Understanding the indirect land use change analysis for Corsia

This new report looks in detail at the assumptions and criteria used to determine the "indirect land use change" of biofuels under the UN's carbon offsets scheme for aviation emissions (known as Corsia). The report, commissioned by T&E from consultancy Cerulogy, reveals several biases in the choice of some crucial modelling assumptions and in the decision on the final ILUC numbers. This explains some of the big differences that can be seen for some feedstocks, such as soy and palm oil, especially compared to the Globiom analysis of 2016.

Corsia, the Carbon Offsetting and Reduction Scheme for International Aviation adopted by ICAO, includes the option for airlines to meet their emission reduction obligations by using alternative aviation fuels that are calculated to have a lower greenhouse gas emissions footprint than the fossil jet fuel they replace. The calculation of indirect land use change (ILUC) emissions is part of this assessment and the US and EU delegations supported ILUC modelling using two different analytical frameworks, the ‘GTAP-BIO’ and ‘GLOBIOM’ models. ILUC factor results from these modelling exercises have become the basis for the default values proposed for CORSIA.

The report first explains the differences between the US and EU models and concludes that: “Neither set of ILUC results is exactly what the respective modelling teams would have produced without external input and the process of model reconciliation. It is clear that some ICAO Member States have an interest in being able to report the highest GHG emissions reductions possible for favoured biofuels. In particular, the decision to base ILUC values on only the lower modelled value where models disagree introduces an obvious and significant optimism bias into the default values that is not analytically justified.”

It also explains the differences between the Globiom analysis for Corsia and the previous Globiom analysis done for the EU. The ILUC results for Corsia are generally lower than those generated in earlier Globiom work for the EU Commission. The report highlights that “to a considerable extent it is a result of the modelling team agreeing to adopt more biofuel-positive assumptions on issues including emission factors for peat and for forgone sequestration, which could reasonably be challenged. These results should therefore not be treated as automatically superseding the 2015 analysis, but as providing alternative scenarios that might be considered alongside the earlier work, with due consideration given to the relative merits of each.