Carbon Sequestration in Wood and Paper Products

Recognition that increasing levels of CO, in the atmosphere will affect the global climate has spurred research into reducing global carbon emissions and increasing carbon sequestration. The main nonhuman sources of atmospheric CO, are animal respiration and decay of biomass (U.S. Congress OTA 1991). However, increases in atmospheric levels are attributed mainly to fossil fuel burning and land use change. While efforts to hold down emissions of CO, continue, increases in CO, emissions can also be offset, to a degree, by accumulation in carbon sinks such as plant biomass and oceans. It is therefore prudent to focus research efforts both on increasing carbon in sinks and reducing carbon emissions. In 1990, U.S. CO, emissions were 1,367 Tg carbon equivalent (Clinton and Gore 1993), where Tg is 1 million metric tons. Wood and paper products play an important role in mitigating these emissions by sequestering carbon. There are currently large stocks of carbon in forests, in wood and paper products in use, and in dumps and landfills. The size of these carbon stocks is increasing. In 1990 approximately 145 Tg of carbon, or 10.6 percent of the level of U.S. emissions was harvested and removed from forests for products. If a substantial portion of this carbon could be prevented from returning to the atmosphere, it could be a notable contribution to mitigating carbon buildup in the atmosphere. We use the term sequestration to refer to the net sequestration, over a period of time, in a stock of carbon: carbon in forests, carbon in forest products in use (including net imports), or carbon in forest products in landfills. This expands the use of the term beyond its common use referring to net sequestration of carbon to forests. Carbon sequestration to wood and paper products has been assessed in several other studies. Some studies assess carbon sequestration for a range of hypothetical conditions of forest growth, harvest, end use, and disposal (Schlamadinger and Marland 1996). A worldwide study by Winjum et al. (1998) estimates net flows of carbon out of forests and into products using the two accounting frameworks used in this study—the stock change method, and the atmospheric flow method. They use simplified assumptions to make estimates of net stock changes, and net emissions to the atmosphere by world region and for selected countries. They include estimates of logging residue and assumed decay. Their results, as noted below, are close to ours even though their methods are very different. Other studies focusing on the United States, similar to this one, estimate the actual stocks and flows of carbon from U.S. forests to products in use, to dumps or landfills, and to burning and emissions from decay including reconstruction of historical flows and projections (Heath et al. 1996; Row and Phelps 1996). This study presents similar results with three improvements: 1) use of greater detail in the changing composition of end uses of wood and paper products; 2) inclusion of net imports of wood and paper products in carbon sequestration estimates; and 3) use of new, much lower decay estimates for wood and paper in landfills including separate estimates of CO2 and CH4 portions. These improvements help provide a clearer understanding of how sequestration to products may change. Our purpose is to show an in-depth method of providing historical estimates and projections of U.S. carbon sequestration to wood and paper products. We compare those estimates to amounts sequestered in U.S. forests (an estimate of carbon stock change in the United States). We also show how amounts used to estimate the net sequestration in products and forests each year may be used to estimate the net removals of carbon from the atmosphere to the United States each year (an estimate of carbon flow to the United States). We discuss how patterns of wood use have changed and will change and how they will influence the pattern and amounts of carbon sequestered.