Various concepts for such ‘carbon dioxide removal’ or ‘negative emissions’ technologies have been proposed, but the most promising involve bioenergy – the production of fuels, electricity, or heat from biomass.  How does this work?  Plants absorb CO₂ from the atmosphere as they grow, and that carbon is then cycled back to the atmosphere once those plants die and decay, or are consumed by herbivores.  Carbon negative bioenergy involves harvesting biomass, extracting usable energy from it, and then preventing some of that carbon from returning to the atmosphere by either pumping CO₂ into geological storage underground (Bioenergy with Carbon Capture and Storage, or BECCS), or by storing the solid by-products of bioenergy conversion in soils (e.g., biochar).

CCS equipment at the ADM corn ethanol facility in Illinois. Image from Ethanol Producer Magazine

Most climate stabilization scenarios suggest that we’ll need to widely deploy such technologies over the next decades to reach the 2 C goal, to the point where on the order of 20% of all human energy use is coming from a carbon-negative bioenergy system.  There is great controversy on whether this is possible within the scientific community – it has been called the “World’s Biggest Gamble”, and researchers have questioned the viability and sustainability of such technologies, and whether they might be a distraction from the hard work of reducing emissions.  However, interest in the topic is growing in both academic and industrial circles.  The world’s first commercial-scale BECCS operation was recently inaugurated at a corn ethanol biorefinery in Illinois that had previously sequestered one million tons of CO₂ in a successful technology demonstration, and biochar production companies are proliferating in both the US and Europe.