Biochar

Carbo Culture uses a carbon-negative microbial process to convert "worthless agricultural and forestry residues" into biochar, or charcoal, which can be used to replenish topsoil—and sequesters CO2 with a very low risk of being released back into the atmosphere. Other startups such as Climate Robotics plan to exploit AI and robotics to automate significant portions of this process. Biochar can also be incorporated into a variety of other green infrastructure including green roofs and stormwater management systems.

This points towards a future where the built and natural environment of cities can become a high-capacity carbon sink and waste streams can be converted to valuable products.