Conclusions
Formidable challenges are associated with the use of carbon dioxide removal (CDR) approaches, including BECCS, to limit global warming to 1.5–2°C. On the one hand, as clearly evidenced by the latest IPCC assessments, it is becoming increasingly difficult to foresee the Paris Agreement targets being achieved without rapid scale-up in deployment of CDR solutions; emission abatement efforts are not progressing anywhere near rapidly enough to engender confidence that these alone will avoid global overshooting of emissions targets. On the other hand, as the IPCC’s SR1.5 report cautioned, ‘CDR deployed at scale is unproven, and reliance on such technology is a major risk in the ability to limit warming to 1.5°C’.68
BECCS is the main option assumed by integrated assessment models (IAMs), but, as we have argued, its prevalence in the models is not based on a comprehensive analysis of its feasibility and impacts, and often rests on the erroneous assumption that biomass for energy is inherently carbon-neutral. To the contrary, there are many reasons to conclude that BECCS cannot be deployed at the scales assumed in the majority of Paris-compliant emissions pathways. It would consume land on a scale comparable to half the current cropland, entailing massive land-use change, particularly in tropical regions with weak governance, high biodiversity and high terrestrial carbon stock. Competition for agricultural land would threaten food production and endanger food security.69 And, depending on the feedstock, BECCS might not even deliver significant volumes of negative emissions over a timescale compatible with the Paris targets – or any negative emissions at all.
This is not to argue that BECCS cannot play a role, but its scope will depend primarily on the type of feedstock used. Agricultural and forestry residues, and industrial and municipal wastes, generally have the lowest impact on land-use change and – depending on the residue type and collection method – soil and forest carbon stocks. But they are also limited in availability and harder to collect, and can have other uses, including the manufacture of wood products and the maintenance of soil carbon and nutrient levels. Afforestation and reforestation initiatives that expand forest cover would increase the supply of forest residues, though their subsequent availability as a feedstock depends partly on whether wood-based industries also expand; in many countries there is likely potential for more extensive use of harvested wood products in climate-mitigating roles, for example in construction.
The use of additional planted forests for feedstocks carries the largest risks to achieving meaningfully negative carbon balances, and is likely to have the most deleterious consequences from extensive use of land, water and other inputs such as fertilizers.
The use of additional planted forests for feedstocks carries the largest risks to achieving meaningfully negative carbon balances, and is likely to have the most deleterious consequences from extensive use of land, water and other inputs such as fertilizers. Dedicated energy crops have greater potential, particularly if sustainably integrated with the existing ecology, where they could bring additional benefits, particularly if appropriately integrated with conventional crops or grown on land not in demand for alternative uses.
The key is to ensure that all such options – and CDR technologies more broadly – are evaluated on a comparable basis. This means, above all, that the assumption that biomass feedstock is inherently carbon-neutral be abandoned. A full lifecycle analysis of carbon balances over time, including carbon stocks in standing forests or crops and the soil, must be part of the analysis of any given BECCS pathway and all other CDR options. Only then can we be sure that CDR solutions are actually removing carbon dioxide over policy-relevant time periods.
Other measures required to guarantee effective and sustainable removals include comprehensive analysis of likely demand for land, water and other inputs, and the consequences of their use; and rigorous assessment of the competing demands and requirements in terms of land and biodiversity/habitat preservation. Such analysis must be fully cognizant of, and make provisions for, weaknesses in land-use governance and law enforcement. Idealized assumptions about effective land management should be avoided. By and large, current IAMs do not contain sophisticated analysis of these issues, with the result that they may lead policymakers to the wrong conclusions.70
This suggests three broad priorities for future climate strategies:
First, accelerate conventional abatement action as rapidly as possible (including, crucially, in the land-use sector, and by changing consumption patterns) to minimize the volume of additional negative emissions required.
Second, rather than assuming that BECCS is the pre-eminent carbon removal solution due to its de facto use in IAMs, consider it alongside all other negative emissions solutions such as nature-based solutions (afforestation, forest ecosystem restoration, etc.), DACCS and enhanced weathering. These evaluations need to be carried out on the basis of full lifecycle emission balances, as well as other local-to-global ecosystem and sustainability co-benefits and trade-offs that will vary by deployment (see Table 1 for an indicative global overview). In the case of BECCS, important factors include the types and locations of the feedstock, land-use changes, harvesting, processing, combustion, transportation and storage impacts – and the extent to which BECCS and nature-based solutions compete with each other for land. Where they do so, there is a strong likelihood that nature-based solutions will, in many cases, provide more effective removals in the near term (i.e. one to two decades). None of these negative emissions options will be a silver bullet, and a portfolio of locally appropriate but globally significant solutions will need to be developed.
Third, take urgent action to rapidly scale up the development and deployment of sustainable approaches to negative emissions. These need to start achieving meaningful levels of CDR in the next decade or so to prevent the overshooting of emissions targets and the potentially calamitous earth-system positive feedbacks this could catalyse, as well as to reduce the scale of negative emissions solutions needed by the end of the century. For land- and forest-based solutions, almost immediate implementation (planting or ensuring natural regeneration) is required, due to the time taken for these natural solutions to realize their full sequestration potential. For technological solutions, a step-change in research and development is required, along with the iteration and deployment of promising options. Both approaches require significant investment and financial mechanisms, and the concomitant development of broadly supportive governance arrangements and safeguards. These are required to ensure that the most appropriate options materialize, both by fostering an enabling environment through the right incentives and by ensuring that rapid progress still adheres to the precautionary principle.71
There is an urgent need for policymakers to be cognizant of, and engaged in, these kinds of debates, so that they can draw informed conclusions and chart a path forwards. Delaying decisions will increase the risk of missing climate goals and will also increase the scale of negative emissions needed in the future. The danger at the moment is that policymakers are ‘sleepwalking towards BECCS’ simply because most models incorporate it – or, almost as bad, it may be that policymakers are simply ignoring the need for any meaningful action on CDR as a whole.72
Table 1: Indicative global CDR abatement costs, deployment potentials and key side effects
— • Desirable change; × Undesirable change; – No significant change; ? No estimate available.
Notes: DACCS is theoretically only constrained by geological storage capacity; estimates presented consider upscaling and cost challenges.
BECCS potential estimates are based on bioenergy estimates in the literature (EJ/yr), converted to GtCO2
Potentials cannot be added up, as CDR options would compete for resources (e.g. land).
* Assessed ranges by Fuss et al. (2018), Negative emissions—Part 2: Costs, potentials and side effects.
** Based on 2100 estimate for mean [max] potentials by Smith et al. (2016), Biophysical and economic limits to negative CO2 emissions.
Source: Compiled from IPCC (2018), Global Warming of 1.5°C; Morrow et al. (2018), Why Talk about Carbon Removal?; Smith et al. (2016), ‘Biophysical and economic limits to negative CO2 emissions’.
Notes: DACCS is theoretically only constrained by geological storage capacity; estimates presented consider upscaling and cost challenges.
BECCS potential estimates are based on bioenergy estimates in the literature (EJ/yr), converted to GtCO2
Potentials cannot be added up, as CDR options would compete for resources (e.g. land).
* Assessed ranges by Fuss et al. (2018), Negative emissions—Part 2: Costs, potentials and side effects.
** Based on 2100 estimate for mean [max] potentials by Smith et al. (2016), Biophysical and economic limits to negative CO2 emissions.
Source: Compiled from IPCC (2018), Global Warming of 1.5°C; Morrow et al. (2018), Why Talk about Carbon Removal?; Smith et al. (2016), ‘Biophysical and economic limits to negative CO2 emissions’.
Table 1: Indicative global CDR abatement costs, deployment potentials and key side effects
Notes: DACCS is theoretically only constrained by geological storage capacity; estimates presented consider upscaling and cost challenges.
BECCS potential estimates are based on bioenergy estimates in the literature (EJ/yr), converted to GtCO2
Potentials cannot be added up, as CDR options would compete for resources (e.g. land).
* Assessed ranges by Fuss et al. (2018), Negative emissions—Part 2: Costs, potentials and side effects.
** Based on 2100 estimate for mean [max] potentials by Smith et al. (2016), Biophysical and economic limits to negative CO2 emissions.
Source: Compiled from IPCC (2018), Global Warming of 1.5°C; Morrow et al. (2018), Why Talk about Carbon Removal?; Smith et al. (2016), ‘Biophysical and economic limits to negative CO2 emissions’.
68 IPCC (2018), Global Warming of 1.5°C, p. 34.
69 Bailey, R. and King, R. (2018), ‘Betting on BECCS? Exploring Land-Based Negative Emissions Technologies’, Hoffmann Centre for Sustainable Resource Economy, 17 May 2018, https://hoffmanncentre.chathamhouse.org/article/betting-on-beccs-exploring-land-based-negative-emissions-technologies/.
70 IPCC (2018), Global Warming of 1.5°C, Chapter 2.
71 See Brack, D. and King, R. (2020, forthcoming), ‘Managing land-based CDR: BECCS, forests and carbon sequestration’, Global Policy.
72 Bailey and King (2018), ‘Betting on BECCS? Exploring Land-Based Negative Emissions Technologies’.