Tackling warming with stone dust
By massively “fertilizing” farmland with crushed rock, we could remove large amounts of carbon from the atmosphere. In theory.
To limit global warming to two degrees Celsius, it is no longer enough to stop greenhouse gas emissions by 2050. We will also need to remove carbon from the atmosphere. By spreading crushed stone dust on agricultural soils, we could remove half to two billion tons ofCO2 from air each year, an international team of scientists figures in Nature.
Specifically, it involves rocks such as basalt, which contain silicates. Those minerals react withCO2 from the air when weathered under humid conditions. In the process, the carbon turns into bicarbonate ions (HCO3-), which eventually end up in the ocean via runoff rainwater. There, some of the carbon ends up as calcium carbonate (CaCO3) in shells, crustaceans and corals, and when they die, eventually on the sea floor.
“In nature, that process is very slow,” said biologist Ivan Janssens (UAntwerpen), who collaborated on the study. ‘But we can accelerate weathering by finely grinding rock debris, which allows more silicates to interact withCO2.’ The researchers see in that approach a way to remove carbon from the atmosphere on a large scale and thus slow global warming.
According to their calculations, the technology’s potential is greatest in China, the United States and India, countries with very large amounts of agricultural land and, coincidentally, the largest emitters of greenhouse gas. In Europe, the possibilities are more limited due to the smaller agricultural area. Yet the five countries with the greatest potential – including Germany, Spain and Poland – could take about a third of Europe’s annualCO2 from the air.
‘The big advantage is that you don’t have to choose between land use for food, energy crops or forest’ biologist Ivan Janssens (UAntwerpen)
The scientists point out that the potential of accelerated weathering is similar to that of better-known techniques, such as (re)forestation, introducing more organic matter into agricultural soils and growing energy crops combined with carbon capture and storage. “The big advantage here is that there is no competition for land,” Janssens says. ‘You don’t have to choose between using land for food, energy crops or forest. Because you can still grow food on the ‘fertilized’ soils. Because you also add other micronutrients such as zinc and selenium, and because the minerals also help combat drought stress and acidification, we even expect a positive effect on food production.’
Brick and concrete
The technology is not entirely new. Stone meal is already used as a soil conditioner in organic farming, among other applications. “The difference is in scale,” Janssens says. ‘We assume an annual application rate of 40 tons per hectare.’ Where should all that stone dust come from? ‘There is no intention to mine massive silicate-bearing rock specifically for this purpose,’ Janssens said. ‘But large quantities of rubble are available worldwide as a byproduct of mining. Also some residues from the metal industry and even crushed brick and concrete are perfectly usable.’
How much should that cost? The researchers estimated that depending on labor and energy costs by country, it would cost between $75 and $250 to remove a ton ofCO2 from the air with accelerated weathering, and that this cost would decrease as the technique is more widely adopted. According to World Bank projections, the price to emit a ton ofCO2 will be $100 to $150 by 2050. In that case, the technology would become profitable in many places, most rapidly in emerging countries such as India, China, Indonesia and Brazil.
The scientists determined the potential of accelerated weathering based on lab tests and models. Lab tests include looking at how quickly rocks weather in potting soils and how much carbon is stored in the process. Among other things, the models take into account the amount of farmland and proximity to suitable rock – it makes little sense to haul rock debris thousands of miles. “The uncertainty is huge,” Janssens acknowledges. ‘We desperately need field trials to gain a better understanding of how fast these processes occur in practice and how we can accelerate them.’
‘Even if we bringCO2 emissions to zero by 2050, we can no longer keep warming below two degrees Celsius,’ Janssens said. ‘For that, we would have to remove the excessCO2 from the air. According to the IPCC, up to 10 billion tons annually by the second half of this century. We will need all possible techniques for that. The earlier we start doing that, the less likely it is that warming will exceed dangerous tipping points.
Organifer rock bran
We have a variety of different rock stems in our assortment. Thus, both lava meal – bassalt meal and lava dust have silicates and contribute to Co2 binding.