Solar geoengineering seeks to mask the warming effect of greenhouse gases by promising to limit the amount of sunlight that reaches Earth. However, it won’t get to the root causes of our climate crisis. On the contrary, it will project false hopes that we can ‘tech’ our way out of the crisis. Such techno-fix rationales risk allowing politicians to backpedal on their commitment to cut greenhouse-gas emissions. To date, more than 500 scientists have signed an appeal for an International Non-Use Agreement on Solar Geoengineering. It does not prohibit atmospheric or climate research in general, but focuses on restrictions to ensure that no field experiments with the atmospheric system are conducted, no patent rights are granted, no technological development or deployment is realised, and solar geoengineering as a policy option for climate action is not considered.

Unrestricted research might lead to large-scale experiments that effectively undermine the current de facto ban on geoengineering. Larger field tests that experiment with the atmosphere would further upset an already destabilised Earth system. The consequences would be on a planetary scale, including unpredictable climate or weather patterns, biodiversity loss, and huge risks to future generations. In addition, the current global governance systems are not fit to regulate the deployment of solar geoengineering, nor does the international state of political affairs look promising to reach a stable, effective, fair agreement on how to govern solar geoengineering globally and over generations. Countries from the Global South that are the most vulnerable to the negative consequences of solar geoengineering deployment have already stood up against it at this year’s United Nations Environment Assembly. Their rights must be respected.

Unrestricted research would also legitimise the speculation about even more hypothetical technologies that could fragment sustainability efforts. The idea of space-based solar geoengineering goes as far as using resources on the Moon to supply the raw materials needed for building a giant sunshade in space. If we live in an artificially engineered world, we might no longer be able to pin down the root causes of climate change.

Xiao-Shan Yap, assistant professor of Innovation and Global Governance at the Faculty of Geosciences, Utrecht University, and a policy advisor to the EPFL Space Center, has signed a petition against solar geoengineering.

There are those who would like to counteract the greenhouse effect by means of solar geoengineering. This is why research is needed. We will only be able to weigh up the potential benefits against the risks involved if we understand what it means to modify solar radiation – especially with regard to the regions most affected by climate change. We need to find out how we can best achieve the UN’s sustainability goals, and whether solar geoengineering could or should be used to this end for a limited period of time.

Let’s be perfectly clear about this: Any modification to solar radiation can only be a means of combatting the symptoms of greenhouse gases, but would not entail removing them from the atmosphere. So the acidification of the oceans, for example, would continue unabated. There is no way around reducing greenhouse gas emissions. All the same, modifying solar radiation could be a meaningful step until other measures are able to take effect and reduce the highest temperature peaks.

Various means of reducing solar radiation have already been considered. In my working group, for example, we’ve been conducting intensive research into whether cirrus clouds could be removed by introducing aerosols such as Saharan dust. Cirrus clouds warm the atmosphere in a way similar to greenhouse gases, and certain aerosols can cause them to form at lower levels where they would form larger ice crystals that would then fall to the ground more quickly. But we have come to the conclusion that new, long-lasting cirrus clouds would actually be formed instead. So this method just wouldn’t work – which in fact surprised us.

There’s a potentially more promising method. Just like in a high-altitude volcanic eruption, aerosol particles could be released into the stratosphere. In addition to the desired cooling effect, however, this would also shift precipitation areas. Depending on the kind of aerosol particles used, they could also deplete the ozone layer. So it would be essential to conduct the appropriate research in order to rule out any measure that could prove counterproductive, or to minimise its potentially negative impact.

Ulrike Lohmann is a professor of Experimental Atmospheric Physics in the Institute for Atmospheric and Climate Science at ETH Zurich. Her research group is investigating the creation of clouds and their impact on the climate.