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Negative emissions: Major breakthrough or empty promise?

It would be necessary to extract CO₂ from the atmosphere on a massive scale. There are already ideas and pilot projects that aim to achieve this. However, in order to make a real contribution to a neutral carbon footprint, the scale would have to be increased by several orders of magnitude.

Negative emissions: Major breakthrough or empty promise?

In their search for new weapons to combat global warming, scientists are eyeing Iceland in the far north of Europe. There, a special facility developed by a Swiss company is filtering carbon dioxide (CO₂) from the air. Dissolved in water, the greenhouse gas is injected 700 meters underground – and thus permanently removed from the atmosphere. This sounds like a clean solution, but so far, it is being operated only on a very tiny scale.

Great hopes are pinned on the project and a handful of other test facilities. Because negative emissions – i.e. the extraction of CO₂ from the atmosphere – will inevitably have to play a major role in a just few years’ time. Virtually all model scenarios that achieve a 1.5 or 2 degree Celsius target rely on carbon sequestration. “Stopping global warming without extracting at least some CO₂ from the atmosphere is unrealistic,” says Sabine Fuss from the Mercator Research Institute on Global Commons and Climate Change (MCC).

Huge potential in theory

In theory, the potential is enormous. But in practice, only homeopathic dosages of CO₂ have so far been extracted from the atmosphere. The Icelandic prototype facility, for example, which applies what is known as the DACCS (Direct Air Carbon Capture and Storage) process, extracts an estimated 50 metric tonnes of CO₂ from the air each year. It is a part of the CarbFix2 project run by the Swiss company Climeworks and is located on the premises of the Hellisheidi geothermal power plant.

According to Climeworks, a larger plant capable of filtering several thousand metric tonnes of CO₂ a year is scheduled to be built over the next year and a half. The Canadian company Carbon Engineering even plans to build a plant with a capacity of one million metric tonnes of CO₂ per year by 2023.

But humankind emits more than 40 billion tonnes (40 gigatonnes) of CO every year – without any noticeable reduction having been achieved so far. If we continue on this path, the UN environmental program UNEP estimates that the temperature rise will reach 3.4 to 3.9 degrees Celsius by the end of the century. If, however, global warming is to be limited to 1.5 degrees, the Intergovernmental Panel on Climate Change states that net emissions must fall continuously, reaching zero in 2050.

Climeworks DACS pilot plant by by Climeworks Zev Starr Tambor

Residual emissions cannot be avoided

According to experts, it will not be possible to completely avoid the emission of greenhouse gases. “Some residual emissions are likely to remain,” says Gunnar Luderer from the Potsdam Institute for Climate Impact Research (PIK). He cites air traffic and cement production as examples, which are difficult to decarbonize entirely. For the equation to work out anyway, negative emissions are indispensable.

In addition to technical solutions, large-scale reforestation could theoretically absorb vast amounts of CO₂. Moreover, a more sustainable approach to agriculture would allow a large amount of CO₂ to be stored in the soil. But as Sabine Fuss from the MCC points out, the agricultural and forestry sectors currently add greenhouse gas to the atmosphere rather than removing it.

Andreas Oschlies from the Geomar Helmholtz Center for Ocean Research in Kiel estimates that in 30 years, around 20 percent of our current CO₂ emissions would have to be offset by negative emissions. That would amount to around eight gigatonnes per year. “That is highly ambitious and very optimistic, but it is feasible,” Andreas Oschlies emphasizes.

So far, the successes in the field of negative emissions using technological approaches have been extremely modest – partly because they are usually very costly. As yet, there are only very few test facilities.

Sequestrating CO₂ while producing bio-energy

One of the most effective facilities to date forms a part of a factory in the small town of Decatur in the US state of Illinois. Here, corn is fermented to produce ethanol. This process also releases CO₂, which is then forced into an underground storage facility. Thus, carbon dioxide, which the corn captured from the air as it grew, is permanently removed from the atmosphere. According to the operator of the plant, a little over half a million tonnes of CO₂ were stored in 2018 using what is known as the BECCS principle (bio-energy with carbon capture and storage). But BECCS has a catch: The method requires vast agricultural areas where no food is produced.

Other approaches such as artificial weathering have so far been researched only in laboratory settings. This method involves distributing finely ground particles of certain types of rock on fields or even in the sea, as Helmholtz researcher Andreas Oschlies, who is himself researching the approach, explains. The particles then react chemically with the CO₂ from the air or the surface water of the sea and thus extract CO₂ from the atmosphere. According to Andreas Oschlies, it would take around one tonne of rock to capture one tonne of CO₂ from the air.

Gunnar Luderer from PIK doubts that any of the technical processes alone will be able to make a significant contribution to climate protection in the next 30 years without active political guidance. CO₂ sequestration would have to experience “extremely high growth rates over a long period of time”, which have hitherto never been observed in virtually any other industrial sector of comparable complexity.

The PIK researcher believes that by 2050, several hundred million tonnes of CO could be sequestered globally using DACCS and BECCS. “Theoretically, one to two gigatonnes are also feasible,” he says. “But only if we take it seriously and start ramping up commercial CO₂ sequestration now.”

Climeworks DACS pilot plant by by Climeworks Zev Starr Tambor

More incentives required

What would have to happen for CO₂ sequestration technologies to gain momentum? Sabine Fuss calls for an increase in research funding to reduce the cost of achieving negative emissions. In addition, high carbon prices would be necessary, which would put pressure on companies to capture CO₂ themselves or to purchase negative emissions from other companies. In any case, it is essential to develop concrete plans for technologies and measures at the national level, as for example in Sweden.

Andreas Oschlies advocates certificates for negative emissions, which would allow companies to sell CO₂ sequestration as a service. Greenhouse gas emitters could then offset negative emissions against their emissions and, on balance, achieve a neutral carbon footprint. The Helmholtz researcher is also counting on the power of consumers: “If the public mood changes, the issue of emission neutrality would develop a PR impact and create a new leverage for CO₂ capture.”

Whether negative emissions will in fact one day grow out of their infancy remains to be seen. “The smart thing to do is to not emit carbon dioxide in the first place,” says Sabine Fuss from the MCC. “If you don’t make a mess, there’s no need to clean it up afterwards.”


Written by Valentin Frimmer, dpa
Photos by Zev Starr Tambor (Climeworks)

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