Plus it would take centuries to capture and put back as much CO2 as has been emitted. According to [0], in 2016 the world consumed 8.561.852.178 "short tons" (freedom tons, about 7.767.000.000 metric tons) per year.

Assuming that 1 kg of your proposed charcoal offsets 1 kg of mined coal, and based on [1] stating a roughly 7:1 ratio for wet wood -> charcoal, you'd need to grow more than 54.369.000.000 (54 billion) metric tons of wood per year, more to offset the harvesting, replanting, charcoaling and other processing of that wood.

I mean don't get me wrong, this is what I thought as well but it'd be a huge operation. I think you could also get away with just straight burying the wood / plant material, as long as it's anaerobic it shouldn't start rotting.

[0] https://www.worldometers.info/coal/

[1] https://forum.driveonwood.com/t/charcoal-production-rough-ru...