The land use change time-accounting failure

Land use change (LUC) is the second human-induced source of greenhouse gases (GHG). This paper warns about the LUC time-accounting failure in internalizing GHG impacts in economic appraisal (within policies). This emerges from (i) relative carbon prices commonly following the Hotelling rule as if climate change were regarded as an exhaustible resource problem and (ii) a uniform annualization (i.e. constant flows over time) of LUC impacts supported by most energy policies. First, carbon prices time evolution should account for the climate change framework specificities (natural carbon absorption, uncertainty), which makes a departure from the Hotelling rule necessary. Second, there is a carbon dynamic after land conversion: GHG impact flows are strictly decreasing over time. With a theoretical framework, I show that the employment of the uniform annualization, within a benefit-cost analysis, enhances both the discounting overwhelming effect and the carbon price increase, whatever the type of impact (emissions or sequestration). It results in skewed values of LUC-related projects as long as relative carbon prices deviate from the Hotelling rule. I apply this framework to global warming impacts of bio-ethanol in France and quantify this bias. In particular, carbon profitability payback periods under the uniform approach do not reflect the LUC effective carbon investment. This potentially modifies the conclusions regarding a project's achievement of imposed environmental criteria. (author)