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Indirect land use change (ILUC) is a major negative consequence of biofuels where land undergoes conversion in a location other than initially intended

Summary

Indirect land use change (ILUC) refers to market-mediated land use changes that occur indirectly in response to biofuel production, often through price fluctuations that incentivize land conversion in other locations. With regard to biofuels, this phenomenon is controversial due to methodological variations and large uncertainties in results. Studies show ILUC can significantly increase carbon intensity of biofuels, with corn ethanol potentially increasing emissions by 93% when ILUC is considered when compared to its fossil fuel equivalent. The main variance with ILUC accounting centers on how much pristine land is converted versus marginal land. Second-generation biofuels grown on marginal land may reduce ILUC effects, but definitions of marginal land vary widely.

Indirect land use change is a major factor in evaluating the sustainability of biofuels. Land use change (LUC) is simply the change of one form of land usage to another. This is most simply illustrated by the expanded urbanization of a city, where formerly agricultural land is converted to urban land. Indirect land use change (ILUC) describes the indirect changes that are mediated by market responses, usually in response to price fluctuations that incentivize land use changes in areas other than the initial intended location of land use change 1.

Indirect land use change is highly controversial due to the variations in methodology, the large uncertainty in the final results, and the ability to include or exclude certain factors that may drastically change the final results 1. The credence given to the effects of indirect land use change also tends to align with the position of the person or organization that is evaluating the merit, with pro-biofuel entities emphasizing the best-case scenario while entities that are against biofuels tend to emphasize the worst-case scenario. Nonetheless, scientific studies that have investigated the effects of indirect land use change for the same crop type such as 1st generation corn ethanol have produced results ranging from significant contributions to increased carbon dioxide intensity, all the way to negligible effects 1.

Indirect land use change with 1st generation biofuels​

Indirect land use change became a major focus around the middle of the 2000s when the United States corn ethanol industry was booming. Causal connections were being observed throughout 2006–2007 between the expansion of corn ethanol and deforestation in the Amazon via the following chain of events that was dubbed the "corn connection" to Amazonian deforestation 2:

  1. Farmers in the United States were incentivized by government subsidies to transition from soybean production to corn production.
  2. Due to the subsidies, corn production increased by 16% while soybean production fell by 15%.
  3. The perturbation in soybean supply led to a near doubling of global soybean prices.
  4. The new high price of soybeans directly led to the clearing of Amazonian forest land to produce soybeans.
  5. A knock-on effect of the high soybean prices also led to the expansion into previously pasture land for cattle, thus pushing cattle farmers deeper into the Amazon.
  6. This then led to another price response for beef, as the higher soybean prices led to high beef prices (as soy is a major feedstock source) contributing to further expansion of pasture land into the Amazon.

Throughout this chain of events, it is also acknowledged that other factors such as dry weather and high fire risk also contributed to the deforestation witnessed. However, the majority of the increases in deforestation throughout the timeframe are generally attributed to rises in beef and soy prices 2.

The first rigorous quantification of the effects of indirect land use change in terms of their impact on carbon dioxide intensity was investigated a year later, with the study contending that the usage of biofuels ultimately comes down to a land use decision 3. The study by researcher T. Searchinger et al., which focused on biodiesel from soybeans, highlighted how ignoring indirect land use change results in biodiesel having a carbon intensity 54% less than conventional diesel over a 30-year timeframe 3. However, when indirect land use change is included, depending on which vegetable oil replaces the diverted soybean oil for biodiesel and the level to which yields increase in relation to oil prices, carbon intensity was between 75 and 299% greater than conventional diesel 3. For bioethanol from corn, the results were similar, with 20% less carbon intensity when indirect land use change is not included, but a 93% increase in emission intensity when indirect land use change is included over the same timeframe 4.

Much of the disagreement in how indirect land use change is calculated relates to how much pristine land (forest, wetlands, peatlands, etc.) is claimed for agriculture as a result of biofuels. If less pristine land and more marginal land is claimed (see section below), then the carbon intensity of the fuel will be significantly lower. Since the initial studies by Searchinger, new models have been developed using updated data sources that predict a diminished effect of indirect land use change 1. United States models such as those used to evaluate subsidies by the Environmental Protection Agency's (EPA) Renewable Fuel Standard 2 (RFS2) or the California Air Resources Board's (CARB) Low Carbon Fuel Standard (LCFS) predict almost half the amount of indirect land use change 1. However, although estimating a similar magnitude of indirect land use change, the RFS2 standard estimates that 65% will be sourced from forest land primarily in Latin America, whereas the LCFS study assigns only 22% of the total indirect land use change to forest land, stating that most of the conversions will occur within the United States 1.

Second generation biofuels and marginal land​

The ability to utilize marginal land for biofuels is a key talking point in assessing the sustainability of 2nd generation biofuels, especially with energy crops, and this ability can dampen the effects of indirect land use change by diminishing the encroachment of agricultural land into pristine land. Crops such as switchgrass, miscanthus, and jatropha have the ability to grow on marginal land at the cost of lower biomass yields, and in some cases, they can rehabilitate areas that are suffering from soil erosion or higher salinity. However, the term 'marginal land' is not well defined, with some definitions including 5:

  • Land that has a low agricultural value where cultivation of food and 1st generation biofuels are not cost effective.
  • Land that has low to zero profitability and a high risk of abandonment.
  • Land that contains biophysical constraints such as steep slopes and coarse rock fragments.
  • Agricultural land that has already been abandoned.
  • Land that contains moderate to high salinity.

As the definitions of marginal land can be based on economic factors or biophysical factors, it can be difficult to determine what is actually meant when saying that energy crops can be grown on marginal land. Nonetheless, attempts have been made to quantify how much marginal land is available in the United States and around the world for the cultivation of energy crops. Estimates for abandoned land are as high as 68 million hectares in the United States 6 and 470 million hectares globally 5. For global marginal lands, depending on the evaluation method, values lie between 247 and 1,248 million hectares 5.

Just because land is defined as marginal or abandoned does not mean that it isn't providing a service to the ecosystem. An example of this is the United States Conservation Reserve Program (CRP), which is a federal program that pays farmers to 'retire' land from agriculture for environmental reasons such as nutrient run off and air quality impacts. Between 2007 and 2012, when corn ethanol production more than doubled, the amount of land enrolled in the program reduced by 7.2 million acres, all while the CRP payments per acre rose by an average of 24% 7. In total, it was estimated the rise in corn ethanol production led to a conversion of 3.2 million acres of unused cropland 7.

Sources​

Footnotes​

  1. Broch, A., Hoekman, S. K., & Unnasch, S. (2013). A review of variability in indirect land use change assessment and modeling in biofuel policy. Environmental Science & Policy, 29, 147–157. https://doi.org/10.1016/j.envsci.2013.02.002 ↩ ↩2 ↩3 ↩4 ↩5 ↩6

  2. Laurance, W. F. (2007). Switch to Corn Promotes Amazon Deforestation. Science, 318(5857), 1721–1721. http://www.jstor.org/stable/20051791 ↩ ↩2

  3. Searchinger, T. D., & Heimlich, R. E. (2008). Estimating greenhouse gas emissions from soy-based US biodiesel when factoring in emissions from land use change. Biofuels Food and Feed Tradeoffs, Miami Beach, FL, January 29. ↩ ↩2 ↩3

  4. Searchinger, T., Heimlich, R., Houghton, R. A., Dong, F., Elobeid, A., Fabiosa, J., Tokgoz, S., Hayes, D., & Yu, T. H. (2008). Use of U.S. croplands for biofuels increases greenhouse gases through emissions from land-use change. Science, 319(5867), 1238–1240. https://doi.org/10.1126/science.1151861 ↩

  5. Russo, C., Cirillo, V., Pollaro, N., & et al. (2025). The global energy challenge: Second-generation feedstocks on marginal lands for a sustainable biofuel production. ChemBioTech Agriculture, 12, 10. https://doi.org/10.1186/s40538-025-00729-7 ↩ ↩2 ↩3

  6. Zumkehr, A., & Campbell, J. E. (2013). Historical U.S. cropland areas and the potential for bioenergy production on abandoned croplands. Environmental Science & Technology, 47(8), 3840–3847. https://doi.org/10.1021/es3033132 ↩

  7. Chen, X., & Khanna, M. (2018). Effect of corn ethanol production on Conservation Reserve Program acres in the US. Applied Energy, 225, 124–134. https://doi.org/10.1016/j.apenergy.2018.04.104 ↩ ↩2