Availability of land
As noted by the IPCC and others, the availability of land for bioenergy is a limiting factor in the deployment of BECCS. The models reviewed in the IPCC’s Fifth Assessment Report assumed the removal of 15–18 GtCO2/year, with energy delivery of 200–400 EJ/year.55 The latter figure included 80–100 EJ/year from the by-products of agriculture and forest industries, but the majority came from dedicated energy crops, which require considerable land for their production; a supply of 100 EJ/year could require up to 500 million ha of land (assuming an average annual biomass yield of 10 tonnes of dry biomass per hectare).56 Assuming that agricultural and forestry by-products require no additional land and are residues from existing land use, producing 300 EJ/year from energy crops would require 1.5 billion ha – an area roughly equal to the total global land area currently planted with agricultural crops.57 Scenarios like this also tend to assume radical changes in consumer behaviour, including a major shift away from eating meat (which theoretically would release much of the land currently used for pasture, or about 3.4 billion ha), together with rapid increases in food yields – in some cases higher than historical rates – sufficient to meet global food demand.
Although the assessment of the potential contribution of BECCS was more cautious in the IPCC’s SR1.5 relative to earlier assessments, the anticipated demand for land remained substantial. One study cited estimated that 25–46 per cent of the world’s arable and permanent crop area would be needed by 2100 to deliver 12 GtCO2/year from BECCS.58 SR1.5 presented three pathways that incorporated BECCS (see Figure 1). Overall, these required land areas of 93 million ha (pathway P2), 283 million ha (P3) and 724 million ha (P4) respectively by 2050. The IPCC report observed:
In general, the literature shows low agreement on the availability of land … Productivity, food production and competition with other ecosystem services and land use by local communities are important factors for designing regulation. These potentials and trade-offs are not homogenously distributed across regions.59
As discussed above, any calculations of the impacts of BECCS must take land-use changes into account, whether these are direct (e.g. conversion of grassland or forest to energy crops) or indirect (e.g. conversion of agricultural areas to energy crops, and subsequent conversion of grassland or forest to agriculture). These impacts can be significant: for example, for switchgrass grown on marginal land with no net emissions from land-use change, the BECCS carbon efficiency is 62 per cent (i.e. 62 per cent of carbon sequestered by biomass is permanently geologically stored), but this falls to 46 per cent when grassland is converted.60 The geographical location of the land used is also important: in general, the governance and enforcement of land-use planning in poor countries tends to be worse than in more prosperous ones (see Box 2), increasing the likelihood of conflicts over competing demands for land use.
In general, the governance and enforcement of land-use planning in poor countries tends to be worse than in more prosperous ones, increasing the likelihood of conflicts over competing demands for land use.
Where feedstock production sites are far from carbon dioxide storage facilities, this increases the requirement for transport either of the feedstock or of the carbon dioxide, with accompanying increases in energy consumption and greenhouse gas emissions. It is estimated that collecting and transporting bioenergy, its feedstocks and/or carbon dioxide on the scale envisioned could entail energy use equivalent to up to half of current total global primary energy consumption.61 The logistics involved may also require construction of a pipeline network (between capture and storage sites) similar in size to the current global natural gas network.62
Box 2: Where on Earth could BECCS go?
Given the scale of potential BECCS deployment and the land required for feedstocks (380–700 million ha by 2100), a key question is where these feedstocks could be sited. Beringer et al.63 consider this question in terms of the availability of land for bioenergy plantations (both with and without CCS, and excluding any consideration of CCS requirements such as geological storage sites). Excluding land that is currently agricultural, severely degraded, in conservation areas, wetlands, or forested where carbon losses from land-use change would not be compensated for within 10 years, the authors consider four scenarios with and without food cropland expansion, and with higher and lower levels of nature conservation.
They find that, on average, South America (26 per cent), sub-Saharan Africa (17 per cent), Europe (14 per cent), North America (11 per cent) and China (7 per cent) collectively provide three-quarters of potential 2050 global biomass yields. Approximately a quarter of the potential comes from woody plantations (coppiced every eight years), including temperate deciduous trees (e.g. poplars and willows) and tropical evergreens (e.g. eucalyptus); the remainder comes from fast-growing grasses (e.g. miscanthus and switchgrass).
These estimates imply 142–454 million ha of new biomass plantations replacing natural vegetation, with about 40 per cent of such plantations replacing natural grasslands and shrublands, 10 per cent replacing semi-natural vegetation proximal to existing agricultural areas, and about 30 per cent being introduced on currently forested areas. In aggregate this would expand the world’s existing cropland area by 10–30 per cent. Despite the sustainability constraints assumed in the model, the ecological, economic and social consequences of converting much of this land to energy crops would still present significant risks.64 Further, given that much of the potential is in poorer countries with chequered histories of land-use planning, it is questionable whether regulatory constraints would be observed in reality. This would potentially jeopardize carbon- and biodiversity-rich natural forests, especially in tropical regions. Alternative, high-energy-density marine sources of biomass such as algae could potentially alleviate some of these spatial and capacity constraints.
55 US National Research Council (2015), Climate Intervention: Carbon Dioxide Removal and Reliable Sequestration, Washington, DC: National Academies Press, p. 64, doi:10.17226/18805.
56 Azar, C., Lindgren, K., Obersteiner, M., Riahi, K., van Vuuren, D. P., den Elzen, K. M. G. J., Möllersten, K. and Larson, E. D. (2010), ‘The feasibility of low CO2 concentration targets and the role of bio-energy with carbon capture and storage (BECCS)’, Climatic Change, 100(1), pp. 195–202, doi:10.1007/s10584-010-9832-7.
57 Food and Agriculture Organization of the United Nations (FAO) (2016), State of the World’s Forests 2016: Forests and agriculture: land-use challenges and opportunities, Rome: FAO, http://www.fao.org/3/a-i5588e.pdf.
58 Smith, P., House, J. I., Bustamante, M., Sobocká, J., Harper, R., Pan, G., West, P. C., Clark, J. M., Adhya, T., Rumpel, C., Paustian, K., Kuikman, P., Cotrufo, M. F., Elliott. J. A., McDowell, R., Griffiths, R. I., Asakawa, S., Bondeau, A., Jain. A. K., Meersmans, J. and Pugh, T. A. M. (2016), ‘Global change pressures on soils from land use and management’, Global Change Biology, 22(3), pp. 1008–1028, doi:10.1111/gcb.13068.
59 IPCC (2018), Global Warming of 1.5°C, p. 343.
60 Fajardy, M. and Mac Dowell, N. (2017), ‘Can BECCS deliver sustainable and resource efficient negative emissions?’, Energy and Environmental Science, 10, pp. 1389–1426. See also correction in Ibid., 10(10), p. 2267.
61 Anderson, K. and Peters, G. (2016), ‘The trouble with negative emissions’, Science, 354(6309), pp. 182–83, doi: 10.1126/science.aah4567.
62 Fuss et al. (2016) ‘Research priorities for negative emissions’.
63 Beringer, T., Lucht, W. and Schaphoff, S. (2011), ‘Bioenergy production potential of global biomass plantations under environmental and agricultural constraints’, Global Change Biology Bioenergy, 3, pp. 299–312, doi: 10.1111/j.1757-1707.2010.01088.x.
64 Ibid.