• Jacob Bourne

Could Cities of the Future be Made of Carbon?

The actual value of a resource is not reflected by the dollar amount ascribed to it but by its benefit to society. Valuable resources solve problems and meet needs. It turns out that carbon dioxide can do both by morphing from a destructive pollutant into a useful material to construct buildings and infrastructure.

The problem is that there’s an enormous surplus of CO2 in the atmosphere — about 417 ppm when there should be about 280 ppm or at least no more than 350 ppm. The excess is diminishing the quality of life on Earth through a decline in agricultural production, natural disasters, droughts and sea-level rise.

One monkey wrench for the laudable and necessary efforts to address the problem by switching from fossil fuel-based energy sources to renewable ones is that even if the whole world went carbon neutral tomorrow, the excess CO2 already emitted would remain there for centuries continuing to wreak havoc. For example, a 2018 study by researchers at the University of Innsbruck found that if nations halted all greenhouse gas emissions, over a third of the cryosphere would melt in the decades ahead.

And the melting is well underway. A July heatwave just caused the Greenland ice sheet to lose 41 gigatons, or eight gigatons per day of meltwater — enough to cover Florida in two inches of water, according to The Polar Portal, reported by The Washington Post.

Such events are what Cambridge University Professor Emeritus of Ocean Physics Peter Wadhams called an indication of a major tipping point triggered in which the Earth’s fragile systems can’t be restored within practical timeframes. Given the crisis we’re facing, Wadhams concluded that we have to remove CO2 from the atmosphere, during a recent interview on Facing Future.

Although the practice of capturing carbon from its industrial sources has been going on for decades to varying degrees and levels of success, direct air capture, or the technology to suck CO2 out of the atmosphere is still in its infancy, and some contend that it can't be viable at full scale. Carbon capture technology has also been contentious as some environmentalists say that it’s just a license for corporate polluters to keep on polluting. This differs from nature-based carbon capture, such as planting forests to sequester carbon, that’s less controversial. However, a study found that nature-based solutions can only mitigate about 37% of emissions, and additionally, competing land-use interests make full implementation of such approaches difficult.

Yet, the atmosphere isn’t the only Earth system that holds CO2. The ocean is a carbon sink that absorbs excess CO2 from the atmosphere leading to ocean acidification, harmful for much aquatic life. University of California Los Angeles Institute for Carbon Management Director Gaurav Sant has proposed capturing carbon from seawater as a more efficient method than direct air capture.

Sant’s research entails using electricity to spark a reaction between CO2, calcium and magnesium in seawater in a process that yields carbonate rock that stores CO2 drawn from the ocean. Meanwhile, the reduced carbon in the sea would trigger removal from the air to maintain equilibrium. Once the leftover water is returned to the sea, the carbonate rock could be used for applications such as cement production. The process also yields hydrogen gas, which could be used as a green fuel source to power the carbon capture method itself.

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As with any new technology, there are concerns about impacts, and ocean-based carbon capture systems are still in development. However, approaches such as Sant’s could yield an effective carbon capture method that also produces a vital resource.

“If we are going to be successful at getting rid of CO2, we need to convert it into something that people need and want and are willing to pay for, and is needed in 40-gigaton per year quantities,” said Wadhams, suggesting that building materials may be the only products that meet the criteria.

Finding a viable way to utilize CO2 effectively could also help spur the scaling up of capturing processes. As opposed to carbon utilization, the geological storage of CO2 captured from industrial sources faces space constraints. Sites for underground storage have to be chosen carefully, and seismic activity risks future leaks, making it a potentially less than permanent strategy. It’s also possible that there may not be enough suitable space to store it all. According to Eelco J. Rohling, author of The Oceans: A Deep History, the total amount of carbon emitted from anthropogenic sources would form a solid graphite column measuring 25 meters in diameter extending from the Earth to the moon.

Building materials aren’t the only way to utilize carbon. CO2 can also be used to produce plastics, fuel and food. However, unlike building materials such as concrete, these other uses aren’t necessarily permanent. Permanent storage means that the sequestered carbon won’t be re-released into the atmosphere within a year, a decade or even centuries.

Cities made of captured carbon may seem like a distant pipe dream, but work is already underway to make it a reality. One company, Blue Planet, uses CO2 captured from industrial sources by a method that doesn’t require an energy-intensive purification process to make carbon-negative concrete. The result is an aggregate made from sequestered CO2 utilizing the carbon mineralization process that’s competitive with standard aggregates from quarried sources in cost, performance and strength, the company states.

Furthermore, when mixed with an additive such as olivine sand, carbon-negative concrete products could continue to absorb CO2.

Given that concrete is one of the most common construction materials and generally has a high carbon footprint due to production, switching to carbon-negative forms to build the world could hold tremendous potential for combating climate change.


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