Blue Carbon

To support broader inclusion of coastal wetlands in future Scoping Plan scenarios, this report provides an overview of available coastal wetland datasets, methods, and scenario considerations. The report covers wetland mapping, greenhouse gas and carbon accumulation data, considerations regarding wetland vulnerability and resilience to sea-level rise, and specific suggestions for coastal wetlands scenarios. Together, this information is intended to (a) enable CARB to move forward with the 8th “blue carbon” NWL type given existing information and available methods, and (b) highlight key focus areas where additional science investment would meaningfully improve existing scenario analysis methods, offering a roadmap to broader inclusion of California’s coastal wetlands in future NWL scenarios. 

Major Findings 

1. Building on current Delta-only Scoping Plan scenarios, sufficient information exists to incorporate an additional 57,000 acres of blue carbon ecosystems outside the Delta into the CARB Scoping Plan and other state and regional climate planning efforts.
2. These currently unaccounted for coastal wetlands in California sequester an estimated 20,000 MT carbon annually in tidal wetland and eelgrass sediments. 
3. Including saline tidal wetlands and eelgrass in the Scoping Plan scenarios would increase the extent of existing wetlands by nearly 70% over the current Delta-only scenarios.
4. Adding 18,000 acres of saline tidal wetland and 3,000 acres of eelgrass restoration in San Francisco Bay to the Scoping Plan proposed scenario would increase total wetland green house gas benefits by 27,000 MT CO2e per year.
5. Conserving existing coastal wetlands, in addition to restoring new ones, is critical for both climate protection and other services to people .
6. Blue carbon ecosystems can contribute meaningfully to California’s climate goals even in their limited spatial footprint, given high rates of carbon accumulation and low rates of methane emissions in saline coastal wetlands. 
7. Coastal wetlands offer numerous benefits in addition to climate regulation, which should be accounted for in climate resilience planning at state and regional levels. 
8. Investment in repeat mapping efforts and biogeochemical data collection would improve the precision and scope of future blue carbon quantification.

The report released in July 2022 was prepared for the California Air Resources Board. The Pew Charitable Trusts provided funding for this project, but Pew is not responsible for errors in this report and does not necessarily endorse its findings or conclusions.

Dates: 

2021 to 2022

Funders: 

The PEW Charitable Trusts

Associated Staff: 

Letitia Grenier

Kendall Harris

Ellen Plane

April Robinson

Lydia Vaughn

Report Download: 

Leveraging Wetlands for a Better Climate Future: Incorporating Blue Carbon into California's Climate Planning

Programs and Focus Areas: 

Resilient Landscapes Program

Delta Science & Management