizer is applied. This constant cycling of carbon makes it difficult to distinguish the carbon captured specifically through ERW from the carbon already present in the soil. As a result, the varying levels of soil carbon create a significant challenge for accurately measuring the precise impact of rock spreading.

Without the ability to directly measure the carbon sequestered in ERW operations, companies are racing to innovate MRV techniques that measure weathering signals so that they can derive the exact amount of additional carbon sequestered. Research shows that weathering can be traced through soil chemistry—specifically, the movement of cations and bicarbonate through the soils. In practice, this means that each project location becomes its science experiment: complete with a control site and a team that regularly sends samples off for lab analyses.

How does it compare to other CDR methods?

ERW performs favorably compared to other CDR technologies. It has high permanence while having a path to low costs at scale:

Source: IPCC, drawing on data from expert interviews; costs are per ton of CO₂ removed and represent 2023 estimates

Key Players

There are 24 enhanced rock weathering companies operating around the world - here are the leading three:

UNDO Carbon* (London) - They are the most operationally scaled; they’ve spread 200,000 tons of crushed silicate rock in the UK, Australia, the US, and Canada since their founding in 2022 and are actively generating revenue. They are one of the industry’s thought leaders and co-authored the ICROA-endorsed Puro.earth ERW MRV methodology. They have a robust science and technology team. They have signed offtakes with customers like Microsoft, British Airways, and McLaren Racing, among others.

Lithos (San Francisco) - Founded by Yale and Georgia Tech professors in 2022, Lithos is another scientific leader in the ERW space, having implemented an MRV technique that relies on frequent soil measurements. Late last year, Lithos won the largest enhanced rock weathering purchase agreement with Frontier, clocking in at $57.1M for the removal of 154,240 tons of carbon dioxide over the next four years.

InPlanet (Munich Germany & Piracicaba, Brazil) - The only ERW developer with scaled operations in South America’s tropical climates. InPlanet is betting that warmer and wetter tropical conditions lead to faster rock weathering rates and thus faster CO₂ drawdown. Also founded in 2022, the company signed a pre-purchase agreement in late 2022 with Frontier.

*Disclaimer: Georgia Carroll interned here this summer

Opportunities for Innovation

Science: Although there is a scientific consensus that enhanced weathering results in permanent CO₂ removal, the industry’s ability to scale has been hindered by the difficulty in measuring the exact timing and quantities of the removals. Since tracking the weathering signal is key to proving MRV, nailing down the science is fundamental to achieving credit verification and unlocking additional buyers at competitive prices. ERW developers are racing to provide the most accurate weathering data at the lowest price possible for several rock types.

Methodology: While developers are racing to establish cost-effective MRV protocols, credit certification platforms are still finalizing their official ERW MRV methodologies. These methodologies specify the exact data points and protocols needed to achieve credit verification, and without a final, industry-wide methodology, credit verification represents a continually moving target for developers. Industry-wide convergence around a methodology that is rigorous while allowing for reasonable room for error is a necessary precursor to the global scaling of ERW technology.

Unlocking the compliance markets: The voluntary market is led by a handful of buyers (Stripe’s Frontier Fund, Microsoft, J.P. Morgan, etc.) that are purchasing high volumes of CDR. In the short term, we will likely continue to see a high willingness to pay from voluntary buyers, which will support market scaling. As the voluntary carbon market matures, however, this type of catalytic capital will inevitably dry up, and the long-term success of ERW will hinge on access to the much larger compliance markets. (Check out our prior Gigaton article on the compliance markets here). Multiple trade organizations such as the Carbon Business Council and the Enhanced Weathering Association lobby compliance markets like Europe’s ETS to incorporate high-permanence CDR solutions.

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Author Bio

Georgia Carroll is a second-year at the Stanford Graduate School of Business. Before Stanford, she worked in sustainable agriculture investing and clean energy investment banking. She just finished up her summer internship at UNDO Carbon in London, working on their strategy team.

Footnotes

(1) Kohler P et al, 2010, Strefler et al, 2018, Beerling et al., 2020, Kelemen et al., 2020

(2) Additional average negative emissions from nature, BECCS and DACS across IPCC 1.5 degree scenarios, which assumed lower rates of decarbonisation of emitting sectors, IPCC Special report on 1.5 degrees (2018)

(3) Ciais et al. 2014

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