Department of Agricultural and Consumer Economics , University of Illinois Urbana-Champaign , 301A Mumford Hall, 1301 W. Gregory Drive, Urbana, IL 61801 , USA.
Interface Focus. 2011 Apr 6;1(2):233-47. doi: 10.1098/rsfs.2010.0016. Epub 2011 Feb 2.
Biofuels have gained increasing attention as an alternative to fossil fuels for several reasons, one of which is their potential to reduce the greenhouse gas (GHG) emissions from the transportation sector. Recent studies have questioned the validity of claims about the potential of biofuels to reduce GHG emissions relative to the liquid fossil fuels they are replacing when emissions owing to direct (DLUC) and indirect land use changes (ILUC) that accompany biofuels are included in the life cycle GHG intensity of biofuels. Studies estimate that the GHG emissions released from ILUC could more than offset the direct GHG savings by producing biofuels and replacing liquid fossil fuels and create a 'carbon debt' with a long payback period. The estimates of this payback period, however, vary widely across biofuels from different feedstocks and even for a single biofuel across different modelling assumptions. In the case of corn ethanol, this payback period is found to range from 15 to 200 years. We discuss the challenges in estimating the ILUC effect of a biofuel and differences across biofuels, and its sensitivity to the assumptions and policy scenarios considered by different economic models. We also discuss the implications of ILUC for designing policies that promote biofuels and seek to reduce GHG emissions. In a first-best setting, a global carbon tax is needed to set both DLUC and ILUC emissions to their optimal levels. However, it is unclear whether unilateral GHG mitigation policies, even if they penalize the ILUC-related emissions, would increase social welfare and lead to optimal emission levels. In the absence of a global carbon tax, incentivizing sustainable land use practices through certification standards, government regulations and market-based pressures may be a viable option for reducing ILUC.
生物燃料因其诸多优势，逐渐受到关注，成为化石燃料的替代品。其中一个原因是，生物燃料具有减少温室气体（GHG）排放的潜力，尤其是在交通运输领域。然而，最近的研究对生物燃料相对于其替代的液体化石燃料在减少温室气体排放方面的潜力提出了质疑。在将生物燃料生命周期内的温室气体强度所产生的直接土地利用变化（DLUC）和间接土地利用变化（ILUC）排放纳入考虑范围后，生物燃料减少温室气体排放的说法受到了质疑。研究估计，由于生物燃料生产和液体化石燃料替代而产生的 ILUC 排放的温室气体排放量可能会超过直接温室气体减排量，从而产生“碳债务”，并需要很长的时间才能偿还。然而，这种偿还期的估计在不同的生物燃料之间差异很大，即使是对于同一种生物燃料，在不同的建模假设下也存在差异。就玉米乙醇而言，这种偿还期的范围从 15 年到 200 年不等。我们讨论了估算生物燃料 ILUC 效应的挑战以及不同生物燃料之间的差异，以及其对不同经济模型所考虑的假设和政策情景的敏感性。我们还讨论了 ILUC 对设计促进生物燃料和减少温室气体排放的政策的影响。在最佳情况下，需要全球碳税来将 DLUC 和 ILUC 排放设定在最佳水平。然而，尚不清楚单边温室气体减排政策，即使对与 ILUC 相关的排放进行处罚，是否会提高社会福利并导致最佳排放水平。在没有全球碳税的情况下，通过认证标准、政府法规和市场压力来激励可持续的土地利用实践可能是减少 ILUC 的一种可行选择。
