Sustainability Assessment of Renewables-Based Products: Methods and Case Studies

Over the past decade, renewables-based technology and sustainability assessment methods have grown tremendously. Renewable energy and products have a significant role in the market today, and the same time sustainability assessment methods have advanced, with a growing standardization of environmental sustainability metrics and consideration of social issues as part of the assessment.

Sustainability Assessment of Renewables-Based Products: Methods and Case Studies is an extensive update and sequel to the 2006 title Renewables-Based Technology: Sustainability Assessment. It discusses the impressive evolution and role renewables have taken in our modern society, highlighting the importance of sustainability principles in the design phase of renewable-based technologies, and presenting a wide range of sustainability assessment methods suitable for renewables-based technologies, together with case studies to demonstrate their applications.

This book is a valuable resource for academics, businesses and policy makers who are active in contributing to more sustainable production and consumption.

For more information on the Wiley Series in Renewable Resources, visit www.wiley.com/go/rrs

Topics covered include:

• The growing role of renewables in our society
• Sustainability in the design phase of products and processes
• Principles of sustainability assessment
• Land use analysis
• Water use analysis
• Material and energy flow analysis
• Exergy and cumulative exergy analysisCarbon and environmental footprint methods
• Life Cycle Assessment (LCA), social Life Cycle Assessment and Life Cycle Costing (LCC)
• Case studies: renewable energy, bio-based chemicals and bio-based materials.

• Language: English
• Publisher: Wiley
• Release date: Nov 17, 2015
• ISBN: 9781118933923

Book preview

Series Preface

Renewable resources, their use and modification are involved in a multitude of important processes with a major influence on our everyday lives. Applications can be found in the energy sector, paints and coatings, and the chemical, pharmaceutical, and textile industry, to name but a few.

The area interconnects several scientific disciplines (agriculture, biochemistry, chemistry, technology, environmental sciences, forestry …), which makes it very difficult to have an expert view on the complicated interaction. Therefore, the idea to create a series of scientific books that will focus on specific topics concerning renewable resources, has been very opportune and can help to clarify some of the underlying connections in this area.

In a very fast changing world, trends are not only characteristic for fashion and political standpoints; science is also not free from hypes and buzzwords. The use of renewable resources is again more important nowadays; however, it is not part of a hype or a fashion. As the lively discussions among scientists continue about how many years we will still be able to use fossil fuels—opinions ranging from 50 to 500 years—they do agree that the reserve is limited and that it is essential not only to search for new energy carriers but also for new material sources.

In this respect, renewable resources are a crucial area in the search for alternatives for fossil-based raw materials and energy. In the field of energy supply, biomass and renewables-based resources will be part of the solution alongside other alternatives such as solar energy, wind energy, hydraulic power, hydrogen technology, and nuclear energy.

In the field of material sciences, the impact of renewable resources will probably be even bigger. Integral utilization of crops and the use of waste streams in certain industries will grow in importance, leading to a more sustainable way of producing materials.

Although our society was much more (almost exclusively) based on renewable resources centuries ago, this disappeared in the Western world in the nineteenth century. Now it is time to focus again on this field of research. However, it should not mean a retour `a la nature, but it should be a multidisciplinary effort on a highly technological level to perform research towards new opportunities, to develop new crops and products from renewable resources. This will be essential to guarantee a level of comfort for a growing number of people living on our planet. It is the challenge for the coming generations of scientists to develop more sustainable ways to create prosperity and to fight poverty and hunger in the world. A global approach is certainly favored.

This challenge can only be dealt with if scientists are attracted to this area and are recognized for their efforts in this interdisciplinary field. It is, therefore, also essential that consumers recognize the fate of renewable resources in a number of products.

Furthermore, scientists do need to communicate and discuss the relevance of their work. The use and modification of renewable resources may not follow the path of the genetic engineering concept in view of consumer acceptance in Europe. Related to this aspect, the series will certainly help to increase the visibility of the importance of renewable resources. Being convinced of the value of the renewables approach for the industrial world, as well as for developing countries, I was myself delighted to collaborate on this series of books focusing on different aspects of renewable resources. I hope that readers become aware of the complexity, the interaction and interconnections, and the challenges of this field and that they will help to communicate on the importance of renewable resources.

I certainly want to thank the people of Wiley’s Chichester office, especially David Hughes, Jenny Cossham and Lyn Roberts, in seeing the need for such a series of books on renewable resources, for initiating and supporting it, and for helping to carry the project to the end.

Last, but not least, I want to thank my family, especially my wife Hilde and children Paulien and Pieter-Jan, for their patience and for giving me the time to work on the series when other activities seemed to be more inviting.

Christian V. Stevens,

Faculty of Bioscience Engineering

Ghent University, Belgium

Series Editor Renewable Resources

June 2005

Preface

It is now almost three decades ago that the United Nations took the challenge to face ‘sustainability’, exemplified by its report, Our Common Future [1]. Although its definition of sustainability was a bit vague for many scientists, engineers and business developers, it has set the agenda in many sectors in our society.

Environmental and socioeconomic scientists started the quest for measuring sustainability; tremendous efforts have been brought forward not only by scientists and academia but also by companies and business associations since then. The sustainability concept has not only triggered but even heavily induced new technologies, especially in technology sectors that feel to be well positioned to make a difference in sustainable development. In particular the renewables-based technology sectors, that is, biomass-, geothermal-, wind- or solar-based technologies, have undergone an immense growth since 1987.

About one decade ago, Wiley felt it was the proper moment to publish a book on sustainability assessment for renewables-based technologies [2]. The book came at the right moment as it could depict the development of sustainability metrics for renewables-based technology after, say, 20 years of making sustainability more concrete in the specific context.

Now another decade later, we could not have imagined the huge leap both renewables-based technology and sustainability assessment have taken since then. Renewable energy and products, for example, wind power, chemical building blocks and packaging materials, have taken a significant position in the market today. At the same time, the evolution in sustainability metrics has been at least equally impressive, with a growing standardization of environmental sustainability metrics, bringing it beyond the environmental pillar, for example, through recent developments in social life cycle assessment.

Today, we as editors are very happy and even proud to be able to present to you Sustainability Assessment of Renewables-Based Products: Methods and Case Studies. As the development of the topic has evolved dramatically, it was not an option to simply update the previous book [2]; instead a completely new book has been developed in order to capture the current reality in the domain. Being active in the field for about 15 years, we are extremely happy to be in a position to have engaged experts from academia, research and policy institutes and businesses located in southern and northern America, Europe, Asia and Oceania as contributors.

The book is organized into four sections. The first section depicts the impressive evolution and roles renewables have taken in our modern society. The second section is devoted to the importance of taking sustainability principles on board in designing new technologies like renewables-based ones. The third and fourth sections are the largest ones: they present a well-balanced selection of sustainability methods suitable for renewables-based technologies and case studies where these methods have been implemented.

We feel this book can be a valuable source of information for academia, businesses and policymakers active in contributing to more sustainable production and consumption, realizing that renewables-based products play an indispensable role.

May 2015

Jo Dewulf

Steven De Meester

Rodrigo A. F. Alvarenga

References

1. Our Common Future. See www.un-documents.net/our-common-future.pdf (accessed 28 September 2015).

2. Renewables-Based Technology: Sustainability Assessment. See http://eu.wiley.com/WileyCDA/WileyTitle/productCd-0470022418.html (accessed 28 September 2015).

1

The Growing Role of Biomass for Future Resource Supply—Prospects and Pitfalls

Helmut Haberl

Institute of Social Ecology Vienna, Alpen-Adria Universität Klagenfurt, Austria

Integrative Research Institute on Transformations of Human-Environment Systems (IRI THESys), Humboldt-Universität zu Berlin, Germany

1.1 Introduction

Biomass is biogenic material derived from living or recently living organisms. It originates from processes of primary production that convert inorganic chemical compounds, mainly carbon dioxide (CO2) and water (H2O), into sugars and other energy-rich organic compounds that build up the bodies of plants, animals, and micro-organisms. Photosynthesis—that is, the conversion of radiant energy from the sun into energy-rich organic compounds within living plant tissues—is the most important process of primary production, although there are organisms also capable of using exothermic chemical reactions as an energy source, a process denoted as chemosynthesis [1]. Biomass is an umbrella term for a huge variety of different mixtures of chemical compounds found in living organisms, including plants, animals, and micro-organisms. Raw materials for energy and material goods mostly stem from plants, although bones, hides or feathers are also used, while food is derived from both plants and animals.

Biomass is a crucial resource for ecosystems as well as humans. In ecosystems, primary producers—most prominently green plants—are the organisms from which this resource originates. The total amount of CO2 assimilated through photosynthesis is denoted as Gross Primary Production or GPP. Plants use a considerable proportion of GPP for their own metabolism (plant respiration), which releases a variable part of the carbon as CO2—as a rule of thumb, one may assume that plant respiration is about half of GPP [2]. The difference between GPP and plant respiration is denoted as Net Primary Production or NPP, which represents the entire yearly resource flow that is available for natural processes in ecosystems (heterotrophic food chains, accumulation of biomass and soil carbon or natural fires) and human uses (food, feed, bioenergy, or raw materials).

As heterotrophic organisms, humans vitally depend on the intake of biomass—food—to sustain their biological metabolism. Because conversion losses amount to ~90% between trophic levels—implying that only ~10% of the biomass fed to livestock is converted into meat, milk or eggs for human consumption [3]—the amount of primary production humans need for feeding themselves strongly depends on the share of animal products in their diet. Globally, at present ~60% of all biomass used by humans is fed to livestock [4]. In addition to their direct (food) and indirect (feed) biomass demand for nutrition, humans use biomass as a source of technical energy (i.e., for energetic uses other than food and feed), as a raw material, and for purposive vegetation fires that helps to clear land for cultivation [5, 6].

Biomass is used as raw material for a multitude of purposes and products. In agriculture, straw, leaves, and twigs are used as bedding material [4]. Wood is an important raw material that has been, and is still, used for a plethora of purposes, including construction and in the manufacture of furniture, pulp and paper, tools, and many other products. Use of timber as a substitute for energy-intensive materials such as steel or concrete in buildings can help reduce greenhouse gas (GHG) emissions [7]. Animal products such as hides, horns, bones, feathers, wool and so on are used for clothing, tools, and many other purposes. Increasingly, purpose-grown plants as well as by-products, biogenic wastes, and residues are used as fiber, raw materials for chemical syntheses of bulk chemicals, fine chemicals, surfactants, solvents, lubricants, or polymers [8]. Use of biomass as raw material for these purposes is expected to rise strongly in the future in order to reduce the use of increasingly scarce minerals as well as for emission reduction [9].

Although use of water and wind power by humans has a long history, biomass was quantitatively by far the most important source of technical energy prior to the large-scale use of fossil energy introduced during the industrial revolution [10, 11]. Indeed, the transition from biomass to fossil energy (and later to other sources such as large-scale hydropower, nuclear energy, etc.) has been described as a characteristic component, or rather as a precondition, of the agrarian-industrial transition [12–14]. In a long-term perspective, the share of biomass in technical primary energy supply has fallen everywhere during the agrarian-industrial transitions, usually from almost 100% to levels between 5 and 20% of primary energy supply [12, 15].

Motivated by concerns over climate change and the finiteness of fossil energy, biomass has gained increasing attention as a possible renewable source of energy and raw materials in the past decades. It is common to distinguish traditional and modern bioenergy, although the boundaries are somewhat blurred. Indoor use of open cooking fires, a widespread traditional bioenergy technology, is inefficient and results in high emissions, including disastrous indoor pollution and, consequently, severe respiratory problems [16]. Modern bioenergy includes a large variety of technologies such as liquid biofuels, biomass-based co-production of electricity and heat or biogas from manures or purpose-grown biomass [17]. Recent assessment reports [7, 16, 18] expect that the production and use of bioenergy will grow from moderate to strong in the next decades and that modern bioenergy will replace traditional bioenergy. By 2050, bioenergy production could grow by a factor of 2–6 over its current level of ~50 EJ/year globally [7, 16, 19].

In this context, the purpose of this chapter is to give an overview of the current and possible future socioecological biomass flows, to discuss the global potential for biomass for non-food purposes and to highlight some critical issues that need to be addressed in order to ensure sustainable biomass production and use. In particular, we discuss possible effects on the global land system (e.g. land-use competition), greenhouse gas emissions resulting from impacts of bioenergy production on the carbon cycle, and the biodiversity impacts of increased biomass use. This chapter is focused on biomass from terrestrial ecosystems; however, the possible production of biomass in aquatic systems and closed techno-structures is beyond its scope. At present, aquatic biomass largely plays a role only for food supply through fisheries or aquaculture, but there is a discussion on the potential of using algae grown in various kinds of installations for energy production in the future [20].

1.2 Global Ecological and Socioeconomic Biomass Flows

How much biomass is produced each year by green plants globally is not exactly known due to uncertainties related to terrestrial global NPP. A recent meta-analysis of 251 estimates of global terrestrial NPP yielded a mean of ~112.4 billion tons of dry-matter biomass per year (Gt/year; 1 Gt = 10⁹ metric tons) with a standard deviation of ±28.6 Gt/year [21]. This is equivalent to a yearly energy flow of ~2.070 EJ/year (1 EJ = 10¹⁸ J) of which ~1.100 EJ/year are above-ground. In this chapter, all biomass flows are reported in units of dry-matter biomass, that is, biomass with zero moisture content, or their energy equivalent given as gross calorific value or GCV. In order to facilitate comparisons, data reported in other units in the underlying sources were converted assuming a carbon content of dry-matter biomass of 50% and a GCV of 18.5 MJ/kg [22]).

Surprisingly, calculations estimating NPP from remote-sensing data using the MODIS (Moderate Resolution Imaging Spectroradiometer) NPP algorithm suggest that global terrestrial NPP was almost perfectly constant from 1982 to 2009 at ~108 Gt/year, with <2% year-to-year variation [23], despite considerable increases in land-use intensity [19]. In contrast, dynamic global vegetation models usually suggest increases in terrestrial NPP reflecting changes in land cover, land use and climate, in particular CO2 fertilization [24]. For example, the LPJmL model indicates that terrestrial NPP rose by 7% from 1980 to 2005 [19]. Further research seems warranted to clarify these contradictions, but another issue may be equally relevant, which is whether and to what extent humans alter NPP and how large the human use of biomass is when compared to annual natural biomass flows. This question is being addressed within the concept of human appropriation of net primary production, abbreviated as HANPP [25, 26]. HANPP research has shown that human activities have a globally significant impact on terrestrial NPP. Human activities alter the productivity of ecosystems. Due to the harvest of biomass for food, feed, raw material, or bioenergy, less biomass is available each year in the ecosystem for food chains of wild-living heterotrophs or for carbon sequestration (i.e., increased carbon storage in biota and soils).

Humans alter NPP by replacing natural vegetation with agro-ecosystems, through the construction of buildings or infrastructures, through afforestation or forest management, land degradation, ecosystem restoration or other purposive interventions. Empirical studies suggest that land use reduces terrestrial NPP globally by ~5–10% [27, 28] compared to a hypothetical situation without land use under current climate conditions (denoted as NPPpot, i.e., the NPP of potential natural vegetation; in the following text, the NPP of the currently prevailing vegetation is denoted as NPPact). The difference between NPPpot and NPPact is denoted as HANPPluc; that is, the alteration of NPP resulting from land use and land conversion.

Through cropping, livestock grazing, and forestry, humans withdraw or destroy biomass in ecosystems, a process that has been denoted as HANPPharv (human appropriation of NPP related to harvest; Figure 1.1). HANPPharv includes biomass extracted and used, such as crop or timber harvest or biomass grazed by livestock; biomass killed during harvest such as roots of crops and trees that are harvested; forest slash and crop residues that remain on site; as well as biomass burned in human-induced vegetation fires. HANPP is the sum total of HANPPluc plus HANPPharv which is equivalent to the difference between NPPpot and the NPP remaining in the ecosystem after harvest (NPPeco). Empirical studies suggest that global HANPP has roughly doubled in the last century from ~13 to ~25% of NPPpot [19]. HANPP maps show that land-use intensity differs greatly around the globe [28]. If only the (accessible) above-ground component is considered, HANPP amounted to almost one third around the year 2000 (Figure 1.1).

Bar chart of global ecological and socioeconomic terrestrial biomass flow in the year 2000 (in billion tons of dry matter biomass) with 71 NPPxsubscriptpot and 67 NPPxsubscriptact above ground and 60 NPPxsubscriptpot and 51 NPPxsubscriptact below ground.

Figure 1.1 Global ecological and socioeconomic terrestrial (land-based) biomass flows in the year 2000, expressed in billion tons of dry matter biomass (Gt/year).

Sources: Haberl et al. [28], Lauk and Erb [6] (fire data)

Figure 1.2 relates global socioeconomic biomass flows in the year 2000 to land-use categories [4, 30]. Note that the socioeconomic biomass flows depicted in that graph refer only to the fraction of HANPPharv defined as used extraction. Figure 1.2 shows the importance of livestock for socioeconomic biomass use. Biomass use for energy is already the largest component of mankind’s final use of biomass, and a considerable fraction of that biomass is derived from residues or by-flows.

Schematic diagram of global land use and socioeconomic biomass flows in the year 2000 displaying infrastructure, <2 Mkmxsupscript2; cropland, >15 Mkmxsupscript2; Grazing, <46 Mkmxsupscript2; forestry, <35 Mkmxsupscript2; and unused forests, <32 Mkmxsupscript2.

Figure 1.2 Global land use and socioeconomic biomass flows in the year 2000.

Source: Reproduced from Haberl [29], with permission from Elsevier

Only approximately one quarter of the Earth’s land—the total of ~130 Mkm² refers to the entire global land mass except Greenland and Antarctica—is at present unused [31]. About three quarters of the 32 Mkm² of unused lands are very unproductive, for example arctic or alpine tundras and deserts. The remainder is productive, but ecologically very valuable, as it hosts the remaining pristine forests. Apart from their possible conversion, future additional biomass will come from land that is already under some form of human use; hence raising biomass supply is likely to result in land-use competition [29, 32]. Additional biomass can be produced by increasing usable biomass production per unit area without land-use change, for example, by raising yields, or through land-use change, for example, by replacing one form of land use with another that delivers more usable biomass per unit area and year—in other words, there is a choice between (i) land-use intensification and (ii) expansion of intensive forms of land use, for example, cropland expansion [33].

1.3 Global Biomass Potentials in 2050

Based on the expectation that the world population will grow to ~9 billion around the year 2050, and that global GDP growth will continue roughly along past trajectories, analysts assume that agricultural output will grow by 70–100% until mid-century over the value in the year 2000 [34, 35]. Future land demand for food and feed—and hence the area available for other purposes, such as energy crops and the conservation of ecosystems and biodiversity—depends on (i) the food demand in terms of both volume and composition, including losses in the food supply chain [36], (ii) the conversion efficiencies from primary biomass harvest to final food supply, in particular livestock feeding efficiency, and (iii) the yields of biomass productivities of cropland and grazing land for food and feed production, respectively [37].

How much biomass could be provided sustainably for energy supply and as a raw material is contentious. Sustainability criteria discussed in this context include social (e.g., food security, land tenure), economic (e.g., food or energy prices) as well as environmental (e.g., GHG emissions, conservation of soil fertility, biodiversity and ecosystems) dimensions [17]. Sustainability concerns differ between the harvest of primary biomass (food crops, energy crops, timber, etc.) and the use of residues and wastes. Regarding the latter, one may distinguish primary, secondary or tertiary residues, depending on where in the biomass utilization chain they are acquired [38]. While use of residues and wastes is largely seen as benign (caveats are discussed later), additional biomass harvesting is discussed controversially, for a host of reasons that mostly relate to issues of land-use competition [30]: producing more biomass requires land, water, and other limited resources [39] that are required for a variety of purposes, including food and feed production and also for the delivery of other highly valued ecosystem services [7].

1.3.1 Primary Biomass Potentials

Additional primary biomass harvest can be expected from purpose-grown plants produced on new or existing cropland, for example, first and second generation energy crops, and additional wood harvests in forestry, including plantation forests. Wood harvests in forests could also be increased, but while the magnitude of the biomass supply potentials from that source is not very controversial (Table 1.1), the sustainability and climate impacts of that option are disputed (Section 1.4.2). Global future potentials of energy crops as well as their sustainability impacts and the net GHG effects of producing them are uncertain and controversial [17]. Estimates of global technical primary biomass potentials span a range of almost two orders of magnitude (from ~50 to >1000 EJ/year; Table 1.1).

Table 1.1 Recent estimates of global potentials for producing primary non-food biomass.

a Dry-matter biomass. If only one of the measures (energy or dry matter, respectively) was given in the original source, dry matter was converted to energy or vice versa assuming a GCV of 18.5 MJ/kg (for illustrative reasons).

b Total global land area. Biomass required for food and feed was subtracted, but areas for food and energy crops were not explicitly distinguished.

Primary biomass potentials from non-forested land are calculated by multiplying an estimate of the land area deemed suitable and available for the respective crop(s) (m²) by an estimate of the potential biomass yield (kg/m²/year). Differences in primary biomass potentials found in the literature stem from disagreements on both factors [22].

Globally, biologically productive land is limited; hence, the area available for growing bioenergy crops is inversely related to the area required for the food system, which in turn depends on factors related to the demand side (population, per-capita food intake, diets, losses in the food supply chain, etc.) as well as to the supply side (yields of food and fodder crops, feeding efficiency, composition of livestock, etc.). Calculations with a biomass balance model that considers roughage demand on grazed land [37, 42, 49, 50] suggest that land availability for energy crops in the year 2050 could vary by a factor of at least three, depending on variations in the above-mentioned factors. The literature compiled in Table 1.1 suggests an even larger range from below one to above 30 million square kilometers (Mkm²). Moreover, some calculations refer to biophysical option spaces, and not plausible scenarios. The highest area availability was found in scenarios combining low food demand, and a low share of animal products in diets, with very high levels of agricultural intensity [37]—a combination that might not be very likely, as higher efficiency of production is usually thought to stimulate demand due to rebound effects [39, 51]. A global transition towards purely plant-based diets would strongly reduce area demand of the food supply system [52], even at relatively low yields [42], while a global transition towards diets currently enjoyed in North America and Western Europe would be difficult to achieve without deforestation [37].

The second factor underlying all assessments of global biomass potentials, that is, possible future yields of energy crops, is also uncertain and is contested. Here, one major issue is related to scale. At the plot scale, well-managed field trials have demonstrated the possibility of achieving high yields of some energy crops, in particular the so-called second generation energy crops such as short-rotation coppice (SRC) and perennial C4-grasses such as Miscanthus spp. and switchgrass (Panicum virgatum). Both crop modeling and empirical data suggest that above-ground biomass productivities of these plants can, by far, surpass the NPPpot of the areas on which they are growing [53].

However, at present, the global average NPPact on croplands is about one third below the NPPpot of these areas [28]. NPPact of croplands exceeds NPPpot in a relatively small fraction of the croplands in humid areas, whereas this phenomenon is common in irrigated drylands. Humid croplands with NPPact > NPPpot are characterized by very intensive management, including the use of large amounts of fertilizer and other agricultural inputs. This has given rise to a discussion on the ecological costs of raising crop yields in terms of energy and other environmentally detrimental inputs [54]. Statistical data suggest that energy crop yields achieved under field conditions are considerably lower than those of field trials [55]. It has been argued that it could be difficult to raise yields of energy crops along the trajectory that has been achieved for food crops, for example, because they are relatively insensitive to the addition of fertilizers and because a major strategy for improving food crops—raising the harvest index, that is, the ratio between grain and entire plant at time of harvest—is not applicable to them [56]. Nevertheless, the assumption that energy crop yields will rise along similar trajectories as those of food crops prevails in many models used to calculate global bioenergy potentials [57]. It remains to be seen whether the productivity of crop plants can be raised above NPPpot on large (sub-continental or continental) scales, which is a precondition for achieving high global energy crop potentials, and if so, what the ecological as well as economic costs of achieving such high yields are [23, 46, 53, 54, 58].

1.3.2 Residue and Waste Potentials

Recent estimates of potentials to use biomass residues and wastes for energy in the year 2050 are collated in Table 1.2, underlining that a strategy of cascade utilization of biomass [43, 60] may unleash substantial energy potentials on the order of 10–20% of the current global primary energy supply. Controversy surrounding these figures is less intensive than that for primary biomass. However, increasing recovery rates of residues left on the field may reduce soil fertility or deteriorate the soil–carbon balance [61]; hence, appropriate recovery rates need to be respected when aiming to use that resource sustainably [43].

Table 1.2 Residue potentials available for non-food biomass (energy, raw materials) supply in the year 2050.

a Dry-matter biomass. If only one of the measures (energy or dry matter, respectively) was given in the original source, dry matter was converted to energy or vice versa assuming a GCV of 18.5 MJ/kg (for illustrative reasons).

b The energy equivalent of the manures is approximately four times larger than the biogas potential, i.e. a biogas potential of 10 EJ/year is equivalent to ~40 EJ/year of manures.

The magnitude of residue and waste potentials depends largely on (i) the expected growth of the production of the main products, for example, crops, animal products, or timber, respectively of the volume of discarded products; (ii) technological factors, such as the harvest index; (iii) recovery rates, that is, the fraction of the entire by-product or waste flow that can be used [62]; and (iv) sustainability criteria related to certain flows, most importantly crop residues [61]. Growth in the production volumes of main products generally results in higher residue potentials, whereas certain forms of crop improvements, in particular of the harvest index, reduce the residue potential. Changes in diets toward a lower share of animal products, reduced losses in the food supply chain, or more efficient livestock feeding systems, as beneficial as they may be in terms of reduced land-use competition [30, 52], would reduce the manure potential accordingly. Residue potentials in forestry would shrink if a lower volume of timber production is assumed [47].

1.4 Critical Socio-Ecological Feedbacks and Sustainability Issues

Possible impacts of a large-scale implementation of bioenergy on food production in terms of both volumes and prices have caused concerns. Other sustainability issues include pressures on ecosystems, biodiversity, and soils as well as GHG emissions related to the production of biomass, in particular when it is intended to be used as a substitute of fossil fuels [9, 16, 17]. Environmental concerns related to biomass use largely boil down to two distinct issues: (1) impacts of the land-use system associated with producing the biomass, for example, an energy crop plantation or a managed forest, and (2) impacts of land-use changes associated directly or indirectly with establishing a biomass production system. Concerns in group (1) are site- and plant-specific; fully reviewing them is beyond the scope of this chapter. If food crops are used, the impacts are basically those of agriculture in general [63]. Cultivation of lignocellulose crops is thought to be environmentally less demanding than food crops [64] and may even be beneficial for soil carbon [65]. However, increases in forestry intensity aimed at raising biomass supply from forests are controversial, for example, in terms of GHG effects (see Section 1.4.2). Impacts on soils can range from detrimental to positive, depending on the site conditions and plants used [66, 67].

1.4.1 Land-Use Competition and Systemic Feedbacks

The rapidly rising prices of various agricultural commodities experienced around the year 2007 coincided with the substantial efforts taken to promote liquid fuels from biomass in both the United States and Europe, triggering the so-called food-vs-fuel debate [9]. The proposal to shift from the so-called first generation biofuels derived from food crops (wheat, maize, soy, rape, sugarcane, etc.) to the so-called second generation lignocellulose crops such as short-rotation coppice or perennial C4-grasses was also motivated by the intention to reduce competition between food and energy for feedstocks. However, those plants also need limited resources like productive land and water, and hence the problem of competition remains on the agenda [32, 39, 68].

Basically, the underlying issue is that approximately three quarters of the earth’s land are already used, hence almost any additional biomass production requires either intensification or replacement of existing land uses by others, that is, land-use competition. The broad land-use classes distinguished by Erb et al. [31] are useful in that context because they can be unambiguously related to main socioeconomic biomass flows [19, 28]; Figure 1.2:

Settlement areas and infrastructures which currently cover ~1.4 Mkm² are expected to grow due to drivers such as population or GDP growth [69], primarily consuming fertile lands that are currently often used for cropping.

Croplands currently cover some 15.2 Mkm² and deliver >50% of all biomass harvested and used by humans. It is expected that cropland yields will continue to rise substantially (by +54% on average), such that a modest growth of cropland area (+9%) could be sufficient to support the expected increases in agricultural output [34]. Not all experts are similarly optimistic, however. For example, it has been argued that yield growth is slowing down in many regions due to soil degradation or exhaustion of potentials to optimize crop plants or due to poor management [70]. Current rates of yield growth will not be sufficient to support a doubling of crop production until 2050 [71]. Analyses of the scenario suggest that the currently existing cropland areas are unlikely to be sufficient for food production except if frugal diets are adopted [37, 52]. Shifts in animal-product consumption from ruminants (cattle, sheep, goats) towards pigs and poultry—though generally beneficial in terms of GHG emissions per food calorie [72]—could drive up cropland demand as only ruminants can subsist exclusively or mainly on roughage. On visualizing a global transition towards organic agriculture, it was estimated that the average crop yields would be 25% lower than in the FAO scenario quoted above, which could affect global cropland demand [42]. The potentials for generating additional biomass for energy or raw material supply from areas currently used as cropland are limited, even if a strong growth in food crop yields is expected [37].

Grazing and other land is a heterogeneous category of land use covering 46.9 Mkm² and currently delivering 3.8 Gt/year of roughage [4]. This land-use class includes all land not explicitly included in one of the other four land-use classes discussed here, that is, meadows and pastures, savannas, drylands or shrublands. Only parts of these classes of land are reasonably productive, and large parts are quite unproductive [31]. Most of this land is grazed, but grazing may be fairly extensive depending on the location. This land-use class includes all land classified as abandoned, degraded or residual, except for reforested land included in the forestry category. NPPact of this land is about 11% lower than NPPpot due to degradation [28]. The amount of NPP remaining in ecosystems (NPPeco) on that land is substantial (37.1 Gt/year), and efforts to raise biomass supply from currently non-forested land will almost always affect that land resource, either directly (by conversion of land within that category) or indirectly (through displacement of food crops). Possible future changes in livestock feeding efficiencies could play an important role for roughage demand as well—as evidenced by the currently huge differences between livestock energy input-output rates prevailing globally [73–75]. However, raising feeding efficiency usually involves increased feed quality, which may result in higher demands for fodder from cropland.

Land used for forestry extends globally over 35 Mkm² and delivers currently some 3.3 Gt/year of dry-matter biomass. This land-use category includes all forests, except those classified as pristine and included in the unused lands category discussed below. Potentials to raise biomass supply from forestry have been discussed in Section 1.3, and their ecological and GHG feedbacks are summarized below. Deforestation of cropland or grazing land would likely reduce the area under forestry and could reduce biomass supply potentials of that land [47].

Unused lands: Remnants of pristine tropical forests are, by and large, the only highly productive ecosystems comprised within that category of land [31]. Both biodiversity losses and carbon emissions resulting from using that land for biomass supply are prohibitively high [9]. This does not imply that these lands will not be used for food, fiber, or energy supply in the future—but model results clearly show that failure to protect these ecosystems would result in strongly reducing if not negating any positive effects that increased biomass use is intended to entail [76].

One may conclude that almost any option to raise primary biomass harvest will result in systemic feedbacks [7, 30]. These need not always be adverse. For example, integration of tree-based bioenergy production with food crops, either through rotations or through mixed land-use patterns, can produce bioenergy while helping to restore degraded or waterlogged agricultural soils and sequestering carbon [66]. However, land deemed suitable for the production of biomass feedstocks [77] is seldom entirely unused: Often it is used for grazing or as fallow land in rotational cropping systems by agro-pastoralists and subsistence-oriented farmers who are not accounted for in official statistics, or for extensive grazing, hunting, forestry and the collection of non-timber forestry products [9, 78]. A recent case study showed that introduction of the energy crop Jatropha to raise fuel output of alleged wastelands in Tamil Nadu, South India, would indeed replace existing subsistence-oriented bioenergy production based on Prosopis, thereby reducing useful energy supply from biomass by about 60–90% [79]. Abandoned land often hosts regenerating vegetation that supports biodiversity and carbon stocks in regenerating vegetation and soils [80, 81]. Therefore, expectations to produce huge amounts of bioenergy from unused or degraded lands [82] without facing trade-offs or issues of land-use competition deserve further scrutiny.

1.4.2 Carbon Cycle Feedbacks

The notion that use of biomass for energy would be carbon neutral vis-a-vis the atmosphere because carbon released during biomass combustion is absorbed during plant regrowth is widespread but inaccurate [83]. This carbon neutrality assumption ignores the complexity of feedbacks associated with producing and using biomass discussed above, as well as the legacy effects related to past land use [84]. Indeed, simple logics dictates that combustion of biomass is only carbon neutral either (i) if the biomass was sourced from plant growth that was additional compared to a hypothetical situation without biomass combustion or (ii) if it was sourced from biomass flows that would have decayed rapidly if not used for combustion—in other words, when feedbacks of biomass use with the terrestrial carbon sink are considered [85].

One of the processes that has gained prominence is the indirect land-use change effect, that is, the displacement effect resulting from the conversion of croplands from food to energy crops that results in increased food crop production and potentially deforestation and hence carbon emissions elsewhere [16, 17, 86]. Although that feedback is difficult to gauge, it is clear that it must be considered to correctly evaluate the full GHG effects of bioenergy [7, 87]. Another important mechanism is that harvest levels in forestry may affect the amount of carbon stored in the forest ecosystems, thereby affecting the forest’s carbon balance [88]. Due to the complexity of stock-flow relations of carbon in forest ecosystems [89] and the multitude of factors involved, this issue is atpresent not satisfactorily resolved [17], but it is clear that the simple assumption that biomass from forests were carbon neutral vis-à-vis the atmosphere needs to be abandoned [90, 91].

Even when timber is used in the construction sector, where it replaces energy-intensive materials such as concrete, steel, or aluminum and a substantial fraction of the carbon is stored for dozens if not hundreds of years in building frames, issues related to the carbon balance of the forests from which the timber is sourced have gained attention [92]. In that case, however, most analysts agree that timber is a low GHG option compared to its substitutes, in particular when forest management and wood use cascades (i.e., use of byproducts and wastes for energy) are optimized [93].

1.5 Conclusions

Biomass is a key resource for humans and ecosystems alike. Great expectations exist that increased biomass use will help to alleviate scarcity of critical raw materials, will help in substituting non-renewable fossil fuels and will contribute to mitigating climate change. While biomass can indeed contribute to those goals, critical issues related to land-use competition and other systemic feedbacks of biomass supply need to be addressed. While the increased use of wastes and residues within a strategy of cascade utilization is seen as largely benign if residue extraction on croplands does not exceed sustainable limits, establishment of dedicated plantations to grow additional amounts of biomass may result in detrimental effects related to land-use competition and hence needs appropriate and effective political framework conditions, for example, land-use zoning [7, 9].

Open scientific questions refer to the area that can be used sustainably for non-food biomass, to the potential to raise crop yields of both food and energy crops through sustainable intensification [94], to the rebound effects that may follow from increases in yield and other measures to raise efficiency, to the trade-offs between environmentally less demanding cultivation methods such as organic agriculture and area demand as well as to options to influence diets and reduce losses in the food-supply chain [30]. An option that merits scrutiny is to jointly optimize food and energy production through improved crop rotation schemes and the re-integration of cropping and livestock to close nutrient cycles. First attempts [95] suggest that such a strategy could indeed help raising both food and energy outputs of agriculture without land-use competition.

Acknowledgements

Research funding within the EU-FP7 project VOLANTE (grant agreement no. 265104) and the Austrian Science Fund (FWF), project P20812-G11 is gratefully acknowledged. This article contributes to the Global Land Project (http://www.globallandproject.org). The chapter was partly written during a research sojourn at the Integrative Research Institute on Transformations in Human-Environment Interactions at Humboldt-University zu Berlin.

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