Net change in carbon emissions with increased wood energy use in the United States
Use of wood biomass for energy results in carbon (C) emissions at the time of burning and alters C stocks on the land because of harvest, regrowth, and changes in land use or management. This study evaluates the potential effects of expanded woody biomass energy use (for heat and power) on net C emissions over time. A scenario with increased wood energy use is compared with a dynamic business-as-usual scenario where wood energy use is driven by its historical relationship with gross domestic product. At the national level, we projected that up to 78% of increased cumulative C emissions from increased wood burning and up to 80% of increased cumulative radiative forcing would be offset over 50 years by change in forest area loss, biomass regrowth on land, C storage in harvested wood products, and C in logging slash left in forests. For example, forest area is projected to decline in both scenarios, but 3.5 million hectares more are retained in the high wood energy-use case. Projected C offsets over a 50 year period differed substantially by US region (16% in the North, 50% in the West, and 95% in the South) not only because of differences in forest regrowth and induced investment in retaining and planting forest, but also because of shifts in competitive advantage among regions in producing various wood products. If wood systems displace coal systems that have 75% of the C emissions of wood energy systems per unit energy, then the nationwide net C emissions offset would be reduced to 71–74%. If displacing natural gas systems that have 40% of the level of wood bioenergy emissions per unit energy, the nationwide net C emissions offset would be 46–52%.