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Can Earth’s Natural Carbon Cycle Accelerate Decarbonization?

Two-year demo project explores carbon sequestration power, plant benefits of enhanced rock weathering

Arleigh Truesdale | December 5, 2023
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The Earth has a natural self-regulation system for balancing carbon dioxide levels in the atmosphere: the long-term carbon cycle. During one phase of the cycle, carbon dioxide (CO2) reacts with water and rocks to transform carbon into a compound that is stable in water over tens to hundreds of thousands of years. Researchers have speculated about the value of ‘enhancing’ natural rock weathering to address excess CO2 emissions that contribute to climate change.

Now, Northwestern researchers will test the carbon capture potential of enhanced rock weathering during a two-year demonstration project. As part of over $1.7M of seed funding awarded by the Trienens Institute, the interdisciplinary team of geologists and plant biologists will partner with the Chicago Botanic Garden and student start-up Vaulterra to back this decarbonization system with hard data.

Enhanced rock weathering (ERW) is a novel method of locking away carbon. But its added potential to stabilize soil acidity, provide nutrients to plants, and increase crop yields is what makes it a champion for mitigating the climate crisis.

If applied on a large scale, ERW could bring together the agricultural, construction, mining, and start-up industries to tackle decarbonization. “Our goal is to deploy seed funding from the Trienens Institute for this demonstration project, gather preliminary data, and seek more support via a larger proposal,” said Andrew Jacobson, professor and director of graduate studies in the Department of Earth and Planetary Sciences at Northwestern.

Throughout the demo project, different types of rock, such as basalt and peridotite, will be applied to simulated natural environments with various crops to measure exactly how much CO2 is taken up through ERW. Beyond carbon, the project hopes to examine any effects the natural technology may have on soil, plant, and human health.

Jacobson and Brad Sageman, professor and director of undergraduate studies in the Department of Earth and Planetary Sciences at Northwestern, bring geological expertise, while ecological elements of the project will be overseen by Nyree Zerega, professor of instruction and director of the Program in Plant Biology and Conservation (a collaboration between Northwestern and the Chicago Botanic Garden), and Louise Egerton-Warburton, adjunct professor at Northwestern and conservation scientist at the Garden.

A natural part of the Carbon Cycle

The release of CO2 into the atmosphere by way of volcanic activity is a part of Earth’s long-term carbon cycle. “This process is responsible for the Earth’s natural thermostat. It has been happening for over 4.5 billion years,” said Sageman. When it rains, CO2 combines with water to form carbonic acid that dissolves rocks and minerals on Earth’s surface and, in the process, buries carbon.

“In water, dissolved atmospheric carbon is stable for tens to hundreds of thousands of years and can serve as a sequestration or negative emission technology,” explained Jacobson.

Waterbodies such as rivers and underground reservoirs then carry the dissolved carbon to oceans, where it can be used to make seashells and other forms of calcium carbonate. Eventually, the movement of the Earth’s crust draws the carbon back down into its interior where it is transformed and rereleased before the cycle continues.

The carbon cycle has allowed the Earth to reach and fluctuate around relatively stable levels of carbon. But human activity and industrialization have led to an atmospheric carbon surplus that is changing the climate.

ERW may provide a way to strategically harness the planet’s natural properties as a tool to address the climate crisis.

The practice of using minerals and rocks to amend soil is not new. “Farmers have long treated croplands with limestone to adjust soil acidity and improve growing conditions,” Jacobson shared. “Basalt and other mafic rocks can work similarly, but once all geochemical reactions are considered, these rocks may offer stronger decarbonization potential.”

“Working with biologists and ecologists will be important to understand how adding basalt to an agricultural field could stimulate the microbiome or, down the road, affect the food supply as plants absorb minerals from these rocks,” Sageman explained.

The project will initially be situated at the Chicago Botanic Garden where the team will set up mesocosms—experimental systems that simulate natural conditions in a closed environment—to measure inputs and outputs like water and CO2 levels. A variety of crops will be treated with basalt and other rocks. As the plants grow, carbon levels in water runoff and soil gases will be monitored on site. Samples will be brought back to core laboratory facilities at Northwestern for additional analyses.

“Plants will take up CO2 through photosynthesis, but they also release it when they respire at night. Exact measurement of all these dynamics is a challenge that uniquely benefits from having our colleagues in plant biology join us to get some first-hand empirical data,” said Sageman.

Carbon capture with co-benefits

Beyond bringing together dynamic perspectives from across the University, the project is a demo of the value of multi-sector collaboration for climate action.  That’s where start-up Vaulterra has a role to play. Patrick Giavelli, graduate student of the Engineering Design and Innovation program at the Segal Design Institute at Northwestern, co-founded Vaulterra in the Farley Center for Entrepreneurship and Innovation class NUvention: Energy, with the goal of working with farmers and miners in the Midwest to bring ERW to market.

Farmers benefit from the soil enhancements of the minerals and earn an additional revenue source for carbon sequestration; miners receive value from redirecting waste and reducing storage and maintenance costs. For the construction industry, ERW offers an opportunity to recommodify concrete from demolished buildings that would otherwise be routed to a landfill. And, large corporations looking for ways to offset their emissions are turning to third parties with innovative solutions.

Multiple carbon offset companies around the world have been in operation since the 1980’s, as have the third-party certifiers who oversee the conversion of corporate investment to real carbon removal. But the carbon capture market is mostly voluntary and there is a need for more scientific measurement, reporting, and verification of offset claims. “We are motivated to test ERW with the highest levels of scientific quality, rigor, and integrity. The burgeoning decarbonization sector should clearly avoid greenwashing,” said Jacobson.

A comprehensive measure of carbon removal

The nascent carbon capture and removal industry is defining its own standards and measures. As ERW becomes more popular, Sageman and Jacobson emphasized the need to develop new metrics to assess food toxicity, rock and mineral dust, environmental justice, and more. “Some of the minerals in these rocks have high levels of titanium and chromiumit’s important to pay attention to the level of uptake in the crops we study,” explained Jacobson.

Two years is a short window of time to study a process like weathering that typically unfolds over hundreds of thousands to millions of years. For businesses like Vaulterra, consistent monitoring of farmland carbon capture may become an ongoing practice. “A true life-cycle assessment or circular economy approach would investigate where the basalt comes from, the energy input needed to crush it down for use and transport it to fields to get a sense of the overall carbon output,” Sageman said. As renewable forms of transportation are increasingly commonplace, Sageman is hopeful that the process can become less carbon intensive.

ERW is one piece of the larger ecosystem of solutions needed to address the global climate crisis. Though early in its application, ERW research is expected to grow in the next few decades. At that point, efforts like this demo project may be able to inform policy and create incentives for multisector participation in carbon offset programs.

The project, “Experimental and numerical development of protocols for enhanced rock weathering: verifying carbon capture criteria and biological impacts,” is set to begin in May 2024.