Potential Use of Biochar to Drawdown Atmospheric Carbon: A Preliminary Assessment for Washington State

Long-term solutions to the climate problem likely will require that large quantities of CO2 be removed from the atmosphere. One approach involves the large-scale production of biochar from abundant woody biomass waste and its storage in soils, where it remains stable for hundreds to thousands of years. Here we present a preliminary assessment of the potential contribution that could be made by biochar production in Washington State over the course of a century. In this state, large quantities of wood waste biomass could be purposed for production of combined heat/power/biochar (CHPB) through existing biomass boilers. Because the carbon emission intensity of Washington’s fuel mix is already relatively low, biochar production from biomass is twice as effective in offsetting GHG emissions as complete biomass combustion of the same biomass. Using existing estimates of waste wood biomass and available soil resources, and assuming that conversion of existing biomass boilers to generate biochar is economically feasible, our preliminary assessment suggests that over the course of a century, Washington State can remove about 0.6 Gt of CO2 from the atmosphere. Based on a previous drawdown of atmospheric carbon several centuries ago, however, the buffering effect of the oceans results in exsolvation of CO2 and yields a net drawdown of about 0.2 Gt CO2. Details of the assumptions made and process used to obtain these values will be presented.