Spreading rock dust on fields could remove vast quantities of carbon dioxide from the air and may be the best near-term way of removing CO2.
Spreading rock dust on farmland could suck billions of tonnes of CO2 from the atmosphere every year, according to the first detailed global analysis of the technique, published in the journal Nature.
The chemical reactions that degrade the rock particles lock the greenhouse gas into carbonates within months, and many think this approach may be the best immediate way of removing CO2 from the air. However, they emphasise that this in no way diminishes the need to cut the fossil fuel burning that releases CO2 in the first place.
Researchers say that the rock dust approach, known as enhanced rock weathering (ERW), has several advantages. First, many farmers already add limestone dust to soils to reduce acidification, and adding other rock dust further enhances fertility and crop yields. The good news, therefore, is that the application could easily become routine and desirable.
Basalt is the best rock for capturing CO2, and many mines already produce dust as a byproduct, so readily available stockpiles already exist. The researchers also found that the world’s biggest polluters, China, the US and India, have the greatest potential for ERW, as they have large areas of cropland and relatively warm weather, which speeds up the chemical reactions.
The analysis estimates that treating about half of farmland could capture 2 billion tonnes of carbon dioxide each year, equivalent to the combined emissions of Germany and Japan. The cost depends on local labour rates and varies from $80 per tonne in India to $160 in the US.
“CO2 drawdown strategies that can scale up and are compatible with existing land uses are urgently required to combat climate change, alongside deep emissions cuts,” said Prof David Beerling, of the University of Sheffield, a lead author of the study. “ERW is a straightforward, practical approach."
Prof Jim Hansen, of Columbia University in the US and one of the research team, said: “Much of this carbonate will eventually [wash into] the ocean, ending up as limestone on the ocean floor. “Weathering provides a natural, permanent sink for the carbon.”
Hansen, who famously warned the US Senate about global warming in 1988, said improving soil could also underpin food security for billions of people.