A new report from NEGEM explores the global potential of land-based NETPs without further pressures on terrestrial planetary boundaries.
This study conducted by NEGEM partners at Potsdam Institute for Climate Impact Research, takes a supply-driven perspective to quantify the global spatially explicit potentials of BECCS, Pyrogenic Carbon Capture and Storage (PyCCS) and reforestation, while considering their impacts on four terrestrial planetary boundaries (biosphere integrity, land-system change, freshwater use, and nitrogen flows).
The project team employed and enhanced the state-of-the-art dynamic global vegetation model LPJmL to simulate second-generation biomass plantations and their impacts on terrestrial planetary boundaries as well as carbon sequestration in forests. Furthermore, the MONET framework was utilized to account for emissions along the BECCS/PyCCS supply chain and convert simulated biomass yields to net CDR.
Opportunities to expand land use for biomass plantations without further transgressions of terrestrial planetary boundaries are very limited. The maximum global CDR potential from plantation-based BECCS outside of agricultural areas is constrained to ~1.2 GtCO2-eq yr-1 . If conversion of forests is additionally precluded, the potential is further reduced to almost zero. This emphasizes that any additional conversion of natural vegetation is extremely difficult to reconcile with terrestrial PBs and other environmental targets.
Simulated scenarios of rededicating 200-400 million hectares of pasture land for reforestation predominantly in tropical and temperate zones (corresponding to 7-16% of global pastures) indicate the potential for achieving 2.0-3.7 GtCO2-eq removals annually, while at the same time reducing land-system change pressures and related impacts on planetary boundaries. These results align well with projections for CDR from agriculture, forestry, and land use in “Paris-compatible” scenarios outlined in the recent IPCC reports.
The assessment of Pyrogenic Carbon Capture and Storage (PyCCS) focused on land- and calorie-neutral biochar provision, utilizing biochar to increase yields and reduce the demand for cropland, thus allowing for the rededication of agricultural areas to biochar feedstock production. This approach provides CDR without additional pressures on planetary boundaries or decreases in calorie production. A conservative estimate assuming low crop yields in the model with nitrogen limitations indicates a relatively low CDR potential of PyCSS ranging from 0 to 0.2 GtCO2-eq per year. However, when optimal nitrogen supply is considered, the potentials increase to0.17 – 0.45 GtCO2-eqper year, therefore further assessment and validation is needed.
As the results underpin that conversion of (semi-)natural land for CDR would further undermine terrestrial planetary boundaries, a comprehensive transformation of the food system, including dietary changes, would be needed to reduce pasture area thereby freeing up additional land for reforestation or for crop cultivation for BECCS.
Although the Planetary Boundaries-compatible potentials estimated here are at the lower end of estimated CDR rates assumed in scenarios compatible with the Paris agreement, they are in line with mitigation scenarios putting a strong emphasis on rapid decarbonisation, reduced energy demand and/or achievement of sustainable development goals.
This underpins that climate change mitigation does not have to come at the cost of other crucial Earth system components, but that rapid socioeconomic transformations are needed to prevent further planetary boundary transgressions.
Full report available here