Technical climate cooling: “This would be a reason for increased international tensions”

Mirrors in space, sulphurous particles high in the atmosphere or manipulated clouds are intended to reduce solar radiation so that the temperature on earth drops - this is so-called solar geoengineering. Due to its high risks, this highly controversial technology is at best considered an emergency solution for climate protection.

Geographer Duncan McLaren has devoted numerous studies to the artificial manipulation of the climate. Recently, the Briton and a colleague put forward a proposal to make research into solar geoengineering possible despite many concerns. In this interview, he explains how the discussion on this sensitive topic could be brought to life.

Tamara Kenyon

The British geographer is a research associate at the Institute for Responsible Carbon Removal at the American University in Washington.

Mr. McLaren, under the new President Donald Trump, the USA is withdrawing from the Paris Climate Agreement. This reduces the chances of successful climate protection. Do you therefore expect increased interest in solar geoengineering?

Interest in solar geoengineering has generally increased significantly in recent years, and this will continue. However, scientists are likely to be more cautious about pursuing this topic under Trump. They fear that this will not reduce emissions, but could promote geoengineering. But Trump surrounds himself with advisors from Silicon Valley - and they are very enthusiastic about solar geoengineering. Venture capitalists there also see this as an opportunity.

However, solar geoengineering is considered a hot topic in research. Why is that?

We should definitely think about all possible ways to improve people's living conditions in the context of climate change, because it is to some extent inevitable. But many researchers are worried about solar geoengineering, and I share those concerns. Because for some countries and some companies, it is very tempting to lower temperatures without reducing emissions. They will use that as an excuse to continue to exploit fossil fuels and damage the environment and human health.

Even if solar geoengineering could perfectly neutralize the climate impact of greenhouse gas emissions - which the technology cannot - we would still have eight million deaths per year from air pollution caused by burning fossil fuels. Reducing emissions brings other positive side effects that solar geoengineering does not have.

Aren't there already many startups in the US that are planning or even conducting experiments in solar geoengineering?

We shouldn't exaggerate how much is actually already happening. There are currently only two well-known startups, Make Sunsets and Stardust Solutions. Only when a venture capitalist comes along and says: "We have a large fund and we're directing it towards geoengineering technology," then perhaps there will be more startups in this area.

However, I am concerned about the existing startups. Make Sunsets, for example, is banking on the idea that solar geoengineering can be financed with carbon credits. Every gram of sulfur dioxide that Make Sunsets releases into the stratosphere (at an altitude of 10 to 50 kilometers, editor's note) to cool the earth would then legitimize and offset existing or future emissions of greenhouse gases.

Are there currently any regulations for these startups?

There are no specific regulations in the US regarding the technical methods of solar geoengineering. Make Sunsets only has to inform the National Oceanic and Atmospheric Administration if the startup wants to launch balloons into the stratosphere. That's all it takes. The company doesn't even have to get a permit. As far as I know, Stardust Solutions hasn't conducted any experiments outside of the laboratory.

Let us assume that a state decided on its own to use solar geoengineering to mitigate global warming: What would this scenario look like technically?

One thing is very important: if this technology is to be used safely, it must be used symmetrically in both hemispheres. This is because the dust particles hardly move back and forth between the two hemispheres. If there is no symmetry, the cooling is also asymmetrical, and then weather bands in the tropics shift, and with them the rainfall. This must be avoided. In order to achieve a uniform cooling effect on the earth, sulphur dioxide injections are needed at many points in the northern and southern hemispheres, possibly at different times of the year. The technical requirements are enormous.

This is one of the reasons why many scientists see the USA as the only plausible country that could use the technology. Because only they have such a widespread network of military bases from which the program could be carried out.

How would the dust particles be brought into the stratosphere?

It would require hundreds or thousands of aircraft launches per day. Ordinary aircraft cannot fly into the stratosphere, especially not with a large load. While representatives of the aircraft industry say they could build such aircraft, I remain somewhat skeptical of this kind of technological optimism.

Would such an action by a single state trigger an international reaction?

Yes, the distribution of sulphur dioxide in the stratosphere would look like a military action, possibly flying over many foreign countries. This would be a reason for increased international tensions, especially if the action were undertaken unilaterally, without any form of prior coordination.

In terms of impact, many things can go wrong, especially with rainfall. For example, what happens if India does something like this and then there is potentially a drought or a flood in Pakistan? Perhaps governments are prudent enough not to see this as a cause for conflict. But in today's world of disinformation and misinformation, it seems inevitable to me that such an action would be interpreted in every possible way.

Has anything like this happened before?

When a Chinese weather balloon flew over the US in early 2023, it raised tensions. And last year, there were reports in Indian newspapers about risks to agriculture due to geoengineering. The National Oceanic and Atmospheric Administration in the US had announced plans for a program to detect geoengineering. The agency had no intention of doing any geoengineering itself. If this technology were to be used one day, we would expect to see a doubling of this kind of misinformation. That would have all sorts of consequences for international relations and social cohesion.

In many countries, not only the use of solar geoengineering is controversial, but even research into it. What arguments are there for exploring this technology in more detail?

We are currently sleepwalking into a world of 2.5 to maybe 3 degrees of warming. Solar geoengineering could be a useful tool to reduce human suffering in such a world. But it is also possible that this technology would make things worse. While there are a lot of studies with computational models, we don't know whether solar geoengineering would actually work. Experiments could help find out.

Would climate research also benefit from experiments in solar geoengineering?

Yes, you could learn something about the physics of clouds, which we don't understand very well yet. There is overlap between cloud research and the research we need to do to better understand the possibilities of solar geoengineering.

Are there any other reasons to research this?

Security experts also want to know more about solar geoengineering. They do not believe that this technology could be used as a targeted weapon, but as a means that could perhaps provide a relative advantage. Security experts also want to know how the technology could be counteracted.

Recently, together with Olaf Corry from the University of Leeds, you called for an international agreement on solar geoengineering. This agreement should not prohibit research, but rather its actual use. What was the reason for the proposal?

The idea of ​​putting a ban or moratorium on solar geoengineering has been floating around for about a decade. What we are proposing is a little different. In our experience, countries cannot agree on how to conduct a research program on solar geoengineering, for example, who should collect the data. They cannot even agree on whether such a program would be desirable at this time. The reason for this is that some countries see such a program as a step on the way to actual deployment. And they think that is unreasonable.

But not all countries think that way, right?

The countries most open to the idea of ​​using solar energy are almost all heavily dependent on fossil fuel production. They see it as difficult to reduce emissions. Solar geoengineering would allow them to slow the transition to a lower-emission economy. But most countries want to reduce emissions more quickly. They also fear that geoengineering may not actually deliver what it promises in practice.

And what exactly is your proposal for the international agreement?

If we banned the use of solar geoengineering - or imposed a moratorium - we would create a space to discuss all of these things calmly. Such an agreement would reduce the fear that research could lead us down a slippery slope to the use of the technology. It would also remove the incentives for commercial use. A start-up could not make money with geoengineering. On the other hand, such an agreement would reduce the fear that all research into solar geoengineering would also be banned.

How should research into solar geoengineering be handled internationally? Would ethical guidelines be necessary?

Absolutely, scientists should not go ahead without such regulations. There are new recommendations on geoengineering research from the American Geophysical Union, which I have been involved in, and from scientific advisors to the EU on research into the solar variant. These recommendations form a good basis and go in a similar direction; they complement each other.

What is the core of these recommendations?

The EU advisers encourage a broad public debate on climate policy and propose a Europe-wide moratorium and global governance to prevent the use of solar geoengineering. They recommend measures to ensure that research in this area is "rigorous, ethical and with explicit consideration of uncertainties". And research should critically address all direct and indirect impacts as well as issues of governance and justice.

The American Geophysical Union proposes a framework for responsible research with ethical oversight, full transparency, broad public participation, and accountability. Research should be focused on climate justice and incorporate relevant social science and ethics expertise.

How common are such guidelines for research?

When a technology is young and we don't yet know what consequences it might have, it is often difficult to set rules for research. But such rules are necessary. Many scientists in medical research work daily with rules developed by ethics committees. Research into geoengineering, with its global risks, should be no exception.