Innovative Carbon Removal Technique
Credit: Paul Nelson
Applying crushed silicate rocks, like basalt, in agricultural fields could potentially eliminate up to 1.1 billion metric tons of carbon dioxide from the atmosphere each year while simultaneously enhancing crop yields, according to global assessments of this innovative method. Nevertheless, some scientists express skepticism about the feasibility of these claims.
This approach, termed enhanced rock weathering, accelerates the natural process of rock breakdown by rain. For millions of years, this mechanism has facilitated the transfer of carbon dioxide from the atmosphere to oceans, helping to regulate Earth’s climate during historical greenhouse periods. Farmers, for generations, have employed crushed limestone to enrich soil nutrient uptake in crops.
“The primary benefit of this method is its ability to mitigate atmospheric CO2 through a chemical reaction,” states Chuan Liao, a researcher at Cornell University, New York. “It also offers additional advantages such as the potential introduction of magnesium and calcium, aiding in soil nutrient enhancement.”
As global emissions persist in escalating, the United Nations climate agency emphasizes the necessity for effective carbon removal solutions to limit warming to 1.5 degrees Celsius over pre-industrial temperatures. Countries like Brazil are advocating for enhanced rock weathering as a strategy to mitigate emissions and reduce fertilizer expenses. Mati Carbon, an Indian startup, achieved the top award of $50 million in Elon Musk’s XPRIZE competition last year, showcasing the large-scale potential for carbon removal through this technique.
Carbon dioxide in the atmosphere undergoes dissolution in rain, forming carbonic acid, which reacts with silicate rocks to trap CO2 in bicarbonate ions. These ions can flow into rivers and oceans, either remaining dissolved for extensive periods or being absorbed into the calcium carbonate structures of marine life such as clams, corals, and sea urchins. Fragmenting the rock enlarges its surface area, enhancing carbon dioxide absorption.
According to the study, considering the volume of rock that farms can accommodate, accelerated rock weathering could contribute significantly, potentially saving up to 5 billion tons of CO2 annually this century. Liao and his colleagues conducted a “reality check” on these estimates by evaluating the rate at which farmers have adopted other innovations like irrigation, and how effectively weathering can occur in various regions.
The models explored limited versus extensive implementation of enhanced weathering and identified a potential removal range of 350 million to 750 million tons of CO2 annually by 2050, escalating to 700 million to 1.1 billion tons by 2100. For context, global fossil fuel CO2 emissions are projected to reach approximately 38 billion tons by 2025.
Initially, Europe and North America will lead this removal effort, but as supply chains for silicate rock are established and costs decline, regions in Asia, Latin America, and sub-Saharan Africa may emerge as frontrunners. Increasing temperatures and precipitation patterns could further accelerate weathering processes in these areas, providing farmers with the opportunity to monetize carbon removal credits for each ton of rock applied.
“For future farmers in the Global South, there will be fewer obstacles to sustainable practices,” notes Liao.
However, Marcus Siedung and colleagues from the Thünen Institute for Climate and Smart Agriculture in Germany raise essential concerns in their recent paper. They highlight significant uncertainties surrounding the accelerated rock weathering estimates; for instance, drought conditions can amplify carbon release, undermining the intended benefits. Siedung suggests that the estimation of 1.1 billion tons being removed is likely overstated.
In calcium-rich soils, rainfall may weather the carbonate instead of the crushed rock, resulting in a reversal of carbon absorption back into the ocean, leading to CO2 release instead of removal. Furthermore, low pH soils can react with crushed rock, resulting in negligible carbon uptake. As acidity diminishes, CO2 emissions from soil microbes may intensify.
Moreover, the carbon released during the mining and transportation of rocks to farms may surpass the amount removed, according to Siedung.
“I approach this with skepticism,” he asserts. “It’s crucial to ensure that CO2 is genuinely captured; otherwise, we risk miscalculating the benefits of carbon removal.” He emphasizes the complexities of the geochemical processes involved.
Others warn that weathering rocks could introduce toxins into the food chain. The olivine used in Liao’s projections entails heavy metals such as nickel and chromium.
Most residual rock from current mines is also likely polluted with metals, states David Manning from Newcastle University, UK. Countries may need to open numerous basalt quarries, which could be a lengthy and costly endeavor.
“To eliminate one gigaton of CO2 annually, approximately five gigatons of rock would be needed each year, and it remains unclear where this rock will be sourced from—this poses a significant challenge to scalability,” Manning concludes.
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Source: www.newscientist.com
