Two Studies Suggest That Carbon Storage Through Enhanced Rock Weathering is Less Durable Than Thought

 

    Two recent studies cast doubt on the carbon removal durability of enhanced rock weathering.

 

Study 1: ‘Critical zone processes limit alkalinity export from natural basaltic systems’

     The first study was published in the journal Nature by researchers from Cornell University. The weathering of basalt, a volcanic rock, was studied in volcanic regions where it outcrops.

     According to the Cornell Chronicle:

“The researchers found that chemical reactions and limited water movement can substantially reduce the amount of weathering-generated alkalinity that leaves soils, moves through rivers and, ultimately, reaches the ocean. That alkalinity helps convert carbon dioxide into forms that can remain stored for long periods.”

     The conclusion of the study is simply that less carbon can be stored via enhanced weathering than previously thought.

“You obviously can buffer some CO2 emissions with this kind of process, but much less than people have hoped,” said lead author Louis Derry, professor in the Department of Earth and Atmospheric Sciences in the Cornell Duffield College of Engineering. “The idea that we’re going to get gigaton levels of CO2 reduction is not going to happen.”

     The researchers show that current methods of estimating the carbon removal effectiveness of enhanced weathering involve the dissolving and disappearance of calcium, magnesium, and other elements from crushed basalt in the upper 10 to 30 centimeters of soil. This is known as base cation depletion in the upper soil.  However, they argue that this is only the first step in the chemical process. As those chemical products pass through streams, soil, and groundwater, they enter the “critical zone,” the reactive layer where rock, soil, water, air, and living organisms interact. As the dissolved minerals move down, they can react with newly formed clays, oxides, and carbonate minerals, which can capture calcium and magnesium or generate acidity that consumes some of the alkalinity created by weathering.

“The net result is that only a modest fraction of dissolution products of weathering reactions – natural or engineered – is actually exported through the critical zone,” Derry said.

     They also challenge the assumption that grinding basalt into smaller particle sizes would enhance the speed of weathering reactions, noting that there is not a strong relationship between smaller particles and more surface area for reactions. I admit I am confused by this. I thought that anything broken into smaller pieces leads to more surface area being exposed. They do note a relationship between particle size and surface area at very fine sizes, however.  

“Among basalt samples proposed or used for enhanced weathering, the paper found no notable correlation between grain size and measured surface area.”

     They also note that enhanced weathering does work faster in wet, tropical environments, but not very fast in the dry, temperate areas that make up the world’s agricultural regions where most enhanced weathering projects have been proposed.

“Enhanced weathering may still provide useful local benefits, including buffering soil acidity, supplying nutrients or modestly offsetting emissions in some settings. But Derry argues that with limited resources available to address climate change, expectations for its global carbon-removal role should be grounded in how real landscapes behave.”

“We’ve got a lot of data from natural systems across a range of conditions,” Derry said. “We consistently see values that are much, much lower than the model studies. If you have finite resources to address a problem, you want to put them where they’re most likely to make a difference.”

     The study provides a good baseline for basaltic weathering. About 6% of the world’s surface is composed of basaltic rocks. Knowing the chemical weathering rates and characteristics of these zones provides important analysis for estimating the effectiveness of  enhanced weathering projects. They describe the findings as “limitations on watershed alkalinity export.” There are two kinds of limitations: 1) the formation of secondary minerals that react with dissolved mineral products in the critical zone, and 2) hydrological limitations where river basin discharge rates may not be enough to export more of the alkalinity.

Study 2: ‘Can enhanced alkalinity store carbon durably? Key questions remain about carbon removal strategies in open environmental systems’

     The second study has similar conclusions to the first, that enhanced weathering is not as durable as previously thought. Similarly, it is noted that reactions in the soil capture and utilize some of the carbon, break it down, and it makes its way to the atmosphere before it gets to the ocean or becomes sequestered underground for a lesser time period.

     According to an article about the study in The Conversation:

“Current models assume carbon captured on land or in coastal waters will reliably make its way into long-term storage in the ocean. However, these models don’t replicate all Earth processes.”

“In reality, part of the engineered capture of carbon can be reversed as water moves through soils, rivers, estuaries and coastal environments. Dissolved elements can become trapped again in new minerals such as clays, reducing how much carbon ultimately remains stored over long timescales.”

     The researchers found, however, that there are carbon losses on the way to the sought-after long-term ocean storage, which can last for thousands of years.

‘However, different materials dissolve at different rates. Climate, rainfall, soil chemistry and biological activity also influence how quickly reactions occur. This means carbon removal can vary enormously between environments.”

“Earth systems also contain many opportunities for the flow of carbon to weaken before it ever reaches the open ocean.”

“As alkalinity moves through the environment, dissolved elements released during weathering can become trapped again in new minerals. These reactions can consume alkalinity and reduce the amount of carbon ultimately stored long term.”

     They also note that while carbon storage is enhanced where enhanced weathering takes place, natural carbon uptake downstream may be impeded, reversing some of the benefits.

“The challenge is whether Earth systems can keep the captured carbon stored or whether we are simply moving carbon across time and space instead of durably removing it from the atmosphere.”

 

References:

 

Study casts doubt on carbon-removal method. Chris Dawson. Cornell Chronicle. August 26, 2026. Study casts doubt on carbon-removal method | Cornell Chronicle

Critical zone processes limit alkalinity export from natural basaltic systems. L. A. Derry, K. Maher & O. A. Chadwick. Nature volume 657, pages150–155 (2026). Critical zone processes limit alkalinity export from natural basaltic systems | Nature

Some technologies use accelerated natural processes to capture carbon – but can they store it durably? The Conversation. May 21, 2026. Some technologies use accelerated natural processes to capture carbon – but can they store it durably?

Can enhanced alkalinity store carbon durably? Key questions remain about carbon removal strategies in open environmental systems. Terry Isson and A. Joshua West. Science. 21 May 2026. Vol 392, Issue 6800, pp. 808-810. Can enhanced alkalinity store carbon durably? | Science