Eventually (ideally sooner rather than later), efforts to reduce greenhouse gas emissions will have to be coupled with a technology that actively removes COtwo from the environment There are several options, from re-cultivating forests to burning biofuels in power plants that capture the emitted COtwo“And we’ll probably need several of them to get us to net zero Emissions Some of these options involve agriculture, and a new feasibility study suggests that one of them, the diffusion of crushed rocks in agricultural fields, deserves serious consideration.
The study was led by David Beerling of the University of Sheffield; It estimates both the potential of this carbon capture method in each country and the cost required to do so.
Carbon crush
Using crushed rocks is not a new idea. Some common minerals react with water and COtwo as they age, turning COtwo of the air in bicarbonate dissolved in water. That bicarbonate can pass the time in the groundwater or reach the ocean. And along the way, it can also turn into solid carbonate. Whichever route you take, it is no longer a greenhouse gas in the air.
For hundreds of thousands or millions of years, this process has a significant stabilizing influence on Earth’s climate. Warmer climates encourage more weathering, removing greenhouse gases from the atmosphere. What we have to do now is accelerate this process so that it has a significant effect on human life.
One way to speed up weathering is to grind that rock into small particles. Just as powdered sugar dissolves in water much faster than large solid caramel, these tiny particles will wear out much faster. The spread of crushed rock over agricultural fields not only exposes it to the elements, but can also be beneficial to the soil, replenishing nutrients and counteracting pH changes in heavily cultivated soils.
To estimate each country’s potential to use this technique, the researchers constructed gridded maps of farmland and weather conditions. A simple chemical model estimated the weathering rate of the crushed rock based on local soil conditions. They also calculated the power requirements based on the distance from the probable rock sources, as well as accounting for the available energy mix to run everything. (The more fossil fuel burned to do the job, the less COtwo removed from the atmosphere in the final accounting.)
Small rocks, big difference
Globally, researchers estimate that this process could be used to capture between 500 and 2 billion tons of COtwo per year in 2050. By way of comparison, scenarios limiting global warming to 2 ° C generally involve capturing between 2 and 10 billion tons per year in a few decades from now.
Most of this catch potential comes from the US, China, India, and Brazil. Many other countries could offset a significant portion of their emissions in this way, but these four countries have the most suitable farmland. For the US and China, it could offset up to 5 to 10 percent of emissions in 2030. India could offset up to 40 percent, and Brazil could fully offset its emissions, although these numbers represent technical capacity, so that would require a strong commitment to this scheme.
After all, this is not free. Estimated costs vary depending on a country’s rock resources, labor costs, and transportation needs. However, it is not that an entirely new industry should be created. Mining and crushing aggregates is not a state-of-the-art or niche industry, and crushed limestone is already used as a soil amendment in some cases.
In the United States, the EU and Canada, researchers estimate that all of this would cost around $ 160 to 190 per ton of COtwo captured, while China, India and Brazil could do so for $ 55 to 120 per ton. That is in the same stadium as other options for atmospheric COtwo elimination. Biofuels burned in carbon capture plants, or using industrial plants to capture COtwo of ambient air, both would cost more than $ 100 per ton. Other methods for sequestering carbon in agricultural soils can be at least slightly less expensive, but multiple methods can be used together. They may even be able to synergize with each other.
Paying the costs
Still, the costs are greater than zero, so something has to be paid for these processes. A carbon emission tax of $ 100 per ton can make many techniques attractive, but current carbon pricing policies (where they exist) lie far south of that number.
Obviously, increasing mining to meet this demand for crushed rock would have separate environmental consequences. But interestingly, the researchers identify some unused resources that could minimize or even eliminate the need to mine. Many rock crushing operations have unwanted dust-sized grain debris that could be perfect. Slag from steelmaking could work, too, as can recycled cement and masonry.
All mineral sources need to be tested in different areas, the researchers say. It could be that some specific materials work better than others or that some release unwanted metals or contaminants. But studies could show that this technique, possibly combined with other additives such as charcoal from untreated organic matter, has really attractive benefits for soil health.
As researchers Johannes Lehmann and Angela Possinger, who were not involved in the study, write in an article accompanying the article in the journal Nature, “The main lesson here could be that several of the major potential technologies for removing atmospheric COtwo Could generate substantial benefits for food production and focus on soil management. Farmers must be entirely behind such a global effort or it will fail … Such an approach of financial support for soil health and crop production could emerge as our best short-term solution to the problem of eliminating COtwo of the environment. “
Nature, 2020. DOI: 10.1038 / s41586-020-2448-9, 10.1038 / d41586-020-01965-7 (About DOIs).
