How advanced is the technology to absorb carbon dioxide?

We must remove 660 billion tons of carbon dioxide from the atmosphere by the end of the century to limit global warming to 1.5°C.

Photo: Pixabay/marcinjozwiak

By the end of the century, humans must remove as much as 660 billion tons of carbon dioxide (CO₂) from the atmosphere to limit global warming to 1.5°C. That’s according to the latest report from the Intergovernmental Panel on Climate Change (IPCC), which is based on estimates of atmospheric carbon dioxide concentrations measured in 2020.

Removing so much carbon dioxide is not just about planting lots of trees. Engineers and scientists are developing direct air capture technology (DAC), which can capture large amounts of carbon dioxide from the atmosphere while using very little land and water.

A typical DAC unit uses a large fan to push air through a liquid or solid material that binds and removes carbon dioxide, similar to how human lungs extract oxygen. The material regenerates when heated, leaving behind concentrated CO2.

Concentrated carbon dioxide can either be permanently stored underground, often in depleted oil and gas reservoirs, or used to produce useful chemicals such as synthetic fuels. These fuels re-release carbon dioxide when burned and are therefore technically carbon neutral.

Advocates of the technology say it could reduce demand for fossil fuels and help hard-to-decarbonize industries such as aviation achieve net-zero emissions. Others worry that DAC will distract from the hard work of cutting carbon emissions.

These critics argue that the high energy costs and materials used for DAC make it prohibitively expensive, making it impractical to avoid catastrophic climate change within a tight time frame. Using a DAC to remove one ton of CO2 can cost up to $600 (£522).

DAC technology is still in its infancy. The International Energy Agency (IEA) forecasts a reduction of 90 million tons per year in 2030, 620 million tons in 2040 and 980 million tons per year in 2050.

But as things stand, only 19 DAC projects have come online since 2010, reducing a total of 0.8 million tons of carbon dioxide per year, equivalent to about 7 seconds of global energy production emissions in 2021.

Projects underway by DAC developers will reduce carbon dioxide emissions by around 1 million tonnes per year in the mid-2020s. But they may struggle to improve energy efficiency and reduce costs fast enough to achieve the necessary scale of CO2 emissions to meet the International Energy Agency’s forecast for the 2030s. That’s why.

DAC deployments gain momentum

The largest installation currently in operation is the Orca plant, which will be built by Climeworks in Iceland in 2021. Orca aims to capture and permanently store up to 4,000 tons of carbon dioxide a year by dissolving it in water and pumping it, which reacts underground to form rock.

Photo: Pixabay/Ver_Ena

This is the amount absorbed in a year by 170,000 trees on 340 hectares of land. Unfortunately, cold weather in early 2022 froze the machines and shut down the factory.

Another DAC developer, Carbon Engineering, plans to deploy a unit in the US state of Texas that it says will remove and store up to 1 million tonnes of carbon dioxide a year once it begins operations in 2024. The joint venture includes multimillion-dollar investments from United Airlines, which is trying to offset emissions from its flights and obtain synthetic fuel.

Carbon-neutral fuels could replace oil in planes and long-haul trucks. But air-fuel technology still requires a more competitive business model than the fossil fuel industry.

This is unlikely to happen anytime soon, as the latter is so well established and subsidized, while the technology behind air-fuel fuels is rudimentary and requires significant investment to scale.

Costs are falling too slowly

The IEA estimates that by 2050, using DAC plants to remove up to 1 billion tons of carbon dioxide from the air will consume up to 1,667 terawatt-hours of energy—equivalent to 1 percent of global consumption in 2019.

Costs are expected to fall to between $125 and $335 per ton of carbon dioxide by the 2030s, and below $100 by 2040. It will be up to the DAC units deployed and the developers to learn from these demonstration units, similar to how the cost of solar energy decreases over time.

DAC may be financially viable in the 2030s if rising carbon prices in the tax system can meet falling costs. According to the International Monetary Fund, in countries where carbon taxes or pricing mechanisms exist, the average price of carbon dioxide hits $6 per ton in 2022 and will increase to $75 by 2030.

The EU Emissions Trading System sets the price for a ton of carbon dioxide at $90 a ton in 2022. Recently, the Reducing Inflation Act increased the tax credit for companies that remove and store carbon dioxide in the United States from $50 to $180 per ton.

But high carbon prices are far from the norm elsewhere. In China, carbon prices hover between $6 and $9 per ton in 2021 and 2022.

DAC may also become feasible if the carbon dioxide it removes is monetized. But this is risky. One application of DAC is enhanced oil recovery, which involves pumping concentrated carbon dioxide underground to extract more oil.

Estimates suggest that for every ton of carbon dioxide removed by this method, 1.5 tons of carbon dioxide is emitted. While this strategy reduces net emissions from conventional oil production, it still increases carbon emissions in the atmosphere.

Opportunities may arise in industries that need to concentrate carbon dioxide, such as food manufacturers. Carbon dioxide prices have surged from $235 a tonne in September 2021 to more than $1,200 recently.

That’s because most of the UK’s carbon dioxide comes from the fertilizer industry, and soaring gas prices have wreaked havoc. While global demand is currently limited to around 250-300 million tonnes per year, DAC will soon provide a more affordable and climate-neutral supply of CO2.

New technology may help make DACs cheaper. For example, a UK-based DAC startup called Mission Zero Technologies aims to use electricity rather than heat to regenerate carbon dioxide-absorbing materials in DAC units. The company claims this will reduce the DAC’s energy needs by a factor of four.

Unfortunately, DAC cost estimates are very uncertain. This is partly because they usually come from the developers themselves rather than independent research. There is no generally accepted way to quantify the actual cost of a DAC, but my research group is working to validate the removal costs claimed by DAC developers and predicted by the IEA with a global network of academics and industrialists.

Will DAC slow global warming?

From 2020 to 2050, the world needs to build around 30 DAC plants capable of removing more than 1 million tons of carbon dioxide per year. Only a handful of such plants are expected to be operational by the mid-2020s, making it difficult to bridge the gap, especially as costs remain high and breakthrough DAC technology has not been discovered and commercialized.

I believe DAC remains an important tool for slowing global warming. When the expected cost reductions are achieved, DAC will open the way for large-scale CO2 removal in the 2030s and beyond with a smaller land and water footprint than other removal technologies.

Rather than compensating for rising emissions in the 2020s, the role of the DAC is to close the emissions gap and reduce atmospheric carbon dioxide concentrations to limit global warming to 1.5°C within a decade and closer to 2050.

That’s why governments and businesses should focus on ending their reliance on fossil fuels, while supporting the development of DAC technologies to reduce their costs.

This article is by David Harnack, Associate Professor of Energy and Process Engineering, Cranfield University, UK. It is republished from The Conversation under a Creative Commons license. Read the original text.

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