As appealing as the ability to turn back the clock on climate crisis sounds, experts and activists alike have warned that these technologies may not be the boon they seem to be.

While the theory may be air-tight, in reality, the existing technology is not enough to meet targets. What’s more, it might actually be adding to emissions rather than curbing them. But before getting into its pros and cons, let’s take a deeper dive into what it means.

Natural carbon removal

Historically, ecosystems (forests, wetlands, etc) would absorb the carbon in the atmosphere and turn it into biomass.

But, like most aspects of natural ecosystems, the human race managed to wreck this as well. We emit more CO2 every day than all the trees in the world can absorb (let’s not forget deforestation).

On April 6, atmospheric CO2 hit the highest ever level of 423.01ppm.

Hence the need for intervention.

Carbon Capture

With an aim to stop carbon entering the atmosphere, CCS is a group of processes that include capturing carbon at the source — large power plants and industrial projects — transport it in a condensed form, and store it away, ideally forever, or reuse it.

There are two approaches for capturing carbon that are currently being deployed around the world on varying scales.

The first is post-combustion capture.

This method would entail separation of CO2 from emissions — flue gases that include water vapour, nitrogen oxide, particulate matter among other gases — to prevent it from reaching the atmosphere, a process not very dissimilar from regular filtration at source.

There are two other modes of separating CO2 from the fuel: One, process the primary fuel before combustion with oxygen to separate CO2 and hydrogen. CO2 can be stored, and hydrogen can be used as a cleaner, greener fuel. Two, use oxygen instead of air to burn primary fuel to produce a flue gas that is water vapour and CO2, which can then be separated.

So far, post-combustion capture has proven to be the most efficient and cost-effective process.

Another largely deployed approach is direct air capture (DAC).

Climeworks, a Swiss company specialising in carbon dioxide air capture technology, describes it: “Air is drawn in through a fan located inside the collector. Once sucked in, it passes through a filter located inside the collector which traps the carbon dioxide particles. When the filter is completely full of CO₂, the collector closes, and the temperature rises to about 100°C — about the same temperature it takes to boil water for a cup of tea! This causes the filter to release the CO₂ so we can finally collect it.”

While this method has more benefits than the post-combustion capture, most importantly the location-independent nature of it, experts say it is too expensive and too energy intensive for the amount of carbon it removes from the atmosphere.

There are currently 18 direct air capture plants operating worldwide, capturing 0.01Mt CO2 every year, according to a September 2022 analysis by the International Energy Agency (IEA).

Now, the storage

Once captured, the CO2 is compressed into a liquid state so it can be transported in a pipeline to a site where it can be stored or reused.

For storage, CO2 is injected into porous rock formations below the surface of earth (geological sequestration) or stored in vegetation and soils (biological sequestration).

The captured carbon can also be reused for so-called enhanced oil recovery, which means injecting the CO2 into formations deep underground, where fossil fuels come from in the first place, to force out remaining pockets of oil.

So, the next logical question is: why not leave it in the ground in the first place then? That’s a story for another time (hint: the global oil industry might have a problem with that.)

The pitfalls of CCS

The cost of carbon capture aside — it can vary from $15-25 per tonne of CO2 for industrial processes to $40-120 per tonne for others, according to the International Energy Agency (IEA) — experts aren’t convinced on the benefits at the current scale of the projects.

In a 2019 research paper titled, ‘The health and climate impacts of carbon capture and direct air capture’, published by the Royal Society of Chemistry, scientists concluded that there was “virtually no carbon benefit of and greater air pollution damage from” carbon capture units.

For a coal carbon capture unit plant, the research suggested a reduction of only 10.5% and 20% of the plant’s overall CO2-equivalent emissions over 20 and 100 years, respectively.

To explain the futility of CDR, David T Ho from the University of Hawaii, used a time travel analogy.

In an article in the journal Nature, he said that each direct air capture facility in the US is expected to extract one million tonnes of CO2 each year. Last year, the world emitted 40.5 billion tonnes of CO2.

"At that rate, for every year of operation at its full potential, each hub would take the atmosphere back in time by almost 13 minutes, but in the time it took to remove those 13 minutes of CO2, the world would have spewed another full year of CO2 into the atmosphere. Meanwhile, if everyone on Earth planted a tree — 8 billion trees — it would take us back in time by about 43 hours every year, once the trees had matured," he wrote.

Further harm to the environment

Activists have also said that carbon credits, wherein companies invest in planting trees or future carbon dioxide removal capacity as part of current decarbonisation commitments, may be a distraction from efforts to reduce emissions in the first place. For instance, the Northern Kenya Grassland Carbon Project, a carbon credit programme replacing unplanned grazing with planned rotational grazing aiming for larger soil carbon storage, has come under fire for altering indigenous practices and being unable to calculate actual carbon savings. The project, being run by a non-profit, aims to sell carbon credits worth 41mn tonnes over the next 30 years, and its clients include Netflix and Meta.

An excerpt from climate activist Greta Thunberg’s book, The Climate Book: The Facts and the Solutions, reads: “Why foster the idea that this underdeveloped technology (CDR) could be a substitute for the immediate, drastic mitigation needed? Why bet our entire civilization on it without making the slightest effort to make it work? Why make the world picture a potential solution so vividly that we include it in every possible future scenario and then fail to invest in it? Could it be that it was never even meant to work at scale?"