The fact is that some prehistoric civilizations of our Earth used biochar and thrived on it. Most notably, ancient Amazonian cultures' livelihoods were actually based upon it. Locations have been found throughout those regions to have soils enriched by biochar.
But you might be thinking, how can burning something--like when making biochar--be good for the environment? And furthermore, how can burning something reduce levels of CO2 in the air? It seems counterintuitive, I know.