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Comment 75 for 2022 Climate Change Scoping Plan (scopingplan2022) - Non-Reg.

First NameLiz
Last NameWhiteman
SubjectRecommending inclusion of best available science on Blue Carbon habitats

To: The California Air Resources Board

From: California Ocean Science Trust (on behalf of the signatories below including members of the Ocean Protection Council Science Advisory Team and additional scientific experts)

Subject: Recommending inclusion of best available science on Blue Carbon habitats in the 2022 Climate Change Scoping Plan

This memo was developed by the California Ocean Science Trust (OST) in consultation with members of the Ocean Protection Council (OPC) Science Advisory Team and leading coastal scientists listed below. OST is a legislatively mandated non-profit organization dedicated to accelerating progress towards a healthy, equitable and productive coast and ocean, formally bridging the gap between cutting edge scientific research and sound ocean and coastal management. OST’s Executive Director serves as co-chair of the OPC Science Advisory Team, an interdisciplinary team of experts who work to ensure that the best available science supports OPC policy and funding decisions.

Dear Chair Randolph and Members of the California Air Resources Board, 

We applaud the California Air Resources Board (CARB) for their extensive efforts to prepare the 2022 Climate Change Scoping Plan (Scoping Plan) with the aim of building a robust and comprehensive strategy for meeting the goals of the Global Warming Solutions Act of 2006 (AB/SB 32). This scale of analysis is no small undertaking, and we commend the work of CARB staff and Board to position California as a national and global leader in developing science-based climate mitigation policies. 

The magnitude of the climate crisis, however, requires that we account for, manage, conserve, and invest in all natural and working lands to achieve carbon neutrality by mid-century. On behalf of members of the OPC Science Advisory Team and the state’s leading coastal scientists, we are writing to recommend that the best available science on California’s coastal “blue carbon” habitats be included in the natural and working lands (NWL) modeling scenarios presented in the draft Scoping Plan. We appreciate inclusion of new modeling of potential emissions reduction opportunities from restoration activities in Suisun Marsh and the Sacramento-San Joaquin Delta (the Delta). However, a critical missing component of the wetland landscape in the draft Scoping Plan includes the scientifically verifiable carbon sequestered and stored within the biomass and soils of the state’s coastal wetlands. 

There are now sufficient data and methods available for inventorying and estimating GHG emissions and removals from coastal wetlands to support their inclusion in the 2022 Scoping Plan. Below, we reference some of the latest information and resources that are contributing to our best estimates of carbon stocks and GHG exchanges across California’s coastal wetland habitats, a field of study which has rapidly advanced over the last decade. We also offer our expertise and commitment to engaging in a process to integrate these data into modeling of management scenarios for coastal wetlands that could be included in the 2022 Scoping Plan and refined in future updates.

California’s blue carbon habitats - also referred to here as coastal wetlands - include tidally-influenced marshes, scrub/shrubs, and eelgrass habitats that consist of organic and mineral soils that are covered or saturated for all or part of the year by water. Coastal wetland organic carbon is derived from above- and below-ground photosynthetic production as well as inputs from coastal watersheds. Based on spatially explicit land cover mapping datasets, these habitats cover over 57,000 acres, including approximately 43,000 acres of tidal marsh and scrub/shrub wetlands and 13,000 acres of eelgrass. According to new analyses, the inclusion of coastal wetlands has the potential to increase the extent of existing wetlands evaluated in Scoping Plan scenarios by nearly 70% (Vaughn, Plane, Harris, Robinson, and Grenier, in prep).


With regards to estimating the statewide standing stock of coastal wetland carbon, California has ample spatial and temporal coverage of peer-reviewed (~140) and unpublished (~250) soil core data that span a range of coastal wetland types, salinity classes, and include restoration sites. These data have been deemed sufficient for carbon stock assessments and carbon sequestration modeling (Holmquist, Wolfe, and Megonigal, 2021), many of which are publicly accessible on the Coastal Carbon Atlas and have been standardized across the Pacific coast. Radiometric dating of soil core profiles provides a historic time series of carbon accumulation over the last 100+ years, thus it is not required to sample stocks annually. 


While data are available for a statewide approach, a regional inventory recently developed for the San Francisco Bay tidal Estuary provides an “off-the-shelf” assessment that can inform the Scoping Plan and serve as a template for expanding statewide (Beers and Crooks, 2022). From the period of 1990 to 2020, coastal wetlands in the San Francisco Estuary were a net carbon sink, with GHG removals increasing through time attributable to significant coastal wetland restoration in the region. In 2020, these habitats sequestered approximately 43,600 metric tons CO2 equivalent (CO2e).  

For a statewide time series of emissions and removals, the US EPA National Greenhouse Gas Inventory (NGGI) of Emissions and Sinks provides state-level estimates of carbon stock change and methane emissions going back to 1990, indicating California’s coastal wetlands are a net sink (EPA, 2022). These data, in combination with state-specific carbon data and land cover mapping, can allow for a more accurate accounting of greenhouse gas (GHG) emissions and removals in coastal wetlands than what is currently included in CARB’s 2018 Natural and Working Lands GHG inventory. 

Continued conservation and restoration of saline tidal wetlands and eelgrass habitats can promote additional carbon storage and further reduce GHG emissions. Management actions can include restoring natural hydrology, reducing nutrient inputs, limiting vulnerability to sea level rise, and avoiding high levels of bioturbation, among others (Macreadie et al., 2017; Moritsch at al. 2021). Loss of wetlands can cause significant release of GHGs like methane, and there is evidence to suggest that restored wetlands can provide greater rates of carbon storage compared with natural systems, particularly in the first decade (Poppe and Rybczyk, 2021). A forthcoming report by Vaughn, Plane, Harris, Robinson, and Grenier provides preliminary analyses and recommendations for expanding existing Scoping Plan scenarios to include management actions for saline tidal wetlands and eelgrass beds based on regional targets and planning efforts. 


In closing, we urge CARB to consider the best available science referenced herein indicating that coastal wetlands can play a critical role in helping achieve the state’s climate change and GHG reduction goals. In addition to long-term carbon storage, significant alternative benefits of restoring these ecosystems have already been observed and quantified - including shoreline protection in response to sea level rise, localized amelioration of ocean acidification, and cultural significance (Akema et al., 2013; Lead et al. 2011; Pinksy et al., 2013; Ricart et al., 2021; Shepard et al., 2011). 

We appreciate the work of CARB staff and Board, and acknowledge the task ahead to continue updating the 2022 Climate Change Scoping Plan. The California Ocean Science Trust, members of the OPC Science Advisory Team, and the state’s leading coastal experts stand at the ready to serve as a resource for continued engagement on this issue to help ensure these critical habitats are recognized in state policy. 


Dr. Sean Anderson, California State University Channel Islands

Dr. Richard Ambrose,* University of California, Los Angeles

Dr. Lisa Beers, Silvestrum Climate Associates

Dr. Kathryn Beheshti, University of California, Santa Barbara

Dr. Kathy Boyer, Estuary & Ocean Science Center, San Francisco State University

Dr. John Callaway, University of San Francisco

Warner Chabot, San Francisco Estuary Institute

Ross Clark, Central Coast Wetlands Group, Moss Landing Marine Labs

Craig Cornu, Pacific Northwest Blue Carbon Working Group

Dr. Matthew T. Costa, Scripps Institution of Oceanography, University of California San Diego 

Dr. Steve Crooks, Silvestrum Climate Associates

Dr. Timothy M. Davidson, California State University Sacramento

Dr. Hany Elwany, President of Coastal Environment Inc

Dr. Matt Ferner, San Francisco Bay National Estuarine Research Reserve and San Francisco State University

Dr. Gary Griggs,* University of California Santa Cruz

Dr. Madeleine Hall-Arber, Massachusetts Institute of Technology (retired)

Dr. James R. Holmquist, Smithsonian Environmental Research Center 

Dr. Christopher N. Janousek, Oregon State University

Dr. Kristy Kroeker,* University of California, Santa Cruz

Dr. Janet Kübler, California State University, Northridge

Dr. Raphael Kudela, University of California Santa Cruz

Dr. Arielle Levine,* San Diego State University

Dr. Sarah Lummis, University of California, Santa Cruz

Dr. Glen MacDonald, University of California, Los Angeles

Dr. Monica Moritsch, University of California, Santa Cruz

Dr. Steven N. Murray,* California State University Fullerton

Dr. Kerry J. Nickols, California State University Northridge

Kevin O'Connor, Central Coast Wetlands Group, Moss Landing Marine Labs

Dr. Patty Y. Oikawa, California State University, East Bay

Manuel Oliva, Point Blue Conservation Science

Dr. Aurora M. Ricart, Bodega Marine Laboratory, University of California, Davis

Dr. Laurie Richmond,* Cal Poly Humboldt

Dr. Jay Stachowicz,* University of California, Davis

Dr. Aaron L. Strong, Hamilton College

Christina Toms, San Francisco Bay Regional Water Quality Control Board and SF Estuary Wetland Regional Monitoring Program

Dr. Melissa Ward, San Diego State University and University of Oxford

Dr. Kerstin Wasson, University of California, Santa Cruz

Dr. Lisa Wedding, University of Oxford

Jaxine Wolfe, Smithsonian Environmental Research Center

Dr. Liz Whiteman,* OPC Science Advisory Team co-chair, California Ocean Science Trust


*Denotes member of the Ocean Protection Council Science Advisory Team, an interdisciplinary body of experts who provide scientific advice to the California Ocean Protection Council (OPC) and works to ensure that OPC policy and funding decisions are informed by the best available science. The OPC Science Advisory Team offers a critical venue to bring state leaders and scientists together on a range of topics with emphasis on state priorities to address issues impacting coastal and marine ecosystems in California. 


Disclaimer: Institutional affiliations are provided for informational purposes. The views and science expressed in this letter represent the collective views of individuals and not their institutions or organizations.



Arkema KK, Guannel G, Verutes G, Wood SA, Guerry A, Ruckelshaus M, Kareiva P, Lacayo M, Silver JM, (2013). Coastal habitats shield people and property from sea-level rise and storms. Nature climate change, 3(10), pp.913-918. 

Beers L, Crooks S (2022). Coastal Wetland Greenhouse Gas Inventory for the San Francisco Bay Estuary. Access PDF here

EPA (2022) Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2020. U.S. Environmental Protection Agency, EPA 430-R-22-003. 

IPCC 2014, 2013 Supplement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories: Wetlands, Hiraishi, T., Krug, T., Tanabe, K., Srivastava, N., Baasansuren, J., Fukuda, M. and Troxler, T.G. (eds). Published: IPCC, Switzerland. 

Holmquist J, Wolfe J, Megonigal P (2021). CCRCN Blue Carbon Inventory. The Coastal Carbon Network at the Smithsonian Environmental Research Center. Access report here

Lead C, Jones L, Stewart Angus AC, Doody P, Everard M, Garbutt A, Gilchrist P, Hansom J, Nicholls R, Pye K, Ravenscroft N (2012). Coastal Margins. 

Macreadie PI, Nielsen DA, Kelleway JJ, Atwood TB, Seymour JR, Petrou K, Connolly RM, Thomson ACG, Trevathan-Tackett SM, Ralph PJ (2017). Can we manage coastal ecosystems to sequester more blue carbon? Frontiers in Ecology and the Environment. 

Moritsch MM, Young M, Carnell P,  Macreadie PI, Lovelock C, Nicholson E, Raimondi PT, Wedding LM, Ierodiaconou D (2021). Estimating blue carbon sequestration under coastal management scenarios, Science of The Total Environment. 

Pinsky ML, Guannel G, Arkema KK. (2013). Quantifying wave attenuation to inform coastal habitat conservation. Ecosphere 4(8), 1-16. 

Poppe KL, Rybczyk JM (2021). Tidal marsh restoration enhances sediment accretion and carbon accumulation in the Stillaguamish River estuary, Washington. PLoS ONE 16(9): e0257244. 

Ricart AM, Ward M, Hill TM, Sanford E, Kroeker KJ, Takeshita Y, Merolla S, Shukla P, Ninokawa AT, Elsmore K, Gaylord B (2021). Coast‐wide evidence of low pH amelioration by seagrass ecosystems. Global Change Biology, 27(11), 2580–2591. 

Shepard CC, Crain CM, Beck MW (2011). The Protective Role of Coastal Marshes: A Systematic Review and Meta-analysis. PLOS ONE 6(11): e27374. 

Vaughn LS, Plane E, Harris K, Robinson A, Grenier L (in prep). Blue Carbon Science in California: Memo to the California Air Resources Board on coastal wetland data and methods for the 2022 Scoping Plan Update. 

Original File NamePublic Comment.pdf
Date and Time Comment Was Submitted 2022-06-23 12:31:04

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