Rock flour produced by the grinding under Greenland’s glaciers can capture climate-heating CO2 when spread on farm fields, research has shown for the first time.
Natural chemical reactions break down the rock powder and lead to CO2 from the air being fixed in new carbonate minerals. Scientists believe measures to speed up the process, called enhanced rock weathering (ERW), have global potential and can remove billions of tonnes of CO2 from atmosphere, helping to prevent extreme global warming.
Soil fertility naturally depends on rock weathering to provide essential nutrients, so enhancing the process delivers an extra benefit. Spreading the Greenland rock flour on fields in Denmark, including those growing barley for the Carlsberg brewery, significantly increased yields.
Greenland’s giant ice sheet produces 1bn tonnes per year of rock flour, which flows as mud from under the glaciers. This means the potential supply of rock flour is essentially unlimited and removing some would have very little effect on the local environment, the researchers said.
The weathering process is relatively slow, taking decades to complete, but the researchers said ERW could make a meaningful difference in meeting the key target of net zero emissions by 2050.
Phasing out the burning of fossil fuels still the most critical climate action, but most scientists agree that ways of removing CO2 from the atmosphere will also be necessary to avoid the worst effects of climate crisis.
“If you want something to have a global impact, it has to be very simple,” said Prof Minik Rosing at the University of Copenhagen, who was part of the research team. “You can’t have very sophisticated things with all kinds of hi-tech components. So the simpler the better, and nothing is simpler than mud.”
Rosing added: “Above all this is a scalable solution. Rock flour has been piling up in Greenland for the past 8,000 years or so. The whole Earth’s agricultural areas could be covered with this, if you wished.”
Other researchers are investigating the use of mechanically ground rock for ERW.
“But unlike other sources, glacial rock flour does not need any processing,” said Dr Christiana Dietzen, professor at the University of Copenhagen. The rock flour weathers extremely slowly in the cold conditions in Greenland, but the process speeds up when it is spread in warmer places.
The research on the CO2 intake of Greenland rock flour, published in the International Journal of Greenhouse Gas Control, estimated that 250kg of CO2 can be trapped per tonne of rock flour. After three years in soil in Denmark, the researchers found about 8% of this had been achieved.
The scientists also calculated that 27m tonnes of CO2 could be trapped if all farmland in Denmark was spread with the rock flour, an amount close to the country’s total annual CO2 emissions.
Another study by the same team, published in the journal Nutrient Cycling in Agroecosystems, indicates that increases in yields of maize and potatoes of 24% and 19% respectively after rock flour was spread in Denmark. Dietzen hopes the first commercial applications will be spread within three years.
Other proposed ways of removing CO2 from the atmosphere include using technology to capture it directly from the air, or growing energy crops, burning them to produce electricity and then burying the CO2 emissions. The 2020 study suggested ERW would be less expensive than either and, unlike energy crops, does not compete with food for land.
