Bioenergy with carbon capture and storage (BECCS) cannot be deployed at the scales assumed in Paris-compliant emissions pathways. This would consume land on a scale comparable to current cropland, entailing massive land-use change in tropical regions with weak governance, high biodiversity and high terrestrial carbon stock. Competition for agricultural land would threaten food production.
This much BECCS is not necessary, but some may be. Greater use of nature-based solutions such as land restoration and soil carbon sequestration can reduce reliance on BECCS and deliver ecosystem co-benefits. Direct air capture (DAC) could achieve negative emissions with a tiny land footprint if economic and technologic challenges can be overcome. More aggressive mitigation action and lifestyle changes – including reducing food waste and meat consumption – could reduce the scale of negative emissions needed and reduce pressure on land. But even with ambitious action on all fronts, modellers cannot envisage limiting temperature rises to 1.5°C without BECCS.
Action on negative emissions must start now. Deployment of negative emissions technologies (NETs)1, whether BECCS, nature-based solutions or DAC, must begin within the next decade to avoid ‘overshooting’ the available 2°C carbon budget and a material risk of passing climate tipping points. Early deployment has the added advantage of reducing the scale of NETs needed by the end of the century.
A precautionary approach to NETs is needed. This could begin immediately with ambitious action on nature-based solutions. These are well understood, and ready, and can be designed to deliver social and environmental co-benefits. This could be followed by a subsequent phase of BECCS deployment if, and when, (re)forested areas developed during the first phase are able to supply sustainable flows of biomass feedstock. This also supposes adequate safeguards and governance arrangements have been developed.
An urgent policy debate is required, but policymakers are behind the curve. Important decisions about when, where and how to achieve negative emissions are due now. Delaying these decisions increases the risk of missing climate goals and increases the scale of negative emissions needed in the future. But the issue is not on the current policymaking agenda. There is little understanding of the scale of negative emissions needed, of the temporal urgency of the problem and of the relative pros and cons of different NETs. Unless carefully managed, discussions could become highly polarized between developed and developing countries and between civil society and industry.
Nature-Based Negative Emissions Options
Engineered Negative Emissions Technologies
There is a non-trivial risk of exceeding climate tipping points without more rapid deployment and scaling of NETs. The vast majority of 2°C-compatible integrated assessment model (IAMs) emissions pathways assume very significant deployment of NETs by the end of the century. 90 per cent of the 2°C scenarios assessed in the IPCC Fifth Assessment Report assume a role for BECCS, and half of all 2°C scenarios rely on BECCS - as well as afforestation and reforestation - to remove at least one-third of all cumulative carbon emissions between now and 2100. Delaying deployment of NETs until the second half of the century increases the risk of ‘overshooting’ and passing irreversible climate tipping points. Conversely, earlier deployment – starting in the next decade – alongside aggressive mitigation action can avoid overshooting the available carbon budget. This also would reduce the scale of NETs required later in the century, potentially reducing competition for land.
There are choices available about how, when and where NETs are deployed, and regarding which approaches and technologies are utilized. The prevalence of BECCS within IAMs reflects the fact that models optimize mitigation costs and contain embedded assumptions about the relative costs of different NETS that favour BECCS. However, it may be preferable to deploy NETs in ways that are not cost-optimal because of other social and environmental considerations such as food security and biodiversity.
Four archetypes of emission pathways
There is no silver bullet.
Feedstock expansion for BECCS is expected to occur primarily in tropical countries with high biodiversity value, weak forest governance and a chequered history of land-use planning, posing the risk of damaging land-use change and conversion of natural forests. Producing the volumes of feedstock required for a ‘BECCS only’ solution would require land areas on the scale of current cropland and would almost certainly result in an ecological catastrophe, contributing to a vicious circle of agricultural expansion and intensification that erodes ecosystem services and contributes to climate change. Although smart interventions at different scales can help optimize ecosystem services from land and reduce competition, it is doubtful that this can be achieved in many of the countries where feedstock production is likely to occur due to lower levels of development and governance.
Nature-based solutions – in particular afforestation and reforestation – would require comparable areas of land, while albedo effects limit the latitudes at which this strategy would be efficacious. Some research suggests that land-demanding natural solutions (i.e. those involving either a land-use change or an avoided land-use change) account for two-thirds of the 2030 cost-effective climate mitigation potential (~7.6 GtCO2e yr-1) from natural solutions and would require in the region of 3 million square kilometres, compared with the 3.8–7 million modelled for BECCS (~12 GtCO2e yr-1) by 2100. Changes in farming practices and soil management can also achieve significant reductions in emissions and increase sequestration potential, although achieving behaviour change among land stewards (i.e. farmers) is not straightforward. Many nature-based interventions are easily reversible and therefore vulnerable to social, political and economic changes in a country.
Climate mitigation potential of 20 natural pathways in 2030
Direct air capture (DAC) is significantly more attractive than BECCS from a land-use perspective but suffers from very high energy costs. This means it is squeezed out in favour of BECCS in cost-optimizing IAMs and therefore it has received relatively little attention to date. However, it is important to examine the assumptions within the models that lead to this outcome. For example, research is needed to examine how deploying DAC with renewable power sources may shift the economics due to declining marginal electricity costs and exploiting DAC’s potential to utilize surplus electricity generated on a diurnal basis. It is also important to understand how the technology costs may change with cumulative deployment volumes, and how DAC facilities might be co-located with cost-effective renewable energy generation and CO2 storage infrastructure.
Dietary shifts and food waste reductions are vital and could free significant amounts of land, but can they be achieved fast enough? Improved diets (reduced consumption of energy-rich food – sugars and saturated fats including livestock products – in line with health recommendations) and halved food waste and losses could reduce agricultural and land-use emissions, and by 2050 could conceivably spare an extensive area of land that could potentially be utilized for producing large volumes of BECCS feedstocks or for afforestation. Public-health costs associated with diet-related non-communicable diseases may spur government interventions to promote healthier and more sustainable diets.
Decoupling biomass production and carbon sequestration from land can help achieve the Paris Agreement without compromising the Sustainable Development Goals. Strategies worthy of greater exploration include:
Algae for biofuel (particularly for aviation) and animal feed;
Artificial photosynthesis (e.g. hybrid water splitting–biosynthetic system);
Substituting animal-derived protein with meat analogues and cultured meats;
Ocean liming to neutralize water acidification and improve atmospheric CO2 absorption.
For many of these options, questions persist regarding the risks and opportunities they present and the scale and speed at which they can be deployed. Answering these questions and pursing promising approaches is a priority.
Questions and challenges.
BECCS appears necessary if the most ambitious climate goals are to be met, but raises its own set of particular questions and challenges. It appears likely that some degree of BECCS deployment is necessary to meet climate objectives, although there are doubts that significant deployment can be achieved without negative implications for other land uses, ecosystem services and biodiversity. Nonetheless, integrated assessment modellers conclude that any chance of limiting temperature increases to 1.5°C will most likely require some BECCS. There is sufficient geological storage, but how do likely locations of plant, storage and feedstock production compare and what does this mean for trade and infrastructure investment? The need to grow new plantations of energy crops or fast-growing trees, to establish sustainable supply chains of feedstock, and to build the necessary infrastructure, indicates that scaling BECCS on short timescales will be challenging.
BECCS may appear more or less attractive to policymakers. On the one hand it has no obvious co-benefits (unlike nature-based solutions) and obvious downside risks. On the other hand, it essentially combines two known technologies (biomass and CCS), possibly making it more tangible for policymakers and the technical and institutional problems more familiar. The climate does not differentiate between a tonne of CO2 captured from a coal power station, a cement plant or a biomass power station, so BECCS can be conceived as one option among others when considering where and how CCS is prioritized. There is therefore an argument for first using CCS to capture emissions from new and existing power and industrial installations before building new BECCS plants. However, rapid advances with solar and wind power as well as battery technologies mean that opportunities for CCS for coal and gas may be receding. Similarly, the long-term prospects for biomass electricity are questionable in the context of declining wind and solar prices, declining battery prices and improved grid flexibility that will erode the value of biomass as a dispatchable power source. In sum, making choices about where to deploy CCS is not straightforward.
IAMs place increasing value on the CCS component of BECCS rather than the energy component (the BE). This is because assumptions about rising carbon prices mean that carbon sequestration becomes increasingly valuable over the course of the century. This raises the possibility of other cost-competitive means of achieving the CCS effect such as biological storage (i.e. burying biomass rather than burning it) and alternative uses for biomass that keep carbon out of the atmosphere such as wood for construction. Given ongoing power-sector transformation, exploring other ways of sequestering carbon from biomass, that avoid the need to build potentially expensive or possibly unnecessary biomass plants, could be worthwhile.
It is now accepted that bioenergy is not carbon neutral, and that harvesting biomass for combustion leads to atmospheric carbon fluxes that may persist for many decades depending on the nature of the feedstock used, the fossil fuel displaced and the rates of forest regrowth. This, coupled with concerns that biomass feedstocks are not limited to those with the shortest payback periods - such as forest residues and sawmill wastes - has made bioenergy a controversial energy source and raises questions about whether BECCS can be scaled without reducing the carbon stock and sequestration potential of forests.
What would a ‘do no harm’ approach for BECCS look like?
The nature-based solutions with the highest potential (e.g. halting deforestation and losses of carbon-rich ecosystems and restoring degraded lands) are arguably solutions that we cannot do without even if other NETs are also deployed. And, unlike BECCS and DAC, they can be undertaken immediately. It therefore makes sense to roll out nature-based solutions at the largest scale and earliest date possible; they are well understood and can be implemented to achieve ecosystem service co-benefits. In a few decades, new forested areas could then, if necessary, provide a sustainable supply of feedstock for BECCS. But this transition will require piloting and planning well in advance to avoid adverse outcomes therefore raising the question of what a set of ‘do no harm’ principles for piloting and planning BECCS might look like. Suggestions include:
Only sourcing feedstocks from wastes and residues;
Growing feedstocks on restored land;
Developing the potential of algae as a feedstock;
Utilizing bioenergy in high-efficiency combined heat and power plants with carbon capture and storage.
Opinions regarding large-scale bioenergy deployments are highly polarized and strong oppositions are raised by many sections of civil society. The scale of land conversion anticipated runs the risk of contentious land acquisitions and there are likely significant but as yet are unquantified trade-offs between BECCS and nature-based solutions that require further exploration. These tensions are likely to come to the fore with the publication of the IPCC special reports on global warming of 1.5°C and climate change and land in 2018 and 2019 respectively. There is a danger that such polarizations could result in policy paralysis therefore efforts should be made to foster a constructive dialogue between civil society, policymakers, scientists and the bioenergy sector in an attempt to establish consensus on a set of ‘do no harm principles’, on which further policies and strategies could be built.
Are policymakers sleepwalking towards BECCS?
Among policymakers there is low awareness and little understanding of the assumptions in, and the limitations of, IAMs with respect to NETs. For example, the scale of BECCS implied by the end of the century and the reasons that models favour BECCS over other NET alternatives. BECCS is essentially a model fix to deliver Paris Agreement-compliant emissions pathways and other options are available, but as the predominant NET in IAM pathways, there is a risk that it is seen as the preferred option without its implications being fully comprehended.
Given the urgency of scaling negative emissions, there is little serious thinking happening at the policymaking level about how to do so. Policy cycles do not move fast enough to incorporate negative emissions on the timescales needed. Opportunities to engender a policy debate on NETs include the UNFCCC 2018 facilitative dialogue leading to resubmissions of nationally determined contributions in 2020, the development of long-term low-emission development strategies, the IPCC special reports on 1.5°C and climate change and land, and the sixth assessment report, the preparation of the Convention on Biological Diversity’s post-2020 biodiversity framework replacing the Aichi biodiversity targets, and the development of the EU long-term decarbonization plan in line with a net-zero emissions target by 2050. But NETs do not always fit seamlessly into current frameworks. For example, do countries need separate negative emissions targets in addition to conventional mitigation targets and what might be considered fair shares in this regard?
BECCS' combination of existing but controversial technologies means it may or may not become a preferred option. Concerns about the sustainability of bioenergy may cause policymakers to question BECCS and lean towards nature-based solutions. These may take the form of afforestation projects in home countries in the first instance that can be financed through carbon market mechanisms. Nonetheless, the fact that BECCS is essentially a combination of two familiar technologies with pre-existing policy arrangements, and can be ‘plugged into’ existing power and biomass markets, provides BECCS with something of an advantage with policymakers compared to other NETs. It also provides economic opportunities for sectoral interests that will lobby to this end which may include the bioenergy, agriculture and forestry industries, but could also include transport and industry, which might benefit from less pressure to decarbonize in the presence of BECCS. Policymakers need to be better informed of the risks and opportunities of BECCS relative to other NETs and a serious discussion about how negative emissions can be safely realized needs to begin now.
This workshop was hosted by the Prince of Wales International Sustainability Unit, Chatham House's Energy, Environment and Resources Department and the Hoffmann Centre for Sustainable Resource Economy.