Quantifying CO2 leakage from enhanced rock weathering suggests a way of removing carbon from the air with minimal leakage when it reaches the ocean
Carbon capture and storage is a key weapon in the fight against greenhouse gases and climate change, and a new technique may aid in that battle.
A technique known as ‘enhanced rock weathering’ may help remove carbon from the atmosphere, and a model shows the method will only leak minimal carbon if its products are stored in the ocean.
Constraining the planet below 1.5°C or 2°C of global warming from a preindustrial baseline by the end of the 21st Century, will be more likely if carbon dioxide currently in the atmosphere is physically removed.
Many climate models include the removal of between five and ten gigatons of carbon dioxide per year through to the end of the century.
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Processing rock materials
Christopher Reinhard, from the Georgia Institute of Technology in the USA, and colleagues used a large number of Earth system model simulations to create a complex representation of the physical and chemical response of the atmosphere and sea to enhanced rock weathering.
Enhanced rock weathering is the practice of processing rock materials in such a way as to encourage chemical reactions between rock and atmospheric carbon, forming substances like bicarbonate, which then keep carbon out of the atmosphere.
Bicarbonate can be added to the ocean and stored for up to 10,000 years before the hydrological cycle eventually transports it back into the atmosphere.
There has been concern, however, that some fraction of the bicarbonate added to seawater will break down almost immediately, rapidly leaking carbon back into the atmosphere.
The models predict that the oceanic storage of carbon is 90% effective and ‘leakage’ on decadal timescales is minimal.
Carbon will leave the ocean as atmospheric levels come down, simply because carbon concentrations seek equilibrium across the skin of the sea, but this flux will not be significantly augmented by leakage from enhanced rock weathering, according to the authors.
Image: Spreading basalt rock dust with a conventional lime spreader on row crop acres in the US corn belt. As the rock dust dissolves in the soil, it converts carbon dioxide to dissolved ions that are eventually transported to the ocean via runoff and stored for thousands of years. © Gavi Welbel.