Towards the implementation of sustainable biofuel production systems
Graphical abstract
Introduction
Boosting economic growth while halting environmental degradation remains one of the major global challenges for humankind [1]. Current unsustainable use of the Earth’s finite natural capital [2] has led to a wide range of negative impacts on the environment [3], including increasing biodiversity losses [4], alterations in the provision and quality of ecosystem services [5], and climate change [6]. These impacts and the decisions that society makes to reduce them, which include balancing human population growth [7] and planning for solutions based on multiple interacting environmental pressures [8], will have profound implications for global socioeconomic and environmental systems.
How to meet increasing energy consumption demands, while reversing environmental degradation, is a matter of debate [9]. Currently, the provision of energy relies primarily on fossil fuels, with around 5.8 × 1011 GJ consumed globally in 2016, of which 81% was derived from coal, petroleum, and natural gas [10]. Their associated greenhouse gas (GHG) emissions are linked to global warming and its negative impacts on biodiversity [11] and ecosystem services [12]. Limiting global warming to well below 2 °C compared to pre-industrial levels, a goal ratified by 185 parties (i.e., on February 2019) following the 21st Conference of the Parties to the United Nations Framework Convention on Climate Change (UNFCCC) in Paris [13], is expected to require the rapid adoption of renewable energy systems for replacing fossil fuels [14]. Consequently, the share of energy from renewable sources could increase from 9% of total primary energy demands in 2016 to 29% by 2040 [10].
While solar, wind and water as renewable energy sources could provide electricity with lower environmental costs compared to fossil fuels [15], liquid fuels are expected to remain necessary in the transport sector—mainly for aviation, shipping, and long-haul trucking—in spite of an expected increase in electric vehicles [16]. In fact, some scenarios for limiting global warming to 2 °C foresee biofuel production increasing from 9.7 × 106 GJ d-1 to 4.6 × 107 GJ d-1 between 2016 and 2040, reaching 16% of total transport fuels [10], though it remains unclear to what degree biofuel adoption would reduce net GHG emissions compared to other climate change mitigation options [17].
Current biofuel production is based on food crops (i.e., first generation biofuels) that compete with agricultural lands and biodiverse landscapes (Box 1, Fig. 1). Furthermore, biofuel production has been linked to several other environmental pressures that may, directly and indirectly, impact biodiversity and the provision of ecosystem services. These pressures [18] include direct and indirect land-use change [19], GHG emissions [20], emission of pollutants (i.e., from pesticides, fertilizers, biofuel production, and final use of biofuels) [21], water depletion [22], soil degradation and erosion [23], and introduction of invasive species [24]. The impacts of biofuels on biodiversity and ecosystem services, however, depend on the type of biofuel production system and several factors associated with its cultivation and production [19], including: the competing land-use and the spatial configurations of biofuel cultivation landscapes [25], their cultivation and conversion technologies [21], their cultivation management practices [26], their invasiveness potential [27], and the presence of co-products (Box 2) [28].
How to identify and implement more sustainable biofuel production alternatives [51], and how to overcome economic obstacles to their implementation, are unresolved challenges [52]. Here, the environmental impacts of several biofuel production alternatives (i.e., first, second, and third generation biofuels) on biodiversity and ecosystem services are evaluated. This information is integrated with criteria and avenues of research for guiding the identification and implementation of sustainable biofuel production alternatives (i.e., those that maximize socioeconomic and environmental benefits). Finally, promising strategies for overcoming economic barriers to adopt more sustainable biofuel production systems are discussed.
Section snippets
An overview of the environmental impacts of several biofuel production alternatives
First generation biofuels, which compete with agricultural and biodiverse lands, have led to habitat loss for native species [53] and associated GHG emissions [20] (Box 3). This mainly occurs by the direct replacement of biodiverse and carbon-rich original systems (i.e., direct land-use change) [19], and by the agricultural expansion outside biofuel production areas [43] as a consequence of increases in food prices generated by the competition with food production (i.e., indirect land-use
Identifying and implementing sustainable biofuel production alternatives
If humankind is to halt further biodiversity losses and overall environmental degradation while limiting global warming [13], the identification and implementation of biofuel production systems must ensure that overall socioeconomic and environmental benefits are achieved (Fig. 3). Price competitiveness, affordability [114], and reliability in comparison to fossil fuels [115] are essential for the deployment of biofuel production systems. Systems that are able to meet biofuel production targets
Economic profitability: a current barrier to the deployment of more sustainable biofuel production systems
Economic profitability is the main barrier to the deployment of more sustainable biofuel production systems. Currently, the lowest biofuel production costs are achieved by first generation biofuels, particularly for sugarcane bioethanol in Brazil and maize bioethanol in the USA, helped in part by government subsidies [160]. High costs for converting lignocellulosic feedstocks into biofuels [160] and high capital and operational costs for setting up microalgal production systems [161], reduce
Articulation of policies at the global, national, and regional level
The transition to a more sustainable transport sector can be fostered through the development of strategic policies that promote the adoption of sustainable biofuel production alternatives that are able to reduce environmental impacts and halt competition with food production [187]. The articulation of policies at global, regional, national, and local scales is a necessary step for guiding the implementation of sustainable biofuels (Fig. 6). The development of an updated global roadmap on
Conclusions
Bioenergy production is expected to increase from 9.7 × 106 to 4.6 × 107 GJ d-1 between 2016 and 2040 [10], and how biofuels are produced will determine their overall environmental impacts. The implementation of more sustainable biofuel production systems, which currently include sustainably sourced wastes, native perennial crop, and microalgal production systems produced on low-biodiversity or degraded lands, could reduce the magnitude of the several socioeconomic and environmental impacts
Acknowledgements
The authors are grateful for financial support from Cooperative Research Centre-Project CRC-P50538 and Meat and Livestock Australia (B.NBP.0695). Diego F. Correa acknowledges financial support for Ph.D. studies by the Colombian institution COLCIENCIAS (Convocatoria 529 para estudios de Doctorado en el exterior), by the University of Queensland (APA scholarship), and by the Australian Government (Endeavor Research Fellowship). We acknowledge the comments of three reviewers.
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