Limited potential to offset CO2 emission through land use change

Regional to global strategies point at terrestrial C sequestration to offset a significant portion of CO2 emissions. We investigated the feasibility of some of the proposed global strategies at a regional scale (Upper Midwest of the U.S.) over a 50 year timeframe based on available data for C sequestration rates associated with land use changes and management practices. Achieving some of the aggressive targets proposed by others, such as a 29% offset of CO2 emissions would require conversion of two-thirds of the current agricultural land of the Upper Midwest of the U.S. into practices with high C sequestration potential, such as forest or perennial grassland. We show that current estimates of high terrestrial C sequestration through land use changes are overly optimistic: even the totally unfeasible conversion of all agricultural land in the Upper Midwest into forest (with high C sequestration rates) would not entirely offset the CO2 emissions of the region. Despite the great interest that policy makers have shown for no-till to sequester carbon, our analysis of the literature indicates negligible C sequestration and high variability in the conversion from conventional to no-till (sequestration rates range from –0.2 to 0.8 Mg C ha-1 y-1). At the scale analyzed in our study, we found that low C sequestration rates for some land use changes together with limited land availability for conversion constrain the application of proposed mitigation strategies. Our results suggest that focusing on land use change as a solution to rising atmospheric greenhouse gas concentrations may distract society from pursuing other C mitigation strategies necessary to achieve significant emissions reductions.