Limited potential for terrestrial carbon sequestration to offset fossil-fuel emissions in the upper midwestern US

Many carbon dioxide (CO₂) emission-reduction strategies currently under consideration rely on terrestrial carbon (C) sequestration to offset substantial proportions of CO₂ emissions. We estimated C sequestration rates and potential land areas for a diverse array of land-cover changes in the Upper Midwest of the US, a "best case" region for this study because of its relatively modest CO₂ emissions and the large areas of cropland potentially available for conversion. We then developed scenarios that apply some of the most widespread mitigation strategies to the region: the first, which aimed to offset 29% of regional CO₂ emissions, required the unrealistic loss of two-thirds of working cropland; the second, which estimated the emission offset attainable by conversion of 10% of harvested croplands (5.8% of the US total), resulted in <5% CO₂ emissions reduction for the region (<1.1% of total US emissions). There is limited capacity for terrestrial C sequestration, so strategies should aim to directly reduce CO₂ emissions to mitigate rising atmospheric CO ₂ concentrations.