Estimating Indirect Land Use Change Emissions from Biofuels

The Clean Air Task Force (CATF) submitted comments to the California Air Resources Board (ARB) arguing against reducing indirect land use change (ILUC) emissions estimates for biofuels. CATF contends that the GTAP model used by ARB undercounts emissions by ignoring water scarcity constraints, failing to distinguish between commercial and non-commercial forests, and using flawed yield improvement assumptions. Specifically, CATF cites research showing that accounting for irrigation constraints can increase land-based emissions by 27.5%. The document also highlights that climate-driven drought in the US Midwest may decelerate corn yields and that the current framework ignores nitrous oxide emissions from increased fertilizer use required to sustain yield growth.

• The GTAP model likely underestimates ILUC emissions because it ignores water scarcity constraints. Research by Taheripour et al. (2013) indicates that when physical limitations on irrigation expansion are factored in, land-based emissions from US ethanol production increase from 35.6 g CO2e/MJ to 45.4 g CO2e/MJ, representing a 27.5% increase.
• GTAP's failure to differentiate between commercial and non-commercial forests artificially suppresses ILUC estimates. The model assumes all forestland is commercially managed, which exaggerates economic limits on conversion and fails to recognize that converting non-commercial forestland would not trigger the same afforestation response as commercial land.
• The use of a single yield price elasticity value for all crops and regions in GTAP is problematic. CATF argues that the high elasticity values observed for corn in the US Midwest are not representative of other crops or regions, such as rice in developing areas, and using them as a proxy likely lowers ILUC estimates.
• Recent research suggests that future corn yields in the US Midwest may decelerate due to climate change. A 2014 study by Lobell et al. found that increased daytime vapor pressure deficit (VPD) caused by hotter and drier Julys could reduce yields by 15% to 30% over the next 50 years.
• The ARB modeling framework undercounts greenhouse gas emissions by failing to account for the nitrous oxide (N2O) produced by increased fertilizer use. While the model counts the benefits of price-induced yield increases, it ignores the climate cost of the nitrogen-based fertilizers required to achieve those yields.
• The implementation of regionalized marginal crop yield estimates in GTAP introduces significant uncertainty. The current method uses 1996 corn data from Iowa as a proxy for all crops globally and assumes net primary productivity (NPP) is a reliable proxy for yield.

APA

Clean Air Task Force (2014). Estimating Indirect Land Use Change Emissions from Biofuels. https://cdn.catf.us/wp-content/uploads/2017/10/21093225/20140519-CATF-Comments-on-ARB-Proposed-ILUC-Analysis.pdf

Chicago

Clean Air Task Force. Estimating Indirect Land Use Change Emissions from Biofuels. 2014. https://cdn.catf.us/wp-content/uploads/2017/10/21093225/20140519-CATF-Comments-on-ARB-Proposed-ILUC-Analysis.pdf.

Wikipedia

{{cite press release |author=Clean Air Task Force |title=Estimating Indirect Land Use Change Emissions from Biofuels |date=19 May 2014 |url=https://cdn.catf.us/wp-content/uploads/2017/10/21093225/20140519-CATF-Comments-on-ARB-Proposed-ILUC-Analysis.pdf |access-date=23 October 2026 |via=Climate Insights Directory}}

BibTeX

@misc{cleanairtaskforce2014estimating, author = {{Clean Air Task Force}}, title = {{Estimating Indirect Land Use Change Emissions from Biofuels}}, publisher = {Clean Air Task Force}, year = {2014}, month = may, url = {https://cdn.catf.us/wp-content/uploads/2017/10/21093225/20140519-CATF-Comments-on-ARB-Proposed-ILUC-Analysis.pdf}, urldate = {2026-10-23}, note = {Indexed by Climate Insights Directory} }