A decade ago Scientist discovered what is known by the Indios as Terra Preta or Black Earth and turned out be a part of instruments at our disposel to combat climate change. A incredible BBC documentary from 2002 reveals this story.

Biochar is a key technology for reaching low carbon dioxide atmospheric concentration targets.

The negative emissions that can be produced by BECCS has been estimated by the Royal Society to be equivalent to a 50 to 150 ppm decrease in global atmospheric carbon dioxide concentrations^[3] and according to the International Energy Agency, the BLUE map climate change mitigation scenario calls for more than 2 gigatonnes of negative emissions with BECCS in 2050. BECCS Wikipedia

Regarding the impact, capacity and sustainability of Biochar at the global level.

The maximum sustainable technical potential of Biochar to mitigate climate change:
Annual net emissions of carbon dioxide (CO₂), methane and nitrous oxide could be reduced by a maximum of 1.8 Pg CO₂-C equivalent (CO₂-C_e) per year (12% of current anthropogenic CO₂-C_e emissions; 1 Pg=1 Gt), and total net emissions over the course of a century by 130 Pg CO₂-C_e, without endangering food security, habitat or soil conservation. Biochar has a larger climate-change mitigation potential than combustion of the same sustainably procured biomass for bioenergy, except when fertile soils are amended while coal is the fuel being offset.

http://www.nature.com/ncomms/journal/v1/n5/full/ncomms1053.html