Can biomass supply meet the demands of BECCS?

In order to reach the reduced carbon emission targets proposed by the Paris agreement one of the widely proposed decarbonizing strategies, referred to as negative emissions technologies (NETs), is the production and combustion of second-generation bioenergy crops in conjunction with carbon capture and storage (BECCS). The international research on NETs has grown rapidly and publications have ranged in scope from reviewing potential and assessing feasibility to technological maturity and discussions on deployment opportunities. However, concerns have been increasingly raised that ungrounded optimism in NETs potential could result in delayed reductions in gross CO₂ emission, with consequent high-risk of overshooting global temperature targets. Negative emissions as a consequence of BECCS are achieved when the CO₂ absorbed from the atmosphere during the growth cycle of biomass is released in combustion and energy production and then captured and stored indefinitely. The simplistic vision of BECCS is that one ton of CO₂ captured in the growth of biomass would equate to one ton of CO₂ sequestered geologically- which we can regard as a carbon efficiency of 1. However, biomass crops are not carbon neutral as GHG emissions are associated with the cultivation of biomass.  Furthermore, throughout the BECCS value chain carbon ‘leaks’. Some life cycle analyses of the entire value chain for a BECCS crop to final carbon storage in the ground have shown leakage of CO₂ to be greater than the CO₂ captured at the point of combustion and thus it has low carbon efficiency. The deployment of BECCS is ultimately reliant on the availability of sufficient, sustainably sourced, biomass for an active CCS industry operating at scale and a favourable policy and commercial environment to incentivise these investments. It has been suggested that the theoretical global demand for biomass for BECCS could range from 50 EJ/yr up to more than 300 EJ/yr, although the technical and economic potential will be significantly less and will be dependent on uncertain social preferences and economic forces. The two most important factors determining this supply are land availability and land productivity. These factors are in turn determined by competing uses of land and a myriad of environmental and economic considerations. It is suggested that removing 3.3 GtC/year with BECCS could annually require between 360 and 2400 Mha of marginal land. The upper bounds correspond to 3x the world’s harvested land for cereal production. The conclusion is that estimates of biomass availability for the future depends on the evolution of a multitude of social, political, and economic factors including land tenure and regulation, trade, and technology. Consequently, the assumptions, in future climate scenarios, that high rates of NETs can be achieved across many countries and land types is not yet demonstrated.