Plant for removing CO2 from the air in Switzerland
Photo: Gaetan Bally / KEYSTONE / picture allianceIt should actually be very simple. In order to limit global warming to two, better one and a half degrees compared to pre-industrial times, mankind will have to radically reduce its greenhouse gas emissions in the coming years. At some point around the middle of the century, the zero emissions mark should be reached. But experts have been warning for years that this may not even be enough.
Many climate scenarios are already based on the fact that, in addition to reducing emissions, carbon dioxide is also actively extracted from the air. This is also important in order to offset unavoidable emissions - for example from long-haul air traffic.
One possibility is to bind the CO2 in certain rocks. To do this, one could scatter rock flour over a large area on arable land. Another option is to grow energy crops such as maize on large areas, then burn them in power plants and store the resulting carbon dioxide in the soil. This process is called "Bio Energy with Carbon Capture and Storage", or BECCS for short.
Unfortunately, quite inefficient
A third variant is to use technical devices to get carbon dioxide directly from the air. This is called "Direct Air Capture", or DAC for short. Devices in Switzerland, Canada and Iceland, among others, show that something like this is technically possible. A study just published in the journal "Nature Climate Change" now suggests that these systems are not only quite inefficient, but could also threaten food security if they spread around the world. Critics repeatedly use the latter argument against BECCS because the cultivation of energy crops can conflict with food production.
With regard to DAC, the researchers led by Andres Clarens, head of the study at the University of Virginia in Charlottesville, identified the water and energy requirements of the systems as a critical factor. By 2050, the machines will need a volume of water that is a third of what is currently used for global power generation. The energy consumption - ideally it should be covered by renewable sources - is high, at around 115 percent of the current global consumption of natural gas.
Widespread use of the technology, according to the researchers, could lead to rising food prices, for example for corn, wheat and rice. Sub-Saharan Africa is particularly affected, where prices could in some cases increase sixfold by the middle of the century. In other parts of the world, such as Europe and South America, there is still a risk that prices will double or triple.
"Very important technology that needs to be developed"
On the other hand, with DAC it is at least possible to actually get significant amounts of CO2 out of the air, according to the researchers. About three gigatons per year are realistic for 2035. If the emissions from 2019 are taken into account, that would be around seven percent of global CO2 emissions.
"I want to make it clear that we are in no way trying to give the DAC development efforts the cold shoulder," clarens study leader Clarens. It is a "very important technology that needs to be developed". However, the simulations showed that the world should not simply rely 100 percent on DAC. There is still a great need for BECCS - with the risks already mentioned that the world population, which is currently increasing, could in future have less cultivation area available.
Manufacturers of DAC systems such as the Swiss company Climeworks criticized the methodology of the study. The fact that there are several technical approaches to extracting CO2 from the air was not taken into account. If this were to be taken into account, the potential of the technology would be "significantly higher and the risks lower".
Icon: The mirrorchs
