A remote sensing assessment of forest carbon offsets in California and opportunities for improvement
S. R. COFFIELD, C. D. VO, J. A. WANG, G. BADGLEY, M. L. GOULDEN, D. CULLENWARD, W. R. L. ANDEREGG, J. T. RANDERSON
Earth System Science Interdisciplinary Center, University of Maryland; NASA Goddard Space Flight Center, 8800 Greenbelt Rd B33 Code 618, Greenbelt, MD 20771

Nature-based climate solutions are often key components of net-zero carbon strategies, including in California. Most carbon offsets in California's cap-and-trade program come in the form of improved forest management (IFM) projects. Since 2012, various landowners have set up IFM projects following the California Air Resources Board's IFM protocol. Now after 10 years of the program’s existence, we have the opportunity to assess the projects’ effectiveness, identify best practices, and suggest improvements toward future protocol revisions. In this study, we used remote sensing-based datasets to evaluate the carbon trends and harvest histories of 37 IFM projects in California. Despite some current limitations and biases, these datasets can be used to quantify carbon accumulation and harvest rates in offset project lands relative to nearby similar “control” lands before and after the projects began. We find five lines of evidence suggesting that the carbon accumulated in offset projects to date has generally not been additional to what might have otherwise occurred due to natural and anthropogenic trends. In doing so, we add to the many existing concerns associated with carbon offsetting while offering insight as to how California’s protocol, and forest management in general, could more reliably lead to additional carbon sequestration.