Combating global warming: diamond dust to cool the planet

The idea is as tempting as it is controversial: simply reflecting some of the sunlight back into space – and thus cooling the heating Earth. Most advocates of this method use volcanic eruptions as a model: sulphur dioxide gas is blown into the upper atmosphere, where it reacts chemically to form reflective sulphuric acid droplets. The eruption of the Mount Pinatuba volcano in the Philippines in 1991, for example, cooled the global climate by around half a degree Celsius for one to two years.

Diamond dust as an alternative

Swiss researchers led by Sandro Vattioni from the Swiss Federal Institute of Technology in Zurich (ETH), however, favor diamond dust as a tool for solar geoengineering. The tiny carbon crystals with diameters of around 300 nanometers reflect light more efficiently and presumably have fewer undesirable side effects, they recently wrote in the journal Geophysical Research Letters. According to the study, limestone crystals or aluminum oxide particles could also be good alternatives to sulfur dioxide.

"Previous studies were highly simplified and only looked at the optical effects, for example. In other words, how much light the aerosols can keep away from the Earth's surface," says Vattioni. His team has now incorporated the optical and physicochemical properties of the particles into a climate model. This is important in order to determine possible undesirable side effects of the cooling measure.

Sulphuric acid, for example, is known to absorb light and heat up in the process. "This local heating affects the global wind circulation and also the distribution of precipitation, i.e. when it rains where and how much," explains Vattioni. In addition, the sulphuric acid droplets promote the activation of reactive chlorine compounds in the stratosphere, which in turn could fuel the depletion of the protective ozone layer.

In order to assess the effect of solid particles such as diamond dust, the researchers worked with computer simulations. In the underlying model, the particles are released at an altitude of 20 kilometers in the stratosphere, where they would remain for one to two years, according to Vattioni. "Further down in the weather-determining troposphere, the residence time is only a few days to weeks. This is partly because the particles are washed back down to earth with the rain within a short time," says the researcher. The interactions between the particles were also included in the simulations. "When they collide and clump together to form agglomerates, their reflectivity is reduced and they also fall out of the stratosphere more quickly."

On the one hand, the simulations show how great the cooling effect would be. "If, for example, we were to release five megatons of diamond dust per year, the radiant power reaching the Earth would drop by minus 2.1 watts per square meter," says Vattioni. "And that in turn could – we estimate – cause an average cooling of surface temperatures by about one degree Celsius."

The calculations on possible side effects on weather patterns were also promising. "As diamond absorbs practically no light, there is hardly any local warming and practically no influence on global winds," reports the scientist. As far as the promotion of ozone depletion is concerned, however, there are still "major uncertainties". This was shown in a previous study. It is true that diamond itself is chemically extremely inert. But if a layer of water forms on the crystals, ozone-depleting chlorine compounds can be activated [-] just like on the sulphuric acid droplets. However, it is still unclear to what extent water accumulates in the very dry stratosphere and how much chlorine is activated as a result.

Challenges of solar geoengineering

The team has not yet calculated the costs of cooling the planet with diamond dust. "Since diamond can be produced synthetically, prices have continued to fall. Nevertheless, the annual production costs would probably be several orders of magnitude higher than those of sulphur dioxide or limestone, which in turn would hardly matter," estimates the researcher.

Ozone depletion and costs are not the only uncertainty factors. Among other things, the effect on the environment is still unclear. The particles in the upper atmosphere increase the amount of diffuse light and the solid dust lands back on the earth – both with as yet unknown consequences.

"Such concerns must be taken seriously. More research is needed before we can even think about a possible application," the scientist is convinced. The researcher advocates further laboratory experiments and model studies. Smaller field trials with a few kilograms of sulphur compounds, diamond or limestone dust should also be considered, he says. "Ultimately, it is important to weigh up the potential risks of solar geoengineering against the risks of the consequences of climate change."

Solar geoengineering is controversial in the scientific community. In an open letter from January 2022, researchers called for the method to be banned worldwide. Negative consequences could not be ruled out with sufficient certainty and global, democratic regulation would be practically impossible. In addition, the technology "threatens to become a powerful argument for industry lobbyists, climate deniers and some governments to delay political measures for decarbonization."

Other scientists responded to this last year with a counter-letter. Solar geoengineering should be further researched as a possible climate adaptation method in view of the further worsening of the climate crisis and its application should not be categorically ruled out, they wrote. Vationi is also convinced: "We have to look into it. If only because the method is so simple and inexpensive that it – whether it is banned or not – may be used at some point. And then we should at least know what we're dealing with."

This article first appeared on t3n.de .

(olb)