Can Carbon Removal Technologies Reliably Store Carbon Durably?
Recent research challenges the optimism surrounding carbon removal technologies like enhanced weathering. While these methods aim to trap CO2, complex natural processes often lead to carbon loss, raising concerns about the long-term durability and true effectiveness of these climate mitigation strategies.
Highlights
- •Emerging carbon removal technologies like enhanced weathering and ocean alkalinity enhancement are moving from concept to field deployment.
- •Recent scientific assessments suggest current carbon removal estimates may be overly optimistic due to complex Earth-system feedbacks.
- •Captured carbon can be lost as it moves through soils and rivers, often becoming trapped in new minerals before reaching the ocean.
- •Long-term durability and the issue of 'additionality' remain critical hurdles for the credibility of global carbon credit markets.
Natural geological phenomena have diligently regulated the climate of Earth for millions of years. Today, various carbon removal technologies are being championed as innovative tools to extract CO2 from the atmosphere, with several moving rapidly from theoretical concepts to tangible real-world deployments.
Among the most prominent methods are enhanced weathering—a process that accelerates the chemical breakdown of specific rock types—and ocean alkalinity enhancement, which seeks to bolster the ocean’s natural capacity to sequester carbon dioxide. Supported by significant investment from major technology firms, including Google and Microsoft, these approaches are already undergoing field trials, with carbon credits beginning to emerge on voluntary trading markets.
Evaluating the Effectiveness of Carbon Removal Technologies
However, a recent assessment published in Science suggests that current projections regarding the efficacy of these carbon removal technologies may be overly optimistic. Existing climate models often assume that carbon captured on land or within coastal zones will transition reliably into long-term storage within the deep ocean. Unfortunately, these simplified models frequently fail to replicate the complex, multifaceted processes of the natural environment.
In reality, the journey of captured carbon is far from straightforward. As water migrates through various landscapes, including soils, rivers, and estuaries, the engineered capture process can be partially reversed. Dissolved elements may become trapped once again within newly formed minerals like clays, which significantly curtails the total amount of carbon that remains sequestered over extended timescales. Consequently, the net additional carbon removed from the atmosphere may prove to be lower than initial headline estimates indicate.
Challenges to Durable Storage
The core challenge lies in achieving truly durable carbon removal. Enhanced weathering aims to speed up natural chemical reactions by spreading pulverized volcanic rocks, such as basalt or ultramafic minerals like dunite, across large areas of agricultural soil. While this increases the surface area for reactions, the rate of dissolution varies drastically depending on climate, rainfall, and soil chemistry. Furthermore, human intervention in these systems may inadvertently interfere with natural carbon sequestration pathways that would have occurred regardless of the technology's presence.
As these initiatives move toward broader deployment, the critical question remains: how much carbon will actually stay out of the atmosphere over the coming decades and centuries? While these technologies undeniably contribute to climate mitigation strategies, researchers emphasize that we must distinguish between simply shifting carbon across time and space versus achieving permanent, durable removal. Future efforts require a more nuanced understanding of how these chemical products move through entire catchments and coastal ecosystems to ensure that the climate benefits are both genuine and sustainable.
