Biofuels, greenhouse gases and climate change. A review Cécile Bessou, Fabien Ferchaud, Benoit Gabrielle, Bruno Mary To cite this version: Cécile Bessou, Fabien Ferchaud, Benoit Gabrielle, Bruno Mary. Biofuels, greenhouse gases and climate change. A review. Agronomy for Sustainable Development, Springer Verlag/EDP Sciences/INRA, 2009, pp.1-79. 10.1051/agro/2009039. cirad-00749753 HAL Id: cirad-00749753 http://hal.cirad.fr/cirad-00749753 Submitted on 8 Nov 2012 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Agron. Sustain. Dev. Available online at: c INRA, EDP Sciences, 2010 www.agronomy-journal.org DOI: 10.1051/agro/2009039 for Sustainable Development Review article Biofuels, greenhouse gases and climate change. A review Cécile B1*,FabienF2, Benoît G2, Bruno M2 1 INRA Environment and agricultural crop research unit, 78 850 Thiverval-Grignon, France 2 INRA, US1158 Agro-Impact, 02 007 Laon-Mons, France (Accepted 23 September 2009) Abstract – Biofuels are fuels produced from biomass, mostly in liquid form, within a time frame sufficiently short to consider that their feed- stock (biomass) can be renewed, contrarily to fossil fuels. This paper reviews the current and future biofuel technologies, and their development impacts (including on the climate) within given policy and economic frameworks. Current technologies make it possible to provide first gener- ation biodiesel, ethanol or biogas to the transport sector to be blended with fossil fuels. Still under-development 2nd generation biofuels from lignocellulose should be available on the market by 2020. Research is active on the improvement of their conversion efficiency. A ten-fold increase compared with current cost-effective capacities would make them highly competitive. Within bioenergy policies, emphasis has been put on biofuels for transportation as this sector is fast-growing and represents a major source of anthropogenic greenhouse gas emissions. Compared with fossil fuels, biofuel combustion can emit less greenhouse gases throughout their life cycle, considering that part of the emitted CO2 returns to the atmosphere where it was fixed from by photosynthesis in the first place. Life cycle assessment (LCA) is commonly used to assess the potential environmental impacts of biofuel chains, notably the impact on global warming. This tool, whose holistic nature is fundamental to avoid pollution trade-offs, is a standardised methodology that should make comparisons between biofuel and fossil fuel chains objective and thorough. However, it is a complex and time-consuming process, which requires lots of data, and whose methodology is still lacking harmonisation. Hence the life-cycle performances of biofuel chains vary widely in the literature. Furthermore, LCA is a site- and time- independent tool that cannot take into account the spatial and temporal dimensions of emissions, and can hardly serve as a decision-making tool either at local or regional levels. Focusing on greenhouse gases, emission factors used in LCAs give a rough estimate of the potential average emissions on a national level. However, they do not take into account the types of crop, soil or management practices, for instance. Modelling the impact of local factors on the determinism of greenhouse gas emissions can provide better estimates for LCA on the local level, which would be the relevant scale and degree of reliability for decision-making purposes. Nevertheless, a deeper understanding of the processes involved, most notably N2O emissions, is still needed to definitely improve the accuracy of LCA. Perennial crops are a promising option for biofuels, due to their rapid and efficient use of nitrogen, and their limited farming operations. However, the main overall limiting factor to biofuel development will ultimately be land availability. Given the available land areas, population growth rate and consumption behaviours, it would be possible to reach by 2030 a global 10% biofuel share in the transport sector, contributing to lower global greenhouse gas emissions −1 by up to 1 GtCO2eq.year (IEA, 2006), provided that harmonised policies ensure that sustainability criteria for the production systems are respected worldwide. Furthermore, policies should also be more integrative across sectors, so that changes in energy efficiency, the automotive sector and global consumption patterns converge towards drastic reduction of the pressure on resources. Indeed, neither biofuels nor other energy source or carriers are likely to mitigate the impacts of anthropogenic pressure on resources in a range that would compensate for this pressure growth. Hence, the first step is to reduce this pressure by starting from the variable that drives it up, i.e. anthropic consumptions. biofuels / energy crops / perennials / LCA / greenhouse gases / climate change / political and economic frameworks / bioenergy potential / land-use change / nitrous oxide / carbon dioxide / agricultural practices Contents 1 Introduction ........................................................ 2 2 Definitions ......................................................... 3 3 Transportation biofuels.............................................. 6 3.1 First generation biofuels ....................................... 6 3.1.1 Biodiesel .............................................. 6 * Corresponding author: [email protected] Article published by EDP Sciences 2 C. Bessou et al. 3.1.2 Ethanol .......................... 7 3.1.3 Biogas .......................... 8 3.2 Current 1st generation biofuel supply worldwide ........ 13 3.3 Towards 2nd and 3rd generations of biofuels ........... 13 4 Political and economic frameworks ................... 18 4.1 Climate change and greenhouse gas emission trends ....... 18 4.2 Biofuel-related policies ...................... 21 4.2.1 European policies ..................... 21 4.2.2 US policies ........................ 22 4.2.3 Chinese policies ..................... 23 4.3 Economic incentives ....................... 24 5 Biofuels and greenhouse gases ..................... 28 5.1 Assessing the environmental impacts of biofuels ......... 28 5.1.1 Life cycle assessment of biofuel chains ......... 28 5.1.2 Limits of the LCA tool .................. 31 5.2 Focus on greenhouse gas emissions from agriculture .......................... 35 5.2.1 Overview of greenhouse gas emissions from agriculture ..................... 36 5.2.2 N2O emissions ...................... 37 5.3 Biofuel greenhouse gas balances ................. 47 5.3.1 Prospects for reducing greenhouse gas emissions from biomass production .................... 47 5.3.2 Improving fertilisation efficiency ............. 50 5.3.3 Other cultural practices .................. 51 6 The quantitative potential of biofuels ................................ 52 6.1 Biomass availability : bottom-up approach ............ 52 6.1.1 Bottom-up models .................... 53 6.1.2 Availability of agricultural land ............. 54 6.1.3 Biomass from forest and residues ............ 56 6.1.4 Geographical distribution ................. 59 6.2 Focus on Europe ......................... 62 6.3 Liquid biofuel potential : top-down approach .......... 63 6.4 Projected worldwide biofuel production and consumption ......................... 65 6.5 Impact of biofuels on agricultural commodity prices ............................... 66 7 Conclusion ............................... 68 1. INTRODUCTION around 6.5 billion people today to 8.3 in 2030 (UN, 2006). World energy demand is expected to rise by some 60% by Until the middle of the 19th century, American citizens lit 2030. More than two-thirds of the growth in world energy their houses with whale-oil lamps. In 1892, the first Rudolf use will come from the developing countries, where economic Diesel motor ran on peanut oil. Liquid fuels can be easily and population growths are highest (CEC, 2006a). Fossil fu- stored and transported and offer, for a given volume, a better els will continue to dominate energy supplies, meeting more exchange surface for combustion compared with solid fuels. than 80% of the projected increase in primary energy demand. Oils, in particular, can deliver a high energy amount by volume Global oil reserves today exceed the cumulative projected pro- unit. No wonder then that biofuels were the first candidates to duction between now and 2030, but reserves will need to be supply the newly developing automotive industry. However, “proved up” in order to avoid a peak in production before the they were almost immediately overtaken by petroleum prod- end of the projection period. Effective exploitation capacity to- ucts that appeared to be an energy godsend, remaining very day is almost fully used, so growing demand for refined prod- cheap for more than a century. However, today the Black Gold ucts can only be met with additional capacity (IEA, 2005). Age is coming to an end. The exact cost of finding and exploiting new resources over In 2005, the world total primary energy supply approx- the coming decades is uncertain, but will certainly be substan- imated 11 430 Mtoe