Weathering Rocks for a Better Planet: How They Can Mitigate Climate Change and Restore Soil Health

Climate change is a global challenge that requires urgent and ambitious actions to reduce greenhouse gas emissions and limit global warming.

However, cutting emissions alone may not be enough to avoid the worst impacts of climate change. We also need to find ways to remove carbon dioxide (CO2) from the atmosphere and store it safely and permanently.

One of the potential solutions is enhanced weathering, a natural process that involves applying crushed rocks to soils to accelerate their chemical breakdown and capture CO2.

Enhanced weathering can not only reduce the amount of CO2 in the atmosphere, but also improve soil fertility, crop yields, and water quality. It can also provide co-benefits for biodiversity, ecosystem services, and human health.

A recent study by researchers at the University of Illinois Urbana-Champaign and the Leverhulme Center for Climate Change Mitigation (LC3M) has quantified the climate benefits of enhanced weathering for the first time.

The study, published in Global Change Biology, showed that applying basalt rock dust to cropland soils in the Midwestern United States can significantly increase carbon sequestration and prevent it from accumulating in the atmosphere.

The process and benefits of enhanced weathering

Enhanced weathering is based on the natural process of rock weathering, which occurs when rocks are exposed to water, air, and biological activity.

Rock weathering can remove CO2 from the atmosphere by dissolving it in water and forming bicarbonate ions, which are then transported to the oceans or groundwater.

The oceans are the largest natural sink for CO2, storing about 40% of the CO2 emitted by human activities.

However, rock weathering is a very slow process that takes millions of years to affect the global carbon cycle.

Enhanced weathering aims to speed up this process by using finely ground rocks that have a high content of silicate minerals, such as basalt.

The benefits of basalt weathering

Basalt is a common volcanic rock that is rich in calcium and magnesium, which react with CO2 to form bicarbonate.

By applying basalt rock dust to soils, especially in warm and humid regions, enhanced weathering can increase the rate of CO2 dissolution and bicarbonate formation.

The bicarbonate ions can then be leached from the soils by rainfall or irrigation and carried to rivers, lakes, or oceans, where they can be stored for long periods of time.

Alternatively, some of the bicarbonate ions can be taken up by plants or microorganisms and converted into organic carbon, which can be stored in biomass or soil organic matter.

Enhanced weathering can also improve soil fertility and crop yields by increasing the availability of nutrients such as calcium, magnesium, potassium, and phosphorus.

The basalt rock dust also increases soil pH and reduces soil acidity, which can benefit plant growth and soil health.

The challenges and uncertainties of enhanced weathering

The study by the University of Illinois Urbana-Champaign and LC3M was conducted at the Illinois Energy Farm, a research facility that grows maize, soybean, and miscanthus crops for bioenergy production.

The researchers applied basalt rock dust to two fields: one with a maize/soybean rotation and one with miscanthus.

They measured the changes in soil pH, water chemistry, carbon fluxes, and crop yields over four years.

The results showed that enhanced weathering increased the amount of bicarbonate in soil water by 20% to 30%, indicating that more CO2 was captured by the basalt rock dust.

The researchers estimated that enhanced weathering could sequester about 1.5 to three tons of CO2 per hectare per year in cropland soils in the Midwestern United States.

This is equivalent to removing about 10% to 20% of the CO2 emissions from biofuel production.

However, enhanced weathering also faces some challenges and uncertainties that need to be addressed before it can be widely adopted.

For example, enhanced weathering requires a large amount of basalt rock dust, which needs to be mined, crushed, transported, and applied to soils.

This can have environmental and economic costs that may outweigh the benefits of CO2 removal.

Moreover, enhanced weathering may have unintended consequences for local hydrology, biogeochemistry, ecology, and climate that need to be carefully monitored and assessed.

Therefore, more research is needed to optimize the performance of enhanced weathering and to evaluate its potential impacts and trade-offs at different scales and locations.

Enhanced weathering should also be integrated with other mitigation and adaptation strategies, such as reducing fossil fuel use, increasing renewable energy sources, enhancing natural carbon sinks, and adapting to climate change impacts.

By combining these approaches, we can create a more resilient and sustainable future for ourselves and the planet.