Environmental implications of the use of agro‐industrial residues for biorefineries: application of a deterministic model for indirect land‐use changes

Biorefining agro‐industrial biomass residues for bioenergy production represents an opportunity for both sustainable energy supply and greenhouse gas (GHG) emissions mitigation. Yet, is bioenergy the most sustainable use for these residues? To assess the importance of the alternative use of these residues, a consequential life cycle assessment (LCA) of 32 energy‐focused biorefinery scenarios was performed based on eight selected agro‐industrial residues and four conversion pathways (two involving bioethanol and two biogas). To specifically address indirect land‐use changes (iLUC) induced by the competing feed/food sector, a deterministic iLUC model, addressing global impacts, was developed. A dedicated biochemical model was developed to establish detailed mass, energy, and substance balances for each biomass conversion pathway, as input to the LCA. The results demonstrated that, even for residual biomass, environmental savings from fossil fuel displacement can be completely outbalanced by iLUC, depending on the feed value of the biomass residue. This was the case of industrial residues (e.g. whey and beet molasses) in most of the scenarios assessed. Overall, the GHGs from iLUC impacts were quantified to 4.1 t CO₂‐eq.ha^?1_demanded yr^?1 corresponding to 1.2–1.4 t CO₂‐eq. t^?1 dry biomass diverted from feed to energy market. Only, bioenergy from straw and wild grass was shown to perform better than the alternative use, as no competition with the feed sector was involved. Biogas for heat and power production was the best performing pathway, in a short‐term context. Focusing on transport fuels, bioethanol was generally preferable to biomethane considering conventional biogas upgrading technologies. Based on the results, agro‐industrial residues cannot be considered burden‐free simply because they are a residual biomass and careful accounting of alternative utilization is a prerequisite to assess the sustainability of a given use. In this endeavor, the iLUC factors and biochemical model proposed herein can be used as templates and directly applied to any bioenergy consequential study involving demand for arable land.     

Competing uses of biomass for energy and chemicals: implications for long‐term global CO2 mitigation potential

Biomass is considered a low carbon source for various energy or chemical options. This paper assesses it's different possible uses, the competition between these uses, and the implications for long‐term global energy demand and energy system emissions. A scenario analysis is performed using the TIMER energy system model. Under baseline conditions, 170 EJ yr^?1 of secondary bioenergy is consumed in 2100 (approximately 18% of total secondary energy demand), used primarily in the transport, buildings and nonenergy (chemical production) sectors. This leads to a reduction of 9% of CO₂ emissions compared to a counterfactual scenario where no bioenergy is used. Bioenergy can contribute up to 40% reduction in emissions at carbon taxes greater than 500/tC. As higher CO₂ taxes are applied, bioenergy is increasingly diverted towards electricity generation. Results are more sensitive to assumptions about resource availability than technological parameters. To estimate the effectiveness of bioenergy in specific sectors, experiments are performed in which bioenergy is only allowed in one sector at a time. The results show that cross‐sectoral leakage and emissions from biomass conversion limit the total emission reduction possible in each sector. In terms of reducing emissions per unit of bioenergy use, we show that the use of bioelectricity is the most effective, especially when used with carbon capture and storage. However, this technology only penetrates at a high carbon price (>100/tC) and competition with transport fuels may limit its adoption.     

The role of bioenergy for global deep decarbonization: CO2 removal or low‐carbon energy?

Bioenergy is expected to have a prominent role in limiting global greenhouse emissions to meet the climate change target of the Paris Agreement. Many studies identify negative emissions from bioenergy generation with carbon capture and storage (BECCS) as its key contribution, but assume that no other CO₂ removal technologies are available. We use a global integrated assessment model, TIAM‐UCL, to investigate the role of bioenergy within the global energy system when direct air capture and afforestation are available as cost‐competitive alternatives to BECCS. We find that the presence of other CO₂ removal technologies does not reduce the pressure on biomass resources but changes the use of bioenergy for climate mitigation. While we confirm that when available BECCS offers cheaper decarbonization pathways, we also find that its use delays the phase‐out of unabated fossil fuels in industry and transport. Furthermore, it displaces renewable electricity generation, potentially increasing the likelihood of missing the Paris Agreement target. We found that the most cost‐effective solution is to invest in a basket of CO₂ removal technologies. However, if these technologies rely on CCS, then urgent action is required to ramp up the necessary infrastructure. We conclude that a sustainable biomass supply is critical for decarbonizing the global energy system. Since only a few world regions carry the burden of producing the biomass resource and store CO₂ in geological storage, adequate international collaboration, policies and standards will be needed to realize this resource while avoiding undesired land‐use change.     

The role of bioenergy and biochemicals in CO2 mitigation through the energy system – a scenario analysis for the Netherlands

Bioenergy as well as bioenergy with carbon capture and storage are key options to embark on cost‐efficient trajectories that realize climate targets. Most studies have not yet assessed the influence on these trajectories of emerging bioeconomy sectors such as biochemicals and renewable jet fuels (RJFs). To support a systems transition, there is also need to demonstrate the impact on the energy system of technology development, biomass and fossil fuel prices. We aim to close this gap by assessing least‐cost pathways to 2030 for a number of scenarios applied to the energy system of the Netherlands, using a cost‐minimization model. The type and magnitude of biomass deployment are highly influenced by technology development, fossil fuel prices and ambitions to mitigate climate change. Across all scenarios, biomass consumption ranges between 180 and 760 PJ and national emissions between 82 and 178 Mt CO₂. High technology development leads to additional 100–270 PJ of biomass consumption and 8–20 Mt CO₂ emission reduction compared to low technology development counterparts. In high technology development scenarios, additional emission reduction is primarily achieved by bioenergy and carbon capture and storage. Traditional sectors, namely industrial biomass heat and biofuels, supply 61–87% of bioenergy, while wind turbines are the main supplier of renewable electricity. Low technology pathways show lower biochemical output by 50–75%, do not supply RJFs and do not utilize additional biomass compared to high technology development. In most scenarios the emission reduction targets for the Netherlands are not met, as additional reduction of 10–45 Mt CO₂ is needed. Stronger climate policy is required, especially in view of fluctuating fossil fuel prices, which are shown to be a key determinant of bioeconomy development. Nonetheless, high technology development is a no‐regrets option to realize deep emission reduction as it also ensures stable growth for the bioeconomy even under unfavourable conditions.     

Time‐dependent climate impact of a bioenergy system – methodology development and application to Swedish conditions

The area of dedicated energy crops is expected to increase in Sweden. This will result in direct land use changes, which may affect the carbon stocks in soil and biomass, as well as yield levels and the use of inputs. Carbon dioxide (CO₂) fluxes of biomass are often not considered when calculating the climate impact in life cycle assessments (LCA) assuming that the CO₂ released at combustion has recently been captured by the biomass in question. With the extended time lag between capture and release of CO₂ inherent in many perennial bioenergy systems, the relation between carbon neutrality and climate neutrality may be questioned. In this paper, previously published methodologies and models are combined in a methodological framework that can assist LCA practitioners in interpreting the time‐dependent climate impact of a bioenergy system. The treatment of carbon differs from conventional LCA practice in that no distinction is made between fossil and biogenic carbon. A time‐dependent indicator is used to enable a representation of the climate impact that is not dependent on the choice of a specific characterization time horizon or time of evaluation and that does not use characterization factors, such as global warming potential and global temperature potential. The indicator used to aid in the interpretation phase of this paper is global mean surface temperature change (ΔT_s(n)). A theoretical system producing willow for district heating was used to study land use change effects depending on previous land use and variations in the standing biomass carbon stocks. When replacing annual crops with willow this system presented a cooling contribution to ΔT_s(n). However, the first years after establishing the willow plantation it presented a warming contribution to ΔT_s(n). This behavior was due mainly to soil organic carbon (SOC) variation. A rapid initial increase in standing biomass counteracted the initial SOC loss.     

Optimal Locations for Methanol and CHP Production in Eastern Finland

Finland considers energy production from woody biomass as an efficient energy planning strategy to increase the domestic renewable energy production in order to substitute fossil fuel consumption and reduce greenhouse gas emissions. Consequently, a number of developmental activities are implemented in the country, and one of them is the installation of second generation liquid biofuel demonstration plants. In this study, two gasification-based biomass conversion technologies, methanol and combined heat and power (CHP) production, are assessed for commercialization. Spatial information on forest resources, sawmill residues, existing biomass-based industries, energy demand regions, possible plant locations, and a transport network of Eastern Finland is fed into a geographically explicit Mixed Integer Programming model to minimize the costs of the entire supply chain which includes the biomass supply, biomass and biofuel transportation, biomass conversion, energy distribution, and emissions. The model generates a solution by determining the optimal number, locations, and technology mix of bioenergy production plants. Scenarios were created with a focus on biomass and energy demand, plant characteristics, and cost variations. The model results state that the biomass supply and high energy demand are found to have a profound influence on the potential bioenergy production plant locations. The results show that methanol can be produced in Eastern Finland under current market conditions at an average cost of 0.22??/l with heat sales (0.34??/l without heat sales). The introduction of energy policy tools, like cost for carbon, showed a significant influence on the choice of technology and CO₂ emission reductions. The results revealed that the methanol technology was preferred over the CHP technology at higher carbon dioxide cost (>145??/t_CO2). The results indicate that two methanol plants (360?MW_biomass) are needed to be built to meet the transport fuel demand of Eastern Finland.     

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.     

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.     

Using ecosystem CO2 measurements to estimate the timing and magnitude of greenhouse gas mitigation potential of forest bioenergy

Forest bioenergy opportunities may be hindered by a long greenhouse gas (GHG) payback time. Estimating this payback time requires the quantification of forest‐atmosphere carbon exchanges, usually through process‐based simulation models. Such models are prone to large uncertainties, especially over long‐term carbon fluxes from dead organic matter pools. We propose the use of whole ecosystem field‐measured CO₂ exchanges obtained from eddy covariance flux towers to assess the GHG mitigation potential of forest biomass projects as a way to implicitly integrate all field‐level CO₂ fluxes and the inter‐annual variability in these fluxes. As an example, we perform the evaluation of a theoretical bioenergy project that uses tree stems as bioenergy feedstock and include multi‐year measurements of net ecosystem exchange (NEE) from forest harvest chronosequences in the boreal forest of Canada to estimate the time dynamics of ecosystem CO₂ exchanges following harvesting. Results from this approach are consistent with previous results using process‐based models and suggest a multi‐decadal payback time for our project. The time for atmospheric carbon debt repayment of bioenergy projects is highly dependent on ecosystem‐level CO₂ exchanges. The use of empirical NEE measurements may provide a direct evaluation of, or at least constraints on, the GHG mitigation potential of forest bioenergy projects.     

On the global limits of bioenergy and land use for climate change mitigation

Across energy, agricultural and forestry landscapes, the production of biomass for energy has emerged as a controversial driver of land‐use change. We present a novel, simple methodology, to probe the potential global sustainability limits of bioenergy over time for energy provision and climate change mitigation using a complex‐systems approach for assessing land‐use dynamics. Primary biomass that could provide between 70 EJ year^?1 and 360 EJ year^?1, globally, by 2050 was simulated in the context of different land‐use futures, food diet patterns and climate change mitigation efforts. Our simulations also show ranges of potential greenhouse gas emissions for agriculture, forestry and other land uses by 2050, including not only above‐ground biomass‐related emissions, but also from changes in soil carbon, from as high as 24 GtCO₂eq year^?1 to as low as minus 21 GtCO₂eq year^?1, which would represent a significant source of negative emissions. Based on the modelling simulations, the discussions offer novel insights about bioenergy as part of a broader integrated system. Whilst there are sustainability limits to the scale of bioenergy provision, they are dynamic over time, being responsive to land management options deployed worldwide.     

Effects of forest management on the carbon dioxide emissions of wood energy in integrated production of timber and energy biomass

The aim of this work was to study the sensitivity of carbon dioxide (CO₂) emissions from wood energy to different forest management regimes when aiming at an integrated production of timber and energy biomass. For this purpose, the production of timber and energy biomass in Norway spruce [Picea abies (L.) Karst] and Scots pine (Pinus sylvestris L.) stands was simulated using an ecosystem model (SIMA) on sites of varying fertility under different management regimes, including various thinning and fertilization treatments over a fixed simulation period of 80 years. The simulations included timber (sawlogs, pulp), energy biomass (small‐sized stem wood) and/or logging residues (top part of stem, branches and needles) from first thinning, and logging residues and stumps from final felling for energy production. In this context, a life cycle analysis/emission calculation tool was used to assess the CO₂ emissions per unit of energy (kg CO₂ MWh^?1) which was produced based on the use of wood energy. The energy balance (GJ ha^?1) of the supply chain was also calculated. The evaluation of CO₂ emissions and energy balance of the supply chain considered the whole forest bioenergy production chain, representing all operations needed to grow and harvest biomass and transport it to a power plant for energy production. Fertilization and high precommercial stand density clearly increased stem wood production (i.e. sawlogs, pulp and small‐sized stem wood), but also the amount of logging residues, stump wood and roots for energy use. Similarly, the lowest CO₂ emissions per unit of energy were obtained, regardless of tree species and site fertility, when applying extremely or very dense precommercial stand density, as well as fertilization three times during the rotation. For Norway spruce such management also provided a high energy balance (GJ ha^?1). On the other hand, the highest energy balance for Scots pine was obtained concurrently with extremely dense precommercial stands without fertilization on the medium‐fertility site, while on the low‐fertility site fertilization three times during the rotation was needed to attain this balance. Thus, clear differences existed between species and sites. In general, the forest bioenergy supply chain seemed to be effective; i.e. the fossil fuel energy consumption varied between 2.2% and 2.8% of the energy produced based on the forest biomass. To conclude, the primary energy use and CO₂ emissions related to the forest operations, including the production and application of fertilizer, were small in relation to the increased potential of energy biomass.     

Life Cycle–based Assessment of Energy Use and Greenhouse Gas Emissions in Almond Production,Part II: Uncertainty Analysis through Sensitivity Analysis and Scenario Testing

This is the second part of a two‐article series examining California almond production. The part I article describes development of the analytical framework and life cycle–based model and presents typical energy use and greenhouse gas (GHG) emissions for California almonds. This part II article builds on this by exploring uncertainty in the life cycle model through sensitivity and scenario analysis, and by examining temporary carbon storage in the orchard. Sensitivity analysis shows life cycle GHG emissions are most affected by biomass fate and utilization, followed by nitrous oxide emissions rates from orchard soils. Model sensitivity for net energy consumption is highest for irrigation system parameters, followed by biomass fate and utilization. Scenario analysis shows utilization of orchard biomass for electricity production has the greatest potential effect, assuming displacement methods are used for co‐product allocation. Results of the scenario analysis show that 1 kilogram (kg) of almond kernel and associated co‐products are estimated to cause between ?3.12 to 2.67 kg carbon dioxide equivalent (CO₂‐eq) emissions and consume between 27.6 to 52.5 megajoules (MJ) of energy. Co‐product displacement credits lead to avoided emissions of between ?1.33 to 2.45 kg CO₂‐eq and between ?0.08 to 13.7 MJ of avoided energy use, leading to net results of ?1.39 to 3.99 kg CO₂‐eq and 15.3 to 52.6 MJ per kg kernel (net results are calculated by subtracting co‐product credits from the results for almonds and co‐products). Temporary carbon storage in orchard biomass and soils is accounted for by using alternative global warming characterization factors and leads to a 14% to 18% reduction in CO₂‐eq emissions. Future studies of orchards and other perennial cropping systems should likely consider temporary carbon storage.     

The future of bioenergy

Energy from biomass plays a large and growing role in the global energy system. Energy from biomass can make significant contributions to reducing carbon emissions, especially from difficult‐to‐decarbonize sectors like aviation, heavy transport, and manufacturing. But land‐intensive bioenergy often entails substantial carbon emissions from land‐use change as well as production, harvesting, and transportation. In addition, land‐intensive bioenergy scales only with the utilization of vast amounts of land, a resource that is fundamentally limited in supply. Because of the land constraint, the intrinsically low yields of energy per unit of land area, and rapid technological progress in competing technologies, land intensive bioenergy makes the most sense as a transitional element of the global energy mix, playing an important role over the next few decades and then fading, probably after mid‐century. Managing an effective trajectory for land‐intensive bioenergy will require an unusual mix of policies and incentives that encourage appropriate utilization in the short term but minimize lock‐in in the longer term.     

Using CO2 to enhance carbon capture and biomass applications of freshwater macroalgae

A major limiting factor in the development of algae as a feedstock for the bioenergy industry is the consistent production and supply of biomass. This study is the first to access the suitability of the freshwater macroalgal genus Oedogonium to supply biomass for bioenergy applications. Specifically, we quantified the effect of CO₂ supplementation on the rate of biomass production, carbon capture, and feedstock quality of Oedogonium when cultured in large‐scale outdoor tanks. Oedogonium cultures maintained at a pH of 7.5 through the addition of CO₂ resulted in biomass productivities of 8.33 (±0.51) g DW m^?2 day^?1, which was 2.5 times higher than controls which had an average productivity of 3.37 (±0.75) g DW m^?2 day^?1. Under these productivities, Oedogonium had a carbon content of 41–45% and a higher heating value of 18.5 MJ kg^?1, making it an ideal biomass energy feedstock. The rate of carbon fixation was 1380 g C m^?2 yr^?1 and 1073.1 g C m^?2 yr^?1 for cultures maintained at a pH of 7.5 and 8.5, and 481 g C m^?2 yr^?1 for cultures not supplemented with CO₂. This study highlights the potential of integrating the large‐scale culture of freshwater macroalgae with existing carbon waste streams, for example coal‐fired power stations, both as a tool for carbon sequestration and as an enhanced and sustainable source of bioenergy.     

Life Cycle Assessment of Electric and Fuel Cell Vehicle Transport Based on Forest Biomass

Use of biomass‐based electricity and hydrogen in alternative transport could provide environmentally sustainable transport options with possible improvements in greenhouse gas balance. We perform a life cycle assessment of electric vehicle (EV) and fuel cell vehicle (FCV) powered by bioelectricity and biohydrogen, respectively, derived from Norwegian boreal forest biomass, considering the nonclimate neutrality of biological carbon dioxide (CO₂) emissions and alteration in surface albedo resulting from biomass harvesting—both with and without CO₂ capture and storage (CCS)—while benchmarking these options against EVs powered by the average European electricity mix. Results show that with due consideration of the countering effects from global warming potential (GWP) factors for biogenic CO₂ emissions and change in radiative forcing of the surface for the studied region, bioenergy‐based EVs and FCVs provide reductions of approximately 30%, as compared to the reference EV powered by the average European electricity mix. With CCS coupled to bioenergy production, the biomass‐based vehicle transport results in a net global warming impact reduction of approximately 110% to 120% (giving negative GWP and creating a climate‐cooling benefit from biomass use). Other environmental impacts vary from ?60% to +60%, with freshwater eutrophication showing maximum reductions (40% for the EV case and 60% for the FCV case) and photochemical oxidation showing a maximum increase (60% in the FCV value chain).     

Projection of the future EU forest CO2 sink as affected by recent bioenergy policies using two advanced forest management models

Forests of the European Union (EU) have been intensively managed for decades, and they have formed a significant sink for carbon dioxide (CO₂) from the atmosphere over the past 50 years. The reasons for this behavior are multiple, among them are: forest aging, area expansion, increasing plant productivity due to environmental changes of many kinds, and, most importantly, the growth rates of European forest having been higher than harvest rates. EU countries have agreed to reduce total emissions of GHG by 20% in 2020 compared to 1990, excluding the forest sink. A relevant question for climate policy is: how long will the current sink of EU forests be maintained in the near future? And could it be affected by other mitigation measures such as bioenergy? In this article we assess tradeoffs of bioenergy use and carbon sequestration at large scale and describe results of the comparison of two advanced forest management models that are used to project CO₂ emissions and removals from EU forests until 2030. EFISCEN, a detailed statistical matrix model and G4M, a geographically explicit economic forestry model, use scenarios of future harvest rates and forest growth information to estimate the future carbon balance of forest biomass. Two scenarios were assessed: the EU baseline scenario and the EU reference scenario (including additional bioenergy and climate policies). Our projections suggest a significant decline of the sink until 2030 in the baseline scenario of about 25–40% (or 65–125 Mt CO₂) compared to the models’ 2010 estimate. Including additional bioenergy targets of EU member states has an effect on the development of this sink, which is not accounted in the EU emission reduction target. A sensitivity analysis was performed on the role of future wood demand and proved the importance of this driver for the future sink development.     

Response of maize biomass and soil water fluxes on elevated CO2 and drought—From field experiments to process‐based simulations

The rising concentration of atmospheric carbon dioxide (CO₂) is known to increase the total aboveground biomass of several C3 crops, whereas C4 crops are reported to be hardly affected when water supply is sufficient. However, a free‐air carbon enrichment (FACE) experiment in Braunschweig, Germany, in 2007 and 2008 resulted in a 25% increased biomass of the C4 crop maize under restricted water conditions and elevated CO₂ (550 ppm). To project future yields of maize under climate change, an accurate representation of the effects of eCO₂ and drought on biomass and soil water conditions is essential. Current crop growth models reveal limitations in simulations of maize biomass under eCO₂ and limited water supply. We use the coupled process‐based hydrological‐plant growth model Catchment Modeling Framework‐Plant growth Modeling Framework to overcome this limitation. We apply the coupled model to the maize‐based FACE experiment in Braunschweig that provides robust data for the investigation of combined CO₂ and drought effects. We approve hypothesis I that CO₂ enrichment has a small direct‐fertilizing effect with regard to the total aboveground biomass of maize and hypothesis II that CO₂ enrichment decreases water stress and leads to higher yields of maize under restricted water conditions. Hypothesis III could partly be approved showing that CO₂ enrichment decreases the transpiration of maize, but does not raise soil moisture, while increasing evaporation. We emphasize the importance of plant‐specific CO₂ response factors derived by use of comprehensive FACE data. By now, only one FACE experiment on maize is accomplished applying different water levels. For the rigorous testing of plant growth models and their applicability in climate change studies, we call for datasets that go beyond single criteria (only yield response) and single effects (only elevated CO₂).     

Diverting residual biomass to energy use: Quantifying the global warming potential of biogenic CO2 (GWPbCO2)

To calculate the global warming potential of biogenic carbon dioxide emissions (GWP_bCO2) associated with diverting residual biomass to bioenergy use, the decay of annual biogenic carbon pulses into the atmosphere over 100 years was compared between biomass use for energy and its business-as-usual decomposition in agricultural, forestry, or landfill sites. Bioenergy use increased atmospheric CO₂ load in all cases, resulting in a ¹⁰⁰GWP_bCO2 (units of g CO₂e/g biomass CO₂ released) of 0.003 for the fast-decomposing agricultural residues to 0.029 for the slow, 0.084–0.625 for forest residues, and 0.368–0.975 for landfill lignocellulosic biomass. In comparison, carbon emissions from fossil fuels have a ¹⁰⁰GWP of 1.0 g (CO₂e/g fossil CO₂). The fast decomposition rate and the corresponding low ¹⁰⁰GWP_bCO2 values of agricultural residues make them a more climate-friendly feedstock for bioenergy production relative to forest residues and landfill lignocellulosic biomass. This study shows that CO₂ released from the combustion of bioenergy or biofuels made from residual biomass has a greenhouse gas footprint that should be considered in assessing climate impacts.     

Biomass for energy in the European Union - a review of bioenergy resource assessments

ABSTRACT: This paper reviews recent literature on bioenergy potentials in conjunction with available biomass conversion technologies. The geographical scope is the European Union, which has set a course for long term development of its energy supply from the current dependence on fossil resources to a dominance of renewable resources. A cornerstone in European energy policies and strategies is biomass and bioenergy. The annual demand for biomass for energy is estimated to increase from the current level of 5.7 EJ to 10.0 EJ in 2020. Assessments of bioenergy potentials vary substantially due to methodological inconsistency and assumptions applied by individual authors. Forest biomass, agricultural residues and energy crops constitute the three major sources of biomass for energy, with the latter probably developing into the most important source over the 21st century. Land use and the changes thereof is a key issue in sustainable bioenergy production as land availability is an ultimately limiting factor.