Past and Present Carbon Storage in U.S. Land Ecosystems


A significant amount of Earth’s carbon is stored in plants growing in land ecosystems such as forests, wetlands, and grasslands—enough that proper land management could help offset carbon dioxide emissions from human activities. Researchers at the Massachusetts Institute of Technology’s Joint Program on the Science and Policy of Global Change used a newly updated land-cover dataset to model past and present carbon storage in land ecosystems across the lower 48 states. The researchers, funded by the Department of Energy’s Integrated Assessment Research Program, National Science Foundation, and Environmental Protection Agency, examined factors such as ecosystem type, forest age, temperature, and precipitation to determine the amount of carbon sequestered, or stored, in ecosystems from 1700 through 2005. They then compared the amount of stored carbon in a state or region to the amount of emissions from fossil fuels to find the percentage of emissions absorbed by local ecosystems. The researchers found that most of the carbon stored in the United States is in forests (97%). From 2001 to 2005, the largest carbon sinks were in the Northeast and Southeast United States, which are areas with young, rapidly growing forests. Areas with older forests stored relatively less carbon. Maine and Mississippi were the only states that were net carbon sinks during this time period. Every other state emitted more carbon than local ecosystems could store. Overall, present-day U.S. ecosystems were able to store 20% of the carbon from fossil fuel emissions. In comparison to historical levels, the researchers estimate that less carbon is stored in land ecosystems today than in 1700, suggesting that modern ecosystems may have the capacity to store more carbon in the future. With this in mind, land carbon sinks might be enhanced in the future with reforestation and careful management of forest age and how woody products from those forests are used.


Lu, X., D. W. Kicklighter, J. M. Melillo, J. M. Reilly, and L. Xu. 2015. “Land Carbon Sequestration within the Conterminous United States: Regional- and State-level Analyses,” Journal of Geophysical Research—Biogeosciences 120(2), 379-98. DOI: 10.1002/2014JG002818.