Indirect land-use change emissions and the GHG effect of biofuels

Searchinger et al. (2008) have found that taking into account indirect land-use change emissions that arise from converting more natural lands to agricultural as a result of biofuels’ displacement of croplands, actually results in major extra GHG emissions compared to fossil fuels. For example, they concluded that the production of ethanol from corn in the US increases GHG emissions relative to fossil fuels for 167 years and double the emissions in the next 30 years, instead of reducing the emissions by 20% as suggested by studies not accounting for indirect land-use changes. Even switchgrass, previously deemed to be particularly GHG-saving, results in 50% increase in emissions in the medium-term, according to Searchinger et al. (2008).

Similarly pessimistic results are obtained by Mellilo et al. (2009), who found that due to the indirect land-use change emissions, greater GHG emissions will result if natural lands conversion is involved (i.e. indirect land-use change), instead of a case where agricultural lands are used more intensely without the extra indirect land-use change emissions. Additionally, the time it takes for the carbon emissions to become favourable is less where no indirect land-use changes are involved, taking 30-50 years on average instead of over 100 years for indirect land-use changes (Table 1). Therefore, due to the major medium-term emissions, the authors suggest that conversion of natural lands will be unfavourable overall, where net GHG saving in the long-term will not compensate for the potential global warming contribution effect caused by the initial indirect emissions. At the same time, a more intensive use of agricultural lands is likely to require so much fertilizer, that this activity may also become unfavourable in terms of nitrous oxide emissions in the longer term. 

Variable       Case 1                                                Case 2

Time period 2000–2030 2000–2050 2000–2100    2000–2030 2000–2050 2000–2100 

Direct land C       11             27                 0                  –52            –24              –7

Indirect land C    190           57                  7                  181             31                1

Fertilizer N₂O      29            28                 20                  30              26                19

Total                    229          112               26                  158             32                13

Table 1. Carbon intensity index using cellulosic biofuels under scenario1 - natural lands are converted to biofuels and scenario 2 - croplands are used more intensively to produce crops and biofuels; in g CO₂eq MJ^–1

If indirect land-use change emissions from natural lands conversion result in unfavourable medium-term emissions and the more intense use of agricultural land results in unfavourable direct emissions, does that mean that biofuels are a blind alley and there is no point in me continuing to write this blog?

Well, fortunately, not all is lost. Firstly, the results of the analysis by Mellilo et al. (2009) only apply to healthy natural lands and to high-value agricultural lands. However, the authors suggest a potentially favourable GHG emissions outcome if using natural degraded lands and low-value lands that were previously utilized for anthropogenic activities, including degraded agricultural areas and lands which have already been deforested.

Secondly, there are some limitations to these studies calculating indirect land-use change emissions. They model uncontrolled biofuel expansion, not accounting for sustainability regulations in the EU such as the prohibition of converting lands where the indirect emissions means emissions reduction is less than 35% compared to fossil fuels (Lange, 2011). Additionally, they attribute 100% of the indirect GHG emissions to biofuels. These limitations make those studies unrealistic, only showing the worst-case scenario.