Indirect effects of land use on greenhouse gas emissions

 

Land use decisions can have substantial effects on “sources and sinks” of greenhouse gases. Although often difficult in practice, it is conceptually a simple matter to estimate the direct effects of a change in management regime on a particular piece of land by measuring carbon stocks on the land before and after the change. Estimating the cumulative and indirect effects of land use decisions at large spatial scales is much more challenging and has emerged as a key technical issue in climate policy debates related to forestry, agriculture and biomass energy.

A creative new model of indirect land use effects is presented in “Greenhouse Gas Mitigation by Agricultural Intensification” (Proceedings of the National Academy of Sciences 107: 12052-12057; available at www.pnas.org/content/107/26/12052.full). The authors are J.A. Burney, S.J. Davis, and D.B. Lobell (Stanford University). The abstract follows.

As efforts to mitigate climate change increase, there is a need to identify cost-effective ways to avoid emissions of greenhouse gases (GHGs). Agriculture is rightly recognized as a source of considerable emissions, with concomitant opportunities for mitigation. Although future agricultural productivity is critical, as it will shape emissions from conversion of native landscapes to food and biofuel crops, investment in agricultural research is rarely mentioned as a mitigation strategy. Here we estimate the net effect on GHG emissions of historical agricultural intensification between 1961 and 2005. We find that while emissions from factors such as fertilizer production and application have increased, the net effect of higher yields has avoided emissions of up to 161 gigatons of carbon (GtC) (590 GtCO2e) since 1961. We estimate that each dollar invested in agricultural yields has resulted in 68 fewer kgC (249 kgCO2e) emissions relative to 1961 technology ($14.74/tC, or ∼$4/tCO2e), avoiding 3.6 GtC (13.1 GtCO2e) per year. Our analysis indicates that investment in yield improvements compares favorably with other commonly proposed mitigation strategies. Further yield improvements should therefore be prominent among efforts to reduce future GHG emissions.