In 2023, the world crossed a somber threshold, emitting over 37 billion metric tons of carbon dioxide into the atmosphere, a record high. This underscores the urgent need for carbon reduction or capture. As the impacts of climate change intensify, the imperative to curb carbon emissions has never been more critical. However, achieving these reductions faces significant obstacles.

Among the solutions being explored, direct air capture (DAC) technology has gained significant attention. But while it holds promise, DAC faces its own set of obstacles—chief among them, is its high energy consumption.

The Promise and Perils of Direct Air Capture

Direct air capture technology involves removing carbon dioxide directly from the atmosphere. The concept is straightforward: large fans pull air into a chamber where CO2 is absorbed by a basic liquid, forming compounds like carbonate (found in concrete) or bicarbonate (used in baking soda). This captured carbon can then be converted into various products, including fuels, plastics, and even carbonated beverages.

Stratos, one of the world’s largest DAC facilities currently under construction in Texas, employs this very approach. However, there’s a significant drawback. To release the trapped CO2 from the solution so that it can be reused, the liquid must be heated to temperatures exceeding 900°C (1,652°F)—a level of heat that renewable energy sources like solar and wind cannot provide. Consequently, this step often relies on burning fossil fuels, which, paradoxically, leads to more CO2 emissions.

“If we have to release CO2 to capture CO2, it defeats the whole purpose of carbon capture,” explains Wilson Smith, a professor in the Department of Chemical and Biological Engineering at the University of Colorado Boulder.

Reassessing Reactive Capture

In response to the energy challenges posed by DAC, researchers have explored a method known as reactive capture. This process uses electricity to separate CO2 from the basic liquid, theoretically allowing the liquid to be reused in a closed-loop system.

The idea has generated buzz in the scientific community, with many hoping it could reduce the energy and costs associated with carbon capture.

However, a recent study published in the journal ACS Energy Letters by researchers at the University of Colorado Boulder, the National Renewable Energy Laboratory, and Delft University of Technology, has cast doubt on the feasibility of reactive capture in industrial settings.

The team found that after just five cycles of CO2 capture and regeneration, the basic liquid’s ability to absorb more CO2 was significantly diminished. In short, the process was not as efficient as initially hoped.

A Sustainable Alternative: Electrodialysis

Despite the limitations of reactive capture, the researchers proposed an innovative tweak to the process: adding a step called electrodialysis. This technique splits water into acidic and basic ions, helping to maintain the liquid’s ability to absorb CO2 while also releasing the gas for further use. Crucially, electrodialysis can be powered by renewable electricity, making it a potentially sustainable solution.

“To me, turning CO2 into rocks has to be one of the leading solutions to keep it out of the air over long periods,” says Smith. By using CO2 to strengthen concrete, a material whose production is responsible for 8% of global carbon emissions, electrodialysis could address multiple environmental issues simultaneously.

The Bigger Picture: Cutting Emissions at the Source

While advances in DAC and related technologies are promising, they should not distract from the most critical step in combating climate change: cutting emissions at the source. According to the Intergovernmental Panel on Climate Change (IPCC), carbon dioxide removal is necessary to achieve global and national net-zero targets.

However, as Smith points out, relying too heavily on carbon capture technologies could be akin to using a small cup to bail water out of a rapidly filling bathtub, without addressing the root cause of the problem.

“Imagining Earth as a bathtub, with the running water from the faucet being CO2. The bathtub is getting full and becoming unlivable. Now, we have two options. We can use a little cup to scoop out the water, cup by cup, or we can turn the faucet off,” Smith says. “Cutting emissions has to be the priority.”

As the world grapples with the realities of climate change, the struggle to reduce emissions will require a multifaceted approach. Direct air capture and other carbon removal technologies may play a role, but they are not a silver bullet.

The priority must remain on cutting emissions at the source, transitioning to renewable energy, and rethinking our industrial processes. Only by addressing the problem from multiple angles can we hope to avoid the worst consequences of climate change and secure a sustainable future for generations to come.