Land and soil
Biochar
Biochar is a stable, carbon rich solid made by heating biomass with very little oxygen, a process called pyrolysis. Its carbon resists decomposition for a very long time, so adding it to soil holds carbon out of the atmosphere while improving how the soil holds water.
It is made the same way as charcoal. The difference is purpose and control: charcoal is made to be burned, biochar is made to be buried, and the process conditions are recorded because they determine how stable it turns out.
Its appeal to carbon buyers is permanence. Once it is in soil there is no straightforward route back to the atmosphere.