Trade‐offs for food production, nature conservation and climate limit the terrestrial carbon dioxide removal potential

Abstract

Large-scale biomass plantations (BPs) are a common factor in climate mitigation scenarios as they promise double benefits: extracting carbon from the atmosphere and providing a renewable energy source. However, their terrestrial carbon dioxide removal (tCDR) potentials depend on important factors such as land availability, efficiency of capturing biomass-derived carbon and the timing of operation. Land availability is restricted by the demands of future food production depending on yield increases and population growth, by requirements for nature conservation and, with respect to climate mitigation, avoiding unfavourable albedo changes. We integrate these factors in one spatially explicit biogeochemical simulation framework to explore the tCDR opportunity space on land available after these constraints are taken into account, starting either in 2020 or 2050, and lasting until 2100. We find that assumed future needs for nature protection and food production strongly limit tCDR potentials. BPs on abandoned crop and pasture areas (~1,300 Mha in scenarios of either 8.0 billion people and yield gap reductions of 25% until 2020 or 9.5 billion people and yield gap reductions of 50% until 2050) could, theoretically, sequester ~100 GtC in land carbon stocks and biomass harvest by 2100. However, this potential would be ~80% lower if only cropland was available or ~50% lower if albedo decreases were considered as a factor restricting land availability. Converting instead natural forest, shrubland or grassland into BPs could result in much larger tCDR potentials ̶ but at high environmental costs (e.g. biodiversity loss). The most promising avenue for effective tCDR seems to be improvement of efficient carbon utilization pathways, changes in dietary trends or the restoration of marginal lands for the implementation of tCDR.

The Effects of Carbon Dioxide Removal on the Carbon Cycle

“…BECCS (Table 1) is the CDR method most often assumed in climate change mitigation scenarios [26] and there are many recent carbon sequestration potential estimates [1••, 27–30, 60, 65]. However, as far as we are aware, global carbon cycle responses to BECCS have only been fully quantified by Muri [31], although there have been offline modeling efforts [60].…”

“…However, as far as we are aware, global carbon cycle responses to BECCS have only been fully quantified by Muri [31], although there have been offline modeling efforts [60]. Research instead usually focuses either on biomass plantations (simulated with offline terrestrial models [29, 30, 32–34, 60]) or the ESM response to atmospheric CO 2 removal, where BECCS is treated as DAC, e.g., Jones et al [15••]. In these DAC-like studies, biomass plantations may be prescribed, but the harvest products are returned to the terrestrial carbon pool as litter or crop residues, rather than being removed from the simulated carbon cycle.…”

“…However, carbon stored in soils is vulnerable to future changes in land use and does not represent the same permanence as geological CO 2 storage. All terrestrial biomass plantation studies have shown that there would be biogeophysical (e.g., albedo, hydrological) and biogeochemical (e.g., nutrients) changes that impacts the carbon cycle [1••, 28–30, 33, 34, 65]. From a global carbon cycle perspective, the net result of terrestrial-based BECCS is to move carbon from the atmosphere to the terrestrial biosphere and then to permanent geological storage (Fig.…”

Global consequences of afforestation and bioenergy cultivation on ecosystem service indicators

“…The total land demand and spatial patterns of these mitigation strategies are highly uncertain due to strong dependencies on underlying assumptions about future environmental and socio-economic changes (Boysen et al, 2017;Slade et al, 2014). BECCS and ADAFF will likely increase pressure on food-producing agricultural areas and, in the case of BECCS, natural ecosystems.…”

Biomass production in plantations: Land constraints increase dependency on irrigation water

“…We also include detailed and spatially explicit datasets of potential land access restrictions to assess whether land or water is the predominant limiting factor regionally and globally. Regional climatic and hydrological conditions, and land/water use constraints, have been considered in earlier studies (Beringer et al, ; Berndes, ; Bonsch et al, ; Boysen, Lucht, & Gerten, ; Boysen, Lucht, Gerten, & Heck, ; Dornburg et al, ; Fraiture, Giordano, & Liao, ; Gheewala, Berndes, & Jewitt, ; Jackson et al, ; King et al, ; Smith et al, ) but, to the best of our knowledge, the interplay between land and water availability has not been addressed at the level of detail captured in this study. Water availability and use is determined at river basin scale to ensure that the interaction between upstream and downstream water availability and use is considered.…”