Sequestering Biomass for Natural, Carbon Efficient, and Low-Cost Direct Air Capture of Carbon Dioxide

Abstract

Corporations and governments aspire to become Net Zero CO2 by 2030-2050. Solutions proposed for reducing CO2 can be placed in two categories: 1) solutions that focus on reducing future CO2 emissions from continued use of fossil fuels; and 2) solutions that can remove CO2 already in the atmosphere. Windmills are an example in the first category. A windmill built today will reduce future emissions of CO2 from continued use of fossil fuel energy they displace. They will not remove CO2 already in the atmosphere. Technologies in the first category are currently falling far short of that needed to achieve Net Zero. Thus, atmospheric CO2 levels continue to build, and there is the need for the second category. These technologies offer a form of Direct Air Capture (DAC) of CO2 already in the atmosphere. The most natural form of DAC is to grow biomass via photosynthesis, and then to permanently sequester that biomass carbon underground. Success requires discouraging biomass decomposition. An understanding of the chemistry phases through which municipal waste decomposition passes provides clues on how this can be achieved. The burial of trees has been proposed before. Here, we propose tree leaves and biomass grown on-purpose, such as high yield switchgrass, as good sources of supplementary biomass. Left unsequestered, leaves decompose with a short Carbon Cycle time constant releasing CO2 back to the atmosphere. In any given year leaves represent a small fraction of above ground biomass. However, when integrated over the life of a tree, leaves can represent a substantial fraction of the total biomass generated. If decomposition can be inhibited, then sequestration of biomass can become a natural, carbon efficient, and low-cost method of Direct Air Capture. Biomass sequestration can provide CO2 removal on gigatonnes per year scale and can be implemented in the needed timeframe (2030-2050).