Enhanced rock weathering could be used to mitigate climate change and meet our national carbon budgets in the UK, while potentially also benefiting soil health and crop yields.
Professor David Beering, director of the Leverhulme Centre for Climate Change Mitigation, outlined how enhanced rock weathering works in a recent Farm of the Future webinar.
Why consider enhanced rock weathering?
In the last 100 years, CO2 emissions rose from just under 10 gigatonnes to 40 billion tonnes. Professor Beering highlighted that even if humanity successfully slow emissions of CO2 by transitioning to clean energy, there is still a need to take CO2 out of the atmosphere.
“We are going to need carbon dioxide renewable technologies, and we can’t wait until 2050 or 2060 to figure out which ones work,” he said. “We need to get on and do the research now, to consider all the different technologies and figure out which ones scale, where the opportunities are and also what the problems are.”
How does enhanced rock weathering work?
Application of crushed basalt to a crop in the field can lead to the removal of CO2 from the atmosphere via the following process:
- The CO2 in the atmosphere combines with water in the soil to form carbonic acid
- Carbonic acid is corrosive, and it acts alongside the roots of the crops and the microbes in the soil to help break down the basalt to release calcium and magnesium ions
- The calcium and magnesium ions are positively charged, so the charge is balanced by reacting with carbonic acid to form bicarbonates
- The bicarbonates, which are essentially soluble CO2, drain into the soils, and then, over time, are transferred from the land via river systems to the oceans.
Overall, the system uses natural processes to remove CO2 from the atmosphere. Once the CO2 reaches the oceans, it is stored there for 10,000 years or more.
Benefits of enhanced rock weathering
Enhanced rock weathering offers the following benefits as a CO2 removal strategy:
It uses natural reactions
The chemical reactions involved in the process are between volcanic rocks, water and CO2, in the presence of plants. These are reactions have been responsible for stabilising climate over geological timescales.
Deployability
Human societies have known for a long time how to do quarrying, and they’ve also applied rocks to the landscape, particularly limestone, for pH management. With the proven history of application of rock dust to landscapes, enhanced rock weathering for CO2 removal could be deployable at scale within a decade or two.
Stackability
Enhanced rock weathering can be deployed with other land-based CO2 removal strategies. For example, basalt could be applied during tree planting as part of an afforestation or reforestation scheme.
Potential impacts on soil
In addition to it’s effectiveness at removing CO2, application of crushed basalt can have several impacts on the soil itself, which has the potential to benefit agriculture. These include:
Reversal of soil acidification
Application of crushed basalt can help reverse soil acidification, so those natural chemical weather interactions that occur in the soil generate alkalinity, which reverses acidification of soils in agricultural soils, mainly caused by nitrogen fertilisers.
Reversal of silica stripping
Growing crops repeatedly on the same soils, then taking the taking the biomass off-site – as is done in agricultural systems – biologically available silica is slowly stripped from those soils. By applying a silica rich rock, like basalt, the bioavailable silica in the soil can be replenished.
Restoration of micronutrients
Similarly to the process of silica stripping, production of food crops and subsequent removal of biomass from sites gradually remove essential micronutrients like molybdenum, phosphorus and potassium from agricultural soils. Again, as the basalt weathers, it can release these nutrients and replenish those pools, making them available for future crops.
Improve overall soil health
Enhanced rock weathering can improve overall soil health by improving cation exchange capacity, which in turn improves nutrient holding capacity, which can stimulate root growth, and that, in turn, produces greater inputs of organic carbon.
There is scope for some of these soil benefits to translate into benefits for farm businesses. For example, if the application of crushed basalt is providing a potassium and phosphorus input to the soil, this could potentially decrease agricultural usage of potassium and phosphorus fertilisers. In turn, that would reduce the carbon footprint of the crop via indirect emissions and reduce cost of production.
The Leverhulme Centre for Climate Change Mitigation has set up a global network of weathering sites, to measure the impacted of crushed basalt in different circumstances, crops and climates.
Evidence gathered from these sites is explained in the ‘Crushed basalt: A sustainable solution for soil acidity, crop yields, and climate?’ webinar, which is now available to RASE members. Watch it here or find out about the results in the US corn belt here.