Decarbonization models and politicians are, due to their respective biases and assumptions, increasingly relying on engineered carbon removals, and this reliance is likely to grow.
At the heart of net zero is a reliance on negative emissions, both engineered and nature-based, to counterbalance what are deemed ‘residual emissions’ from sectors such as agriculture, shipping and aviation that are technically and economically very difficult to decarbonize. This counterbalancing of hard-to-abate fossil fuel and other greenhouse gas emissions is critical to efforts to close the global ‘emissions gap’.
Net zero policies must assess costs alongside environmental objectives. To achieve the required negative emissions, engineered removal technologies will need to be deployed on a mass scale. This scaling up cannot be achieved without substantial investments in infrastructure and equipment, along with durable revenues to cover ongoing operational expenses – including fuel inputs to the removal technologies.
Carbon removals are broadly classified into two groups: nature-based solutions including tree-planting; and engineered carbon removals, such as bioenergy with carbon capture and storage (BECCS), and direct air carbon capture and storage (DACCS), which rely on human-made technology. It is important to note that while carbon capture and storage (CCS) can be applied to fossil fuel generators, this results in emissions reductions, and not – as through BECCS and DACCS – carbon removals or negative emissions.
BECCS involves integrating carbon capture technologies with biomass energy production, which requires diverting vast amounts of heat from the burning of that biomass to run the CCS equipment. DACCS systems need large-scale infrastructure to take in ambient air and scrub the carbon dioxide (CO₂) from it, requiring large amounts of heat and electricity. Both BECCS and DACCS then require the permanent storage of their captured CO₂ in underground geological features, including old oil and gas wells.
For many years, academics and policymakers have viewed the need to tackle fossil fuel emissions and decarbonize their economies through the lens of the ‘energy trilemma’, which asserts that there are three pillars for decision-makers to consider: sustainability, security and affordability. With the rise of geopolitical tensions and conflict in oil- and gas-producing regions, and historically low investment in upstream oil and gas, a new era of energy security and affordability concerns risks trumping the climate imperative of energy sustainability. It is through this shift in focus, and with net zero costs increasingly under scrutiny, that this paper examines whether the high energy input – and hence high cost – of engineered removals technologies needs to be managed under a more collaborative and cooperative international approach, where the costs and risks are shared and minimized.
Previous Chatham House work has investigated how the issues of biomass feedstock carbon debt and payback periods, as well as supply chain emissions, could reduce the net negativity of BECCS, and how land use tensions can arise at scale. This paper acknowledges these issues (for a summary discussion, see Box 1), but broadly sets them aside, instead focusing on the direct costs of BECCS and DACCS.
The remainder of this chapter examines how countries have baked reliance on engineered removals into their climate action targets and policies, and why politicians are drawn to these technologies. Chapter 2 explores how present geopolitical shifts and conflicts, compounded by the impacts of declining investment in upstream oil and gas over the last decade, put energy costs in a highly volatile and potentially ongoing inflationary period. Chapter 3 investigates the future costs of BECCS and DACCS, arising from their large energy input requirements and the rising costs of wood pellets for BECCS. Chapter 4 makes the case that greater international collaboration around BECCS and DACCS could aid in delivering cost-optimal and risk-reduced deployment at scale of engineered removals, drawing on the example of international cooperation in the civil nuclear industry, and touches on how demand reduction could reduce reliance on BECCS and DACCS. The concluding chapter draws together the key themes and provides substantive recommendations for policymakers.
Why do the models used by the IPCC drive a reliance on engineered removals?
Integrated assessment models (IAMs) play a crucial role in shaping climate policy both globally and nationally. They serve as the foundation for the decarbonization pathways outlined by the IPCC, which governments rely on when setting their own climate targets and legislation. While the IPCC acknowledges that high reliance on engineered removals enables high consumption lifestyles, its cost-optimizing models and associated optimistic assumptions tend to select them.
IAMs are tools used by researchers to analyse and evaluate the complex interactions between human activities, the economy, energy systems, land use and the environment. IAMs provide a framework for assessing the potential impacts of various policy interventions, technological changes and socioeconomic developments on key sustainability goals, such as climate change mitigation, energy security, air quality and economic growth.
It should, however, be noted that many of the academics who run the IAMs often go to lengths to reinforce that the models are not forecasts, that they come with many caveats, and that their very varied outputs between the various IAMs are neither policy prescriptions nor a representative sample that can be statistically assessed as to the likely global decarbonization trajectory.
The decarbonization pathway outputs of IAMs informed the creation of the net zero goal of the 2015 Paris Agreement. IAMs are very clear that negative emissions should be additional to renewable deployment, not instead of, and should not be used to offset fossil fuel emissions. In essence, this means that reductions in emissions must be prioritized, with negative emissions only offsetting residual emission sectors. Often, however, the application of net zero targets within country-level targets, legislation and policies does not adequately define residual emission sectors, and there are growing calls to do this, as well as for broader reforms of net zero, including splitting out CO₂ reduction and removal targets. Such reforms of net zero could ensure a greater real-world adherence to the IAMs’ modelling outputs of negative emissions being additional to renewable energy generation, and not offsetting of fossil emissions.
The reliability of IAM outputs is contingent on the quality of the underlying assumptions. For example, in the case of BECCS, assumptions include factors such as biomass feedstock production and yields and resulting land use change, energy production from biomass feedstocks, CO₂ capture rates, and supply-chain emissions.
IAMs aim to identify the most cost-effective means of achieving a specific temperature limit. Because of this emphasis on cost-optimization, many IAM scenarios heavily rely on BECCS. In the 2018 IPCC special report Global Warming of 1.5°C (SR1.5), 81 of the 90 scenarios relied on negative emission technologies (NETs). Because BECCS is expected to both produce energy and remove atmospheric CO₂, IAMs may exhibit a bias towards selecting BECCS. Concerns arise because many cost assumptions within IAMs, including those related to BECCS, may be outdated. Notably, the real-world costs of deploying traditional renewables like solar and wind have decreased significantly over the past decade, enabled by the modular nature and repetitive manufacturing of these technologies, with, for instance, around 70 billion solar cells expected to be produced in 2024. Meanwhile, the cost of BECCS remains high and uncertain, as will be explored in the following chapters. In 2019, researchers noted that a paper published in 2015 reporting on the results from one IAM included solar PV and storage capital costs based on a 2008 analysis.
The real-world costs of deploying traditional renewables like solar and wind have decreased significantly over the past decade, while the cost of BECCS remains high and uncertain.
An analysis conducted in 2020 offers valuable insights into the quality of BECCS parameters within IAMs. The study highlights a lack of transparency in many assumptions, particularly regarding the technological aspects of BECCS, such as CO₂ transport and storage. Additionally, all six IAMs assessed in the study assume that the bioenergy used in BECCS facilities is carbon-neutral, meaning that the emissions generated during bioenergy production are offset over the biomass’s lifetime growth period. Another study, published in 2021, has shown that some of the IAMs contain unrealistic land-use change allocations in their modelling architecture. This is crucial, given that BECCS requires significant areas of land to produce its biomass fuel. The study states that some IAMs have ‘highly regionalized land use and land cover changes with rates of conversion that are contrary to or exceed rates observed in the past’.
The efficiency of BECCS producing electricity from its biomass feedstock, for sale to its energy consumers, is central to its revenue base and economic competitiveness, and hence its selection by the cost-optimizing IAMs. As previous Chatham House analysis has shown, based on trials of BECCS technology, power-generation efficiencies from wood pellets are likely to be in the low 20–25 per cent range. However, within four IAMs assessed by a 2019 study, BECCS was assumed to have a 2020 power-production efficiency of 26–36 per cent, increasing to 31–39 per cent by 2030. Looking out to 2050, these IAMs assume the power-production efficiency of BECCS increases by less than 1 per cent per year, commensurate with empirical evidence as to how thermal power plants in Europe improved their efficiency between 1990 and 2010. However, in order to meet the average assumed power efficiency in 2050 within these four IAMs, starting from where BECCS trials indicate the technology stands currently, production efficiency would need to increase by around 2 per cent annually.
Not only are many of the modelling assumptions pertaining to engineered removals questionable, and potentially overly optimistic. Additionally, the severity of risks they assume need to be avoided may be under-represented. In their 2021 paper, economists Nicholas Stern and Joseph Stiglitz state: ‘[T]he estimates of damages from climate change in these IAMs is much smaller than is likely to occur.’ Stern and Stiglitz go further, identifying that there is ‘a systematic bias towards reducing the strength of action on climate change, that results from underestimating the benefits and overestimating the costs of such action’; and concluding:
In 2022, the European Commission highlighted research that showed that, of the IPCC scenarios (underpinned by the IAMs), only 5 per cent involved substantial energy demand reduction from current levels by 2100. The research argued that IAMs have a techno-economic focus, and under-represent the potential for global energy demand reduction to contribute to carbon mitigation targets, particularly in reducing dependence on CO₂ removal techniques. The European Commission also pointed to research that argues that the lack of demand reduction is limited due, in part, to ‘an imperative to maintain GDP growth, which is typically closely coupled with energy demand’.
Countries are already baking in reliance on engineered removals
With G20 countries accounting for almost 80 per cent of global fossil fuel emissions, their decarbonization plans and relative reliance between technologies and demand-side action is crucial in assessing how likely it is that the world will be able to avoid overshooting the 1.5°C Paris Agreement target – and, by extension, avoid the risk of triggering runaway climate change.
The reliance of G20 members on engineered removals varies from country to country. Members have diverse climate targets and commitments, ranging from pledges to achieve net zero emissions by 2050 to more modest emission-reduction goals. Those with more ambitious targets tend to be more reliant on engineered removals in order to achieve those targets.
Several countries have included engineered removals within their nationally determined contributions (NDCs) under the Paris Agreement, and in their reporting to the UN Framework Convention on Climate Change (UNFCCC). However, the specific details and extent of the inclusion of engineered removals in NDCs vary significantly between countries. Some countries explicitly mention engineered removals as part of their mitigation strategies, while others incorporate them indirectly through national policies. As countries update and revise their NDCs over time, it’s likely that more will incorporate engineered removals in their mitigation strategies.
A recent study, published in 2024, found that relative to 2020, the most ambitious national targets imply that CO₂ removals, across all forms of greenhouse gas removal (GGR) types, increase by 0.5 GtCO₂ per year (GtCO₂/yr) by 2030, and 1.9 GtCO₂/yr by 2050. The same study found that these GGR scale-up pledges fall short of holding global temperatures to the 1.5°C Paris target, but that if countries were to pledge dramatically more ambitious emissions reductions while holding the GGR scale-up at the same levels, the emissions gap could be closed. This type of scenario is also consistent with low energy-demand scenarios.
A further 2024 study, found that NDC documents submitted to the UNFCCC indicate that countries plan to increase land-based GGRs from 2 GtCO₂/yr in 2020 to around 2.1 GtCO₂/yr in 2030 based on unconditional pledges, and to around 2.6 GtCO₂/yr based on conditional pledges. Importantly, the study found that no country currently quantifies contributions from ‘novel’ GGRs, i.e. from engineered removals. However, several countries include engineered removals in their qualitative description of mitigation efforts within their NDCs.
Looking out to 2050, rather than 2030, only 31 countries have outlined long-term scenario strategies with quantifiable levels of GGR, 12 of which are EU member states. Based on these 31 countries, the study finds that projected CO₂ removals range between 2.5 GtCO₂ and 3.6 GtCO₂ in 2050, of which conventional land-based GGRs represent between 78 per cent and 73 per cent of removals, respectively. Therefore, the upper-end projection of engineered removals is around 0.97 GtCO₂/yr of ‘novel’ GGRs, equivalent to 3.3 per cent of the fossil fuel emissions from G20 countries in 2023. This is largely driven by the US (52 per cent share), the EU (27 per cent) and Canada (21 per cent). However, it should be noted that this excludes various countries that are in the process of developing engineered removals technology roadmaps, among them China, Norway, Australia and Saudi Arabia.
The same study compared the country pledge analysis of land-based and engineered (or ‘novel’) CO₂ removal reliance against three scenarios, based on IAMs outputs, finding that depending on the level of demand reduction and renewables deployment, reliance on engineered removals ranged from zero to 3.5 GtCO₂/yr in 2050, equivalent to 11.9 per cent of the fossil fuel emissions from G20 countries in 2023. It should be noted that across all the illustrative mitigation pathways (IMPs) assessed by the IPCC, engineered removals are 2.75 (0.52–9.45) GtCO₂/yr for BECCS in 2050, and considerably less for DACCS, at 0.02 (0–1.74) GtCO₂/yr. Combined, engineered removals would therefore, by 2050, be sufficient to sequester 9.4 per cent of 2023 fossil fuel emissions from G20 countries, with 99 per cent coming from BECCS. For comparison, negative emissions from agriculture, forestry and other land use (AFOLU) across the same IMPs in 2050 are 2.98 (0.23–6.38) GtCO₂/yr, meaning that negative emissions from BECCS and AFOLU are on a similar level.
Another important conclusion to draw from the 2024 study of NDC pledges is that, even based only on the 31 countries’ long-term scenarios that quantify levels of GGRs, the upper-end projection of 0.97 GtCO₂/yr of ‘novel’ GGRs in 2050 is more than one-third of the way towards the 2.77 GtCO₂/yr level within the IMPs assessed by the IPCC.
This review illustrates that, in 2050, engineered (or ‘novel’) CO₂ removal techniques, relative to 2023 G20 fossil fuel emissions, represent:
- 3.3 per cent, based on quantified country plans
- 9.4 per cent, based on IPCC illustrative mitigation pathways
- 11.9 per cent, based on pathways with a high reliance on engineered removals with limited demand reduction within societies
Decision-makers understandably default to technological innovation to try to solve problems, while simultaneously aiming to deliver growth
Considering the revolutionary power of technology to change lives, mainly for the better, it is no wonder that politicians often, and rightly, turn to technology and innovation to resolve many of the world’s problems.
At the same time, technological innovation is fundamental to economic growth. Labour, capital and technological progress are the primary factors governing the rate of production, or economic growth, under the neoclassical growth model, also known as the Solow-Swan growth model. Under the Solow-Swan model, the long-term growth prospects of an economy are determined by technological progress, as returns on capital diminish with no technological progress.
Estimating the proportion of global GDP that is derived from technological innovation is extremely complex, and highly uncertain. However, technological innovation is widely recognized as a key driver of economic development and productivity growth. In its Global Innovation Index reports, the World Intellectual Property Organization (WIPO) highlights the role of innovation in driving economic growth and competitiveness across countries and regions. And OECD data show that countries with higher levels of investment in research and development (R&D), technology adoption and innovation tend to exhibit higher rates of growth.
Perhaps, then, it is no surprise that politics has to some extent influenced the scientific advice emerging from the IPCC, resulting in a degree of breakdown of the old adage that policymakers ‘follow the science’. The most reported and widely acknowledged instance of political influence over IPCC reports concerns the Summary for Policymakers, which must be approved by governments. The approval session of the 2023 summary is reported to have seen a group led by Saudi Arabia push for an emphasis on carbon removals and CCS, while European countries pushed for statements that solar and wind electricity ‘is now cheaper than energy from fossil fuels in many regions’. Notably, too, France and Germany are reported to have ‘cautioned that CDR [carbon dioxide removal] deployment at scale is unproven and risky’, and to have asked for more detail on the limits and risks of CDR methods.
But political influence over the mitigation pathways of the IPCC goes deeper, specifically over engineered removals, as reported by a 2018 study by academics at the University of Cambridge. Due to the vast array of potential decarbonization pathways the world could take, contingent on the weighting ascribed to competing technologies, the IPCC defines Representative Concentration Pathways (RCPs) that
represent the outputs of many IAMs. The selection of the RCPs is therefore open to judgment in order to condense the possible pathways down to a manageable number.
In 2007, the IPCC moved away from an older system and towards this RCP system, eventually landing on four pathways: RCP 2.6, RCP 4.5, RCP 6 and RCP 8.5. At an expert meeting, the decision to select RCP 2.6 over an alternative RCP 2.9 scenario proved controversial. The RCP 2.6 scenario had only been produced by one modelling group. Both the pathways prescribed significant emissions reductions, but RCP 2.6 included a massive roll-out of BECCS by giving large expanses of land over to growing fuel crops. An EU-funded project saw the two main European IAM teams invited to produce 2.6 pathways ‘with which they were comfortable’, which ultimately led to the BECCS-heavy RCP 2.6 being selected and the proposed RCP 2.9 dropped. The Cambridge authors found:
We need to be increasingly aware that politics not only influences the IPCC Summary for Policymakers reports, but also the decarbonization scenarios themselves. The policy tail is wagging the science dog.
