How Direct Air Capture Affects Our Atmosphere

How Direct Air Capture Affects Our Atmosphere

This video will help you to understand what direct air capture is and how it affects our atmosphere

Last month, Shopify – Canada’s most valuable company – signed a deal to pull 11,023 tonnes of carbon dioxide (CO2) from the atmosphere. It is the largest publicly announced corporate purchase of direct air capture (DAC) ever. Carbon Engineering has promised to store CO2 underground for Shopify, equivalent to the emissions from 132 tanker trucks of petrol. However, their DAC facility will not be operational until at least 2024.1

Why would an online retail platform like Shopify pay for DAC? To offset their carbon emissions, of course.

What is direct air capture?

Direct air capture is a technology that can help with climate change by capturing CO2 directly from the air. It uses an engineered, mechanical system to capture greenhouse gas.2 Carbon capture technologies typically focus on capturing emissions at the source, for instance, from power plants or industrial facilities. However, this is impractical for small and numerous sources, such as vehicles.3 Therefore, DAC overcomes this challenge.

The captured CO2 from DAC plants can then be stored permanently underground. This stops it from trapping heat in space and contributing to the greenhouse effect.4 Alternatively, the CO2 may be used to produce fuels, chemicals, building materials or other products.5 In the latter case, the CO2 will be released back into the atmosphere. Accordingly, DAC only provides climate change mitigation when the captured carbon is stored underground.6

Direct Air Capture Plant

How does carbon capture trap CO2?

There are different approaches in use to capture CO2 directly from the air. One system uses fans to pull air across a filter. This filter is soaked in a caustic chemical, for instance potassium hydroxide solution. It removes the CO2 and leaves the remaining air ready for return to the environment.7 The mixture of hydroxide and captured CO2 must then be heated to high temperatures to release the CO2. The hydroxide can subsequently be reused and the CO2 stored or repurposed.8

CO2: Liquid vs. solid sorbent

Alternatively, instead of a liquid solvent, a solid sorbent may be used.9 In this case, air is similarly pulled over the solid sorbent where chemicals react with and bind to the CO2.10 After the CO2 has been captured, the solid sorbent is heated. This regenerates the solid sorbent for future use. It also releases the CO2 for transportation.11

A third approach is still in development by the Swiss firm Climeworks. In this case, amine absorbents in small modular reactors capture the CO2. At present, this system is more costly. But, the design makes its application on a production line easier. It also requires lower temperatures to release the CO2 for storage. Requiring less heat and less energy may make it cheaper overall.12

What are the pros and cons of this technology?

Since the Industrial Revolution began, humans have increased the concentration of CO2 in the atmosphere by 47 per cent. This is “the most important long-lived ‘forcing’ of climate change”, according to NASA.13 Consequently, we need to reduce the amount of CO2 in the air. Direct air capture appears to offer one solution to this problem. 

Pros of direct air capture

Trees perform a similar role to DAC. They naturally absorb CO2 from the air and store it for centuries. However, trees absorb more carbon as they grow and can take a long time to mature. They also release the carbon they have stored when they die and decompose or are burned.14 

Planting forests also takes up a lot of space. Some scientists have suggested replanting trees on destroyed forest areas the size of the United States.15 By contrast, DAC plants have a limited land footprint. Unlike trees, they can be constructed anywhere in the world. They can also store the captured CO2 forever.16

Landscape of mountain and lake unaffected by CO2 emissions

Cons of direct air capture

A major con of direct air capture is the nascence of the technology. At present, just 15 air capture plants operate worldwide. Together, they capture more than 9,000 tonnes of CO2 per year.17 In comparison with the 40.12 billion tonnes of CO2 that we emit annually, this is insignificant.18

The scale-up of DAC plants

Evidently, a large scale-up of DAC plants is needed to capture significant CO2. However, a 2019 study found that the key factor limiting the technology’s deployment is the rate at which it can be scaled up.19 For instance, to merely keep pace with global CO2 emissions, it would require about 30,000 large-scale DAC plants to be built. With an estimated cost of up to USD $500 million per plant, the total price estimate comes to USD $15 trillion.20

Liquid and solid sorbent availability

Moreover, even if 30,000 DAC facilities were under construction today, supplying them with solvents to absorb CO2 is currently impossible. It would require one and a half times the entire global supply of that chemical to stock that many DAC plants with potassium hydroxide. It would also take a sixth of total global energy to power all those plants.21 This is neither sustainable nor economical.

The study’s authors conclude that assuming DAC can be deployed at scale and subsequently finding it to be unavailable would lead to “a global temperature overshoot of up to 0.8°C”. Therefore, DAC must develop alongside – not instead of – other climate combatting measures.22 

aerial image of trees absorbing co 2
Source: Thiago Japyassu from Pexels

DAC as a weapon against climate change: Coal, oil and natural gas

To fight climate change, we cannot rely on any single approach. We must not neglect the protection and enhancement of natural climate mitigation, such as forests, peat bogs and the oceans. Nor should we let exciting new technologies distract us from the source of the majority of greenhouse gases: fossil fuels. It is both futile and foolish to think that we can suck enough CO2 out of the air to offset the emissions caused by coal, oil and natural gas.

Sources

  1. Hiar, C. (2021). Direct Air Capture of CO2 Is Suddenly a Carbon Offset Option. [online] Scientific American. Available at: https://www.scientificamerican.com/article/direct-air-capture-of-co2-is-suddenly-a-carbon-offset-option/.
  2. Carbon Engineering. (2019). Direct Air Capture Technology | Carbon Engineering. [online] Available at: https://carbonengineering.com/our-technology/.
  3. Swain, F. (2021). The device that reverses CO2 emissions. [online] www.bbc.com. Available at: https://www.bbc.com/future/article/20210310-the-trillion-dollar-plan-to-capture-co2.
  4. NASA (2018). The Causes of Climate Change. [online] Climate Change: Vital Signs of the Planet. Available at: https://climate.nasa.gov/causes/.
  5. Direct Air Capture. (2020). International Energy Agency. [online] 22 Jun. Available at: https://www.iea.org/reports/direct-air-capture.
  6. Lebling, K., McQueen, N., Pisciotta, M. and Wilcox, J. (2021). Direct Air Capture: Resource Considerations and Costs for Carbon Removal. www.wri.org. [online] Available at: https://www.wri.org/insights/direct-air-capture-resource-considerations-and-costs-carbon-removal [Accessed 26 Apr. 2021].
  7. Direct Air Capture. (2020). International Energy Agency. [online] 22 Jun. Available at: https://www.iea.org/reports/direct-air-capture.
  8. Evans, S. (2019). Direct CO2 Capture Machines Could Use “A Quarter of Global Energy” in 2100. [online] Carbon Brief. Available at: https://www.carbonbrief.org/direct-co2-capture-machines-could-use-quarter-global-energy-in-2100.
  9. Lebling, K., McQueen, N., Pisciotta, M. and Wilcox, J. (2021). Direct Air Capture: Resource Considerations and Costs for Carbon Removal. www.wri.org. [online] Available at: https://www.wri.org/insights/direct-air-capture-resource-considerations-and-costs-carbon-removal.
  10. Direct Air Capture. (2020). International Energy Agency. [online] 22 Jun. Available at: https://www.iea.org/reports/direct-air-capture.
  11. Lebling, K., McQueen, N., Pisciotta, M. and Wilcox, J. (2021). Direct Air Capture: Resource Considerations and Costs for Carbon Removal. www.wri.org. [online] Available at: https://www.wri.org/insights/direct-air-capture-resource-considerations-and-costs-carbon-removal.
  12. Evans, S. (2019). Direct CO2 Capture Machines Could Use “A Quarter of Global Energy” in 2100. [online] Carbon Brief. Available at: https://www.carbonbrief.org/direct-co2-capture-machines-could-use-quarter-global-energy-in-2100.
  13. NASA (2018). The Causes of Climate Change. [online] Climate Change: Vital Signs of the Planet. Available at: https://climate.nasa.gov/causes/.
  14. Erickson-Davis, M. (2019). Tall and old or dense and young: Which kind of forest is better for the climate? [online] Mongabay Environmental News. Available at: https://news.mongabay.com/2019/05/tall-and-old-or-dense-and-young-which-kind-of-forest-is-better-for-the-climate/.
  15. Taylor, M. (2019). Scientists question mass tree planting as climate change panacea. Reuters. [online] 22 Oct. Available at: https://www.reuters.com/article/us-global-forests-climate-change-idUSKBN1X1173 [Accessed 26 Apr. 2021].
  16. Direct Air Capture. (2020). International Energy Agency. [online] 22 Jun. Available at: https://www.iea.org/reports/direct-air-capture.
  17. Direct Air Capture. (2020). International Energy Agency. [online] 22 Jun. Available at: https://www.iea.org/reports/direct-air-capture.
  18. Statista. (2017). CO2 emissions worldwide 2017 | Statista. [online] Available at: https://www.statista.com/statistics/276629/global-co2-emissions/.
  19. Realmonte, G., Drouet, L., Gambhir, A., Glynn, J., Hawkes, A., Köberle, A.C. and Tavoni, M. (2019). An inter-model assessment of the role of direct air capture in deep mitigation pathways. Nature Communications, [online] 10(1). Available at: https://www.nature.com/articles/s41467-019-10842-5.
  20. Swain, F. (2021). The device that reverses CO2 emissions. [online] www.bbc.com. Available at: https://www.bbc.com/future/article/20210310-the-trillion-dollar-plan-to-capture-co2.
  21. Swain, F. (2021). The device that reverses CO2 emissions. [online] www.bbc.com. Available at: https://www.bbc.com/future/article/20210310-the-trillion-dollar-plan-to-capture-co2.
  22. Realmonte, G., Drouet, L., Gambhir, A., Glynn, J., Hawkes, A., Köberle, A.C. and Tavoni, M. (2019). An inter-model assessment of the role of direct air capture in deep mitigation pathways. Nature Communications, [online] 10(1). Available at: https://www.nature.com/articles/s41467-019-10842-5.