Humans today inject roughly 36 billion tons of CO₂ into the atmosphere a year, a figure that has been climbing steadily. Roughly half that CO₂ stays in the atmosphere. Much of the rest goes into two of Earth’s major carbon sinks: land, where it’s stored in trees and soils, and oceans. But how much carbon can these two ecosystems absorb—and can they do it indefinitely?

Blue carbon—carbon stored in tidal wetlands and other coastal ecosystems—ranks among the most valuable forms of carbon storage. The Global Change Research Wetland is measuring how much CO₂ tidal wetland plants and soils absorb, and forecasting the future of the carbon stored in tidal marshes. But wetlands also emit methane (CH₄), a greenhouse gas even more powerful than CO₂. Mangroves are another powerful carbon sink SERC scientists study, storing roughly two times as much carbon per year as salt marshes. SERC scientists study blue carbon across sites in the Smithsonian’s Marine Global Earth Observatory and in countries like Abu Dhabi. Since tidal wetlands store more carbon and emit less methane than other wetlands, SERC scientists are also leading the effort to develop methodologies for awarding carbon credits to tidal wetland projects.

Forests are also strong carbon absorbers. But like wetlands, some trees emit methane, a new discovery SERC ecologists are exploring more deeply. One SERC forest is part of the Smithsonian’s Forest Global Earth Observatory (ForestGEO), a network of over 60 forest plots worldwide. Scientists sample ForestGEO plots to measure, among other things, how much carbon their forests absorb and how the carbon dynamics of forests are changing, especially in response to climate change.

The largest carbon sink by volume is the ocean. However, the more CO₂ it absorbs, the more acidic waters become—which can drastically impact aquatic life. SERC research focuses especially on coastal acidification, which can stunt oyster shell growth and is typically accompanied by reduced oxygen which, when extreme, can create dead zones. Browse the projects below to learn more.