The capture and concentration of carbon dioxide is vital to mitigating the impact of anthropogenic climate change, with the potential to rapidly decarbonize the existing energy infrastructure. One of the more exciting carbon capture and concentration approaches that has been developed is direct air capture (DAC) systems, which extract existing carbon dioxide from the air. These approaches work by using materials or molecules to bind tightly with carbon dioxide from the air as it flows through a DAC system, effectively filtering carbon dioxide from the air. However, current approaches need heat to release the concentrated carbon dioxide for storage once it is captured and allow the chemical capture agents to once again filter out additional carbon dioxide. The need to use heat to recycle the capture agents causes several limitations. First, these systems need to be located near a powerful heat source, restricting where they can be deployed. Second, the use of heat limits the overall energy efficiency of these processes. Finally, generating heat requires energy, which often results in additional carbon dioxide emissions, blunting the environmental benefits of these DAC systems.

The team of Jenny Yang (UC Irvine), Anastassia Alexandrova (UCLA), and Fikile Brushett (MIT) think they have a solution: a heatless carbon capture system.  The team proposes to develop a process that uses electricity to capture and then concentrate atmospheric carbon without the need for added heat. This approach has the potential to be much more efficient than heat-based systems, and it can be powered by renewable electricity. Using computational modeling and laboratory experiments, they will identify and test different materials and chemical processes for potential use in a heatless carbon dioxide filtering system. If successful, the project would represent a major advance in carbon dioxide capture and concentration technology, one with the potential to vastly increase its effectiveness as a tool in the fight against climate change.

Some negative emissions solutions bring together the best of technological innovation and natural processes, enhancing and amplifying these natural processes by helping the Earth to pull more carbon from the atmosphere than it otherwise would. There are many ways nature removes carbon from the air and locks it safely away, most well-known in trees, plants, and soil. Yet there is another substance that can play a key role in capturing and storing carbon: rocks.

Rock weatherization and mineralization are natural processes that already remove carbon from the atmosphere. In some places, rock previously underground is brought to the surface. These newly uplifted minerals chemically interact with water that is rich in carbon dioxide, solidifying that carbon that is contained to form veins of carbonate minerals. But these processes presents a puzzle. Sometimes, this in situ mineralization reaction itself further cracks and fragments the rock, opening up new pores and pathways that themselves mineralize, creating a positive feedback loop. In other cases, the mineralization process has exactly the opposite effect. Pores in the rock become clogged with carbonates, sealing the rockface and closing off further mineralization. Since such clogging would hinder the performance of this carbon sequestration strategy, understanding the factors that accelerate or hinder these carbon mineralization reactions is critical.

Columbia researchers Christine McCarthy, Alissa Park, Marc Spiegelman, and Peter Kelemen are working to get to the bottom of this puzzle. If we can understand why mineralizing rocks sometimes crack and other times clog, we may have the ability to determine the optimal conditions for enhancing positive feedbacks during these processes and remove large amounts of carbon dioxide from the atmosphere at relatively low cost. The team will use laboratory experiments to study how variations in temperature, pressure, and acidity affect mineralization rates, as well as how the chemical composition of different fluids used in the process either augment or slow down mineralization. They will also use computer models to understand how to extend  their work across larger regions and, ultimately, to gain insight on reservoir-scale dynamics and consequences. Their work is at the forefront in developing an entirely new strategies to combat climate change.

Agriculture presents many appealing opportunities to contribute in the reduction of greenhouse gas emissions, both in the United States and around the world.  Soils themselves can be a sink for atmospheric carbon, with plants pulling carbon from the atmosphere and storing it safely in the ground. What is not yet known, however, is how powerful these tools can be, and thus how useful they are as a potential avenue for atmospheric carbon reduction. Innovation in the agricultural sector is needed to determine which actions, both on their own and taken in concert with one another, could be adopted and are most effective in solving these challenges. 

A multi-disciplinary team lead by Laura Lindsey at The Ohio State University is working to do just that and advance our understanding of how changes in agricultural practices could impact atmospheric carbon levels. The team plans to examine three potential reforms, which alone or in combination could help turn agricultural fields into sites of carbon reduction.  The first is the use of biochar, a charcoal-like substance that acts as a magnifier of carbon sequestration, helping certain arable soils store carbon and improve soil health. The second is the planting of various cover crops, which are plant species that help the soils in which they are planted to better store carbon. The third is reforming nitrogen-management practices in agriculture, which would reduce the amount of nitrous-oxide—a potent, if short-lived, greenhouse gas—that is released in the air during fertilization. 

In a series of five field studies, Lindsey and her team will rigorously examine how the three reforms perform in real world farming plots, advancing our understanding of their potential use as a tool to lower atmospheric carbon. If successful, this team’s research will help reduce uncertainties and provide critical information necessary to illuminate how these practices might be scaled and implemented in the future.

In addition to the pressing need to transition electricity generation to more widespread use of renewables, attention needs to be given to how these low-carbon systems might be integrated with other net zero interventions. While wind and solar power deservedly receive much attention, not only is geothermal energy an attractive alternative to burning fossils fuels, but there are creative ways of integrating geothermal systems with other net zero approaches to create a virtuous cycle of clean power generation and carbon sequestration.

A team led by Brian Ellis at the University of Michigan will address these challenges by examining the potential to pump carbon dioxide underground—which is captured from industrial processes such as coal-fired power generation—in order to enhance renewable geothermal power systems. How might these carbon dioxide streams get pumped into the subsurface? They are sent underground using excess electricity generated by wind or solar installations. These researchers will examine various dimensions of such systems that might allow carbon dioxide to boost renewable energy production while simultaneously being sequestered underground. First, they will investigate basic geological characteristics related to how differences in rock pore size and mineralogy may influence how these carbon-rich fluids flow in underground reservoirs. Second, they will look to aggregate this information about basin-scale geological characteristics to shed light on the viability of using such carbon-rich fluids to enhance geothermal energy production across power systems that have rather different power production and geographical characteristics. The results, if successful, have the potential to inform how such net zero systems might be optimized to help make renewables like geothermal power even more attractive as a twenty first century energy source.