Projects that spread rock dust on farms are removing more carbon dioxide from the atmosphere than competing technologies – but CO2 removal efforts remain far short of what is needed to avoid dangerous levels of global warming.
Known as enhanced rock weathering, the method involves spreading crushed volcanic rocks over fields to accelerate the natural weathering process by which CO2 in the atmosphere is converted to stable mineral form. Spurred by its relative simplicity – and new evidence that the rock dust can improve crop yields as well as sequester carbon – this year has seen a flurry of such projects around the world.
Together, those projects removed around 30,000 tonnes of CO2 in 2023, according to estimates in this year’s , which is based on removals reported by companies. That is a much larger amount than the CO2 removed by other new technologies. For instance, direct air capture projects, which use giant fans to blow air over materials that absorb CO2, removed just 4000 tonnes in 2023.
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“Enhanced weathering is definitely on the move,” says at the University of Wisconsin-Madison. However, he says these technologies are in such an early stage that these numbers don’t yet indicate the viability of one approach over another.
As more direct air capture plants come online, the giant fan approach may soon catch up to crushed rocks. One massive plant under construction in Texas is expected to be able to remove half a million tonnes per year once it powers on in 2025. “Both [approaches] need to grow exponentially to become material to the climate by mid-century,” says Nemet.
Older plant-based CO2-capture methods, such as biochar, are still removing substantially more carbon dioxide than more recent geology-based enhanced rock weathering or direct air capture projects. And removals from all of these technologies are dwarfed by the roughly 2 gigatonnes of CO2 captured each year by expanding forests. However, it is unclear if these approaches can scale up quickly enough – or store carbon for long enough – to make a difference for the climate.
To put the challenge in perspective, burning fossil fuels emitted more than a million times more carbon dioxide this year than was removed by new CO2 removal methods like rock dust. Meeting climate targets will require removing billions of tonnes of CO2 each year by 2050, depending on how much more we emit.
