Searchinger et al. (2008) have shown by careful modelling of land use change that a large and fast expansion of bioethanol production from corn in the USA is coun­terproductive in tackling climate change. This is largely related to the land use change necessary for displaced food and feed production, which leads to a large desequestration of C. It is likely that a similar conclusion applies to biofuel produc­tion in Europe. Regarding Brazil, it has been shown that soybean-based biodiesel is counterproductive in tackling climate change (Reijnders and Huijbregts 2008a), and the same holds for palm-oil-based transport biofuels for which tropical forests are cleared (Danielsen et al. 2008; Fargione et al. 2008; Reijnders and Huijbregts 2008a).

As explained in Chap. 3 and as also pointed out by Fargione et al. (2008), any strategy aiming at expanding transport biofuel production by converting native wooded ecosystems to cropland is likely to be counterproductive in tackling climate change in the coming decades. When abandoned or fallow land over a number of decades has developed into a secondary forest (e. g. Grau et al. 2003), the same will probably apply. In the case that abandoned or fallow agricultural land is peat land, further C losses from soil will be greater than C gains to be made by reductions in fossil fuel use associated with biofuel use, possibly for many centuries (Reijn — ders and Huijbregts 2007; Danielsen et al. 2008; Fargione et al. 2008; Reijnders and

Huijbregts 2008a). Moreover, restoration of peat bogs may lead to the additional sequestration of C (Tuittila et al. 1999; Dukes 2003).

This leaves a limited number of terrestrial transport biofuel options conducive to tackling climate change. It would seem that from the point of view of effectiveness in limiting climate change, the burning of biofuels in power plants for use in electric traction is to be preferred, as the solar energy conversion efficiency is relatively high and net greenhouse gas emissions relatively low, as indicated in Chaps. 2 and 4.

The biofuel options that can help in tackling climate change are the following:

1. Linking biofuel use to the man-made sequestration of C in soils. This may be done as soil organic matter (Blaine Metting et al. 2001; Read 2008), as ‘biochar’ (Lehman et al. 2006) or as CO2. Examples of the latter option are: burning biofuels in power plants for electrical traction and sequestration of CO2 in de­pleted oil and gas fields or aquifers (Haszeldine 2006; Mathews 2008). Simi­larly, CO2 generated during fermentation or anaerobic conversion of biomass (into compounds such as ethanol, methane and hydrogen) might be captured or sequestered.

2. Limited use of residues of forestry and agriculture as feedstocks for biofuel production. Limitations in part stem from sustainability requirements. The scope of residue removal is, as pointed out in Chap. 3, limited by the need to maintain soil carbon and nutrient stocks, because otherwise future productivity will be impaired. Moreover, some conversions of agricultural residues do not appear to make energetic sense, such as, for instance, the conversion of swine and bovine manure into methane in NW Europe (cf. Chap. 2).

3. Producing biofuels in areas with currently relatively little aboveground biomass, as also discussed in Sect. 6.3, for instance within the framework of reclaiming deserts and reclamation of saline soils and on abandoned lands (Lal and Bruce 1999; Banetjee et al. 2006; Germer and Sauerborn 2007; Danielsen et al. 2008; Lal 2008).

However, from the point of view of mitigating climate change, alternative uses of land with currently little aboveground biomass merit consideration. In the case of abandoned and fallow agricultural mineral soils which may support secondary forests, transport biofuel production — as, for instance, proposed by Cunha da Costa (2004) for deforested areas in the Brazilian Amazon — may be compared to C se­questration linked to re-growth of forest. For instance, in the case of Saccharum spontaneum grasslands in Panama that preclude forest regeneration, it has been found that low-cost management options exist for restoring forest cover (Hooper et al. 2005). And also in other contexts, feasible ways have been developed to convert degraded agricultural land into secondary forests (Vieira and Scariot 2006; Cummings et al. 2007). In doing so, high levels of C sequestration may be achieved. Steininger (2000) found in the Brazilian Amazon a biomass accumulation of, on average, 9.1Mgha~1year~1 over a 12-year period, whereas Zarin et al. (2001), studying re-growth of Amazonian forests, found for a 20-year period an average sequestration of about 6 Mg biomass ha^year-1. These values are well above the amount of C that can be displaced by, for example, growing soybeans for biodiesel production (Reijnders and Huijbregts 2008b). Righelato and Spracklen (2007) esti­mated that as to tackling climate change during the coming decades, the gains per hectare of reforestation would be higher than those from most biofuels. Expansion of secondary forests is now a substantial development in Latin America, Africa and Southeast Asia (Lambin et al. 2003) and is known to have been successful in coun­tries like Puerto Rico, Bhutan, Vietnam, Gambia and Cuba (Chazdon 2008). All in all, an estimated 96 x 106 ha of abandoned agricultural land has been reforested (Field etal. 2008).

Another alternative that merits consideration in cases where forests may be re­established is agroforestry, which has been advocated as more in line with the press­ing needs of local populations than plantations (De Foresta and Michon 1996), and has now been successfully applied in a number of countries, including the Philippines, Peru, Indonesia, China and Vietnam (Chazdon 2008). Agroforestry allows for substantial sequestration of C. For instance, the cacao agroforests of humid Africa sequester up to about 62% of the C of primary forests (Duguma et al. 2001), and rates of C sequestration in agroforests varying from 2-9 Mg C ha-1year-1 have been found (Pandey 2002). Of course, comparisons with alterna­tives such as secondary forests and agroforestry are only meaningful when there is not a fixed mandate for biofuel production. When there is such a fixed man­date, growth of crops for transport biofuel production will move elsewhere, and may, for instance, be associated with cutting down virgin forests (a phenomenon called leakage, discussed in Sect. 1.4). Also, as stated in Sect. 1.4, one should re­alize that expansion of secondary forests and agroforestry as such do not provide fuels.