States Improve How They Assess Coastal Wetlands’ Impacts to Reduce Climate Pollution

Updated Smithsonian-led ‘blue carbon report card’ measures efforts to quantify how much—and how effectively—tidal wetlands store carbon

Article By: Alex Clayton Moya
Projects: U.S. Conservation
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States Improve How They Assess Coastal Wetlands’ Impacts to Reduce Climate Pollution
Staff members of the Smithsonian Environmental Research Center in Edgewater, Maryland, work in the Chesapeake Bay’s Moneystump Swamp on a federal project studying how the conversion of degrading coastal forests to tidal marshes affects climate-warming greenhouse gas (GHG) emissions. The center recently updated 2021 Pew-commissioned research that grades U.S. coastal states on the quantity and quality of data about GHG-capturing coastal wetlands.
Courtesy of Cameron Davidson

As coastal states grapple with the best nature-based solutions to reduce the effects of climate change on their residents and economies, organizations are developing tools to help assess and quantify the role that “blue carbon” habitats play in this effort.

Jaxine Wolfe works in the Guanacaste region of Costa Rica. Wolfe, a research technician with the Smithsonian Environmental Research Center, is one of the conservationists who developed the Coastal Carbon Atlas and Library and the Pew-commissioned blue carbon report card.
Steve Crooks

Although nothing will slow global climate change faster than reducing overall greenhouse gas emissions, boosting blue carbon—the atmospheric carbon dioxide that habitats such as seagrasses and salt marshes absorb and sequester—can make a difference. When healthy and left undisturbed, the roots, stems, and soils of these ecosystems are remarkably efficient at storing and accumulating carbon over centuries. Blue carbon habitats—which are often culturally and historically significant places—also provide homes and breeding grounds for fish, birds, and other wildlife; opportunities for recreational and economic development; and protection from floods and severe storms.

With an eye toward these benefits, some states are developing ways to keep existing tidal wetlands healthy and intact, and to restore degraded habitats. A challenging part of this equation is understanding how much carbon is stored—and how much more could be stored—in wetlands. Enter the Smithsonian Environmental Research Center (SERC). Headquartered in Maryland along the Chesapeake Bay—the nation’s largest and the world’s third-largest estuary—the center directs coastal ecosystems research that can lead to policies and practices supporting a more sustainable planet.

“Wetlands are pulling a lot of weight in mitigating climate change, especially given the relatively small amount of land they occupy on the planet,” said Jaxine Wolfe, a research technician with the center. “That means we can leverage these ecosystems to mitigate the effects of climate change. You can make a difference by conserving wetlands or restoring them.”

Read Pew partner U.S. Nature 4 Climate’s Q&A with Jaxine Wolfe, who coordinated the Smithsonian Environmental Research Center’s blue carbon report card.

‘Report card’ showed improvements for most coastal states

Led by Jim Holmquist, the center’s wetland ecologist, Wolfe and fellow data technicians Rose Cheney and Henry Betts developed and updated one of SERC’s defining blue carbon projects: the Coastal Carbon Atlas and Library, a digital compilation of global blue carbon data. From that data, the center in 2021 developed a state-level “blue carbon report card” for the 23 coastal states, a Pew Charitable Trusts-funded initiative that provided composite scores of soil carbon data for each of the states examined, based on four metrics:

  • Data quantity (the number of “cores”—or soil samples—compared with total coastal wetlands in the state).
  • Data quality (how well the cores assess blue carbon).
  • Spatial representation (how well dispersed sampling efforts are across the state’s coastal wetlands).
  • Habitat representation (how well habitats sampled match their estimated area in the state).

The highest-ranking states across composite scores in the inaugural 2021 report card were Louisiana, Massachusetts, Oregon, and Washington. The research also concluded that at least five states lagged in the quantity and quality of their data in SERC’s database: Maine, Maryland, New Jersey, New York, and Virginia.

Recognizing that “collaboration between researchers and networks to increase data access is really important,” Wolfe said, SERC in July 2023 launched a data stewardship effort to help researchers across the country submit coastal carbon data to the atlas, with a primary goal of bolstering data from those underrepresented states.

This led to an updated report card, released in mid-June 2024, that showed that most states were rated at least “fair” across all metrics—an improvement over 2021—and that most improved across several parameters.

Of the 23 coastal states, 21—or 91%—improved the quantity of their data, while 16—or 70%—improved their data’s quality. Among the “most improved” states, Alabama, Maine, and New Hampshire scored the greatest gains in data quantity, while Alabama, Mississippi, and Oregon registered the strongest advances in data quality.

Three factors that contributed to the improvements:

  • Establishing agreements and protocols to share data among state agencies, academic institutions, nongovernmental organizations, and private sector entities involved in blue carbon research and monitoring.
  • Developing and standardizing how data is collected, managed, and reported.
  • Asking the Coastal Carbon Network, a consortium of coastal land managers and researchers aimed at accelerating the pace of coastal wetland science, and other federal and regional initiatives to provide technical assistance, training, and funding that support state- and federal-level blue carbon data needs and priorities.

Better and expanded data leads to greater accuracy and applicability

These efforts resulted in more expansive and accurate data that helps states better understand how much carbon their coastal wetlands store, which in turn enables officials to set measurable conservation and restoration goals for these habitats.

Alongside the updated report card, SERC has connected data in the atlas to carbon accumulation rates, or measurements over time of how much carbon dioxide is captured from the atmosphere and stored as blue carbon. This information can help states and federal agencies understand the extent to which tidal wetlands function as “carbon sinks”—places that capture and store more carbon than is released—as well as how land use activities that destroy wetlands may impact carbon storage, and where restoration of wetlands could deliver climate benefits.

Coastal carbon stocks and stores are analogous to money in a bank account,” Wolfe said. “Wetlands capture and store blue carbon similar to the way people deposit money into banks. Blue carbon accumulation rates are like the interest on those bank deposits. By protecting and allowing these ecosystems to mature, they do the work of accumulating carbon each year, just like bank account interest, providing more and greater benefits to the environment.

Taken together, the atlas and the accumulation rate data can help states measure and improve how they manage their tidal wetlands, with an eye toward maintaining and expanding these natural carbon sinks and reducing the overall effects of climate change.

Alex Clayton Moya is an officer with Pew’s U.S. conservation project.