Turning plant waste into biochar captures loads of carbon. New research suggests it stays trapped for much longer than scientists thought.
For all its plant and animal life aboveground, the Amazon rainforest's soils are surprisingly poor in nutrients necessary for growing food. Thousands of years ago, the region's Indigenous peoples solved this problem by creating "terra preta" from table scraps and charcoal and tucking it away in the hostile soil. Today, that ancient bit of ingenuity is a powerful climate solution. As biomass like trees and crops grow, they sequester carbon in their leaves and branches. Heat that biomass up without fully consuming it and it turns to nearly pure carbon known as biochar, which farmers soak in compost or fertilizer to "charge" it with nutrients, then add to their soils. (In 2023 the global biochar market was worth $600 million, and is expected to grow to $3 billion this year.) That simultaneously improves crop yields and better retains water, all while locking carbon away from the atmosphere. Rising demand from farmers and big business is expected to push the global market for biochar from $600 million two years ago to $3 billion this year. The nagging question, though, is exactly how long that carbon stays in the soil. A new study adds to a growing body of evidence that scientists have been underestimating the staying power of biochar, meaning the technology is actually an even more powerful way to store carbon than previously thought. "I'm talking about over 90 percent very easily surviving multi-thousands of years," said Hamed Sanei, a professor of organic carbon geochemistry at Denmark's Aarhus University and lead author of the paper published in the journal Biochar. The research suggests that biochar is much more resilient than currently calculated by researchers. "The current model that we're talking about is saying 30 percent of almost all biochar that's being produced will be gone in 100 years." Nailing down exactly how long biochar can hold onto carbon is crucial for the carbon-removal credit industry, where companies like Microsoft and Google fund projects…