Enhanced weathering: When climate research takes unexpected turns

Enhanced weathering: When climate research takes unexpected turns

By Brittany Edelmann and Carly Menker, Dec. 5, 2021 –

Oxford University Ph.D. student Frankie Buckingham collected the 30, 1-meter-long cylindrical tubes of soil she needed for climate research in August 2018 on a British farm in North Oxfordshire. The farm had previously cultivated oats and barley in the soil. A variety of crushed rocks and minerals, such as basalt, olivine and volcanic ash, were added to the 30 cores and then positioned on the roof of Oxford’s Earth Sciences Department building. From October 2018 to June 2021, Buckingham analyzed the soils to watch for the effects of enhanced weathering on climate change impacts. But, what she found wasn’t quite what she expected.

Buckingham’s study focused on “enhanced weathering” as a carbon dioxide removal technique involving the application of crushed rock to agricultural soil.

Carbon dioxide in the atmosphere is a thermostat for climate change, holding in heat that drives global warming and driving changes in our climate as we know it. Carbon dioxide levels today are more than 35% higher than at any point in at least the past 800,000 years and rose 30% just since 1970. The last time the atmospheric CO2 levels matched today’s concentrations was over 3 million years ago, during the Mid-Pliocene Warm Period. Temperatures then ranged from 2 degrees to 3 degrees Celsius (3.6 degrees to 5.4 degrees Fahrenheit) higher than during the pre-industrial era and sea level leveled off at 15 to 25 meters (50 to 80 feet) higher than today, according to the National Oceanic and Atmospheric Administration (NOAA).

Enhanced weathering is a process that aims to accelerate natural silicate weathering during which carbon dioxide reacts with rocks, a process that usually takes millions of years. Silicate weathering begins with the reaction between water, carbon dioxide and silicate rocks, which breaks down the rock. Eventually, the dissolved components are washed into the ocean where the carbon is stored for hundreds of thousands of years, either as mineral sediments or dissolved in the water, according to Buckingham. Enhanced weathering amps up this process by breaking down silicate rocks, such as basalt, into tiny pieces in a way of skipping slow weathering processes. The powder made from this is spread on agricultural land and the process can be further accelerated by fungi and roots in the soil.

Buckingham, on the roof of her research building, extracts water from the soil cores for further analysis of enhanced weathering processes. (Photo credit: Frankie Buckingham)

As a young child, Buckingham was already interested in climate change. She obtained a master’s degree in Earth Sciences from the University of Oxford, focusing on past periods of climate change and studying cave deposits.  During her Ph.D. program, she switched gears to try to answer the question of “how we might be able to prevent rising global temperatures?”

“The emergency of the climate crisis makes it a thrilling area to work in,” Buckingham said.

Buckingham started her presentation about her research at the 2021 Comer Climate Conference talking about The Paris Agreement, an international treaty pledging to limit greenhouse gas emissions so that the average global temperature rise is kept under 2 degrees Celsius and preferably under 1.5 degrees. Despite having already sparked low-carbon solutions and new markets, there are still many actions that need to be implemented, one of them being negative emission technologies to help remove carbon dioxide from the atmosphere. This is where enhanced weathering comes in.

Buckingham’s results so far focus strictly on crushed basalt instead of crushed olivine, which most researchers have used. Why has research favored olivine? It has been shown to dissolve the quickest, absorbing CO2 in the process, Buckingham said. But further research indicated that olivine releases harmful chromium and nickel into the soils, something that takes a toll on the environment.

Assumptions made from previous research using simple experiments conducted in the laboratory – beaker experiments – gave a more optimistic view of the weathering process, Buckingham said. Her research differed because it was conducted in a way that was “as close to the field (as) you can get.”

Buckingham explained findings on why some mineral treatments dissolve quicker. She connected her field research back to beaker research with olivine, which revealed that olivine is one of the mineral that dissolves the quickest. Contrary to original expectations, Buckingham’s research showed crushed basalt actually dissolves three to four orders slower than previously expected.

Buckingham cuts soil core into 10-centimeter segments and measures for different physical properties. (Photo credit: Frankie Buckingham)

She elaborated on how many current enhanced weathering calculations assume that basalt can be applied to crops year after year – safely compared with olivine – and that it will dissolve. But, when looking at the crushed basalt in the soil cores, her research revealed that 99% of the crushed basalt does not dissolve.

“Within 50 years, you will have 25 centimeters (10 inches) of a basalt layer,” Buckingham said, which can affect agriculture and farmers who use the crushed basalt in their soil.

Previous thinking also expected the dissolution products (the components that separated from the rock) to travel from the soil into the oceans to help stem ocean acidification and increase the pH content within the ocean water. By consuming acidic ions during dissolution and by releasing important ions such as calcium and magnesium,  enhanced weathering sequesters CO2  and helps counteract ocean acidification.

But, Buckingham found that the “dissolution products were retained in the core.”

“The dissolution products can be sticky and can be chemically removed from the water,” Buckingham said, which prevents the dissolution products from getting into the oceans.

Negative emission technologies

Enhanced weathering is one type of negative emission technology to remove CO2 from the environment. And, as Buckingham’s research shows, more than one process is needed to have an impact on the pace at which the world generates CO2 emissions from fossil fuel use. There are “a plethora of negative emissions technologies” to help combat climate change, according to Buckingham. We cannot rely on just one, she said.

Some other examples include planting new trees, biochar, ocean alkalinization and bioenergy carbon capture and storage. Mature trees don’t sequester carbon dioxide as quickly, so this is where young trees come in to help. Organic material is burned into biochar, which then locks up the carbon. Ocean alkalinization can help to draw down carbon dioxide by spreading alkaline crushed rocks directly into oceans, which ultimately will raise the alkalinity of the ocean water. Bioenergy with carbon capture and storage (BECCS) is a process where biomass, such as crops or wood, that sequester carbon dioxide when grown, are burned for heat and electricity. The carbon dioxide emitted during burning is captured and transported for underground storage.

Where do we go from here?

Buckingham emphasized how her research shows that enhanced weathering may not draw down as much carbon dioxide as previously anticipated and can have “major impacts to soil chemistry.” But “that’s not a reason to lose hope,” she said. Her research was done in the U.K., as opposed to a warmer, more humid climate like the tropics. In tropical climates, more CO2 is drawn out faster due to the quicker breakdown of crushed rock and minerals.

Research is done to figure out answers to questions. The hope is that positive findings result, she said.

This research showed different results from previous assumptions. Jeff Servinghaus, professor of Geosciences at the Scripps Institution of Oceanography at the University of California, San Diego, expressed gratitude to Buckingham at the conference.

“It’s very important work, because you know if we chase down dead ends, that’s just wasted time and money, right? So thank you for that,” he said

Geologist Richard Alley, emcee of the Comer Conference and a geosciences professor at Pennsylvania State University, said the more research that is done, the clearer it is that it’s easier to keep carbon dioxide out of the air than taking it out.

“If you can enrich your soil that’s good and if you can take a little carbon dioxide down that’s great, but don’t count on that to solve the problem,” Alley said.

“And although this might sound quite negative, it highlights the more realistic situation that we need to be aware of,” Buckingham said.

Brittany Edelmann is a registered nurse. She is health, environment and science reporter and a Comer Scholar at Medill. Follow her on twitter @brittedelmann

Carly Menker is a health, environment and science reporter for the Medill News Service and a Comer Scholar at Medill.  Follow her on Twitter @carlymenker.


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