In a forest filled with birch and oak trees on the Isle of Mull, off the west coast of Scotland, a startup will soon begin spreading crushed basalt rock on the ground. The goal: to run a large-scale test of “enhanced weathering,” a process that could potentially help capture gigatons of carbon dioxide if it’s used in forests and on farms around the world.
The startup, called The Future Forest Company, also works on reforestation. But the team realized that restoring forests couldn’t go far enough on its own to pull excess CO2 out of the atmosphere. “The problem that you come up against with reforestation is the scale—basically, there’s just not enough land on the planet to remove the emissions we need to remove through reforestation alone,” says Jim Mann, the founder of Future Forest. The company decided to explore enhanced weathering as a way to help fill the gap.
The approach speeds up a natural process. When rains falls through the atmosphere, it dissolves CO2 in the air, forming a weak carbonic acid. When that hits basalt, it reacts to form a carbonate mineral that stores the carbon dioxide. “Effectively, when that process has occurred, the carbon dioxide is locked up for hundreds of thousands or even millions of years,” Mann says. By crushing the rock into a dust and spreading it out, it increases the surface area so there’s more contact between rain and the basalt, and sequestration can happen faster. While small trials suggest that it works, the new project will be the first to test it in a much larger area. The study will also look for any unanticipated effects of the work, though no red flags have been discovered so far; this is in contrast to olivine, another mineral used in weathering, which can sequester more carbon but contains more heavy metals that could end up accumulating in the ground.
Because weathering remineralizes the soil, it can also make plants grow faster. There’s some evidence that trees could grow 40% faster over 20 years, says Mann, so trees can also capture more CO2 as they grow. The biology of forest soil, in turn, helps weathering happen faster; a study in Iceland that compared enhanced weathering in a forest to the same process on bare rock found that weathering happened faster in the woods. The mycorrhizal fungi associated with tree roots seem to accelerate the process. (Though forests may be the ideal location for speed, weathering can also happen on farmland, where it can help reduce the use of fertilizer.)
In the test in Scotland, the company will get local basalt from a nearby quarry—rock pieces that are too small to be used for other purposes—and use renewable energy to crush it. Because of the area’s heavy rainfall, weathering should happen quickly. The startup expects to have early results about whether the process works, though it will keep running a longer-term study to look for unanticipated impacts. “We’re basically putting in a 20-year science experiment,” says Mann.
The tech company Stripe recently announced that it would give Future Forest a research grant and purchase $300,000 in advance carbon removal credits. Assuming that a peer-reviewed study shows the trial is a success, Stripe will buy another $1 million in carbon removal credits.
There’s plenty of room to deploy the solution, since it can happen on land that’s already being used as a forest or farm. There’s also plenty of rock available. Future Forest is beginning to work on technology that could autonomously spread the crushed rock over land. Though the whole process is in the early stages, it could end up being cheaper than technology like direct air capture, which uses machines to suck CO2 out of the air. It also sequesters CO2 permanently, without the need for additional steps. And deployed at scale, it could remove billions of tons of CO2. “It could be a significant part of the climate solution or mitigation to climate change,” Mann says.