In lush South Florida, trees and bushes grow all year round. And that means yard waste and dead trees never stop piling up. But leaving them in a landfill is a climate-warming issue. Two South Florida governments think they have a new solution — light it on fire, but in a planet-friendly way. Miami-Dade County and Coral Gables are both turning to new technology that leans on ancient farming practices to transform wood waste into a charcoal-like material called biochar. The material known as “black carbon” has the potential to clean dirty water, nourish soil and even be used in roads. Plus, it has lower emissions than a simple bonfire, leading to cleaner, healthier air that contributes less to climate change. …Gables leaders are getting ready to drop millions to create a facility that will use large, futuristic ovens to bake fallen trees and other vegetative waste into biochar.