Enhanced Weathering
Enhanced weathering (EW) is a geochemical carbon removal solution that speeds up the natural weathering process. Weathering involves a series of chemical reactions that remove CO₂ from the atmosphere and ultimately stores the carbon securely in minerals.
Introduction
Enhanced rock weathering is a simple, multifunctional, and permanent solution that combines natural processes with human intervention. This process of weathering is sometimes called Earth’s natural thermal regulator as it sequesters and stores carbon naturally over thousands to hundreds of thousands of years.
This solution fast forwards the natural regulating cycle with clever human intervention. The geochemical storage of carbon is durable location and has multiple added benefits when applied to soils, oceans, coasts, or even landscaping.
Different types of Enhanced Weathering
Weathering refers to the breakdown and dissolution of rocks and minerals on Earth’s surface. In the process, CO₂ is removed from the atmosphere and is incorporated into carbonates. Enhanced weathering involves artificially speeding up this process by adding pulverised silicate rocks to different ecosystems, as outlined below:
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Agriculture
Ultra-fine silicate rock particles, dispersed onto agroecosystems, react with carbonic acid (CO₂ dissolved in rain water) to form carbonates. This increases the inorganic carbon content of soils and introduces additional minerals which help boost crop yields.
Coasts and Oceans
Ground silicate rock is directly spread on beaches or on the sea surface, where wave action drives it into the oceans. There, the rock particles react with hydrogen ions, altering the ocean’s chemistry and enabling it to absorb more CO₂ from the atmosphere.
Landscaping
Due to their beautiful appearance silicate rocks can also be used in landscaping. For example, one of the most common rocks used in enhanced weathering, olivine, has a striking green colouration. The CO₂ sequestration and storage process is the same as in agriculture systems.
How it works
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Olivine
Olivine denotes a group of silicate rock-forming minerals, typically found in basalt. Its composition is rich in magnesium and iron, and it is the main component in the Earth’s upper mantle. However, it is also abundantly found at the surface and so can easily be mined. It is the most common mineral used in enhanced weathering as it is already a fast weathering mineral under natural circumstances and therefore, facilitates relatively rapid CO₂ sequestration.
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Grinding
Grinding mechanically activates minerals. This technique breaks the minerals into smaller pieces with greater surfaces areas. The greater the surface area, the faster the weathering process as the reactivity potential is enhanced. There are two grinding processes: wet and dry. Both approaches are equally effective at reducing particle size. However, wet grinding is preferred as dry grinding is more energy-demanding, and therefore more costly.
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Carbon Storage
Magnesium and iron silicates present in olivine minerals are involved in a series of chemical reactions that result in the formation of stable bicarbonates. Bicarbonate ends up in oceans by the action of the water cycle where, through a series of reactions, they are converted to calcium carbonate (CaCO3). CaCO3 is used by ocean organisms (e.g., corals) to grow, and once they die the carbon trapped in their biomass becomes embedded in sediments on the ocean floor. Here, carbon is stored for centuries to millennia.
A simple, multifunctional, and permanent solution
Enhanced weathering is a high-potential CDR method that securely stores carbon dioxide underground for millions of years. In addition to CO₂ sequestration, this geochemical solution provides several co-benefits in regard to climate change mitigation. However, large scale changes in natural processes could lead to undesirable impacts. For instance, a rapid and uncontrolled change in the pH of oceans could damage aquatic ecosystems. Therefore, the unknown risks associated to this method need to be further examined.
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Weathering is the most important mechanism in which nature keeps atmospheric CO₂ levels down. It currently absorbs about 1.1 Gt CO₂ per year. An enhancement of this slow natural process could remove substantially higher amounts of CO₂ : up to 4 Gt CO₂ annually.
The process emits CO₂ during the steps of mining and grinding of rocks as well as the transport to the places where it is spread. However, these emissions would be offset by the scaled process. Rapid scaling is possible as the necessary knowledge and infrastructure to mine, grind, and spread the minerals already exists.
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The utilization of silicate rocks in enhanced weathering (EW) leads to several positive impacts. When used in farming, the supply of these minerals back into soils improves crop health and provides protection against pests and diseases. This results in a reduction in the usage of fertilizers and pesticides, and hence, it reduces food production cost and contributes to food security.
EW also counteracts one of our greatest environmental problems: ocean acidification. Moreover, EW provides the carbonates necessary for the survival and proliferation of shellfish, corals, and some plankton specie.
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