Scientists are examining whether accelerated versions of natural geological processes can effectively capture carbon from the atmosphere and store it for the long term, as startups backed by major tech firms push these methods into field trials. Enhanced weathering and ocean alkalinity enhancement are among the approaches gaining traction, with investment rising rapidly and carbon credits appearing on voluntary markets.
According to a new assessment published in Science, current models may overestimate how much carbon these technologies ultimately remove. The study points out that while natural processes have regulated Earth’s climate for millions of years, replicating them at scale introduces uncertainties about durable storage.
Enhanced weathering speeds up the chemical breakdown of rocks containing calcium and magnesium, such as basalt and dunite. Finely crushed minerals are spread across agricultural soils to increase surface area for reactions with rainwater and carbon dioxide. Ocean alkalinity enhancement aims to boost the sea’s natural capacity to absorb and store atmospheric carbon dioxide.
"Natural geological processes have been regulating Earth’s climate for millions of years," the assessment states. Startups supported by companies including Google and Microsoft have already begun applying these techniques in real-world tests.
Many assessments assume that once minerals dissolve, the resulting alkalinity and carbon will reach the ocean for long-term storage lasting thousands of years. However, the Science paper highlights that Earth systems contain multiple points where carbon flow can weaken before reaching the open ocean.
Dissolved elements can become trapped in new minerals such as clays as water moves through soils, rivers, estuaries and coastal environments. These reactions consume alkalinity and reduce the amount of carbon stored over long timescales, according to the researchers.
Climate, rainfall, soil chemistry and biological activity all influence reaction rates, leading to wide variations in carbon removal between different environments. The true additional carbon removed from the atmosphere may therefore be smaller than headline estimates suggest.
The assessment notes that some approaches could interfere with natural carbon removal pathways. Increasing alkalinity in one area may reduce natural dissolution or weathering processes elsewhere, meaning the net benefit could be less than projected.
"Many field trials focus on changes occurring at the application site itself, but much of the long-term carbon storage depends on what happens downstream – across entire catchments, rivers and coastal oceans," the paper reports.
New Zealand is cited as a potential location for better understanding these dynamics due to its volcanic rocks, high rainfall and strong land-to-sea connectivity. Researchers say this setting could help track how alkalinity and carbon move through the Earth system.
The central question remains how much carbon stays removed from the atmosphere over decades to centuries and whether that removal is truly additional to what would occur naturally. The assessment emphasizes that these technologies still contribute to climate mitigation efforts.
"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," the authors conclude. Larger-scale deployments will require clearer answers on durability before generating carbon credits at global scale.