Feeding Crops and Weathering Climate Change

August 13, 2020

James Hansen:

Weathering, nature’s process of removing CO2 from the air, can be sped up by grinding silicate materials into fine dust and spreading it on soils that can otherwise benefit from the addition. Many farmers are accustomed to liming their fields, and have equipment for such purpose. The silicate particles will dissolve slowly, react with CO2, forming carbonates. Much of this carbonate will eventually find its way to the ocean, ending up as limestone on the ocean floor.

In order for enhanced weathering to play an important role in CO2 drawdown it will be necessary to demonstrate that it provides a significant benefit in increased soil fertility and crop yield. If governments also provide a financial incentive via a carbon market, the chances of obtaining large-scale buy-in by farmers will be much increased.

Other CO2 drawdown approaches, such as reforestation, are important, but require management to assure that the carbon sink is maintained. We will need the combination of reforestation, enhanced weathering, and other techniques to draw down atmospheric CO2 to a safe level.

Of course, the most important action required to avoid dangerous climate change is to phase over to carbon-free energies as rapidly as is economically justified. In that event, it should be possible to bring down atmospheric greenhouse gas levels before slow amplifying climate feedbacks occur, the most dangerous climate impacts need never occur, and we can bend the climate curve back toward the climate within which that humanity and nature lived during the Holocene.

University of Sheffield:

Applying rock dust to croplands could absorb up to 2 billion tonnes of
CO2 from the atmosphere, research shows

● Major new study shows adding rock dust to farmland could remove carbon dioxide (CO2)
equivalent to more than the current total emissions from global aviation and shipping
combined – or around half of Europe’s current total emissions
● Research identifies the nation-by-nation potential for CO2 drawdown, as well as the costs
and the engineering challenges involved
● Findings reveal the world’s highest emitters (China, India and the US) also have the
greatest potential to remove CO2 from the atmosphere using this method
● Scientists suggest unused materials from mining and the construction industry could be
used to help soils remove CO2 from the atmosphere

Adding crushed rock dust to farmland could draw down up to two billion tonnes of carbon dioxide (CO2) from the air per year and help meet key global climate targets, according to a major new
study led by the University of Sheffield.
The technique, known as enhanced rock weathering, involves spreading finely crushed basalt, a natural volcanic rock, on fields to boost the soil’s ability to extract CO2 from the air.

In the first nation-by-nation assessment, published in Nature, scientists have demonstrated the method’s potential for carbon drawdown by major economies, and identified the costs and engineering challenges of scaling up the approach to help meet ambitious global CO2 removal targets. The research was led by experts at the University of Sheffield’s Leverhulme Centre for Climate Change Mitigation, and the University’s Energy Institute.
Meeting the Paris Agreement’s goal of limiting global heating to below 2C above pre-industrial levels requires drastic cuts in emissions, as well as the active removal of between two and 10 billion tonnes of CO2 from the atmosphere each year to achieve net-zero emissions by 2050. This new research provides a detailed initial assessment of enhanced rock weathering, a large-scale
CO2 removal strategy that could make a major contribution to this effort.
The authors’ detailed analysis captures some of the uncertainties in enhanced weathering CO2 drawdown calculations and, at the same time, identifies the additional areas of uncertainty that future work needs to address specifically through large-scale field trials.
The study showed that China, the United States and India – the highest fossil fuel CO2 emitters – have the highest potential for CO2 drawdown using rock dust on croplands.

Together, these countries have the potential to remove approximately 1 billion tonnes of CO2 from the atmosphere, at a cost comparable to that of other proposed carbon dioxide removal strategies (US$80-180 per tonne of CO2). Indonesia and Brazil, whose CO2 emissions are 10-20 times lower than the US and China, were also found to have relatively high CO2 removal potential due to their extensive agricultural lands, and climates accelerating the efficiency of rock weathering.

The scientists suggest that meeting the demand for rock dust to undertake large-scale CO2 drawdown might be achieved by using stockpiles of silicate rock dust left over from the mining industry, and are calling for governments to develop national inventories of these materials.


Enhanced silicate rock weathering (ERW), deployable with croplands, has potential use for atmospheric carbon dioxide (CO2) removal (CDR), which is now necessary to mitigate anthropogenic climate change1.

ERW also has possible co-benefits for improved food and soil security, and reduced ocean acidification2,3,4. Here we use an integrated performance modelling approach to make an initial techno-economic assessment for 2050, quantifying how CDR potential and costs vary among nations in relation to business-as-usual energy policies and policies consistent with limiting future warming to 2 degrees Celsius5.

China, India, the USA and Brazil have great potential to help achieve average global CDR goals of 0.5 to 2 gigatonnes of carbon dioxide (CO2) per year with extraction costs of approximately US$80–180 per tonne of CO2. These goals and costs are robust, regardless of future energy policies.

Deployment within existing croplands offers opportunities to align agriculture and climate policy. However, success will depend upon overcoming political and social inertia to develop regulatory and incentive frameworks.

We discuss the challenges and opportunities of ERW deployment, including the potential for excess industrial silicate materials (basalt mine overburden, concrete, and iron and steel slag) to obviate the need for new mining, as well as uncertainties in soil weathering rates and land–ocean transfer of weathered products.


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 percent 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 percent 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.

Geologic cycle

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/WikipediaCC 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 United States 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.

One Response to “Feeding Crops and Weathering Climate Change”

  1. rhymeswithgoalie Says:

    I knew my Dr. Evil® brand Volcano Eruptor™ would come in handy some day.

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