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Photo: Gaetan Bally / Keystone / picture alliance
What is geoengineering?
Geoengineering involves a multitude of far-reaching interventions in the earth system in order to mitigate the effects of man-made climate change.
A large number of ideas are offset by a few, small-scale experiments, so that there is currently no well-researched or even tested geoengineering method.
Geoengineering is very controversial both ecologically and ethically: too little is known about possible side effects.
It could also lead people to refrain from taking any further measures to save CO2.
However, even the Intergovernmental Panel on Climate Change (IPCC) assumes that the Paris climate targets can hardly be achieved without technical countermeasures.
What are the geoengineering options?
Geoengineering can be divided into two possible modes of operation: "Solar Radiation Management" (SRM) aims to influence solar radiation, while "Carbon Dioxide Removal" (CDR) aims to bring carbon dioxide back from the atmosphere. The SRM is about reducing the incident sunlight or reflecting it more so that the earth warms up less. With the help of the albedo effect, this can already be done by simple, albeit ineffective means - painting the roofs white - but also by the laborious placement of mirrors in space. The currently most promising method, however, is to deploy aerosol particles in the stratosphere. Similar to large volcanic eruptions, this would cool the earth down relatively quickly, but would only have a temporary effect.No SRM method has an influence on the atmospheric greenhouse gas concentration and would not, for example, counteract ocean acidification.
In contrast, CDR techniques start directly with the atmospheric CO2 content. If it is not possible to reduce carbon dioxide emissions to zero in time or in full, climate neutrality can still be achieved through so-called "negative emissions". With the help of fast-growing plants, the greenhouse gas can be extracted from the air and captured during the subsequent incineration used to generate energy. The CO₂ obtained in this way or captured directly from the atmosphere would then be stored underground in former natural gas reservoirs. In addition to the possibly unsafe storage, the main problems here are technical hurdles and an enormous amount of agricultural land that would be in competition with food production.
Ocean fertilization experiments have already been carried out to circumvent these problems. Algae blooms should be brought about through targeted nutrient inputs, which in turn remove CO₂ from the atmosphere. So far, however, the attempts have not proven to be very effective. Another possibility is the weathering of special types of rock, in which CO₂ is permanently removed from the air through chemical reactions. In order to accelerate this process, which is rather slow in nature, researchers want to grind the rock and scatter it on agricultural fields. Regular cultivation would make the reactions faster and the areas under cultivation might even be richer in nutrients. However, since this method has to be used to mine enormous masses of rock, it is considered problematic from an ecological point of view.
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