Bioethanol potential from miscanthus with low ILUC risk in the province of Lublin,Poland

Increasing production of biofuels has led to concerns about indirect land‐use change (ILUC). So far, significant efforts have been made to assess potential ILUC effects. But limited attention has been paid to strategies for reducing the extent of ILUC and controlling the type of LUC. This case study assesses five key ILUC mitigation measures to quantify the low‐ILUC‐risk production potential of miscanthus‐based bioethanol in Lublin province (Poland) in 2020. In 2020, a total area of 196 to 818 thousand hectare of agricultural land could be made available for biomass production by realizing above‐baseline yield developments (95–413 thousand ha), increased food chain efficiencies (9–30 thousand ha) and biofuel feedstock production on underutilized lands (92–375 thousand ha). However, a maximum 203–269 thousand hectare is considered legally available (not protected) and biophysically suitable for miscanthus production. The resulting low‐ILUC‐risk bioethanol production potential ranges from 12 to 35 PJ per year. The potential from this region alone is higher than the national Polish target for second‐generation bioethanol consumption of 9 PJ in 2020. Although the sustainable implementation potential may be lower, the province of Lublin could play a key role in achieving this target. This study shows that the mitigation or prevention of ILUC from bioenergy is only possible when an integrated perspective is adopted on the agricultural and bioenergy sectors. Governance and policies on planning and implementing ILUC mitigation are considered vital for realizing a significant bioenergy potential with low ILUC risk. One important aspect in this regard is monitoring the risk of ILUC and the implementation of ILUC mitigation measures. Key parameters for monitoring are land use, land cover and crop yields.     

How is biodiversity protection influencing the potential for bioenergy feedstock production on grasslands?

Sustainable feedstock supply is a critical issue for the bioenergy sector. One concern is that feedstock production will impact biodiversity. We analyze how this concern is addressed in assessments of biomass supply potentials and in selected governance systems in the EU and Brazil, including the EU Renewable Energy Directive (RED), the EU Common Agricultural Policy (CAP), and the Brazilian Forest Act. The analysis focuses on grasslands and includes estimates of the amount of grassland area (and corresponding biomass production volume) that would be excluded from cultivation in specific biodiversity protection scenarios. The reviewed assessments used a variety of approaches to identify and exclude biodiverse grasslands as unavailable for bioenergy. Because exclusion was integrated with other nature protection considerations, quantification of excluded grassland areas was often not possible. The RED complements and strengthens the CAP in terms of biodiversity protection. Following the RED, an estimated 39%–48% (about 9–11 Mha) and 15%–54% (about 10–38 Mha) of natural and non‐natural grassland, respectively, may be considered highly biodiverse in EU‐28. The estimated biomass production potential on these areas corresponds to some 1–3 and 1.5–10 EJ/year for natural and non‐natural grassland, respectively (depending on area availability and management intensity). However, the RED lacks clear definitions and guidance, creating uncertainty about its influence on grassland availability for bioenergy feedstock production. For Brazil, an estimated 16%–77% (about 16–76 Mha) and 1%–32% (about 7–24 Mha) of natural and non‐natural grassland, respectively, may be considered highly biodiverse. In Brazil, ecological–economic zoning was found potentially important for grassland protection. Further clarification of grassland definitions and delineation in regulations will facilitate a better understanding of the prospects for bioenergy feedstock production on grasslands, and the impacts of bioenergy deployment on biodiversity.     

Impact of agronomic uncertainty in biomass production and endogenous commodity prices on cellulosic biofuel feedstock composition

This study evaluates the effect of agronomic uncertainty on bioenergy crop production as well as endogenous commodity and biomass prices on the feedstock composition of cellulosic biofuels under a binding mandate in the United States. The county‐level simulation model focuses on both field crops (corn, soybean, and wheat) and biomass feedstocks (corn stover, wheat straw, switchgrass, and Miscanthus). In addition, pasture serves as a potential area for bioenergy crop production. The economic model is calibrated to 2022 in terms of yield, crop demand, and baseline prices and allocates land optimally among the alternative crops given the binding cellulosic biofuel mandate. The simulation scenarios differ in terms of bioenergy crop type (switchgrass and Miscanthus) and yield, biomass production inputs, and pasture availability. The cellulosic biofuel mandates range from 15 to 60 billion L. The results indicate that the 15 and 30 billion L mandates in the high production input scenarios for switchgrass and Miscanthus are covered entirely by agricultural residues. With the exception of the low production input for Miscanthus scenario, the share of agricultural residues is always over 50% for all other scenarios including the 60 billion L mandate. The largest proportion of agricultural land dedicated to either switchgrass or Miscanthus is found in the southern Plains and the southeast. Almost no bioenergy crops are grown in the Midwest across all scenarios. Changes in the prices for the three commodities are negligible for cellulosic ethanol mandates because most of the mandate is met with agricultural residues. The lessons learned are that (1) the share of agricultural residue in the feedstock mix is higher than previously estimated and (2) for a given mandate, the feedstock composition is relatively stable with the exception of one scenario.     

Marginal lands for bioenergy in China; an outlook in status,potential and management

Energy consumption and CO₂ emissions have been increasing continuously over the past few decades in China and there is a pressing need to replace the fossil fuel‐based economy with an efficient low‐carbon system, tailor‐made to future requirements. China is starting an energy transition with the aim of building an energy system for the future. China has made tremendous progress in increasing the amount of renewable energy and reducing the cost of renewable energy over the last 20 years. According to the 14th 5 year plan, China aims to incorporate 20% of renewable energy to the primary energy mix and attain 27% reduction in CO₂ emissions. Bioenergy crops constitute a significant proportion of biomass‐based bioenergy and have recently been promoted by the Chinese Government to help overcome food and fuel conflict. Steps are being taken to promote bioenergy crops on marginal lands in China, and various regions across the country with soil marginality have been evaluated for bioenergy crop cultivation. The present paper reviews the status of bioenergy in China and the potential status of marginal lands from different regions of China. It also elaborates on some of the policies, subsidies and incentives allocated by the Chinese Government for the promotion of biomass‐based energy. Land management and plant improvement strategies were discussed, which are effective in making marginal lands suitable for bioenergy crop cultivation. Managing planting strategies, intercropping and crop rotation are effective management practices used in China for the utilization of marginal lands. A national investigation is desirable for creating an inventory of technical and economic potential of biomass feedstocks that could be planted on marginal lands. This would assist with highlighting the pros and cons of using marginal lands for bioenergy production and effective policy making.     

Bioenergy and climate change mitigation: an assessment

Bioenergy deployment offers significant potential for climate change mitigation, but also carries considerable risks. In this review, we bring together perspectives of various communities involved in the research and regulation of bioenergy deployment in the context of climate change mitigation: Land‐use and energy experts, land‐use and integrated assessment modelers, human geographers, ecosystem researchers, climate scientists and two different strands of life‐cycle assessment experts. We summarize technological options, outline the state‐of‐the‐art knowledge on various climate effects, provide an update on estimates of technical resource potential and comprehensively identify sustainability effects. Cellulosic feedstocks, increased end‐use efficiency, improved land carbon‐stock management and residue use, and, when fully developed, BECCS appear as the most promising options, depending on development costs, implementation, learning, and risk management. Combined heat and power, efficient biomass cookstoves and small‐scale power generation for rural areas can help to promote energy access and sustainable development, along with reduced emissions. We estimate the sustainable technical potential as up to 100 EJ: high agreement; 100–300 EJ: medium agreement; above 300 EJ: low agreement. Stabilization scenarios indicate that bioenergy may supply from 10 to 245 EJ yr^?1 to global primary energy supply by 2050. Models indicate that, if technological and governance preconditions are met, large‐scale deployment (>200 EJ), together with BECCS, could help to keep global warming below 2° degrees of preindustrial levels; but such high deployment of land‐intensive bioenergy feedstocks could also lead to detrimental climate effects, negatively impact ecosystems, biodiversity and livelihoods. The integration of bioenergy systems into agriculture and forest landscapes can improve land and water use efficiency and help address concerns about environmental impacts. We conclude that the high variability in pathways, uncertainties in technological development and ambiguity in political decision render forecasts on deployment levels and climate effects very difficult. However, uncertainty about projections should not preclude pursuing beneficial bioenergy options.     

Demand for biomass to meet renewable energy targets in the United States: implications for land use

Renewable energy policies in the electricity and transportation sectors in the United States are expected to create demand for biomass and food crops (corn) that could divert land from food crop production. We develop a dynamic, open‐economy, price‐endogenous multi‐market model of the US agricultural, electricity and transportation sectors to endogenously determine the quantity and mix of bioenergy likely to be required to meet the state Renewable Portfolio Standards (RPSs) and the federal Renewable Fuel Standard (RFS) if implemented independently or jointly (RFS & RPS) over the 2007–2030 period and their implications for the extent and spatial pattern of diversion of land from other uses for biomass feedstock production. We find that the demand for biomass ranges from 100 million metric tons (MMT) under the RPS alone to 310 MMT under the RFS & RPS; 70% of the biomass in the latter case can be met by crop and forest residues, while the rest can be met by devoting 3% of cropland to energy crop production with 80% of this being marginal land. Our findings show significant potential to meet current renewable energy goals by expanding high‐yielding energy crop production on marginal land and using residues without conflicting with food crop production.     

A quantitative assessment of crop residue feedstocks for biofuel in North and Northeast China

Crop residue resources may affect soil quality, global carbon balance, and stability of crop production, but also contribute to future energy security. This study was performed to evaluate the spatial and temporal variation in residue quantities of field crops in five provinces of North China (NC) and three provinces of Northeast China (NEC). The availability of biomass resources was derived from statistical data on crop yields for all crops on the provincial and even county level. We found that cereals – wheat, maize, and rice – were the biggest resource of crop residue feedstock. The ranking of these crops as a source of biomass for bioenergy is determined by the acreage in each region and the crop‐specific yield. Annually, the average amount of total residue of 83.0 Mt (Mt = Mega tonnes) in NC (16.9 Million ha) comprised 76.6 Mt field residues and 6.4 Mt process residues on an air‐dried basis. The average amount of total biomass residue of 105.7 Mt in NEC (19.8 Million ha) comprised 92.8 Mt field residues and 12.9 Mt process residues. Averaged for 2008, 2009, and 2010, the total standard coal equivalent (SCE) in NC amounted to 46.4 Mt, which comprised 42.4 Mt field residues and of 3.9 Mt process residues. In NEC, the SCE value of 57.0 Mt comprised 49.7 Mt field residues and 7.4 Mt process residues. The temporal availability of field residues was mainly concentrated in the period between July and September, followed by the period between October and December. In the period between July and September, the amount of field residue available amounted to 40.9 and 53.1 Mt in NC and NEC, respectively. An accurate assessment of field residues may guide policy makers and industry to optimize the utilization of the crop residue resource.     

Modeled spatial assessment of biomass productivity and technical potential of Miscanthus × giganteus,Panicum virgatum L., and Jatropha on marginal land in China

This article identifies marginal land technically available for the production of energy crops in China, compares three models of yield prediction for Miscanthus × giganteus, Panicum virgatum L. (switchgrass), and Jatropha, and estimates their spatially specific yields and technical potential for 2017. Geographic Information System (GIS) analysis of land use maps estimated that 185 Mha of marginal land was technically available for energy crops in China without using areas currently used for food production. Modeled yields were projected for Miscanthus × giganteus, a GIS‐based Environmental Policy Integrated Climate model for switchgrass and Global Agro‐Ecological Zone model for Jatropha. GIS analysis and MiscanFor estimated more than 120 Mha marginal land was technically available for Miscanthus with a total potential of 1,761 dry weight metric million tonne (DW Mt)/year. A total of 284 DW Mt/year of switchgrass could be obtained from 30 Mha marginal land, with an average yield of 9.5 DW t ha^?1 year^?1. More than 35 Mha marginal land was technically available for Jatropha, delivering 9.7 Mt/year of Jatropha seed. The total technical potential from available marginal land was calculated as 31.7 EJ/year for Miscanthus, 5.1 EJ/year for switchgrass, and 0.13 EJ/year for Jatropha. A total technical bioenergy potential of 34.4 EJ/year was calculated by identifying best suited crop for each 1 km² grid cell based on the highest energy value among the three crops. The results indicate that the technical potential per hectare of Jatropha is unable to compete with that of the other two crops in each grid cell. This modeling study provides planners with spatial overviews that demonstrate the potential of these crops and where biomass production could be potentially distributed in China which needs field trials to test model assumptions and build experience necessary to translate into practicality.     

Global simulation of bioenergy crop productivity: analytical framework and case study for switchgrass

A global energy crop productivity model that provides geospatially explicit quantitative details on biomass potential and factors affecting sustainability would be useful, but does not exist now. This study describes a modeling platform capable of meeting many challenges associated with global‐scale agro‐ecosystem modeling. We designed an analytical framework for bioenergy crops consisting of six major components: (i) standardized natural resources datasets, (ii) global field‐trial data and crop management practices, (iii) simulation units and management scenarios, (iv) model calibration and validation, (v) high‐performance computing (HPC) simulation, and (vi) simulation output processing and analysis. The HPC‐Environmental Policy Integrated Climate (HPC‐EPIC) model simulated a perennial bioenergy crop, switchgrass (Panicum virgatum L.), estimating feedstock production potentials and effects across the globe. This modeling platform can assess soil C sequestration, net greenhouse gas (GHG) emissions, nonpoint source pollution (e.g., nutrient and pesticide loss), and energy exchange with the atmosphere. It can be expanded to include additional bioenergy crops (e.g., miscanthus, energy cane, and agave) and food crops under different management scenarios. The platform and switchgrass field‐trial dataset are available to support global analysis of biomass feedstock production potential and corresponding metrics of sustainability.     

Global advanced bioenergy potential under environmental protection policies and societal transformation measures

Bioenergy plays an important role in low greenhouse gas stabilization scenarios. Among various possible sources of bioenergy, dedicated bio‐crops could contribute to most of the potential. However, large scale bio‐crop deployment raises sustainability concerns. Policies to alleviate the pressure of bio‐crops on the terrestrial environment can affect bioenergy potential and production costs. Here, we estimated the maximum bioenergy potential under environmental protection policies (biodiversity and soil protection) and societal transformation measures from demand and supply side (demand‐side policy includes sustainable diet; supply‐side policy includes advanced technology and trade openness for food) by using an integrated assessment modelling framework, which consists of a general equilibrium model (Asian‐Pacific Integrated Model/Computable General Equilibrium) and a spatial land use allocation model (Asian‐Pacific Integrated Model/Platform for Land‐Use and Environmental Model). We found that the global advanced bioenergy potential under no policy was 245 EJ/year and that 192 EJ/year could be produced under US$5/GJ. These figures were 149 EJ/year and 110 EJ/year, respectively, under a full environmental policy. Biodiversity protection has a greater impact than soil protection due to its larger coverage and stronger implementation. Societal transformation measures effectively increase them to 186 EJ/year and 143 EJ/year, respectively, even under full environmental policies. These results imply that the large‐scale bioenergy deployment possibly needed for the climate target to limit the global mean temperature increase well below 2°C compared to the preindustrial level might face a trade‐off with environmental protection targets and that possible mitigation pathways in harmony with other environmental issues need to be explored.     

Functional group and fertilization affect the composition and bioenergy yields of prairie plants

Prairies used for bioenergy production have potential to generate marketable products while enhancing environmental quality, but little is known about how prairie species composition and nutrient management affect the suitability of prairie biomass for bioenergy production. We determined how functional‐group identity and nitrogen fertilization affected feedstock characteristics and estimated bioenergy yields of prairie plants, and compared those prairie characteristics to that of corn stover. We tested our objectives with a field experiment that was set up as a 5 × 2 incomplete factorial design with C₃ grasses, C₄ grasses, legumes, and multi‐functional‐group mixtures grown with and without nitrogen fertilizer; a fertilized corn treatment was also included. We determined cell wall, hemicellulose, cellulose, and ash concentrations; ethanol conversion ratios; gross caloric ratios; aboveground biomass production; ethanol yields; and energy yields for all treatments. Prairie functional‐group identity affected the biomass feedstock characteristics, whereas nitrogen fertilization did not. Functional group and fertilization had a strong effect on aboveground biomass production, which was the major predictor of ethanol and energy yields. C₄ grasses, especially when fertilized, had among the most favorable bioenergy characteristics with high estimated ethanol conversion ratios and nongrain biomass production, relatively high gross caloric ratios, and low ash concentrations. The bioenergy characteristics of corn stover, from an annual C₄ grass, were similar to those of the biomass of perennial C₄ grasses. Both functional‐group composition and nitrogen fertility management were found to be important in optimizing bioenergy production from prairies.     

Should China subsidize cofiring to meet its 2020 bioenergy target? A spatio‐techno‐economic analysis

China has developed ambitious bioenergy installation targets as part of its broader goals to increase its renewable energy‐generating capacity and decarbonize its economy. A key target feedstock for bioenergy is the 800 million tonnes of agricultural residues that China produces each year. At present, the main financial incentive to support bioenergy generation from agricultural residues is a feed‐in‐tariff provided for bioenergy that is produced by units that take 80% or more of their feedstock energy from biomass. Although this policy has catalysed the construction of many bioenergy units, there are reports that these projects are experiencing serious financial and technical problems, leading to low operational efficiency and even closure. An alternative option for China's agricultural residues is cofiring with coal in existing power stations. However, this is currently unprofitable for power station operators, as cofiring is not eligible for financial assistance through the bioenergy feed‐in‐tariff. In the light of China's ambitious target to install 30GW of bioenergy generation capacity by 2020, this study investigates the extent to which extension of the bioenergy feed‐in‐tariff to include cofiring could contribute towards this goal. The results suggest that 39% of China's straw energy resources are located within 50 km of a power station. Assuming cofiring ratios of up to 10% coal energy replacement, an annual 89–117TWh of electricity could be generated by cofiring agricultural residues collected within 50 km radii of power stations. If China extends its bioenergy subsidies to include cofiring, an annual 62–92TWh can be produced at an internal rate of return of 8% or more. This equates to 42–62% of the bioenergy generation that China might expect if it met its 2020 target of installing 30GW of bioenergy capacity. Overall, this indicates a strong case for the Chinese government to extend its existing bioenergy feed‐in‐tariff to include cofiring at low energy replacement ratios.     

Range and uncertainties in estimating delays in greenhouse gas mitigation potential of forest bioenergy sourced from Canadian forests

Accurately assessing the delay before the substitution of fossil fuel by forest bioenergy starts having a net beneficial impact on atmospheric CO₂ is becoming important as the cost of delaying GHG emission reductions is increasingly being recognized. We documented the time to carbon (C) parity of forest bioenergy sourced from different feedstocks (harvest residues, salvaged trees, and green trees), typical of forest biomass production in Canada, used to replace three fossil fuel types (coal, oil, and natural gas) in heating or power generation. The time to C parity is defined as the time needed for the newly established bioenergy system to reach the cumulative C emissions of a fossil fuel, counterfactual system. Furthermore, we estimated an uncertainty period derived from the difference in C parity time between predefined best‐ and worst‐case scenarios, in which parameter values related to the supply chain and forest dynamics varied. The results indicate short‐to‐long ranking of C parity times for residues < salvaged trees < green trees and for substituting the less energy‐dense fossil fuels (coal < oil < natural gas). A sensitivity analysis indicated that silviculture and enhanced conversion efficiency, when occurring only in the bioenergy system, help reduce time to C parity. The uncertainty around the estimate of C parity time is generally small and inconsequential in the case of harvest residues but is generally large for the other feedstocks, indicating that meeting specific C parity time using feedstock other than residues is possible, but would require very specific conditions. Overall, the use of single parity time values to evaluate the performance of a particular feedstock in mitigating GHG emissions should be questioned given the importance of uncertainty as an inherent component of any bioenergy project.     

Land‐use legacies regulate decomposition dynamics following bioenergy crop conversion

Land‐use conversion into bioenergy crop production can alter litter decomposition processes tightly coupled to soil carbon and nutrient dynamics. Yet, litter decomposition has been poorly described in bioenergy production systems, especially following land‐use conversion. Predicting decomposition dynamics in postconversion bioenergy production systems is challenging because of the combined influence of land‐use legacies with current management and litter quality. To evaluate how land‐use legacies interact with current bioenergy crop management to influence litter decomposition in different litter types, we conducted a landscape‐scale litterbag decomposition experiment. We proposed land‐use legacies regulate decomposition, but their effects are weakened under higher quality litter and when current land use intensifies ecosystem disturbance relative to prior land use. We compared sites left in historical land uses of either agriculture (AG) or Conservation Reserve Program grassland (CRP) to those that were converted to corn or switchgrass bioenergy crop production. Enzyme activities, mass loss, microbial biomass, and changes in litter chemistry were monitored in corn stover and switchgrass litter over 485 days, accompanied by similar soil measurements. Across all measured variables, legacy had the strongest effect (P < 0.05) relative to litter type and current management, where CRP sites maintained higher soil and litter enzyme activities and microbial biomass relative to AG sites. Decomposition responses to conversion depended on legacy but also current management and litter type. Within the CRP sites, conversion into corn increased litter enzymes, microbial biomass, and litter protein and lipid abundances, especially on decomposing corn litter, relative to nonconverted CRP. However, conversion into switchgrass from CRP, a moderate disturbance, often had no effect on switchgrass litter decomposition parameters. Thus, legacies shape the direction and magnitude of decomposition responses to bioenergy crop conversion and therefore should be considered a key influence on litter and soil C cycling under bioenergy crop management.     

A spatiotemporal assessment of field residues of rice,maize, and wheat at provincial and county levels in China

China has a huge resource potential for biomass‐based renewable energy development, but the resources of field residues are still not effectively used. Rice, maize, and wheat made up 89% of staple crop production in China in 2009. A comprehensive assessment of field residues of these three crops is necessary for the development of biomass‐based industries. This research was based on multiyear county‐level data of crop production, area and yield, as well as the crop phenology information from agrometeorological stations. Spatial and temporal analyses were conducted to quantify the spatial patterns, seasonal variations, and temporal trends of the three major field residues. The mean amount of field residue of rice, maize, and wheat was 470.8 Mt/year from 2002 to 2009. Rice residue topped the field residues at 188.5 Mt/year, followed by maize (152.6 Mt/year) and wheat (129.8 Mt/year). The resource supply of field residues varied temporally throughout the season, where peak months are May, June, September, and October. The resources of all three field residues increased from 2002 to 2009, topped by maize residues at a rate of 10.0 Mt/year. Spatially, high production counties had the fast growth rate and a strong positive spatial autocorrelation. The results showed that the intersection area of East and South Central regions has a spatially concentrated residue density and a stable supply for 5 months. The region can be considered as a suitable region for bioenergy development. A better understanding of spatial and temporal distribution of crop residues could facilitate strategic and tactical bioenergy planning.     

Sugarcane as a Bioenergy Source: History,Performance, and Perspectives for Second-Generation Bioethanol

For hundreds of years, sugarcane has been a main source of sugar, used as a sweetener, and alcohol, fermented from the plant juice. The high cost of petroleum towards the end of the twentieth century stimulated the development of new fermentation technologies for producing economically viable bioethanol from sugarcane as an alternative to importing petroleum. More recently, awareness of the effects of greenhouse gas emissions due to the global climate changes propelled bioethanol as a viable renewable fuel. Consequently, sugarcane gained importance as a bioenergy feedstock. However, the lack of knowledge about sugarcane physiology, notably on aspects of photosynthesis and source–sink relationship, has slowed the advance of this expanding bioenergy-producing system. Besides the changes in source–sink relationship, another option to increase bioethanol production even more would be to use a greater fraction of the total biomass of plants, i.e., not only the soluble sugars but also the sugars present in the cell wall fractions. Here, we review the history of sugarcane as a bioenergy crop and discuss some of the relevant routes that could be adopted in the near future to make sugarcane an even better feedstock for producing biofuels.     

Mitigation potential and environmental impact of centralized versus distributed BECCS with domestic biomass production in Great Britain

New contingency policy plans are expected to be published by the United Kingdom government to set out urgent actions, such as carbon capture and storage, greenhouse gas removal and the use of sustainable bioenergy to meet the greenhouse gas reduction targets of the 4th and 5th Carbon Budgets. In this study, we identify two plausible bioenergy production pathways for bioenergy with carbon capture and storage (BECCS) based on centralized and distributed energy systems to show what BECCS could look like if deployed by 2050 in Great Britain. The extent of agricultural land available to sustainably produce biomass feedstock in the centralized and distributed energy systems is about 0.39 and 0.5 Mha, providing approximately 5.7 and 7.3 Mt_DM/year of biomass respectively. If this land‐use change occurred, bioenergy crops would contribute to reduced agricultural soil GHG emission by 9 and 11 /year in the centralized and distributed energy systems respectively. In addition, bioenergy crops can contribute to reduce agricultural soil ammonia emissions and water pollution from soil nitrate leaching, and to increase soil organic carbon stocks. The technical mitigation potentials from BECCS lead to projected CO₂ reductions of approximately 18 and 23 /year from the centralized and distributed energy systems respectively. This suggests that the domestic supply of sustainable biomass would not allow the emission reduction target of 50 /year from BECCS to be met. To meet that target, it would be necessary to produce solid biomass from forest systems on 0.59 or 0.49 Mha, or alternatively to import 8 or 6.6 Mt_DM/year of biomass for the centralized and distributed energy system respectively. The spatially explicit results of this study can serve to identify the regional differences in the potential capture of CO₂ from BECCS, providing the basis for the development of onshore CO₂ transport infrastructures.     

Energy crops: current status and future prospects

Energy crops currently contribute a relatively small proportion to the total energy produced from biomass each year, but the proportion is set to grow over the next few decades. This paper reviews the current status of energy crops and their conversion technologies, assesses their potential to contribute to global energy demand and climate mitigation over the next few decades, and examines the future prospects. Previous estimates have suggested a technical potential for energy crops of～400 EJ yr^?1 by 2050. In a new analysis based on energy crop areas for each of the IPCC SRES scenarios in 2025 (as projected by the IMAGE 2.2 integrated assessment model), more conservative dry matter and energy yield estimates and an assessment of the impact on non‐CO₂ greenhouse gases were used to estimate the realistically achievable potential for energy crops by 2025 to be between 2 and 22 EJ yr^?1, which will offset～100–2070 Mt CO₂‐eq. yr^?1. These results suggest that additional production of energy crops alone is not sufficient to reduce emissions to meet a 550 μmol mol^?1 atmospheric CO₂ stabilization trajectory, but is sufficient to form an important component in a portfolio of climate mitigation measures, as well as to provide a significant sustainable energy resource to displace fossil fuel resources. Realizing the potential of energy crops will necessitate optimizing the dry matter and energy yield of these crops per area of land through the latest biotechnological routes, with or without the need for genetic modification. In future, the co‐benefits of bioenergy production will need to be optimized and methods will need to be developed to extract and refine high‐value products from the feedstock before it is used for energy production.     

A reassessment of global bioenergy potential in 2050

Many climate change mitigation strategies rely on strong projected growth in biomass energy, supported by literature estimating high future bioenergy potential. However, expectations to 2050 are highly divergent. Examining the most widely cited studies finds that some assumptions in these models are inconsistent with the best available evidence. By identifying literature‐supported, up‐to‐date assumptions for parameters including crop yields, land availability, and costs, we revise upper‐end estimates of potential biomass availability from dedicated energy crops. Even allowing for the conversion of virtually all ‘unused’ grassland and savannah, we find that the maximum plausible limit to sustainable energy crop production in 2050 would be 40–110 EJ yr^?1. Combined with forestry, crop residues, and wastes, the maximum limit to long‐term total biomass availability is 60–120 EJ yr^?1 in primary energy. After accounting for current trends in bioenergy allocation and conversion losses, we estimate maximum potentials of 10–20 EJ yr^?1 of biofuel, 20–40 EJ yr^?1 of electricity, and 10–30 EJ yr^?1 of heating in 2050. These findings suggest that many technical projections and aspirational goals for future bioenergy use could be difficult or impossible to achieve sustainably.     

Investment risk in bioenergy crops

Perennial, cellulosic bioenergy crops represent a risky investment. The potential for adoption of these crops depends not only on mean net returns, but also on the associated probability distributions and on the risk preferences of farmers. Using 6‐year observed crop yield data from highly productive and marginally productive sites in the southern Great Lakes region and assuming risk neutrality, we calculate expected breakeven biomass yields and prices compared to corn (Zea mays L.) as a benchmark. Next we develop Monte Carlo budget simulations based on stochastic crop prices and yields. The crop yield simulations decompose yield risk into three components: crop establishment survival, time to maturity, and mature yield variability. Results reveal that corn with harvest of grain and 38% of stover (as cellulosic bioenergy feedstock) is both the most profitable and the least risky investment option. It dominates all perennial systems considered across a wide range of farmer risk preferences. Although not currently attractive for profit‐oriented farmers who are risk neutral or risk averse, perennial bioenergy crops have a higher potential to successfully compete with corn under marginal crop production conditions.