Forget whiz-bang technologies that are supposed to solve climate change. An ancient agricultural practice that removes carbon from the atmosphere is getting fresh attention and game-changing cash from big companies. Biochar is a black substance similar to charcoal that when buried underground sequesters carbon dioxide, the primary greenhouse gas that causes climate change. It has long been used to improve soil. Now it has suddenly become a lucrative business thanks to carbon credits that companies use to offset their own emissions.

---