Dr Adi MacArtney looks at the controversial area of geo-engineering and the Stratospheric Controlled Perturbation Experiment planned by Harvard University

You probably use it to brush your teeth, you swallow it to relieve heart burn and you sprinkle it into cake mixes. We use it in paper, cement, rubber, plastics and oil refining industries. Calcium carbonate is one of the most useful and versatile minerals on the planet, comprising approximately 4% of the Earth’s crust. 

Now, many scientists believe the naturally occurring white rock may help mitigate the worst effects of climate change. A proposed experiment plans to crush calcium carbonate (CaCO3) into a fine powder before releasing it via high altitude balloons, in small 100g batches. It is hoped the tiny particles will remain floating 20 km up in the stratosphere for a long time, their aerial migrations closely monitored.  

It may be prudent to imagine solar geo-engineering as the plaster on the wound.

The stratosphere is a calm region of the atmosphere, well above the rain, snow and other weather. Most particles cannot reach this region, but when they do, such as during large volcanic eruptions, they can stay there for years. Any particles that settle at this altitude will reduce the amount of sunlight entering the atmosphere, acting like a shade, and reflecting at least some of the light back into space. A reduction in sunlight causes the Earth’s radiative budget to shrink, creating a slight global cooling; and herein lies the value of the technique. 

The experiment will be conducted by Harvard University in Cambridge, Massachusetts, and is called the Stratospheric Controlled Perturbation Experiment (SCoPEx). Hopefully launching in 2020, it is a small-scale trial, injecting volumes of calcium carbonate measured in grams, compared to millions of tonnes of sulfur dioxide particles that volcanoes can release. 

Intentional-made alterations to the Earth’s natural systems is called geo-engineering. The concept often raises fierce controversy and opposition from environmentalists, who believe that taking control of such natural systems is both recklessly dangerous and ethically immoral. Attempts to control sunlight levels is variously termed solar geo-engineering, solar radiation management (SRM) or stratospheric aerosol albedo modification. 

Because of such concerns, the university recently announced that the experiment will have an oversight advisory committee comprising seven independent experts from fields such as climate law, policy and Earth science research. 

If successful, the test will be the first of its kind, after a number of earlier attempts were cancelled due to patent issues. The research is part of a $12 million package, partly funded by Bill Gates and other keen philanthropists. The SCoPEx experiment may open the way to larger scale experiments, and a potentially lucrative market of geo-engineering techniques. Solar radiation management is currently a much cheaper option, costing between $0.03–1 per tonne of CO2 offset, compared to carbon capture and storage techniques, which can cost anywhere between $30-1000 per tonne of CO2 captured. 

Land-surface temperature from Copernicus Sentinel-3 satellite. Credit: Copernicus Sentinel data (2018), processed by ESA. 

It is worth noting in such price comparisons that solar geo-engineering simply modifies immediate local or global temperatures and does not reduce carbon in the atmosphere or oceans. Such carbon causes problems such as ocean acidification and coral reef destruction, that solar geo-engineering will never mitigate. It may be prudent to imagine solar geo-engineering as the plaster on the wound and carbon capture, storage and utilisation as the process of healing.

Geo-engineering is breaking new scientific ground, and through doing so courts doubt, fear and controversy. We do not know all the ecosystem repercussions such experiments may have if scaled up, and therefore opposition to even minor geo-engineering tests is high. Yet not taking pro-active steps to control the climate has its own risks; the dangerous inertia of our current trajectory. As Samuel Johnson once said, “nothing will ever be attempted, if all possible objections must be first overcome.” 


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