Land-Use Implications of Strategies for Stabilizing CO2 Concentrations

Stabilizing atmospheric CO2 concentrations carries implications for land use, agricultural production and the potential for bioenergy systems. Using the Integrated Assessment model MiniCAM to explore the global energy system and land-use dynamics under scenarios where all carbon emissions, including those from terrestrial systems, are valued provides new insights into the consequences of stabilization pathways. Scenarios for stabilization of atmospheric CO2 at 450, 500 and 550 ppmv were tested under two policy environments: where only carbon from fossil fuel and industrial processes is considered and where all carbon, including terrestrial carbon resources, has an equal value. When terrestrial carbon emissions are valued at the same rate as fossil fuel and industrial emissions in a 450 stabilization scenario, the terrestrial ecosystem shifts from being a source of 184 PgC to a sink of 37 PgC over the next century. The cumulative difference, 221 PgC, over the period 2005 to 2095, is approximately 25 percent of total emissions mitigation in the 450 ppm scenario. When carbon from terrestrial systems is not valued, there is dramatic growth in the use of dedicated bioenergy crops and, consequently, large scale change in global land use. When all carbon is valued the dominant use of bioenergy is power generation with CO2 capture and storage (CCS), not transportation fuels. Net global carbon emissions eventually become negative when CO2 concentrations are set to stabilize at 550 ppm in 2095 and both bioenergy and CCS technologies are jointly employed. 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. Assumptions concerning the rate of change in agricultural crop productivity have emissions consequences of up to several billion tons of carbon and therefore are a critical determinant of future global land use and stabilization pathways. 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. Failure to take into account the value of terrestrial carbon storage, and avoidance of land-use change emissions in atmospheric stabilization policies could have dramatic consequences for forests and unmanaged lands.