Article II of the Paris Agreement requires signatories hold the increase of global average temperature to below 2°C above pre-industrial levels and to pursue efforts to hold to 1.5°C. These goals cannot be achieved merely by substituting renewable energy. They require carbon dioxide removal (CDR). The present range of CDR options includes:
changes to land use management;
bioenergy with carbon capture and storage (BECCS); and
direct air capture (DAC).
Quantitative assessments have been undertaken for each of these options. Prior studies have largely externalized the labor and energy required to bring these methods to scale. Applying a biophysical economics analysis, we conclude that it would be possible to economically scale four of the five techniques to achieve drawdown (net sequestration over emissions) by mid-century if fossil emissions reductions were also forthcoming. The fifth technique (DAC) fails on net energy grounds.
BECCS would also fail were it limited to its common conceptualization relying upon low EROI biomass energy to pay for fragile and suspect geological storage of carbon dioxide. However, by substituting pyrolysis for combustion and adding biochar and carbon co-products, both feedstocks and storages diversify and the finance becomes favorable.