Building upon estimates of statewide ecosystem carbon inventories made in the 2018 report, the California Air Resources Board (CARB) will be updating the methods used to calculate the inventories in each of the following landscape types and associated soils as well as in the harvested wood products that California keeps within its borders.
California’s NWL will experience change through the coming years, whether through climate change, wildfires, or increased climate action and management. Further, an ever-increasing number of local and regional jurisdictions are interested in including NWL into their climate action or general planning. To increase the sensitivity of the NWL inventory to change, and enhance accuracy at scales lower than statewide, CARB staff have developed proposed methods to use to develop the inventory for a 2025 update. See the technical writeups that outline these methods below:
These methods were presented at a public workshop on February 7, 2025. You can see the recording and public feedback from that meeting on the Nature Based Strategies Meetings and Workshops page.
The NWL Carbon Inventory summary report provides background information on the legislative directives and the history of NWL Inventory development at CARB, presents the fundamentals of the inventory accounting framework, and summarizes the current understanding of ecosystem carbon stocks and trends in stock change in California. The technical support document describes the detailed methods, data, assumptions, and parameters used in the development of the NWL Inventory.
Separate from the CARB NWL Carbon Inventory, the California Board of Forestry (BOF) and the California Board of Forestry and Fire Protection (CAL FIRE) maintain an inventory of carbon in California’s forests. CARB and the BOF launched their respective forest carbon inventory efforts in different years in response to different legislative mandates. CARB began developing new inventory methodology in 2009 and completed an inventory report in response to the 2016 legislation Senate Bill 859. The BOF inventory was initiated after the 2010 legislation Assembly Bill 1504, calling for the BOF to ensure a certain level of forest carbon sequestration in California’s forests. Due to differences in objectives and legislative mandates, the two inventories cover different land types and time periods and use different methodologies. The different approaches complement each other and help identify ways to further refine future estimation. Staff in the two agencies collaborated to prepare a detailed inventory comparison and an FAQ summarizing the inventories’ differences and similarities. The two agencies’ staff will continually work together to further refine the two inventories.
The forest and other natural lands inventory includes carbon uptake by vegetation, carbon losses associated with wild and prescribed fires, the decomposition and combustion of residues from harvest, and conversion to other land types. Previous inventory estimates for this category were based on a 2004 California Energy Commission study which quantified carbon stocks and change in forests and rangelands in the northern part of the State from 1994 to 2000. Results from the study were extrapolated to include the entire state and to other years, and the estimation approach afforded few options for updating. In 2015, researchers from UC Berkeley developed a data-driven methodology for assessing carbon stocks and changes for all land categories in California except agricultural and urban areas. The methods use California specific land-based data sets and satellite remote sensing data.
The covered ecosystems include forests, woodlands, shrublands, grasslands, wetlands and other natural lands. The method includes carbon contained in live and dead vegetation pools. Data sources for the method include ground-based data from the Forest Inventory and Analysis (FIA) program of the USDA-Forest Service, remote sensing products from NASA's MODIS sensor, geospatial vegetation attributes and disturbance activity (fire, harvest etc.) data from the federal Landscape Fire and Resource Management Planning Tools Project (Landfire.gov), and ancillary data on shrublands and grasslands. The method enables analysts to retrospectively assess ecosystem carbon stocks and to attribute stock-changes to fire and other processes. Results of a recent analysis for the period spanning 2001 to 2010 are presented here.
Inventory tables for forest and other natural lands during the 2001-2010 period:
Technical Support Document, companion to the inventory for the 2001-2010 period:
Development of the new methodology reports: