In order to protect the climate, emissions must be drastically reduced. But that’s not enough. According to the Intergovernmental Panel on Climate Change, the goal agreed in the Paris Agreement of limiting the rise in temperature to 1.5 degrees Celsius by 2050 is no longer realistic. Instead, the panel is now proposing to adapt to climate change. In order to prevent warming of two degrees or more, CO2 emissions still have to be further reduced.

From a political point of view, however, things are progressing slowly. Germany’s Finance Minister Christian Lindner recently threatened to boycott the EU-wide ban on combustion engines with a veto. The climate policy, which has been criticized as insufficient, is driving activists onto the streets to protest. (Climate) scientists also take part in pasting campaigns in the hope that their research results will be heard politically. Meanwhile, others are still looking for solutions to stop global warming.

Recently, a research group led by the renowned climate scientist James E. Hansen spoke out in an open letter in favor of doing more research on geoengineering projects. These are measures that are used to artificially stop global warming. The open letter, which was signed by 60 researchers, was mainly about the so-called “Solar Radiation Modification” (SRM). So far, the field of geoengineering has hardly been researched, and the risks are unknown, critics warn. An overview of the current status:

The Intergovernmental Panel on Climate Change defines the technical term as “a broad group of methods and technologies aimed at intentionally changing the climate system in order to mitigate the consequences of climate change”. One possibility is “Solar Radiation Modification” (SRM). Small particles are intended to deflect the sun’s rays so that the earth does not continue to warm up.

The idea of ​​filtering CO2 from the air or taking it directly from coal-fired power plants and storing it on the seabed or underground is also a geoengineering method. Norway already stores liquid carbon in former natural gas and oil fields. The Wintershall Dea Group is also planning to store up to 1.5 million tons of carbon dioxide under the seabed in Denmark by 2025 and 8 million tons by 2030 as part of the Greensand project.

The open letter from the 60-strong research group is about how to control global warming in the atmosphere. This method is at least as interesting in science as it is controversial and not particularly old. It was formed after the volcanic eruption of Mount Pinatubo in the Philippines in 1991. During the eruption, sulfur particles entered the atmosphere, which reflected the sun’s rays and lowered the earth’s temperature by half a degree. Science now wants to take advantage of this in the fight against climate change. A large-scale experiment has been taking place in the USA for several years. The largest US research campaign on artificial climate cooling started in February.

There are three different types of SRM method, but the principle remains the same:

Researchers at the National Oceanic and Atmospheric Administration (NOAA) are currently examining the stratosphere for particles to verify their composition and abundance. The largest measurement campaign started in January in the state of Texas. Further measurement flights over Costa Rica and over the southern hemisphere are planned for the coming year. In the journal Science, however, the researchers emphasized that this is still basic research.

Meanwhile, a team of researchers from the US state of Utah has found that an artificial cloud made of lunar dust could lower global temperatures. So far, however, this has only been tested by computer simulation, because it is still unclear how all this is to be implemented technically.

The climate goals have become unattainable. Therefore, geoengineering is considered a promising method to continue the fight against climate change. The removal of carbon from the air is considered to be a lower-risk variant than blowing particles into the atmosphere to protect them from the sun’s rays.

Overall, however, geoengineering remains controversial. The field has hardly been researched so far, so the risks are uncertain. Example of carbon storage: It is still completely unclear how long the CO2 can be stored underground or on the seabed. The greenhouse gas could escape again as a result of natural disasters, wars or accidents. In addition, the machines for filtering the CO2 have an immense energy consumption. Researchers also consider it unlikely that removing carbon dioxide from the air will be able to prevent dangerous climate changes in the short term.

Much more controversial, however, is the method of smuggling particles into the atmosphere and deflecting the sun’s rays. The Intergovernmental Panel on Climate Change currently advises against this. Because the SRM is a massive intervention in nature. Advocates of the method may counter that humans have already massively influenced the climate. Uncertainty is currently the biggest counter-argument.

On the one hand, there is the question of how the aerosols are supposed to get into the stratosphere. The particles have a survival time of about a week, so the stratosphere would have to be “filled” regularly. The Max Planck Institute has calculated that at least 7,000 flights with special aircraft would be necessary every day to save one degree per year.

It is also unclear which particles would be most suitable. Sulfur particles could damage the ozone layer, dust darken the sky. As a result, more people are likely to develop depression. In addition, experts reckon that SRM could affect the summer monsoons in countries such as China and India. It also remains unclear whether the method has to be used permanently – or what happens when no more particles are smuggled into the stratosphere.

A massive increase in temperature would be conceivable, since this method offers no incentive to reduce emissions. Protests against geoengineering projects are already forming in Mexico: In Mexico, scientists have signed a document in which they are calling for an agreement to renounce the use of solar geoengineering. All experiments were forbidden.

At the same time, geoengineering could fuel political conflicts. Because the aerosols in the stratosphere do not stop at national borders. Accordingly, the world community would have to agree on the implementation of such experiments.

Environmental and climate experts from well-known bodies such as the United Nations or the Intergovernmental Panel on Climate Change do advocate further research into the field of geoengineering. Nevertheless, they currently see only one solution to stopping climate change: emission reduction.

Sources: Climate Intervention Research Letter, The Case for an International non-use Agreement, UN Environment Program, Max Planck Institute, Max Planck Society, German Climate Consortium, Federal Environment Agency, “Science”, “Plos Climate”, ARD Alpha, Wintershall Dea