Ultimately (ideally, sooner rather than later), technologies that actively remove carbon dioxide must be used to reduce greenhouse gas emissions.2 From the atmosphere. There are many options-from replanting forests to burning biofuels that capture emitted CO in power plants2-And we may need a few of them to make us Net zero emission. Some of these options involve agriculture, and a new feasibility study suggests that one of them-shattering gravel on farmland-should be seriously considered.
The study was led by David Beerling of the University of Sheffield. It estimates the potential of each country to adopt this carbon capture method and the cost required for this.
Using gravel is not a new idea. Some common minerals will react with water and carbon monoxide2 As the weather changes, convert CO2 From air to bicarbonate dissolved in water. Bicarbonate may loiter in groundwater or enter the ocean. And along the way, it can also become a solid carbonate. No matter which route is taken, it is no longer a greenhouse gas in the air.
Over hundreds of thousands or millions of years, this process has had an important and stable impact on the earth’s climate. A warm climate will encourage more weathering and release greenhouse gases out of the atmosphere. What we need to do now is to speed up this process in order to have a meaningful impact on human life.
One way to accelerate weathering is to crush the rock into small particles. Just as powdered sugar dissolves in water much faster than large solid candies, the weathering of these small particles is also much faster. Spreading gravel on farmland can not only be well exposed to the soil, but also benefit the soil, supplement nutrients and offset the pH changes of a large number of cultivated soils.
To estimate the potential of each country to use the technology, the researchers drew a grid map of farmland and climatic conditions. A simple chemical model estimates the weathering rate of gravel based on local soil conditions. They also calculated energy requirements based on the distance to possible rock sources, and considered the energy mix available to run all energy sources. (The more fossil fuels consumed for this work, the less CO2 Removed from the atmosphere in the final accounting process. )
Small stones, big difference
Researchers estimate that the process can be used to capture 500 million to 2 billion tons of carbon dioxide globally2 In contrast, a scenario that limits global warming to less than 2°C usually requires the capture of about 20 to 1
Most of this capture potential comes from the United States, China, India and Brazil. Many other countries can offset a considerable part of their emissions in this way, but these four countries have the most suitable farmland. For the United States and China, by 2030, it can offset up to 5% to 10% of emissions. India can offset up to 40% of emissions, while Brazil can completely offset its emissions-although these figures represent technical capabilities, this requires a very strong commitment to this plan.
After all, this is not free. The estimated cost depends on a country’s rock resources, labor costs, and transportation needs. However, this does not seem to require the creation of a completely new industry. Aggregate mining and crushing are hardly a frontier or niche industry, and crushed limestone has been used as a soil amendment in some cases.
Researchers estimate that in the United States, the European Union, and Canada, all these costs will cost about $160 to $190 per ton of carbon dioxide.2 In China, India and Brazil, the fishing price is 55 to 120 US dollars per ton. This is on the same course as some other options for atmospheric CO2 Remove. Biofuels burned in carbon capture plants, or biofuels used in industrial plants to capture carbon monoxide2 Extracted from the surrounding air, the cost per ton will exceed $100. Other methods of carbon sequestration in agricultural soils may be at least cheaper, but multiple methods can be used together. They may even collaborate with each other.
Pay the fee
Nevertheless, the cost is still greater than zero, so these processes must be paid for. A carbon emission tax of $100 per ton can make many technologies attractive, but current carbon pricing policies (if any) are much lower than this number.
Obviously, increasing mining to meet this demand for gravel will have separate environmental consequences. But what is interesting is that the researchers found some unused resources that can minimize or even eliminate the need for mining. In many rock crushing operations, excess powdery grains remain, which may be perfect. Slag produced by steelmaking can also work, as can recycled cement and masonry.
Researchers say all these mineral resources need to be tested in different regions. It may be that certain materials are more effective than others, or some may release unwanted metals or contaminants. But research shows that this technology (which may be used in combination with other additives such as charcoal in untreated organic matter) is truly attractive to soil health.
Researchers Johannes Lehmann and Angela Possinger (not involved in this study) wrote in a paper in the journal Nature: “The main lesson here may be several major potential technologies for removing atmospheric CO2 It can bring considerable benefits to food production and is centered on soil management. Farmers must fully support this global effort or they will fail… This method of providing financial support for soil health and crop production may be our best short-term solution to the problem of decarbonization2 From the atmosphere. “
Naturally, 2020. DOI: 10.1038/s41586-020-2448-9, 10.1038/d41586-020-01965-7 (about DOI).