Reframing the policy approach to greenhouse gas removal technologies

Energy Policy 78 (2015) 125–136

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Energy Policy journal homepage: www.elsevier.com/locate/enpol

Reframing the policy approach to greenhouse gas removal technologies Guy Lomax a,n, Mark Workman b, Timothy Lenton c, Nilay Shah d a

Energy Futures Lab, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom Grantham Institute for Climate Change, Imperial College London, London, United Kingdom College of Life and Environmental Sciences, University of Exeter, Exeter, United Kingdom d Department of Chemical Engineering, Imperial College London, London, United Kingdom b c

H I G H L I G H T S








Greenhouse gas removal (GGR) must be decoupled from geoengineering discussions. GGR shares many characteristics with existing mitigation and offset measures. GGR brings key economic value and flexibility to mitigation efforts. Delaying action on GGR policy risks missing short and long term opportunities. The ultimate goal should be GGR “policy parity” with emissions reduction.

art ic l e i nf o

a b s t r a c t

Article history: Received 8 May 2014 Received in revised form 31 August 2014 Accepted 7 October 2014

Greenhouse gas removal (GGR) methods such as direct air capture, bioenergy with carbon capture and storage, biochar and enhanced weathering have recently attracted attention as “geoengineering” options to reverse the build-up of greenhouse gases in the atmosphere. Contrary to this framing, however, we argue that GGR technologies can in fact form a valuable complement to emissions control within on-going mitigation efforts. Through decoupling abatement from emissions sources, they add much-needed flexibility to the mitigation toolbox, increasing feasibility and reducing costs of meeting climate targets. Integrating GGR effectively into policy raises significant challenges relating to uncertain costs, side effects, life-cycle effectiveness and accounting. Delaying policy action until these uncertainties are resolved, however, risks missing early opportunities, suffocating innovation and locking out the long-term potential of GGR. Based on an analysis of bioenergy with carbon capture and storage, we develop four policy principles to begin unlocking the potential of GGR: (i) support further research, development and demonstration; (ii) support near-term opportunities through modifying existing policy mechanisms; (iii) commit to full GGR integration in carbon accreditation and broader climate policy frameworks in future; (iv) develop sector-specific steps that lay the groundwork for future opportunities and avoid lock-out. & 2015 Published by Elsevier Ltd.

Keywords: Greenhouse gas removal Geoengineering Climate change policy

1. Introduction 1.1. Background There has been an increasing consensus in recent years that global efforts to reduce CO2 emissions will not be sufficient to meet the widely recognised upper stabilisation limit of 450 ppmv atmospheric CO2 concentration, the level thought to be consistent with a global average temperature rise of 2 1C (IEA, 2012). Even if all nations that have made national pledges meet their most ambitious near-term mitigation targets, an “emissions gap” of 8 gigatonnes of

n

Corresponding author. Tel.: þ 44 7899 948 460. E-mail address: [email protected] (G. Lomax).

http://dx.doi.org/10.1016/j.enpol.2014.10.002 0301-4215/& 2015 Published by Elsevier Ltd.

CO2-equivalent per year in 2020 will still exist between projected emissions and trajectories with a 66% chance of limiting warming to 2 1C (UNEP, 2013). Similarly, latest estimates from the IPCC (2013a) suggest that humanity has used over half of the cumulative “carbon budget” associated with the same goal. Furthermore, improved understanding of climate tipping points and long-term feedbacks has led Hansen et al. (2008), among others, to suggest that 350 ppmv is in fact the upper limit for long-term climate stabilisation, a point passed in the late 1980s (IPCC, 2013a). Such realisations have driven a surge in interest in greenhouse gas removal (GGR), also known as carbon dioxide removal (CDR) or negative emissions technologies (NETs). The term describes any method that results in long-term removal of CO2 or other GHGs from the atmosphere either through enhancing and expanding natural sinks or creating new sinks (IPCC, 2013a).

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The concept in its current form was brought to global attention by the Royal Society (2009), which framed it as one branch of geoengineering, a “deliberate, large-scale intervention in the Earth’s climate system in order to moderate warming”, in parallel to a group of techniques aiming to modify the Earth’s albedo known as solar radiation management (SRM). In this view, planetscale GGR represents a way for humanity to undo the damage caused by GHG emissions and return atmospheric concentrations to within safe limits. This initial framing, emphasising large-scale deployment, safety and regulation, has dominated early discussion of governance and policy for GGR (e.g. Bracmort et al., 2011; MacCracken et al., 2010; House of Commons, 2010). However, recent discussion has pointed out that GGR approaches in fact have very little in common with SRM proposals. Instead they typically share much more with related emissions reduction approaches and can play a valuable role within the context of current mitigation efforts (Boucher et al., 2013; Heyward, 2013; Meadowcroft, 2013). In this view, the distinction between GGR and emissions reductions is in many ways artificial and is an unconstructive basis for developing effective policy. The aims of this work are to evaluate the state of GGR technologies and the value they could bring to near-term and long-term efforts to tackle climate change, develop a framing of GGR that is useful for developing policy and suggest ways that policymakers can begin to make useful progress in this sector. It stresses the framing of GGR technologies as diverse and potentially valuable options of variable maturity that in many cases have much in common with “traditional” mitigation approaches. In this light, it re-examines the policy needs for effective support of GGR and the key challenges, finally recommending four classes of policy priorities that can start to take advantage of the opportunity that GGR provides. Section 2 will first review the concept of GGR and a sample of proposed technologies. Section 3 reviews the strengths and limitations of how GGR has been framed in policy discussion so far and develops a new framing based on the value that GGR can bring to climate mitigation efforts. A discussion of the challenges facing attempts to integrate GGR into climate policy, and the urgency of addressing them, is presented in Section 3. Section 4 offers four broad policy recommendations for realising the potential of these technologies in the long term. Section 4 also summarises and concludes. 1.2. Greenhouse gas removal systems 1.2.1. Overview of GGR systems There have been several excellent recent reviews of the growing range of methods for removal of GHGs from the atmosphere (see e.g. McGlashan et al., 2012; McLaren, 2012, 2011; Vaughan and Lenton, 2011) so the technologies will not be discussed in detail here. A brief description of a selection of the most widely discussed approaches is given in Table 1. Note that cost estimates should not be taken as definite, especially for less mature technologies, but simply illustrate the expected order of magnitude of abatement cost through GGR. Classification of technologies is based on McLaren (2011). 1.2.2. Policy relevant features of GGR technologies A number of policy-relevant conclusions can be drawn from a review of the current status of GGR technologies. The following conclusions are drawn chiefly from points raised by the Royal Society (2009), Vaughan and Lenton (2011), McGlashan et al. (2012) and McLaren (2011): 1. GGR technologies are very diverse, making use of a range of capture pathways and carbon storage reservoirs. They may

share nothing beyond their conceptual aim of removing atmospheric CO2. 2. Many technologies are at an early stage of scientific and technical development, and this is reflected in often large uncertainties in estimates of their costs, effectiveness and any undesirable impacts. Ocean and soil-storage methods broadly face uncertainties surrounding underlying carbon cycling processes, quantifying storage and environmental impacts. Uncertainties in engineering-based systems such as direct air capture and bioenergy with CCS also relate to technical challenges and costs. 3. Predicted costs for some technologies overlap with those of some of today’s “mitigation” options with estimated abatement costs of the order of $10–100/tCO2 (IPCC, 2007). 4. Some technologies may be associated with significant cobenefits or co-products, such as ecosystem services, improved agricultural yields or management of ocean acidification. These can make them worthwhile even in the absence of carbon benefits. Bearing these characteristics in mind, we now explore the role that GGR can play in near-term and long-term climate strategy.

2. Methods This work is a synthesis, building on the insights of a re-framing of greenhouse gas removal that is emerging in the literature with ideas developed through a series of semi-structured interviews on the specific question of combining bioenergy with carbon capture and storage conducted in 2013 (detailed in Lomax, 2013). An extensive literature review focused on characterising the evolution of the wider discourse surrounding GGR over the last few years in order to synthesise the main themes into a new framing of GGR developed in Sections 3.1 and 3.2. New perspectives on the role and prospects of GGR, as well as the key policy strategy recommendations presented in Section 3.3, were developed from an in-depth analysis of the example of bioenergy with carbon capture and storage, which has sometimes been characterised as the GGR technology closest to widespread deployment (McGlashan et al., 2012). GGR approaches are very diverse, and BECCS may have few specific features in common with other options, such as ocean liming. When designing policy, it will of course be important to tailor it to the specific issues raised by particular technologies. However, BECCS shares many specific challenges with other GGR technologies that integrate bioenergy and those that integrate CCS, and raises the same high-level questions that are relevant to GGR methods considered as a group, surrounding their appropriate role and unique conceptual challenges. Therefore, it is argued that BECCS is a useful illustrative case study to develop broad principles of policy integration for GGR. However, since BECCS is arguably most closely tied to energy system technologies and policies, more specific recommendations may not apply equally to other approaches. Where other technologies raise particular issues, or interact with other policy systems, we briefly discuss in the text. The prospects of BECCS were explored through a series of twelve semi-structured interviews conducted over July to September 2013. The latest academic perspectives were introduced to interviewees from a range of backgrounds in order to develop new insights and derive a more balanced picture of a technology than review of academic literature alone. In order to reduce bias, representative experts and stakeholders from diverse groups, including different branches of academia, industry and related groups, NGOs and public sector policy researchers, were sought in

Table 1 Overview of a selection of GGR systems.

Biological methods

State of stored carbon

Description

Published cost estimates

Possible products or co-benefits

Afforestation and reforestation

Biomass and soil organic carbon

$20–100/tCO2a

Wetland restoration

Biomass and soil organic carbon

Agricultural soil sequestration

Soil organic carbon (SOC)

Restoring cleared forests and planting new forests on suitable land Restoring damaged, carbon-dense wetlands such as peatlands and mangrove forests Adopting a range of practices on arable and grazing lands that enhance soil carbon levels, including reduced tillage and new cropping patterns

Biochar

Charcoal in soils

Converting biomass to long-lived solid charcoal through pyrolysis and incorporating into soils for agricultural benefits

o $60/tCO2, depending on system and feedstockf,g

Bioenergy with carbon capture and storage (BECCS)

Pressurised CO2 in geological storage

Capturing CO2 from biomassfuelled power plants or industries and storing it in geological reservoirs

$60–120/tCO2i, but perhaps as little as $25/tCO2 in niches such as bioethanol productionj

Appropriate implementation can bring environmental and economic benefitsa Other ecosystem services including water quality and flood protectionc Improved SOC associated with many benefits, including fertility, efficiency of fertiliser use (and reduced pollution from runoff) and management of floods and droughtse Evidence that significant benefits to soil health, fertility and retention of water and fertiliser are possible.h Valuable co-products, e.g. bio-oils Produces fuels or electricity, as in conventional bioenergyi

Direct air capture (DAC)

Pressurised CO2 in geological Storage

Capturing CO2 directly from the air using chemical sorbents and storing it in geological reservoirs

Widely varying estimates, from $30–1000/tCO2, depending on system and assumptionsk

Enhanced silicate weathering

Dissolved bicarbonate and carbonate in groundwater or oceans

$20–130/tCO2 assuming complete reactionm

Ocean liming

Dissolved bicarbonate and carbonate in oceans

Spreading finely ground silicate mineral powder on land or ocean to accelerate natural reaction with atmospheric CO2 Adding lime or other metal oxides/ hydroxides to the ocean to convert dissolved CO2 to bicarbonate and drive drawdown from the atmosphere

On the order of $10–100/tCO2 in some casesb $0–100/tCO2, with some practices cost-negatived

$70–160/tCO2o

CO2 may be used for EOR or other industrial use; provides a feedstock for “carbon-neutral” synthetic hydrocarbon fuelsl Potential benefits to soil pH and nutrient value, although more research requiredn

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Chemical methods

System

Local alleviation of ocean acidificationo

a

Canadell and Raupach (2008). Worrall et al. (2009). c Parish et al. (2008). d Smith et al. (2007). e Victoria et al. (2012). f Roberts et al (2010). g Pratt and Moran (2010). h Biederman and Harpole (2013). i McGlashan et al (2012). j Karlsson et al (2010), discussed by McLaren (2011). k Goeppert et al. (2012). l Lackner et al. (2012). m Renforth (2012). n Hartmann et al. (2013). o Renforth et al. (2013). b

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order to provide a wide range of perspectives. Interview technique and qualitative content analysis of interview transcripts then followed the methodology detailed by Gillham (2000) to maximise openness, freedom and authentic capture of interviewees’ perspectives. Interviews and subsequent analysis yielded a coherent picture of the challenges and uncertainties facing BECCS, and a group of policy principles with which to mitigate them. Through further integration with the GGR literature, consultation with GGR developers and specialists, these findings were able to be generalised to the GGR space as a whole, and yielded the four high-level policy strategies developed in Section 3.3.

3. Results and discussion 3.1. The role of GGR in climate change mitigation 3.1.1. Beyond geoengineering The current interest in GGR was largely stimulated by the Royal Society (2009), who considered large-scale GGR as one of two geoengineering options to counteract and ultimately reverse the effects of climate change. In this view, GGR is a potentially globalscale intervention in the climate system that is distinct from climate change “mitigation”, and more closely related to solar radiation management (SRM). Treating GGR as a geoengineering method raised questions about the extent to which humanity was capable of “managing” the climate system, questions about who would have control over target CO2 levels, ethical questions of justice and consent, and other complex social, ethical and political issues (Royal Society, 2009), and led to the idea of incorporating GGR within an international geoengineering governance framework to be implemented before deployment (House of Commons, 2010; Rayner et al., 2013). The first problem with this framing, pointed out by Heyward (2013), Meadowcroft (2013) and Boucher et al. (2013), is that the vast majority of GGR approaches have very little in common with SRM measures that aim to directly and globally manage the Earth’s radiative balance. Any global ethical and governance issues relating to GGR as intentional “climate management” would only be of relevance with a GGR industry on a scale comparable to the global fossil fuel industry. Their joint consideration under the geoengineering banner has given the false impression that “all the technologies in the two categories of response always raise similar challenges and political issues” (Heyward, 2013), and hence must be dealt with by policy within a single geoengineering framework. Considering GGR as “geoengineering” poses a huge challenge to policymakers. By focusing on deployment at a multi-gigatonne scale, capable of reversing human emissions many decades in the future, it takes the discussion far beyond the domain of current scientific knowledge, global experience and policy planning timescales. It emphasises vast uncertainties and global-scale risks that encourage a focus on regulation through application of the precautionary principle. Policy is then required to develop a unified, decisive governance mechanism to control the future development of a rapidly changing, heterogeneous set of technologies, the future of which we cannot confidently predict. Meadowcroft (2013) therefore concludes that this concept of GGR as “climate recovery” is of little relevance to policy today. Instead, GGR can be more usefully thought of as an “emissions offset” within overall mitigation strategy: a route to negating ongoing anthropogenic emissions (see Section 3.1.4). Indeed, both afforestation and soil carbon sequestration approaches, classed here as GGR approaches, have been included within mainstream mitigation frameworks as “enhancement of sinks” for many years (Heyward, 2013; IPCC, 2013b), and afforestation in particular has

been deployed specifically as an emissions offset through the Clean Development Mechanism (CDM). We argue that more novel GGR approaches are not conceptually any different from such sink enhancement. These other techniques differ only in the process and medium of stored carbon. At moderate scales, GGR techniques can form a valuable complement to mitigation that can be usefully integrated into emission reduction efforts. 3.1.2. Integrated assessment modelling and the role of GGR Increasing inclusion of certain GGR systems in long-term integrated assessment models (IAMs) has served to further emphasise this climate recovery framing. UNEP (2013), in their annual meta-analysis of models providing least-cost pathways to meeting global temperature targets, found that about a third of scenarios reviewed with a likely chance of meeting 2 1C targets required global “net-negative emissions” before 2100, and that these scenarios had reduced mitigation costs and less urgent rates of CO2 reduction in the near term. Recent modelling focusing on BECCS (Azar et al., 2013, 2010; Edmonds et al., 2013; Kriegler et al., 2013; van Vuuren et al., 2013) and direct air capture (Chen and Tavoni, 2013) has confirmed the potential impact these technologies could have on least-cost scenarios of meeting mitigation targets. Where models are allowed to choose the suite of technologies that minimises aggregate cost of meeting emissions, average temperature or radiative forcing targets, or where rising carbon prices are introduced to the same ends, models with a wide range of assumptions and constraints yield substantial deployment of these two technologies. Crucially, much of the economic value in these models arises from the ability to postpone the costs of mitigation through “overshoot” scenarios, in which discount rates applied to such late-century costs make this more economically desirable. Such modelling tends to emphasise a role for BECCS and direct air capture that is concentrated in the second half of the century, in which rapid scale up and global net emissions removal play a key role. Azar et al. (2013), for example, arrive at emissions pathways in which BECCS only gains significant scale from around 2050, while the model of Chen and Tavoni (2013) that the optimal role of Air Capture is an extremely high rate of deployment beginning in 2065. 3.1.3. The limitations of integrated assessment modelling as a basis for policy The results of such IAMs give some suggestion of the value that GGR can bring in adding flexibility to our mitigation options and potentially reducing overall costs. However, in emphasising the large-scale deployment of such immature technologies over such long timescales, the models cannot on their own provide a solid foundation for GGR policy. Meadowcroft (2013) has emphasised that the level of uncertainty surrounding quantitative parameters of the models and qualitative assumptions are very high. The evolving relationship of a technology’s costs relative to other emissions abatement options is extremely difficult to predict, and depends on countless details of its development over the next decades as well as the technology itself. This is true of many emissions reduction options as well as GGR, and the errors become even larger when the technology under consideration has not proven itself at commercial scale. Additionally, while models assume an economically-optimal (or near-optimal) deployment strategy, in reality many factors beyond mitigation cost influence whether a technology will be deployed, and at what scale, particularly in the controversial environment of energy policy. Again, this is true for both GGR and conventional approaches. A further risk is added by the possible presence of irreversible climate “tipping points” at relatively modest levels of warming

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(Lenton et al., 2008). Such events could increase the cost of climate damages in a non-linear fashion. If, for example, irreversible climate damages were triggered during an “overshoot” period, this would cast further doubt on the wisdom of relying on GGR as a climate recovery tool. Most importantly, it is vital that the “economically optimal” pathways produced from the modelling are not taken to represent optimal strategies for climate policy. Accepting a slackening of mitigation efforts in the short term on the assumption that it will be more economical for GGR to make up the difference late in the century could be a disastrous error due to the large uncertainties in the underlying assumptions and represents a high-risk strategy. Such models must be interpreted as an illustrative exercise rather than a prediction or policy recommendation. The sudden appearance and rapid deployment of large-scale GGR several decades in the future in models could imply that such a transition will not require significant policy action in the near term. This could unwisely encourage a wait-and-see approach, in which no policy action is taken until the uncertainties are resolved. It is notable that besides forestry or soil carbon approaches, policy engagement with GGR has indeed so far tended to consider it either as something that may be needed in the long term, largely framed as a climate recovery measure, (e.g. House of Commons, 2010; Bracmort et al., 2011; Wentworth, 2013). The UK Bioenergy Strategy (DECC, 2012) has noted the potential value of BECCS in a 2050 energy system, but has not yet explored steps to support this end goal. Such a perspective neglects the scientific, technical and policy challenge associated with developing technologies currently in the lab to the point where they are viable options in the mitigation toolbox. It also neglects the extensive broader groundwork that is needed to allow such long-term potential to be realised. Finally, IAMs to date have tended to focus on BECCS and DAC (with a modest contribution from Afforestation) (UNEP, 2013), generally because their scalability and quantifiable behaviour are best suited to current modelling methods. While the models demonstrate the value of even these more expensive approaches, they also neglect the value of other GGR methods that are less easily quantifiable and cannot be extended to the same multigigatonne scales. These less quantifiable approaches, such as soil carbon improvement, biochar and enhanced weathering, may have the potential to be valuable and cost-effective opportunities even in the near term.

3.1.4. The value of GGR to mitigation GGR technologies, in spite of their diversity, share a few key characteristics that define the role they could play in a coherent global climate change strategy. Most fundamentally, in developing atmospheric sinks, they uniquely allow net GHG reduction independently of the sources of the emissions. That is, the nature and costs of mitigation are decoupled from emissions sources in the energy system in both time and space (Keith, 2009; Meadowcroft, 2013). This is the source of their key advantage to the mitigation agenda. Through GGR, reduction in net anthropogenic GHG emissions is no longer bound to the incumbent energy system to the same degree, allowing them in many cases to sidestep specific technical, economic, geographical, political or behavioural barriers to achieving a particular emissions reduction. This flexibility brings the following valuable traits to mitigation efforts: 1. They can provide alternative routes to offsetting emissions from sectors or particular sources that are either extremely expensive to decarbonise directly on the necessary timescale, or for which there are simply no feasible technology options

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currently available (Kriegler et al., 2013; Meadowcroft, 2013). Such difficult sources include distributed and mobile sources such as in the transport sector, where the utility of energydense carbon-based fuels cannot be easily matched by clean technologies (Keith, 2009). 2. Similarly, since various GGR technologies are relatively decoupled from existing energy infrastructure, they may be less constrained by its historic development of existing energy systems. This decoupling can to some degree allow GGR projects to be situated flexibly, where conditions and economic contexts are most favourable (e.g. areas of stranded energy resources or CO2 storage capacity (Keith et al., 2005)). In this context, even the more expensive GGR options deployed in optimal contexts can potentially achieve more economical abatement than emissions reductions in unfavourable contexts. Depending on how, specifically, climate policy and GGR deployment are directed, this flexibility allows GGR approaches to play several key roles within the mitigation context (Meadowcroft, 2013): 1. They can reduce the costs of meeting a given climate target by displacing some of the most costly emissions reduction measures. 2. They can “buy time” for the technical development and widespread deployment of clean energy technologies and the adjustment of societal practices. 3. They can make a more aggressive reduction target feasible by providing parallel avenues for reducing net emissions. 4. They could enable limited continued fossil fuel use (either temporary or long-term) in sectors where alternatives cannot yet meet the performance required. Furthermore, many GGR technologies do in fact seem likely to offer GHG removal at meaningful scale at costs in a similar range to many conventional mitigation technologies, even in the near term (Table 2). This is especially true in the case of biological routes to sequestration, many of which are likely available at costs well below $100/tCO2 (McLaren, 2012) in the near term and may provide many additional benefits such as improved soil quality and ecosystem services (Barrow, 2012; Smith et al., 2007). Even the more expensive technologies may also provide moderate levels of low-cost mitigation potential in some contexts. Proponents of direct air capture technologies, for example, point to their ability to supply CO2 to isolated oil fields to meet growing demand for the gas in enhanced oil recovery (EOR) (Keith, 2009; Lackner et al., 2012). Since the majority of proposed GGR options are not currently recognised in international accounting or carbon trading, there is potential for low-hanging fruit even in the short term. In the longer term, abatement cost estimates for some of the more expensive and scalable options such as DAC or BECCS are comparable to those of some more advanced emissions reduction technologies. Cost projections of Solar PV and Concentrating Solar Power in the electricity sector, for example, have been associated with abatement costs above $100/tCO2 (IPCC, 2007). In sectors that are more dependent on fossil fuels, achieving full potential emissions cuts hinges on the development and deployment of similarly costly technologies. Achieving the majority of mitigation potential in industry is projected to require novel process technologies, fuel switching and CCS options with costs of $50–200/ tCO2 (IEA, 2011; IPCC, 2013b). In the oil-dominated transport sector, abatement costs are highly sensitive to life-cycle assumptions and oil prices, but estimated ranges for options including aircraft efficiency, road transport electrification and certain biofuels cover ranges of $0–400/tCO2 (IPCC, 2013b). Even accepting the uncertainties, it is likely that GGR with cost estimates in these

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Table 2 Examples of near-term, low-cost opportunities for various GGR approaches and equivalent estimates for abatement potential through conventional “mitigation” approaches. Near-term opportunity

Approximate global scale estimates in 2030 Estimated abatement costs

1600 MtCO2/year 2700 MtCO2/year 1400–1500 MtCO2/year 4000–4300 MtCO2/year Biochar 1200 MtCO2/year—biochar stove or kiln projects in developing countriesc 600 MtCO2/year—commercial projects in developed countriesc Enhanced weathering (wastes)—accelerating carbonation 700–1200 MtCO2/year if current global of reactive minerals in industrial wastes mineral waste flows are carbonatedd Conventional CCS on coal combustion 490 MtCO2/year economic potentialf Nuclear power 1,880 MtCO2/year economic potentialf Wind generation 930 MtCO2/year economic potentialf Solar PV and concentrated solar power 250 MtCO2/year economic potentialf Bioenergy (without CCS) 330 MtC/year economic potentialf

Afforestation/reforestation (including avoided deforestation) Agriculture/soil carbon enhancement

o $20/tCO2a o $100/tCO2a o $20/tCO2b o $100/tCO2b o $30/tCO2c o $50/tCO2c One estimate states as little as $8/tCO2 for a simple system of cycling aerated water through wastese $20–50/tCO2 o $20/tCO2 o $50/tCO2 4$50/tCO2 $0–100/tCO2

a

Nabuurs et al. (2007). Smith et al. (2007). Pratt and Moran (2010). d Renforth et al. (2011). e Stolaroff et al. (2005). f Global estimates of economic potential by the IPCC (2007). b c

ranges (such as DAC, BECCS, enhanced silicate weathering and ocean liming, Table 1) could provide more economical mitigation of such emissions in favourable circumstances. These two key advantages provide powerful reasons for policymakers to consider the economic and strategic value of GGR to the mitigation agenda and to find ways to include it in climate policy. Even if a given GGR technology does not in reality attain the scales or average costs projected by its advocates, there are still likely to be many particular opportunities where offsetting via GGR is more economical or otherwise desirable than other mitigation routes. 3.2. Policy integration of GGR 3.2.1. Policy challenges facing GGR The opportunity provided by GGR, however, is balanced by the significant uncertainties surrounding many of them concerning costs, prospective scale, extent of positive or negative side-effects, carbon accounting, permanence of storage and true life-cycle GHG balance that must be addressed in some form by any attempt to integrate GGR into policy. The first barrier to informed discussion of GGR in policy concerns the extensive technical and scientific uncertainties that are associated with many methods (McLaren, 2011; Meadowcroft, 2013). A large part of this stems from the limited research base on GGR and the lack of real-world deployment of many methods. In methods that make use of natural systems such as wetland restoration and enhanced weathering, the complexity of the processes involved is also an important factor, and there are unknowns around how such sinks can be most effectively harnessed (Parish et al., 2008; Hartmann et al., 2013). The resulting wide uncertainties in ultimate effectiveness, design, cost and potential impacts, exacerbated by the long timescales over which they are being considered, make it difficult for policymakers to plan for future integration. A further troubling source of uncertainty concerns possible environmental side effects, particularly for approaches that make use of natural ecosystems (terrestrial or oceanic) for either capture or storage. It is not clear how desirable deployment of some of these options will be in future, particularly at large scales. It is partly these unknowns that have driven calls for regulation and governance, driven by application of the “precautionary approach” (Royal Society, 2009). Proper application of this principle for GGR must consider the balance of risks between such impacts and

climate risks of failing to develop valuable technologies, and should ideally find ways to contain and mitigate such consequences as far as possible while supporting the most promising approaches. In this context, it is useful to distinguish between two types of environmental risks that have been associated with GGR: local environmental risks, and broader system-level risks. For example, silicate minerals applied to soils could plausibly entail locally detrimental ecological impacts through ions released to soils and groundwater (Hartmann et al., 2013), while aggressive BECCS deployment raises system-level issues of sustainability and land use impacts of rising biomass demand (McLaren, 2012). For the first class, a precautionary approach suggests that direct impacts should be assessed and constrained through empirical research before active deployment as GGR. System level effects can be explored via modelling, but are difficult to constrain empirically without actual deployment. Building on the example of bioenergy, such risks are best dealt with by a combination of gradual scale-up and regular review of impacts and policy safeguards (Khanna et al., 2011; DECC, 2012). A more fundamental challenge to GGR integration arises from the inherent difference between carbon stored through GGR and carbon that is never emitted from fossil fuel burning in the first place. GGR technologies store carbon in different forms and reservoirs to fossil fuels, and via processes that are very different to combustion. This fact raises two substantial complications for attempts to integrate GGR into existing policies and GHG accounting systems:


First, practical quantification of carbon stored in many GGR




technologies is more difficult than quantification of carbon emitted by fossil fuel combustion. For biological and soil-based routes, in particular, sequestration may occur at varying rates over long timescales, entail complex flows between carbon reservoirs (e.g. between biomass, soils and groundwater), influence emissions of other GHGs (e.g. nitrous oxide emission suppression in biochar) and be very sensitive to details of the specific situation (climate, soil type etc.) (McLaren, 2011; Smith, 2012; Mohren et al., 2012). Accurate measurement of total stored carbon can also be extremely difficult in natural systems. Approaches based on biomass must also contend with life-cycle emission estimates of biomass supply. Second, sequestered carbon may go on to interact further with the carbon cycle and atmosphere—the problem of

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impermanence (Boucher et al., 2013; Meadowcroft, 2013). This could manifest itself in many forms, depending, including gradual decay of biochar in soils (Lehmann et al., 2009), diffuse leakage of CO2 from geological storage (IPCC, 2005), catastrophic release of forest carbon in a wildfire (Canadell and Raupach, 2008) or re-release of CO2 from dissolved carbonate due to effects on calcifying organisms (Renforth et al., 2013). The risks or mechanisms of this happening are often poorly understood, and, as with storage itself, monitoring or quantification of any loss is often difficult. Full inclusion of GGR within mitigation requires that these unpredictable, hard-to-quantify sequestration systems must be integrated into national accounting in a way that reflects their true effectiveness. This is partly a matter of improving models, measurement methodologies and monitoring for particular technologies, but also of extending existing frameworks to both recognise greenhouse gas removal and establish standards for accounting. The issue of impermanence and liability for carbon release must similarly be addressed. This will require a co-evolution of technology-specific development of monitoring methods and establishing plausible routes to including this aspect in policy frameworks.

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While these challenges are certainly significant, however, they are not necessarily greater than those that already face many proposed emissions reduction technologies or existing offset measures, and in many cases are already being directly addressed through current research and policy development. Table 3 reviews a selection of recent policy and GHG accounting developments in the areas of carbon capture and storage, bioenergy and forestry that are relevant to various GGR techniques. Policies in these mitigation sectors are facing many of the same challenges, such as impermanence of storage, poorly constrained life-cycle emissions and management of system-level effects, as GGR techniques, and in some cases are directly relevant to related GGR methods. These policies have not eliminated the uncertainties and challenges of accounting and sustainable deployment, and some have been widely criticised (e.g. Macintosh, 2012). Nonetheless, the lessons for GGR are twofold. First, there are existing policy structures in place or in development for various emissions reduction methods, combined with a substantial scientific and policy research base, that can form the foundation for GGR accounting. Even for GGR techniques that raise new monitoring and accounting challenges, such as enhanced weathering, these approaches provide models for how uncertainties might be addressed. Second, they demonstrate that perfect life

Table 3 Selected mitigation policy developments relevant to GGR techniques. Mitigation sector

Direct GGR applicability

Examples of existing policy developments

Broader issues addressed

CCS

Direct air capture, BECCS

Long-term monitoring requirements, impermanence and liability

Bioenergy

BECCS, biochar

Afforestation, ecosystems and soils

Afforestation, wetland restoration, agricultural soil carbon and bioenergy options (BECCS and biochar)

EU CCS Directive (2009)a—a legal framework for geological CO2 storage, establishing best practice requirements to reduce leakage risks and environmental harm, monitoring obligations for storage and leakage, and liability mechanisms for leakage EU ETS integration (2008) b—mechanisms treating for stored CO2 as “not emitted”, and requiring surrender of emissions allowances for future leakage IPCC Guidelines (2006) c—principles and methodologies for monitoring and reporting in all stages of carbon capture and storage, including negative emissions where biomass is used UK Bioenergy Strategy (2012) d—details sustainability criteria for biomass and biofuels to minimise life cycle production emissions EU policy progress (ongoing) e—Bioenergy is classed as zero-emission, but there is active policy development towards sustainability criteria to minimise local and global environmental impacts of biomass and biofuels, emphasis on feedstocks and sources at lowest risk of indirect land use change emissions, and life-cycle quantification including trade-offs between emissions and removals at different points in time (carbon debt) IPCC Guidelines (2006) c—principles and methodologies for monitoring and reporting GHG storage and flows associated with biomass and soils, within the Agriculture, Forestry and Other Land Use (AFOLU) category of national accounting UNFCCC Clean Development Mechanism (CDM) f—the latest iteration of methodologies and requirements for design, monitoring and accounting of afforestation sequestration projects to sufficient standards to yield carbon credits for Kyoto Protocol compliance. Future improvements may integrate ecological criteria into the requirementsg

a

Tysoe (2009). CCSA (2014). IPCC (2006). d DECC (2012). e European Commission (2014). f UNFCCC (2013). g Ma et al. (2014). b c

System level impacts and emissions, uncertainty in accounting, ecosystem GHG fluxes, complex time profiles of emission and sequestration

Uncertainty in accounting, ecosystem GHG fluxes, long-term monitoring requirements, impermanence and liability

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Table 4 Review of key R&D challenges facing GGR technologies. GGR system

Example scientific and technical challenges and unknowns

Afforestation/reforestation Wetland restoration

Albedo effect of afforestation; quantifying soil carbon; vulnerability to future climate changea Accurately quantifying carbon sequestration; monitoring non-CO2 GHGs such as methane; effect of different conditions on sequestration rates; vulnerability to future climate changeb,c Uncertain effectiveness of some practices; soil process understanding; effects on non-CO2 GHGs such as methane and nitrous oxide; quantifying soil carbon; vulnerability to future climate changed,e Relationships between feedstock, process conditions and biochar properties; stability of biochar in soils; effects of different biochars in different soil types; effects of biochar on non-CO2 GHGs in soilsf,g,h Development of biomass pre-processing systems; adapting fossil combustion and CCS systems to physical properties, chemical compositions and combustion behaviour of biomass feedstocks; novel CO2 capture technologies for biomass combustioni,j CO2 sorbent development to improve capture rate, reduce regeneration energy costs and improve lifetime; optimising system design to minimise energy use, water requirements and costs; development of full-scale systemsk Mineral dissolution rates and control by key processes; optimising rock grinding methods; ecological impacts; ecological and geochemical feedbacks; quantification and monitoringl Optimising rock grinding methods; assessing ecological impacts; monitoring fate of added alkalinity; novel or improved technologies for calcination; integration with silicate mineral carbonationm

Agricultural soil carbon Biochar BECCS

DAC Enhanced silicate weathering Ocean liming

a

Canadell and Raupach (2008). Parish et al. (2008). McLeod et al. (2011). d Stockmann et al. (2013). e Powlson et al. (2011). f Sohi et al. (2009). g Biederman and Harpole (2013). h Gurwick et al. (2013) i Dai et al. (2008). j IEAGHG (2011). k Goeppert et al. (2012). l Hartmann et al. (2013). m Renforth et al. (2013). b c

cycle accounting is not a necessary precondition for initial deployment and policy support. Approximate methodologies, with safeguards to avoid supporting projects with risks of poor life-cycle performance, can be effective in encouraging deployment. As is occurring in mitigation efforts, more refined policy can then be developed over time in tandem with our growing experience.

3.2.2. The need for action on GGR The IAM projections of GGR arriving in late century, the perceived need to regulate it as geoengineering and the substantial scientific, technical and accounting uncertainties surrounding many GGR technologies can all imply that these technologies are solely a concern for the future. In this view, policymakers would be wisest to focus on the undeniably severe challenges of emissions control measures in the near term and postpone consideration of GGR until the uncertainties have been largely resolved and the problems with existing emissions-based approaches have been dealt with to some extent. However, we argue that such a view is mistaken, and that delaying action on GGR integration would represent a serious missed opportunity. At the most basic level, it would entail missing out on the nearterm opportunities to develop greenhouse gas sinks at relatively low costs, including soil carbon methods, biochar and carbonation of reactive wastes. Such systems can feasibly provide significant sink capacity (Table 2). Second, excluding GGR from policy discussion at this stage provides no incentive for businesses and research institutions to commit effort and investment to developing GGR technologies, resolving the key technical and scientific uncertainties and engaging with policy to build supporting systems for successful GGR-oriented business models. Some GGR options are more technically mature than others, but all have significant remaining scientific and technical uncertainties and challenges that will require ongoing research,

investment and technical development (Table 4). DAC, BECCS and ocean liming, in particular, have large long-term potential (McLaren, 2012), but also face some of the most significant technical and engineering challenges to cost-effective implementation at scale. A refusal to engage with GGR in the near term risks suffocating the early process development and innovation that are necessary for realising the long-term opportunity of such options. Third, this same lack of forethought risks “locking out” an extensive future role for GGR systems through insufficient or unfavourable development of physical infrastructure, technology choices, practices or institutions. The concept of “lock-in” in relation to the dominance of fossil fuels in the energy system was introduced by Unruh (2000), and referred to the codevelopment of mutually supportive technologies, infrastructure, knowledge, institutions, interests and policy in such a way that fossil-based technological systems are perpetuated in the face of more desirable alternatives. The comparable notion of GGR lockout introduced here refers to the evolution of such factors towards systems that obstruct significant GGR scale-up in future. Some less technically mature GGR options are projected to have high long-term potential, but are unlikely to be deployed at scale in the near term. However, achieving required rates of scale-up in future will require a supportive environment for this scale-up, comprising not only sufficient development of technologies, but also resource supply capacity, relevant physical assets and infrastructure, available markets and demand pull mechanisms, commercial experience, financing mechanisms, required skills and expertise and supportive regulatory environments, among others. The risks of lock out are highest for those technologies likely to become important in the longer term (such as BECCS, DAC and ocean liming), where uncertainties are highest, and those that are most closely associated with other industries, technologies or policies (such as BECCS, biochar and agricultural methods), where other pressures may drive developments in these wider social and technological systems that are not conducive to later GGR scale up.

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A full exploration of lock-out possibilities is not within the scope of this paper, but the concept can be clarified with a few illustrative examples of risks:


Technology choice—through early emphasis on fossil-CCS, cap-






ture technologies may come to dominate that are less appropriate for integration with biomass combustion (IEAGHG, 2011). Infrastructure development—investment in long-lived CO2 transport and storage infrastructure may not allow for additional future capacity needed for GGR projects. Resource supply—constrained supply of and competing demands for biomass may limit scale up of BECCS and biochar. Capacity and skills—training, skill development and equipment in the agricultural sector may evolve towards intensive practices not conducive to carbon sequestration.

An important element in such lock-out is that the relevant factors are often not obvious from a technology-focused perspective, but develop from the interactions of various mutually supportive elements. Since choices made today will affect the context in which GGR may be deployed over several decades, it is desirable that developing policy does not inadvertently close down the future GGR potential. 3.3. A policy strategy for greenhouse gas removal 3.3.1. Goals for GGR policy To briefly summarise the discussion above, policy needs to reconcile the following considerations that apply to GGR approaches: 1. They can provide economically valuable mitigation potential in the short and long term and may be vital to meeting emissions targets, as demonstrated by modelling. 2. The immaturity of many approaches and the interactions of some with natural systems mean there are extensive uncertainties over their effectiveness, costs, impacts and long-term potential role, and many practical and political challenges to successful implementation. 3. Policymakers cannot afford to wait until these uncertainties are resolved before initiating action on GGR without missing nearterm opportunities, neglecting necessary R&D on key technologies and risking lock-out of the long-term potential.

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Here we develop four “pillars” of a policy strategy that can begin to address these conflicting imperatives while allowing for the many factors currently outside policy control. These four pillars are summarised in Table 5: (i) Support research, development and deployment of GGR approaches, (ii) Support deployment of promising near-term GGR opportunities, (iii) Commit to formal integration of GGR into emissions accounting and policy support frameworks and (iv) Build system flexibility and avoid lock-out. 3.3.2. Four approaches to GGR integration 3.3.2.1. Support research, development and demonstration of promising GGR approaches. As discussed in Section 3.3.1, many proposed GGR methods are still technically relatively immature. For those methods that depend largely on engineered systems (“technology” in the traditional sense), many of the challenges lie in the early stage of technical development and uncertain final feasibility and costs. For methods that aim to make use of natural processes and ecosystems as sinks, the uncertainties largely centre on the mechanisms at work, sensitivity of the processes to particular conditions, side effects and measuring the net carbon stored. Developing any of these technologies to the point where they can economically, consistently and quantifiably remove GHGs from the air will require considerable and ongoing investment in research, technology demonstration and monitoring methods. Such work will also help to clarify broader policy requirements around these systems, including control of environmental risks. Any policy support or regulation can then evolve with the developing knowledge base. Global Research, Development and Demonstration (RD&D) spending for clean energy technologies exceeded US$16.8 billion in 2011 across a wide range of technologies (IEA, 2013). Given the increasingly apparent importance of GGR to meeting emissions targets, and the significant likely potential of diverse GGR systems to economically offset the most costly and difficult emissions from sectors such as transport and industry (Section 3.1.4), they are arguably deserving of expanded levels of RD&D investment within this portfolio. 3.3.2.2. Support deployment of near-term opportunities. There exists a diverse array of GGR options that could provide relatively low-cost abatement at various scales in the near term, such as agricultural methods, forestry, biochar, CCS from bioethanol production and

Table 5 Summary of the four key recommendations for developing GGR policy. GGR policy principle

Motivation

Examples

Continue support for CCS and bioenergy conversion technologies; develop scientific knowledge and monitoring methods for soil carbon; support development and proving of early DAC systems Support soil carbon practices and biochar through agricultural 2. Support deployment of promising Capture low-cost, early abatement opportunities in various near-term opportunities sectors; highlight unforeseen and system-level issues; build skills policies; support co-firing BECCS through existing subsidy schemes; integrate safe systems with robust accounting into and experience in relevant sectors carbon markets where appropriate 3. Commit to formal integration of Signal to stimulate investment, research and innovation in this N/A sector; provide the first step towards an evolving, integrated GGR into emissions accounting accounting system and carbon pricing framework for GGR, with and policy support frameworks the ultimate aim of “accreditation and policy parity” with emissions reduction 4. Build system flexibility to avoid Develop steps to lay the groundwork for future GGR and avoid Steps taken will be very specific to technologies and policy context. Early engagement with relevant industries and lock-out lock out of valuable opportunities; enable rapid, economically stakeholders is a key first step efficient development of promising future approaches as they For BECCS, develop capture-ready requirements for bioenergy arise; avoid premature commitment to particular technologies plants and incentives for fossil CCS to enable conversion to biomass

1. Support research, development and demonstration of promising GGR approaches

Reduce scientific and technical uncertainties; constrain costs; develop reliable, low-cost monitoring methodologies; develop immature technologies to the point of being “policy-tractable”

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carbonation of natural reactive mineral wastes from industry (Table 2). Supporting such near-term opportunities will not only capture the explicit GHG abatement benefits, but will also be vital to building experience in the relevant sectors and practices (reducing lock-out risks) and highlighting unforeseen challenges on the scientific or policy side. Early, small-scale deployment of a few more advanced options may also allow any wider risks or side effects to be identified and mitigated in advance of larger scale deployment, facilitating ongoing development of safeguards and sustainability standards. In some cases, such opportunities may be directly integrated into existing carbon markets or pricing schemes. Such schemes have already been successfully used to support forestry and agriculture projects in some areas (World Bank, 2014), and promising GGR options could be included within such schemes where appropriate. Carbon markets may not always be the most appropriate tool for supporting GGR in the short term, however. Challenges of reliable accounting and risks of impermanence have hampered direct integration of such activities into some carbon markets (European Commission, 2014), and several proposed GGR options pose similar risks. Existing carbon markets have also experienced problems of low credit prices and volatility, potentially hindering their ability to stimulate GGR projects (World Bank, 2014). As has been the case with mitigation options, targeted incentives and removal of barriers through other policy mechanisms will likely also be important in stimulating innovation, development and deployment. Such mechanisms could be integrated into existing policy and technology support schemes such as those relating to energy or agriculture. For BECCS, for example, potential early opportunities are cofiring of biomass with early fossil CCS plants and connecting bioethanol plants (which naturally generate near-pure CO2 through fermentation) to emerging CO2 transport and storage networks (e.g. Gough and Upham, 2010). From a UK perspective, three example policy steps that could encourage these might be (i) provide slightly elevated feed-in tariff for electricity produced through co-firing relative to fossil-CCS only, (ii) double-count the contribution of “carbon-negative” bioethanol to biofuel blending targets and (iii) ensure that mechanisms exist for smaller facilities such as bioethanol plants to access CO2 transport infrastructure. Examples of supporting GGR through agricultural policies might include requirements for sustainable management practices in frameworks such as the EU Common Agricultural Policy and programmes to reduce destructive practices such as rangeland burning (Smith et al., 2007).

3.3.2.3. Commit to formal integration of GGR into emissions accounting and policy support frameworks. GGR systems will likely seek to derive much of their revenue through integration into a carbon-pricing framework as accounting methodologies improve and the scope of such frameworks is broadened. Carbon stored will either be rewarded with a direct payment, perhaps equal to the level of a carbon emission tax, or will generate emission credits to be traded freely on carbon markets (Ricci, 2012). As discussed previously, such mechanisms will require significantly improved monitoring and quantification methodologies for some GGR options (see Table 4), as well as systems to account for risks of impermanence of stored carbon and mechanisms for ensuring broader sustainability of contributing projects. Different GGR approaches will require different methodologies, and will therefore need to be introduced on a case-by-case basis. Lessons learned from existing offset systems incorporating afforestation, such as the Californian Emissions Trading Scheme and the UNFCCC CDM, should inform GGR integration (World Bank, 2014).

As carbon trading expands in scope, such schemes should be carefully designed to ensure GGR is best used to attain the desired goals. McLaren (2012) notes that the level of the emissions cap will determine whether carbon market integration results in greater overall mitigation or simply reduces the costs of meeting the same targets by displacing more costly measures. Additionally, the cumulative sequestration capacity of some GGR approaches is finite: biomass sinks may saturate, for example, or local geological storage may be filled (Lenton, 2010; McLaren, 2012). Even the net economic benefits of GGR could therefore be reduced if this limited capacity is used to offset cheaper, more feasible mitigation options in the short term, rather than to offset more challenging emissions (McLaren, 2011). Whatever the final form, however, an important first step to initiating this discourse is the public commitment to future recognition of removed GHGs within such frameworks. Work can then begin on the best ways to integrate each technology into the accreditation and support systems that now cover emissions reduction. Ultimately, this commitment is the first step towards bringing GGR into accreditation and policy “parity” with emissions reduction in the long term, to the extent that this is appropriate.

3.3.2.4. Build system flexibility to avoid lock-out. If ambitious proposals for rapid, large-scale roll-out of GGR technologies such as BECCS or DAC in the long-term are to have any chance of being realised, there must be significant groundwork to ensure the broader landscape is favourable to such a scale-up. The above three steps all go some way to reducing lock-out risks by encouraging early development of the technologies, skills, institutions, regulatory systems and demand pull mechanisms necessary. However, there are also further challenges and barriers specific to each technology. It is therefore important to engage closely and openly with stakeholders in each system to identify some of the risks and requirements. Prediction of technology evolution over such timescales is associated with large uncertainties, and the desirability of some of these systems at scale is not yet clear, so detailed policy “roadmaps” for long-term GGR deployment may be premature. However, it is nonetheless important that near-term policy decisions with bearing on GGR keep the opportunity of future deployment open as far as possible. This abstract discussion is best illustrated with some examples revealed through the aforementioned analysis of BECCS (Lomax, 2013). BECCS technologies encounter significant risks of lock-out as a consequence of combining two dissimilar clean energy technologies (CCS and bioenergy). Allowing the bioenergy industry and the fossil-CCS industry to develop independently risks development of long-lived physical assets, technologies, business models and skills bases that are optimised for the particular requirements of each industry and make their subsequent combination into BECCS challenging. An illustrative list of challenges and possible policy solutions are given below:


One route by which BECCS power plants could develop is




through retrofitting of pure bioenergy plants with CCS technology and infrastructure. Should bioenergy policy be developed without planning for this, such plants may end up sited or designed in such a way that such retrofit is unfeasible. A possible route to improving flexibility would be to explore low-cost Capture-Ready requirements or incentives for bioenergy plants, although this raises similar challenges to those identified in the fossil fuel equivalent (Markusson and Haszeldine, 2010). Another route to BECCS is conversion of fossil-CCS plants to be largely or completely biomass-fired. Co-firing at low levels ( o15%) is straightforward in current-generation coal plants,

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for example, but higher levels (up to 50%) require increasing levels of biomass pre-processing and limited boiler modification (Cremers, 2009; Dai et al., 2008). Conversion to 100% biomass firing requires significant plant refit to account for different heat content, mechanical properties and ash compositions of biomass. Again, possible solutions include early R&D investment into the technical challenges and pre-processing options for co-firing and conversion of different fossil CCS options, and incentives that encourage plant design to account for future refit. The physical and chemical properties of biomass and typical smaller scale of biomass power plants mean that the optimal choices of CCS technology for BECCS plants are likely to differ from those in fossil plants (Bhave, 2012). It is therefore important that RD&D funding is directed to these technologies (such as chemical looping) as well as those more suited to fossil fuel combustion.

4. Conclusions and policy recommendations A large class of valuable climate change mitigation approaches aiming to enhance global carbon sinks, greenhouse gas removal, has been largely neglected in climate policy discussion so far in favour of an emphasis on emissions control and fuel switching. The current policy framing of greenhouse gas removal is as a class of technologies distinct from the conventional emissions reduction approaches. It tends to emphasise their potential role in recovering from overshoot of climate targets, and hence focuses the debate on deployment at huge scale and in the distant future. This is an unhelpful basis for policy discussion for several reasons. First, it emphasises actions on such a large scale that any would likely entail major environmental and social consequences, and so over-emphasises the need for regulation and precaution over possible advantages. Second, it emphasises a role for GGR concentrated towards the end of the century and beyond, supported by results of integrated assessment modelling. This gives the false impression that effective policy engagement with GGR in the nearterm is unnecessary and, in fact, of little value given the uncertainties associated with planning over such timescales. Third, it obscures the value that GGR could bring to near-term emissions reduction efforts in parallel with conventional approaches. GGR technologies are diverse, but they all bring to mitigation the key advantage of physically decoupling emissions reduction from emissions sources. This gives them an economically and strategically valuable role to play in offsetting emissions that are impractical or very expensive to eliminate through conventional mitigation. Furthermore, since many GGR technologies have been overlooked in climate policy to date, there are likely to be substantial opportunities for low-cost emissions reduction through GGR systems, especially through biomass and soil carbon methods associated with low capital costs and potential for broader benefits to environment and soil quality. In the near-term, many GGR systems could represent valuable additions to the emissions reduction toolbox. However, the sector is immature and various technologies are subject to large uncertainties surrounding cost, potential scale, LCA emissions, potential side effects and particularly monitoring and accounting for stored carbon that pose substantial barriers to integrating them directly into existing policy. Furthermore, the long-term prospects of many are tied to complex social and environmental issues. On the other hand, delaying policy consideration of these approaches risks missing near-term opportunities and locking-out the long term potential. The overriding challenge for policy in the near future in this field is therefore to identify steps that can support the

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successful development of these systems while allowing for the uncertainties. However, the challenges and uncertainties of many systems are not significantly greater than those policymakers are already facing with current and planned mitigation measures such as afforestation, bioenergy and CCS. This suggests that effective policy support for GGR can be developed flexibly in tandem with the growing state of knowledge and evolving mitigation policy. Based on these principles and a detailed analysis of one GGR technology, bioenergy with carbon capture and storage, this paper therefore argues for four principles to guide an effective policy approach to this area: 1. Support scientific research and technical demonstration to address technology-specific uncertainties and challenges, to constrain costs and risks and to develop monitoring methodologies. 2. Develop support for a range of early, low-risk and low-cost GGR opportunities that can already provide economical GHG reductions, ideally through existing policy mechanisms. 3. Commit to integration of GGR into wider policy support, carbon price mechanisms and accounting over the longer term to stimulate to investment, R&D, innovation and planning for future opportunities. 4. Develop and identify steps that address future barriers to GGR and lay the groundwork in relevant systems, in order that future opportunities are not locked-out and can be deployed rapidly when they become attractive.

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