Enhanced Weathering is a carbon capture process that could remove over 2bn tons of CO2 each year (for comparison, the U.S. emitted 5.3bn in 2018), explains Benjamin Houlton at the University of California. Silicate minerals exposed to the weather have been sequestering atmospheric carbon and turning it into rock since the dawn of time, but it’s a process that normally takes thousands of years. This period can be cut to two years by grinding silicate rocks into a fine powder, thus increasing its surface area and its contact with CO2. As a further step, spreading the rock dust on croplands gives it immediate contact with CO2 being produced by plant roots and soil microbes. The minerals will also increase farm yields, providing farmers with an incentive (along with negative emissions credits) to become a link in this carbon capture chain. And the other links? They’re already there, explains Houlton. Global mining and fertiliser supply chains already exist at scale. Houlton describes the results of experiments at a 50 acre site in California, the world’s largest demonstration project.
Why has Earth’s climate remained so stable over geological time? The answer just might rock you.
Rocks, particularly the types created by volcanic activity, play a critical role in keeping Earth’s long-term climate stable and cycling carbon dioxide between land, oceans and the atmosphere.
Scientists have known for decades that rock weathering – the chemical breakdown of minerals in mountains and soils – removes carbon dioxide from the atmosphere and transforms it into stable minerals on the planet’s surface and in ocean sediments. But because this process operates over millions of years, it is too weak to offset modern global warming from human activities.
Acid rain damage to buildings and monuments, like this sandstone statue in Dresden, Germany, is a form of chemical weathering / Slick/Wikipedia
Now, however, emerging science – including at the California Collaborative for Climate Change Solutions’ (C4) Working Lands Innovation Center – shows that it is possible to accelerate rock weathering rates. Enhanced rock weathering could both slow global warming and improve soil health, making it possible to grow crops more efficiently and bolster food security.
Natural rock chemistry sequesters CO2… but very slowly
Many processes weather rocks on Earth’s surface, influenced by chemistry, biology, climate and plate tectonics. The dominant form of chemical weathering occurs when carbon dioxide combines with water in the soil and the ocean to make carbonic acid.
About 95% of Earth’s crust and mantle – the thick layer between the planet’s crust and its core – is made of silicate minerals, which are compounds of silicon and oxygen. Silicates are the main ingredient in most igneous rocks, which form when volcanic material cools and hardens. Such rocks make up about 15% of Earth’s land surface.
When carbonic acid comes in contact with certain silicate minerals, it triggers a chemical process known as the Urey reaction. This reaction pulls gaseous carbon dioxide from the atmosphere and combines it with water and calcium or magnesium silicates, producing two bicarbonate ions. Once the carbon dioxide is trapped in these soil carbonates, or ultimately washed into the ocean, it no longer warms the climate.
When carbonic acid dissolves calcium and magnesium silicate minerals, they break down into dissolved compounds, some of which contain carbon. These materials can flow to the ocean, where marine organisms use them to build shells. Later the shells are buried in ocean sediments. Volcanic activity releases some carbon back to the atmosphere, but much of it stays buried in rock for millions of years. Gretashum/Wikipedia, CC BY-SA
The Urey reaction runs at a higher rate when silicate-rich mountains such as the Himalayas expose fresh material to the atmosphere – for example, after a landslide – or when the climate becomes hotter and moister. Recent research demonstrates that humans can speed up the process substantially to help fight modern global warming.
Accelerated weathering
The biggest limit on weathering is the amount of silicate minerals exposed at any given time. Grinding up volcanic silicate rocks into a fine powder increases the surface area available for reactions. Further, adding this rock dust to the soil exposes it to plant roots and soil microbes. Both roots and microbes produce carbon dioxide as they decompose organic matter in the soil. In turn, this increases carbonic acid concentrations that accelerate weathering.
One recent study by British and Americans scientists suggests that adding finely crushed silicate rock, such as basalt, to all cropland soil in China, India, the U.S. and Brazil could trigger weathering that would remove more than 2 billion tons of carbon dioxide from the atmosphere each year. For comparison, the U.S. emitted about 5.3 billion tons of carbon dioxide in 2018.
Farming with crushed rocks
One compelling aspect of enhanced weathering is that, in controlled-environment studies involving basalt amendments of soil, cereal grain yields are improved by roughly 20%.
As basalt weathers, it increases vital plant nutrients that can boost production and increase crops yields. Mineral nutrients such as calcium, potassium and magnesium create healthier soils. Farmers have been amending soil with rock minerals for centuries, so the concept is nothing new.
Spreading lime on a field in Devon, England to improve soil quality. Mark Robinson/Wikipedia, CC BY
World’s largest demonstration project
At the Working Lands Innovation Center, we are conducting perhaps the largest enhanced weathering demonstration experiment on real farms in the world. We are partnering with farmers, ranchers, government, the mining industry and Native American tribes in California on some 50 acres of cropland soil amendment trials. We are testing the effects of rock dust and compost amendments on greenhouse gas emissions from the soil, carbon capture, crop yields, and plant and microbial health.
Our initial results suggest that adding basalt and wollastonite, a calcium silicate mineral, increased corn yields by 12% in the first year. Working with California’s greenhouse gas emissions trading program and our state’s diverse agricultural interests, we hope to establish a pathway that would offer monetary incentives to farmers and ranchers who allow enhanced rock weathering on their lands. We aim to create a protocol for farmers and ranchers to make money from the carbon they farm into the soil and help businesses and industry achieve their carbon neutrality goals.
At Bowles farm, 6 acres of rock dust (meta basalt) addition to cropland soil, large scale CO2 capture project underway, 40 more acres to go!!!! @ucdavis @UCDavisJMIE pic.twitter.com/Ub2WoCiLfJ
— Benjamin Z Houlton 🌍 (@BenHoulton) October 15, 2019
Negative emissions, not just carbon capture
Under the 2015 Paris climate agreement, nations have pledged to limit global warming to less than 2 degrees Celsius above pre-industrial levels. This will require massive cuts in greenhouse gas emissions.
Pulling carbon dioxide from the air – also known as negative emissions – is also necessary to avoid the worst climate change outcomes, because atmospheric carbon dioxide has an average lifespan of more than 100 years. Every molecule of carbon dioxide that is released to the atmosphere through fossil fuel combustion or land clearing will remain there for many decades trapping heat and warming Earth’s surface.
[VIDEO: In an even faster version of enhanced weathering, scientists pump supercritical carbon dioxide underground into basalt formations, where it reacts with minerals to form new solid rock.]
The supply chain is already in place!
Nations need a portfolio of solutions to create negative emissions. Enhanced weathering is poised for rapid scale-up, taking advantage of farm equipment that’s already in place, global mining operations and supply chains that currently deliver fertilisers and seeds worldwide. By addressing soil erosion and food security along with climate change, I believe rock weathering can help humans escape the hard place we find ourselves in today.
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Benjamin Houlton is Professor of Global Environmental Studies, John Muir Institute of the Environment, University of California, Davis
This article is republished from The Conversation under a Creative Commons license. Read the original article.
What would be the long term effects on soils ? Are you not trying to solve one mess by creating another one ?
Long term impact on the soil, very positive, heavy soils (clay, black earth, salt marshes) become lighter and more fertile and only depleted and poor soils (sand) do not improve. But if you add not Basalt, but Saponite (clay mineral), then they also improve. It is much better to introduce into the soil not Basalt, but Zeolite. Its use in soils has been used in Europe for over 30 years. The effect is only positive. Giving a yield increase of up to 30%. The use of Zeolites and Saponites to improve soil fertility has a long history in Ukraine. In addition, the energy consumption for grinding basalt in comparison with the consumption for grinding Zeolite 2 1, for grinding Saponite in general 2 0, 5. Because Zeolite is porous and easier to grind than Basal, and Saponite is generally clay.
Shouldn’t you take into account the energy (presumably electricity from a power plant) required to mill the rock to dust? I could see a benefit if you were to only mill during off-peak hours (i.e., the same argument used for electric vehicles).
I’m always deeply suspicious of the motivation of any advocate of what amounts to geo-engineering. If you are in a hole, stop digging! That’s the first rule. Advocacy of cloud seeding, atmospheric CO2 removal, putting things in space to do whatever crazy theory, all miss the point. Our greed and consumption has to stop. We’ve reached, and surpassed, the limits of our planet to sustain our population.
And this scheme suffers from that misconception. Just dig out a mega-mine for minerals or demolish a mountain. Crush it spread it and the problem goes away. No, it doesn’t. The problem is still there! We are consuming too much. Too much petrol, too much air travel, too much fossil generated electricity, too many needless plastic trinkets, too much throw away fashion.
The solution is to reduce consumption, not further to crush up our environment and hope that it will suck the products of our greed out of the atmosphere. A drunk who spills his beer on the bar’s floor is always happy for the barman to wipe up the mess and put another pint in front of him to allow him to forget his problems. Geo-engineering is akin to this.
Aside from destroying habitat any possibly people’s homes there’s also the question of what CO2 emissions this scheme causes? What energy (thermal heat, CO2) is required to dig the mine or crush the mountain? How many truck journeys are required to deliver the mountains to the farmers? How many tractor hours to spread it? How much CO2 is released to the atmosphere due to destruction of the habitat destroyed to produce the rock?
Other methods are not considered in the article you write, either. Farming that reduces ploughing keeps CO2 captured in the soil. Planting hedgerows enhances habitats and captures CO2. Organic farming reduces inputs of fertiliser and other chemicals, thereby reducing CO2.
When will people realise that mankind cannot destroy nature and build it’s way out of its problems, that our insatiable greed creates?
Certainly no disrespect intended, but the argument that mankind needs to contain its “insatiable greed” as the primary way of stemming GHG emissions is naïve. Literally, since the dawn of man, we’ve relied on technology to improve the human condition. Think back to the 1960’s. Uncontrolled coal plants were spewing out sulfur dioxide, producing acid rain, and destroying lakes and streams. Being that “necessity is the mother of invention”, the scientists and engineers developed a technology (FGD) to “scrub” the sulfur from the flue gas coming from coal plants. Some plants could afford to install this technology, while others couldn’t and were forced to retire. Again, no disrespect intended, buy I’d argue that the strategy of fostering guilt about our “insatiable greed” is exactly the opposite of what should be done to solve the problem. Instead, encouraging innovation will be more effective. Certainly, some ideas will be goofy, and others too expensive, but some may have merit. The so-called “ponies in the pile.”
Hi Phil and thank you for your reply.
I’m sorry if you think I’m naive. I remember this sort of allegation being levelled at me back in the 80’s, although less politely: The phrase “Tree hugging (expletive deleted) hippy” was used then when the issue of recycling, not killing whales and global warming were discussed in public. Despite the efforts of a large part of industry (especially the oil industry) trying to refute these issues, they are now mainstream and ironically, among enlightened companies, they are now hot topics of conversation.
I entirely agree with you about the need to address ills caused by technology, I think we are singing from the same hymn sheet? Flue gas desulphurisation, catalytic converters and the removal of lead from petrol have all improved health immeasurably, in the face of enormous opposition from big business. The point I’d make here is that if there was a public campaign to make people widely aware of the need to cut consumption then that too is a part of the answer.
To give you one example, here’s a headline from WRAP who deal with the issue of tackling waste in the UK:
WRAP research shows we now (2018) throw away 6.6 million tonnes of household food waste a year in the UK, compared to 8.1 million tonnes in 2007. 2. Of the 6.6 million tonnes we throw away, almost three quarters (70% of the total) is food we could have eaten (4.5 million tonnes)
https://wrap.org.uk/sites/files/wrap/Food_20surplus_and_waste_in_the_UK_key_facts_Jan_2020.pdf
And another comment regarding food waste across the EU:
In the EU, an estimated 20% of the total food produced is lost or wasted, while 43 million people cannot afford a quality meal every second day. Households generate more than half of the total food waste in the EU (47 million tonnes) with 70% of food waste arising at household, food service and retail (FUSIONS, 2016)
https://ec.europa.eu/food/safety/food_waste/stop_en
With all that food waste, why do we need to indulge in grinding a mountain (or quarry full) of rock to increase food yields? (ref: “Our initial results suggest that adding basalt and wollastonite, a calcium silicate mineral, increased corn yields by 12% in the first year.”) More food is not needed; it’s public education about the waste of food that’s needed.
Organic farming typically has lower yields:
We therefore compiled and analyzed a meta-dataset of 362 published organic–conventional comparative crop yields. Our results show that organic yields of individual crops are on average 80% of conventional yields, but variation is substantial (standard deviation 21%).
https://ec.europa.eu/knowledge4policy/publication/crop-yield-gap-between-organic-conventional-agriculture_en#:~:text=We%20therefore%20compiled%20and%20analyzed,substantial%20(standard%20deviation%2021%25).
So organic farming produces 20% less food, but we waste 20% of the food we use, so why try to produce more by spreading rock, fertiliser or anything else on our fields? Especially when conventional agriculture produces more CO2 emissions than organic agriculture:
The global food system, from fertilizer manufacture to food storage and packaging, is responsible for up to one-third of all human-caused greenhouse-gas emissions, according to the latest figures from the Consultative Group on International Agricultural Research (CGIAR), a partnership of 15 research centres around the world.
https://www.nature.com/news/one-third-of-our-greenhouse-gas-emissions-come-from-agriculture-1.11708
Adding the crushing of rock to this will further increase CO2 emissions. For what? We don’t need more; we have enough, I’d argue that we need education about our effect on the planet.
And now, perhaps, I hear you say that people won’t change? Well, what has happened with people’s response in the face of Covid-19? Where they’ve had good information, not clap-trap about 5G broadband masts, they’ve stayed indoors, socially distanced and worn masks.
It’s not naive to say that people people are greedy; they are. In ‘The West’ we are enormously wealthy, and enormously greedy with the power that wealth has given us. Statistics on obesity are stark evidence of that, as are the shortage of landfill sites in which to dispose of vast amount of rubbish that gets thrown away every year.
But people can change. It’s a question of having a desire to implement that change in the face of a capitalist system that demands incessant growth to fuel profit. But, Phil, that is changing too. Read some corporate social responsibility literature. Here’s just one headline:
Worcester and London universities to trial sustainable diets behaviour change programme
https://www.edie.net/news/6/Worcester-and-London-universities-to-trial-sustainable-diets-behaviour-change-programme/
Where organisations choose to adopt corporate targets that include limiting environmental impacts, change can, and does, occur. One personal example: I volunteered at an environmental charity years back that had groups of recycling bins placed at regular intervals around the office. They had only one ‘Rubbish’ bin in the whole office. You had to make a conscious effort to get up and walk to it to throw anything out! It was empty.
So how about reducing what we use, then reusing stuff and then recycling what we can’t avoid in order to cut our emissions? And if that requires new technology, I’m not against it, for example LED bulbs vs incandescent. Why are they not an international requirement? People would bitch about it for a while and then get on with it. You’re from the US, I guess, from your spelling of the word ‘sulfur’. So here’s an American example of what reduction in consumption could achieve, from the US government:
Energy Savings
LED is a highly energy efficient lighting technology…Residential LEDs…use at least 75% less energy, and last 25 times longer, than incandescent lighting.
Widespread use of LED lighting has the greatest potential impact on energy savings in the United States. By 2027, widespread use of LEDs could save about 348 TWh (compared to no LED use) of electricity: This is the equivalent annual electrical output of 44 large electric power plants (1000 megawatts each), and a total savings of more than $30 billion at today’s electricity prices.
https://www.energy.gov/energysaver/save-electricity-and-fuel/lighting-choices-save-you-money/led-lighting#:~:text=Energy%20Savings&text=By%202027%2C%20widespread%20use%20of,billion%20at%20today's%20electricity%20prices.
Perhaps that’s one simple technological fix that could save a whole lot of mountains and needlessly dug quarries from which to crush rock, to spread on fields to absorb CO2 pumped out by power stations. But it won’t happen, because industry wants you, me and everyone to carry on buying More! Even if that requires, unfortunately, someone’s or something’s habitat to be destroyed in order to achieve it.
To avoid potential problems with the dumping of minerals on agricultural fields, with unknown long term effects, you should consider the use of char. It is a by product of an incomplete combustion of biomass, when the supply of oxygen. is restrained. Almost pure carbon is a by product of this type of combustion. If biomass is burned, the risks of contamination of soils by unwanted minerals or chemicals is very limited.
For centuries farmers in Europe burned their fields after the harvest. The result is that particles of carbon remained in the ground. They facilitated the development of microorganisms and bacteries, and absorbed water. The fertility of the black earths of Ukraine is possibly the result of an accumulation of such carbon, but for thousands of years. So large quantities were incorporated in the soils, that they changed its color.
If you want to risk the use of minerals in soils, you should also pay attention to the capture of nitrogens by soils. The agriculture is a major generator of NO and NO2, and contribute therefore significantly to the warming of the climate. Some minerals, such as byproducts of the aluminum industry can be used to fix nitrogen in the soil.
These issues are worth a cruisade, but you need to fix yourseld simple and realistic objectives.
The long-term impact on the soil of the introduction of aluminosilicate minerals is very positive, heavy soils (clay, chernozem, salt marshes) become lighter and more fertile and only depleted and poor soils (sand) do not improve. But if you add not Basalt, but Saponite (clay mineral), then they also improve. Soil acidity is also significantly reduced. The effect of the impact of layered and porous silicates on soil fertility has been studied by several scientific Institutes of Ukraine for many years. and No adverse effects were found.
It is much more effective to introduce into the soil not Basalt, but Zeolite. Its sorption and, which is very important, ion exchange capacity is much higher. Its use in soils has been used in Europe for over 30 years. The effect is only positive. Giving a yield increase of up to 30%. The use of Zeolites and Saponite to improve soil fertility has a long history in Ukraine. In addition, the energy consumption for grinding Basalt, in comparison with the consumption for grinding Zeolite 2 1, for grinding Saponite in general 2 0, 5. Because Zeolite is porous and easier to grind than Basal, and Saponite is a three-layer clay. In the United States there are large deposits of zeolites, and there are much more basalts, but the cost of grinding them is also much higher.