Most life-cycle studies have found that a reduction of greenhouse gas emissions can be achievable by replacing petroleum-based plastics with bioplastics made from renewable feedstock, but these analyses have failed to count the carbon emissions that occur as farmers worldwide convert forest and grassland to new cropland to replace the corn diverted to bioplastics. By excluding emissions from land use change, most previous accountings were one-sided because they counted the carbon benefits of using land for bioplastics but not the carbon costs, the carbon storage, and sequestration sacrificed by diverting land from its existing uses. The accounting for the land use change emissions can limit the attractiveness of bioplastics for the displacement of petroleum-based plastics, at least from an environmental point of view. The use of agricultural by-products as bioplastic feedstock is a valid solution to the problem. Alternatively, recycling of bioplastic wastes could contribute to reducing the land use change emissions. From this point of view, it is clear that the incineration or the landfilling of the bioplastic products are not a valid alternative for a real solution of the problem.