Scientists are investigating a range of technologies they hope can capture lots of carbon without a lot of cost.
Farmers could play a role by applying finely crushed silicate rocks to their land under one of the options being promoted. Crops would benefit.
An account of what is being done has been reported (here) by Annie Sneed in Scientific American.
To limit climate warming to meet internationally agreed targets, she writes, nations will likely need to physically remove carbon from the atmosphere. This means they will have to deploy “negative emissions technology”, or techniques that scrub CO2 out of the air.
Researchers acknowledge they have yet to invent a truly cost-effective, scalable and sustainable technology that can remove the needed amount of carbon dioxide.
But they maintain the world should continue to look into the options.
Several negative emissions strategies, along with the drawbacks, were presented at the American Geophysical Union conference in San Francisco last week.
Earth’s surface naturally removes carbon dioxide from the atmosphere through the chemical breakdown of rocks, but the phenomenon occurs extremely slowly. Scientists have proposed speeding up this process—which is called “weathering”—with man-made intervention.
At the AGU conference, David Beerling, director of the Leverhulme Centre for Climate Change Mitigation, explained an agricultural technique that could quicken weathering and theoretically benefit crops as well.
In this method, farmers would apply finely crushed silicate rocks to their land. The roots of crops and fungus in the soil would accelerate the chemical and physical breakdown of the silicate rocks, and at the same time, carbon dioxide would be pulled from the air into the soil due to a chemical reaction that occurs as part of the weathering process. Grinding the silicate rocks into the size of pellets or sand grains would speed up natural weathering because it increases the amount of rock surface area available to react.
In addition to capturing carbon dioxide, the weathered rocks would release valuable nutrients such as phosphorus and potassium into the soil, which would help crops grow. The rocks would provide plants with silica as well, which Beerling says could help them build stronger cells to better fend off pests.
“You could reduce fertilizer and pesticide use, which would reduce the cost to the farmers as well,” he explains.
The enhanced weathering may also help with ocean acidification, according to Beerling. Some of the carbon dioxide that’s captured would stay in the soil, but much of it would get flushed into the ocean as a compound called bicarbonate.
Bicarbonate is basic, which means it could potentially balance out the increasingly acidic oceans.
But this technique has major drawbacks. Among them, it would cost a lot to grind and transport rocks and both those steps would require a lot of energy, which could create more emissions.
Rob Jackson, professor of earth sciences at Stanford University, is concerned about the environmental disturbance, too, and says “this would essentially be a massive mining operation”although he likes the potential benefits.