Negative emissions: carbon dioxide

Icelanders are sitting on a resource that is most valuable when it just stays where it is, hundreds of meters underground.

Then the basalt rock could bind carbon dioxide that was once pulled from the ground, burned and unfolded its climate-damaging effect in the atmosphere.

At least that's the idea behind "Orca".

Anna-Lena Niemann

Editor in business.

• Follow I follow

Orca is a pilot system for direct air capture technology, or DAC for short, which does not yet play a role in climate protection, but could become an important component in twenty or thirty years' time. Because even if fossil fuels remain in the ground in the future, the atmosphere is still filled with historical ballast from the time when it was different. There are also chemical processes that are difficult to imagine without CO2 emissions. Steel can be decarbonised, but it is more difficult with cement. That is why technology that filters carbon dioxide from the air appears somewhere in most climate pathways. The latest IPCC report also brings it into play as a kind of safety net or emergency plan.

DAC differs from the CCS (Carbon Capture and Storage) technologies that companies in the fossil and chemical industries have been using for a long time, mostly to capture exhaust gases directly in their industrial park.

Because of the high concentration in the exhaust air, the process is quite efficient there.

However, the previously released greenhouse gas is usually not permanently withdrawn from the atmosphere, but used as a raw material.

Not only, but also to increase the oil yield when injected into boreholes.

The plants are not world savers

Orca's harvest is supposed to end differently. It has been running for two months now. The responsible start-up from Switzerland, Climeworks, has been operating a similar facility near Zurich for four years before it more than quadrupled the size for Iceland. Orca is supposed to extract 4,000 tons of CO2 from the atmosphere every year. That corresponds to the annual CO2 footprint of 360 Germans. The facility, the largest of its kind in the world, is not yet a world saver.

It filters CO2 directly from the air, the partner company Carbfix pumps it mixed with water underground, where it mineralises in connection with the basalt in about two years. CO2 becomes harmless carbonate rock. This is the short version. The long one is a lot more complex, but decisive for the question of how great the benefit of DAC technology actually is. It has been proven that the technology works. How efficient it is, however, how expensive, how effective it is in achieving the climate targets - there are hardly any reliable answers to these questions. Just like the question of whether there are really negative emissions at the end of the equation, i.e. less CO2 remains in the atmosphere, or whether it is only about net zero. This is the case,if the separated carbon dioxide is processed further and remains part of the cycle as synthetic fuel, for example.

How much energy does it take to store a ton of CO2?

A study by the University of Freiburg, which has just been published in the journal

has appeared. In it, the authors compare the two DAC technologies that have so far been tested in pilot plants: the one that Climeworks relies on and that of the Canadian company Carbon Engineering. The former rely on a process with low temperatures, the others on one with high temperatures. The scientists looked at the entire life cycle of the systems for both of them and calculated their ecological balance, from the construction of the important components to their scrapping, which is due after around 20 years. And they have transferred the numbers into environmentally relevant categories: How much water, land area, metals or chemicals do you need? How much fine dust do they release? And above all: How much energy does it actually take to extract even a ton of CO2 from the atmosphere, transport it and press it into the ground?