Humanity must remove up to 660 billion tons of carbon dioxide (CO₂) from the atmosphere by the end of the century to limit global warming to 1.5°C. This is in line with the most recent report by the Intergovernmental Panel on Climate Change (IPCC), which based its estimate on measured atmospheric concentrations of CO₂ in 2020.
Removing so much carbon dioxide will involve more than just plant many trees. Engineers and scientists are developing direct air capture (DAC) technologies that supposedly extract large amounts of CO₂ from the atmosphere using very little land and water.
A typical DAC unit uses large fans to push air through a liquid or solid material that can bind and remove carbon dioxide, similar to how human lungs absorb oxygen. The material regenerates when heated, leaving behind concentrated CO₂.
Concentrated CO₂ can be stored permanently, usually underground in depleted oil and gas fields, or used to produce useful chemicals such as synthetic fuels. These fuels would release CO₂ when burned, so they are technically carbon neutral.
DAC, a controversial technology
Proponents of the technology say it could reduce the need for fossil fuels and help difficult-to-decarbonize industries like aviation achieve net zero emissions. Others fear that the DAC provides a distraction from the hard work of reducing carbon emissions.
These critics suggest that the high cost of energy and materials used for DAC makes it prohibitively expensive and so impractical in the short term that it remains to avoid catastrophic climate change. The cost of removing a ton of carbon dioxide with DAC can be as high as $600 (£522).
DAC technology is still in its infancy. The International Energy Agency (IEA) predicts that it will eliminate 90 million tons per year in 2030, 620 million tons in 2040 and 980 million tons per year in 2050.
But as it stands, only 19 DAC projects have come online since 2010, collectively removing 0.008 million tonnes of CO₂ each year, which equates to about seven seconds of global emissions from energy production in 2021.
DAC developers are working on projects that will remove about 1 million tonnes of CO₂ a year by the mid-2020s. But they may struggle to improve energy efficiency and cut costs fast enough to eliminate CO₂ on the scale needed. to meet IEA forecasts for the 2030s. Here’s why.
DAC implementation is gaining momentum
The largest unit currently in operation is the Orca plant, which was built by the Climeworks company in Iceland in 2021. The two-container size Orca aims to permanently capture and store up to 4,000 tonnes of carbon dioxide a year by dissolving it in water. and pump it underground, where it will react to form rock.
That’s what 170,000 trees on 340 hectares of land would absorb in a year. Unfortunately, cold weather in early 2022 froze the machines and closed the factory.
Carbon Engineering, another DAC developer, plans to implement a facility in Texas, US, which it says will remove and store up to 1 million tonnes of CO₂ per year once it starts operating in 2024. This company includes a billion-dollar investment from United Airlines trying to offset the emissions from their flights and buy synthetic fuels.
Carbon-neutral fuels can replace oil in aircraft and long-haul cargo vehicles. But air fuel technologies still need a more competitive business model than the fossil fuel industry.
This is unlikely to happen quickly as the latter is very well established and subsidized, while the technology behind air fuel is rudimentary and needs substantial investment to grow.
Costs are falling very slowly
The IEA has estimated that removing up to one billion tonnes of CO₂ per year from the air with DAC plants in 2050 will consume up to 1,667 terawatt hours of energy, equivalent to 1% of global consumption in 2019.
Costs are expected to fall by between $125 and $335 per ton of CO₂ in the 2030s, with the prospect of reaching below $100 by 2040. This will depend on DAC units being deployed and developers learning from they. cost of solar energy has dropped over time.
DAC could become financially viable in the 2030s if falling costs are covered by rising carbon prices in tax regimes. According to him International Monetary Fund the average price of CO₂ in countries with carbon taxes or pricing mechanisms reached US$6 per ton in 2022 and will increase to US$75 by 2030.
The EU Emissions Trading System has priced a tonne of carbon dioxide at US$90 per tonne in 2022. The Inflation Reduction Act recently increased tax credits for companies that remove and store CO₂ in the US from $50 per ton to $180.
But high carbon prices are far from the norm elsewhere. In China, the price of carbon ranged between US$6 and US$9 per ton in 2021 and 2022.
DAC may also be viable if the carbon dioxide (CO₂) 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 this method could emit 1.5 tonnes of CO₂ for every ton removed. While this strategy could reduce net emissions from conventional oil production, it would still add carbon to the atmosphere.
The opportunity may arise in industries that need concentrated carbon dioxide, such as food manufacturers. The price of CO₂ has risen from $235 a ton in September 2021 to over $1,200 recently.
This is because most of the CO₂ in the UK comes from the fertilizer industry, where high natural gas prices have wreaked havoc. While current global demand is limited to around 250 million to 300 million tonnes per year, DAC could soon offer a more affordable, climate-neutral supply of carbon dioxide.
New technologies can help make DAC cheaper. For example, a UK-based DAC startup called Mission Zero Technologies aims to use electricity instead of heat to regenerate CO₂ absorbing material in DAC units. This, the company claims, would reduce DAC power requirements by four times.
Unfortunately, cost estimates for DAC are highly uncertain. This is in part because they often come from the developers themselves rather than from independent research. There is no commonly accepted approach to quantifying the actual costs of DAC, but my research group is working to verify the disposal costs declared by DAC developers and predicted by the IEA with a global network of academics and industry.
Will CAD slow global warming?
The world needs to build around 30 DAC plants capable of removing more than 1 million tonnes of CO₂ per year between 2020 and 2050. As only a few of these plants are expected to be operational by the mid-2020s, it will be difficult to overcome this deficit, especially if costs remain high and innovative DAC technologies are not discovered and commercialized.
I believe that DAC remains an essential tool to contain global warming. When anticipated cost reductions are achieved, DAC will pave the way for large-scale CO₂ removal with a much smaller land and water footprint than other removal technologies in the 2030s and beyond.
The DAC’s role is not to offset the increase in emissions in the 2020s, but rather to close the emissions gap and reduce the atmospheric concentration of carbon dioxide to limit global warming to 1.5°C during the decade and shortly before. from 2050 .
That’s why governments and companies need to focus on ending their dependence on fossil fuels by supporting research and development of DAC technology to reduce their costs.
This article was written by Dawid Hanak, Associate Professor of Energy and Process Engineering at Cranfield University, UK. It is republished from The Conversation under a Creative Commons license.. Article in English