ReviewBiofuels, biodiversity, and people: Understanding the conflicts and finding opportunities
Introduction
Fossil fuels (oil, natural gas, and coal) contribute to ∼80% of total world energy supply (Goldemberg and Johansson, 2004, Goldemberg, 2007). Depending on production and consumption rates, the presently known reserves of fossil fuels are estimated to last anywhere from 41 to ∼700 years (Goldemberg and Johansson, 2004, Goldemberg, 2007). The finitude of fossil fuels, concerns for energy security and the need to respond to climate change have led to growing worldwide interests in renewable energy sources such as biofuels. An increasing number of developed [e.g., the United States (US)] and rapidly developing nations (e.g., China) see biofuels as a key to reducing reliance on foreign oil, lowering emissions of greenhouse gases (GHG), mainly carbon dioxide (CO2) and methane (CH4), and meeting rural development goals (Fulton et al., 2004, Armbruster and Coyle, 2006, Pickett et al., 2008). Between 1980 and 2005, worldwide production of biofuels increased by an order of magnitude – from 4.4 to 50.1 billion litres (bbl Fig. 1; Murray, 2005, Armbruster and Coyle, 2006), with further dramatic increases since (FO Licht 2008). However, political and public support for biofuels has been undermined due to environmental and food security concerns as well as by recent reports questioning the rationale that biofuels substantially reduce carbon emissions. The diversion of food crops or croplands to produce biofuels has been blamed for global food shortages and associated increasing costs of staple food crops such as maize and rice (James et al., 2008, Josserand, 2008, Rahman et al., 2008). Also, recent research suggests that certain biofuel production pathways may lead to net positive GHG emissions or substantial carbon debts (e.g., the conversion of carbon-rich peatland to oil palm plantations in Southeast Asia; Crutzen et al., 2008, Fargione et al., 2008, Scharlemann and Laurance, 2008, Searchinger et al., 2008). Nevertheless, some policy makers and scientists remain optimistic that with the development of ‘next generation’ biofuels such as cellulosic ethanol, there are real opportunities for using biomass to meet some of our energy needs (Farrell et al., 2006, Ragauskas et al., 2006, Field et al., 2008). The overall objectives of this review are to (i) discuss the promise of biofuels as a renewable energy source, (ii) critically evaluate the environmental and societal costs of biofuel use, and (iii) highlight on-going developments in biofuel feedstock (raw material) selection and production technologies, and the implications of these developments for biodiversity and conservation.
Section snippets
The promise of biofuels
Biofuels are renewable fuels derived from biological feedstocks, and include both liquid forms such as bioethanol (gasoline-equivalent) or biodiesel (diesel-equivalent), and gaseous forms such as biogas (e.g., methane) or hydrogen. In this review, we focus our discussion on liquid biofuels. Bioethanol is by far the most common biofuel in use worldwide (Fulton et al., 2004). Global bioethanol production increased from 4.4 bbl in 1980 to 46.2 bbl in 2005 (Fig. 1; Murray, 2005, Armbruster and Coyle,
Environmental and societal tradeoffs
Despite the considerable benefits of biofuel use, they are not without their tradeoffs. We discuss some of these below.
The future of biofuels
Over the last few years, biofuels have garnered worldwide interests for their potential to reduce GHG emissions, improve energy security, and enhance rural development. At the same time, reports on the environmental and societal costs associated with biofuel production have stirred up a storm of controversy. Nevertheless, there remain several silver linings – in terms of on-going developments in feedstock selection and production technologies – that may yet allow biofuels to fulfill their
Conclusion
Rising fuel prices coupled with concerns about carbon emissions are making biofuel production more cost competitive and attractive (Table 1). There are global implications for the shift towards biofuels, and in this review paper, we have highlighted net positive GHG emissions, threats to forests and biodiversity, food price increases, and competition for water resources as the key negative impacts of biofuel use. On the other hand, we have also shown that the development and use of next
Acknowledgements
L.P.K. is supported by an ETH Fellowship for postdoctoral research. We thank P. Levang and R.A. Butler for comments and discussion.
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