James Linow: Is it not possible to place a sail (consisting of many separate parts) in front of the sun in outer space, which could, for example, shade the north or south pole and thus stop the warming of the earth?
Joel Mesot: The proposal to artificially shade the Earth from space is one of many so-called geoengineering ideas that are currently being circulated due to the lack of progress in the fight against global warming. Aside from the issue of public acceptance, such a solar sail in space, which would cause, so to speak, partial solar eclipses every day, would be technically very complex and associated with gigantic costs. Calculations showed that tens or hundreds of millions of tons of material would be required to create such an umbrella. This is at best a very distant dream of the future. But we must act now and exhaust the possibilities that are available to us as earthlings.
Similar ideas for reducing solar radiation exist here on Earth, for example, by introducing aerosols – i.e. solid and liquid suspended particles – into the stratosphere, i.e. air at an altitude of 10 to 50 km, which also contains the ozone layer. This proposal is based on the effect of volcanic eruptions, which release large amounts of sulfur dioxide into the stratosphere. Then sulfate aerosols are formed there, which lead to increased scattering of sunlight and, thus, to some darkening of the earth’s surface. This means that after massive volcanic eruptions, the global average temperature on earth drops noticeably over a period of one to three years.
How this temperature-lowering effect can be artificially created by aerosols is actually being investigated, including at ETH Zurich. However, this is still basic research to better understand such a system and its side effects. What these and other approaches have in common is that they will represent interventions in the global climate system with consequences that are difficult to predict. Accordingly, they also cause controversy in the scientific community.
There is no doubt that massive technology deployment will be required in the next few years to decarbonize our energy systems.2-free of charge, and at the same time introduce “negative emissions”, i.e. CO2 filter the air. This is also an assessment by the Intergovernmental Panel on Climate Change, which believes that negative emission technologies (NETs) are needed to reach the zero target by 2050. This means, for example, technical solutions such as those developed by Climeworks, a subsidiary of ETH, to reduce CO emissions.2 removed from the atmosphere and mineralized in underground rocks.
It seems to me that, given the relevance, we must clearly prioritize the promotion of “earthly” solutions, which, on the one hand, CO2 avoid and, on the other hand, remove it from the atmosphere. After all, the problem is not in the sun’s rays, but in the greenhouse gases that we emit. Finally, there is an important non-technical part of the solution to the climate problem that has to do with us and our behaviour.
Many thanks to Prof. Ulrike Lohmann and Prof. Tom Peter from ETH Zurich for their valuable input.