The Implications of Limiting CO2 Concentrations for Agriculture, Land Use, Land-use Change Emissions and Bioenergy
Limiting atmospheric CO2 concentrations carries implications for agriculture, land use, unmanaged ecosystems, “second-generation” bioenergy, and the global energy system. Using PNNL’s integrated assessment modeling system, MiniCAM, we find that improving conventional crop productivity has the potential to reduce land-use change emissions by hundreds of billions of tons of carbon over the 21st century. The importance of the potential role of crop productivity specifically as a means of climate change mitigation has gone largely unrecognized. We further find that limiting the concentration of greenhouse gases in the atmosphere carries implications for land use that are unavoidable and independent of the production of bioenergy crops. Land is a scarce resource and the carbon associated with unmanaged ecosystems provides a carbon storage service that, if valued, becomes increasingly valuable with time. This in turn means that relative to a reference scenario, a larger stock of unmanaged ecosystems and managed forests is desirable, which in turn raises land rents, raises crop prices, decreases crop production and the land that is used to produce crops. We find that crop and forest product waste streams are a potentially important source of bioenergy with or without a carbon price. We find very little dedicated bioenergy crop production before 2035 and therefore no noticeable effect on crop prices until after the middle of the century (absence non-climate-related subsidies). Failure to take into account the value of terrestrial carbon storage services by unmanaged ecosystems and managed forests could have dramatic consequences for unmanaged ecosystems if CO2 concentrations are limited. When terrestrial carbon is valued and both waste-derived and purpose-grown bioenergy technologies are available, the cost of limiting the concentration of CO2 is reduced in some scenarios by half. When carbon is valued the dominant use of bioenergy is power generation with CO2 capture and storage (CCS), not transportation fuels. We find that net global carbon emissions eventually become negative when CO2 concentration limits are set below 550 ppm in 2095 and both bioenergy and CCS technologies are jointly employed.