Enhanced Weathering

Learn about the potential of enhanced weathering. Enhanced weathering involves pulverizing silicate rocks and spreading them over the ground or over water. The idea has origins in the traditional practices of several agricultural societies and in the sciences in the 1800s when German agronomist Julius Hensel discovered he could increase the productivity of his garden with rock dust that he called “stone meal.” The idea of using crushed silicates to trap carbon dioxide was first proposed in 1990, but it did not take off until 2006 when it was identified as a potential large-scale climate solution.

• A major advantage of enhanced weathering is that the required minerals are abundant, making up a quarter of all known minerals and 40 percent of the most common ones in the Earth’s crust. According to one study, the UK alone has enough silicates to remove 430 gigatons of carbon dioxide from the atmosphere.
• The two minerals most frequently proposed for use are olivine and basalt. Often a green color, olivine is also known as peridot, the August birthstone. Certain types of olivine, especially forsterite, when exposed to rain or ocean water, can absorb a lot of carbon dioxide. Basalt’s advantage is that it can be ground to dust and spread on agricultural fields, where it acts as a fertilizer, improving crop yields while sequestering atmospheric carbon.
• When applied to coastal waters, enhanced weathering could reverse ocean acidification and possibly prevent red tides, which can produce toxic compounds harmful to humans and marine organisms.
• Pulverized rock used in enhanced weathering takes up very little space since it would be added to existing farmland or coastal waters. Initially, it would not even require additional mining since crushed basalt and silicates are a by-product of certain kinds of hard rock mining.

Learn about challenges to the implementation of enhanced weathering. There are several hurdles to overcome in order for enhanced weathering to be scaled up and implemented as a key climate solution.

• Energy. It takes a lot of energy to crush rocks. The energy required for rock-milling machines and transportation is still mostly dependent on fossil fuels. Renewable energy is needed to maximize the climate benefits of enhanced weathering, particularly with basalt, which requires a higher tonnage of material to draw down the same amount of carbon as olivine.
• Quantity. Sequestering a ton of atmospheric carbon with enhanced weathering requires 1.6–3.7 tons of silicates, requiring large amounts of minerals in order to draw down meaningful amounts of carbon. Mining at this scale might cause environmental degradation if not done carefully. Recycling mine waste is an option, with the added benefit of removing troublesome waste from mine sites.
• Cost. It is expensive to crush and transport enormous quantities of rock, especially at smaller grain sizes.
• Safety. Silicates contain elements such as chromium and nickel, which can surpass safe levels when applied to an agricultural field or coastal waters in large quantities. Stringent safeguards and careful monitoring are needed to prevent harm to consumers and marine organisms.
• Scientific uncertainty. The long-term effects of applying crushed silicates to soils and oceans are uncertain. Coastal enhanced weathering involves deploying sand-size particles and letting the power of ocean waves finish breaking down and dissolving the silicates. However, more evidence is needed to prove this strategy works and wouldn’t harm marine life.

Buy rock dust. Pulverized silicate rocks are often marketed as rock dust for use in gardens or orchards. Rock dust can boost productivity by providing nutrients such as phosphorous, potassium, magnesium, and calcium to depleted soils. Rock dust is generally considered acceptable for organic use, but it might depend on the source of the silicates. Rock dust is sold in small enough quantities to allow gardeners to experiment with different types for different crops.

• Rock dust is popular and aggressively marketed, but its benefits are sometimes overhyped, as this video explains. It is not a substitute for organic compost. Get to know the pros and cons of rock dust. See the Compost Nexus for more information.
• Various types of carbon-absorbing pulverized rock can be purchased online. Consider buying from local operations, sellers that mill with renewable energy, or rock flour made from mining by-products, all good strategies for maximizing net carbon drawdown.

Incorporate silicate rock dust into farm soil. Carbon-absorbing minerals can benefit different types of crops. Precise numbers are highly particular to climate, soil conditions, crop type, and silicate source, but in general, the practice is thought to be most helpful for impoverished soil in the tropics.

• After two years of basalt application to a cocoa plantation, the trees that received rock dust were 50 percent taller and 60 percent thicker than the trees that received no rock dust.
• When applied to agricultural land, many kinds of rock dust can boost crop productivity or maintain productivity while replacing expensive, polluting fertilizers. One experiment in the Central Valley of California found that waste from local mining was rich in potassium and zinc, boosting corn, alfalfa, and almond productivity by 15–20 percent.
• Silica in weathered rock can also promote plant health by strengthening their cell walls, promoting resistance to pests and diseases like basal stem rot in oil palms and stalk borers in sugarcane, and also increasing their ability to handle drought conditions.
• Fertilization or water use-efficiency benefits have also been documented for corn, alfalfa, almonds, rice, and sorghum.
• Farmers can receive payments from the start-up Lithos, which is currently asking interested parties to get in touch about their rock dust spreading and monitoring program.

Partner with scientists. Partnerships between the agriculture and research sectors are critical for understanding the impacts of enhanced weathering.

• Farmers that are applying limestone to their fields to counter acidification are particularly needed, as the same or additional productivity benefits could be achieved using material like basalt, utilizing the same equipment.
• Landowners and farmers in Scotland and Northern England can contact UNDO for more information.

Conduct research on enhanced weathering co-benefits, impacts, and potential scale. A major factor limiting interest in enhanced weathering is uncertainty about its potential impacts on agriculture and coastal ecosystems. More research is needed, particularly in the tropics, where enhanced weathering may be more impactful on depleted soils but where carbon benefits might not be as strong initially.

• Establish enhanced weathering extension projects. Agriculture is a promising context for enhanced weathering, particularly given the potential for productivity upsides. However, more research is needed to establish when, where, and how much impact such additives could have, as some projects have found unexpected results or systems where enhanced weathering is counterproductive.
• Improving ocean health by decreasing toxic algal blooms is an intriguing possibility. However, the idea is largely theoretical and requires additional research to prove that it works in practice.
• More research is needed on the impact of enhanced weathering on local flora and fauna. Natural green sand beaches rich in olivine, such as Papakolea on the island of Hawaii, offer lessons as natural experiments.
• One particular challenge that needs further research is on the impact that undissolved particles of silicates could have on stream and river health.
• Using the energy of the ocean to break down silicates into their smallest grain sizes would save a huge amount of energy, but it’s not clear if and where it would be a viable approach and what impacts it would have on coastal species. Project Vesta is one group leading research in this area.

Share the science. Despite years of research, enhanced weathering is still off the radar as a climate solution. One of the most effective ways to get the word out on enhanced weathering is for scientists to engage with the public on the potential of enhanced weathering as a climate solution.

• Scientists Grace Andrews and Mel Murphy gave interviews for videos on enhanced weathering that have collectively been viewed millions of times.

Invest in enhanced weathering pilot projects. Enhanced weathering initiatives are still in their infancy and need stable financial investments and partnerships to explore their full potential. Projects that boost crop productivity or reverse ocean acidification while durably reducing carbon in the atmosphere should be particularly attractive to companies who are bumping up against the limits of other ways they can reduce their greenhouse gas emissions.

• Puro.Earth carbon dioxide removal certificates could be considered carbon onsets (see Onsets Nexus) because of their high standards.
• Mining companies that produce large amounts of crushed silicates as a by-product can proactively reach out to groups like the Leverhulme Center for Climate Change Mitigation, which has pioneered research on turning tailings into enhanced crop productivity and carbon drawdown.
• The Carbon to Value Initiative is a climate solutions company incubator that supports fledgling companies interested in carbon removal strategies, including enhanced weathering.
• A major moment for enhanced weathering came from the initiation of the nonprofit Project Vesta and their green beaches concept, which involves the power of kinetic coastal environments, such as wave-battered beaches, to reduce costs. They are preparing field trials in the Dominican Republic and Long Island following intensive community outreach and coordination with government regulators.
• Lithos is a start-up that applies basalt rock dust to farms in the United States using innovative techniques to speed the dissolution of the rock dust and to verify carbon removal from the atmosphere. They are currently selling carbon onset credits and recently raised $6.2 million in seed money.
• The UK-based company UNDO applies crushed basalt to agricultural fields and has been able to source its minerals entirely from mining by-products. UNDO is operating a mineral weathering project in Scotland for Wren, a service where individuals can support verified carbon removal initiatives.

Turn mine tailings into sequestered carbon. Some by-products of mining include minerals that can be used for enhanced weathering. Special attention is needed to make sure enhanced weathering projects are not leading to pollution, however, given that source rocks can contain harmful compounds, especially the metals chromium and nickel.

• The mining company BHP is looking to speed up the natural carbon mineralization of its tailing pond at a nickel mine in Australia. The large amount of magnesium naturally binds with carbon dioxide and water. BHP believes they can enhance this process to entirely offset the greenhouse gas emissions of their operations at the mine.

Enhanced Weathering: What You Need to Know (2022) by Patrick Niedermayer (13 mins.)

Enhanced Rock Weathering for Carbon Dioxide Removal by the Leverhulme Centre for Climate Change Mitigation (4 mins.)

Coastal Carbon Capture—Accelerating Mineral Weathering with Kelly Erhart of Project Vesta by We Are Carbon (50 mins.)

The Reality of Carbon Capture by Undecided with Matt Ferrell (16 mins.)

"Enhanced Rock Weathering" by Dan Ferber / Anthropocene Magazine

Enhanced Weathering: Making Rocks Weather Faster to Undo Climate Change by Climate Science

"How Adding Rock Dust to Soil Could Help Get Carbon into the Ground" by Susan Cosier / Yale Environment 360

Phytoprevention of Heavy Metal Contamination from Terrestrial Enhanced Weathering: Can Plants Save the Day? by Tim Jesper Suhrhoff / Frontiers

"Stripe-Backed Eion Digs Up $12M Series A to Help Farms Capture Carbon with Green Rock Dust" by Tim De Chant / Tech Crunch

"Carbon Brief: How “Enhanced Weathering” Could Slow Climate Change and Boost Crop Yields" by Prof David J Beerling and Prof Stephen Long / Carbon Brief

"Could Putting Pebbles on Beaches Help Solve Climate Change?" by Peter Fimrite / San Francisco Chronicle

Researchers Suggest a Different Way for Farmers to Reduce Their Carbon Footprint by NPR (3 mins.)

Changing the Rock Dust Applied to Farm Fields Could Help Reduce Carbon Emissions by Jonathan Ahl / NPR (4 mins.)