Editing IPCC:AR6/SRCCL/Chapter-4 (section)

=== 4.5.2 Risks of land degradation from expansion of bioenergy and land-based CDR ===

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The large-scale implementation of high-intensity dedicated energy crops, and harvest of crop and forest residues for bioenergy, could contribute to increases in the area of degraded lands: intensive land management can result in nutrient depletion, over-fertilisation and soil acidification, salinisation (from irrigation without adequate drainage), wet ecosystems drying (from increased evapotranspiration), as well as novel erosion and compaction processes (from high-impact biomass harvesting disturbances) and other land degradation processes described in Section 4.2.1.

Global integrated assessment models used in the analysis of mitigation pathways vary in their approaches to modelling CDR (Bauer et al. 2018 <sup>[[#fn:r695|695]]</sup> ) and the outputs have large uncertainties due to their limited capability to consider site-specific details (Krause et al. 2018 <sup>[[#fn:r696|696]]</sup> ). Spatial resolutions vary from 11 world regions to 0.25 degrees gridcells (Bauer et al. 2018 <sup>[[#fn:r697|697]]</sup> ). While model projections identify potential areas for CDR implementation (Heck et al. 2018 <sup>[[#fn:r698|698]]</sup> ), the interaction with climate-change-induced biome shifts, available land and its vulnerability to degradation are unknown. The crop/forest types and management practices that will be implemented are also unknown, and will be influenced by local incentives and regulations. While it is therefore currently not possible to project the area at risk of degradation from the implementation of land-based CDR, there is a clear risk that expansion of energy crops at the scale anticipated could put significant strain on land systems, biosphere integrity, freshwater supply and biogeochemical flows (Heck et al. 2018 <sup>[[#fn:r699|699]]</sup> ). Similarly, extraction of biomass for energy from existing forests, particularly where stumps are utilised, can impact on soil health (de Jong et al. 2017 <sup>[[#fn:r700|700]]</sup> ). Reforestation and afforestation present a lower risk of land degradation and may in fact reverse degradation (Section 4.5.3) although potential adverse hydrological and biodiversity impacts will need to be managed (Caldwell et al. 2018 <sup>[[#fn:r701|701]]</sup> ; Brinkman et al. 2017 <sup>[[#fn:r702|702]]</sup> ). Soil carbon management can deliver negative emissions while reducing or reversing land degradation. Chapter 6 discusses the significance of context and management in determining environmental impacts of implementation of land-based options.

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