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

=== 4.5.1 Potential scale of bioenergy and land-based CDR ===

<div id="section-4-5-1-potential-scale-of-bioenergy-and-land-based-cdr-block-1"></div>

In addition to the traditional land-use drivers (e.g., population growth, agricultural expansion, forest management), a new driver will interact to increase competition for land throughout this century: the potential large-scale implementation of land-based technologies for CO <sub>2</sub> removal (CDR). Land-based CDR includes afforestation and reforestation, bioenergy with carbon capture and storage (BECCS), soil carbon management, biochar and enhanced weathering (Smith et al. 2015 <sup>[[#fn:r678|678]]</sup> ; Smith 2016 <sup>[[#fn:r679|679]]</sup> ).

Most scenarios, including two of the four pathways in the IPCC Special Report on 1.5°C (IPCC 2018a <sup>[[#fn:r680|680]]</sup> ), compatible with stabilisation at 2°C involve substantial areas devoted to land-based CDR, specifically afforestation/reforestation and BECCS (Schleussner et al. 2016 <sup>[[#fn:r681|681]]</sup> ; Smith et al. 2016b <sup>[[#fn:r682|682]]</sup> ; Mander et al. 2017 <sup>[[#fn:r683|683]]</sup> ). Even larger land areas are required in most scenarios aimed at keeping average global temperature increases to below 1.5°C, and scenarios that avoid BECCS also require large areas of energy crops in many cases (IPCC 2018b <sup>[[#fn:r684|684]]</sup> ), although some options with strict demand-side management avoid this need (Grubler et al. 2018 <sup>[[#fn:r685|685]]</sup> ). Consequently, the addition of carbon capture and storage (CCS) systems to bioenergy facilities enhances mitigation benefits because it increases the carbon retention time and reduces emissions relative to bioenergy facilities without CCS. The IPCC SR15 states that, ‘When considering pathways limiting warming to 1.5°C with no or limited overshoot, the full set of scenarios shows a conversion of 0.5–11 Mkm <sup>2</sup> of pasture into 0–6 Mkm <sup>2</sup> for energy crops, a 2 Mkm <sup>2</sup>  reduction to 9.5 Mkm <sup>2</sup>  increase [in] forest, and a 4 Mkm <sup>2</sup>  decrease to a 2.5 Mkm <sup>2</sup> increase in non-pasture agricultural land for food and feed crops by 2050 relative to 2010.’ (Rogelj et al. 2018, p. 145). For comparison, the global cropland area in 2010 was 15.9 Mkm <sup>2</sup> (Table 1.1), and Woods et al. (2015) <sup>[[#fn:r686|686]]</sup> estimate that the area of abandoned and degraded land potentially available for energy crops (or afforestation/reforestation) exceeds 5 Mkm <sup>2</sup> . However, the area of available land has long been debated, as much marginal land is subject to customary land tenure and used informally, often by impoverished communities (Baka 2013 <sup>[[#fn:r687|687]]</sup> , 2014 <sup>[[#fn:r688|688]]</sup> ; Haberl et al. 2013 <sup>[[#fn:r689|689]]</sup> ; Young 1999 <sup>[[#fn:r690|690]]</sup> ). Thus, as noted in SR15, ‘The implementation of land-based mitigation options would require overcoming socio-economic, institutional, technological, financing and environmental barriers that differ across regions.’ (IPCC, 2018a <sup>[[#fn:r691|691]]</sup> , p. 18).

The wide range of estimates reflects the large differences among the pathways, availability of land in various productivity classes, types of negative emission technology implemented, uncertainties in computer models, and social and economic barriers to implementation (Fuss et al. 2018 <sup>[[#fn:r692|692]]</sup> ; Nemet et al. 2018 <sup>[[#fn:r693|693]]</sup> ; Minx et al. 2018 <sup>[[#fn:r694|694]]</sup> ).

<span id="risks-of-land-degradation-from-expansion-of-bioenergy-and-land-based-cdr"></span>