Forests, grasslands and shrublands in the West sequester nearly 100 million tons of carbon each year, an amount equivalent to counterbalancing the emissions of about 83 million passenger cars a year in the United States, according to a new USGS report.

Carbon that is absorbed or “sequestered” through natural processes reduces the amount of carbon dioxide in the atmosphere.

While the study showed that western ecosystems are a strong carbon sink now, the region could experience a decline in storage potential between now and 2050, depending on future changes in land-use, climate and wildfires. Future carbon stocks are inextricably linked to these drivers because as ecosystems, forests or agricultural lands are converted for other uses, their ability to capture and store carbon is affected.

From the Rocky Mountains to the Pacific Coastal Waters

The area USGS studied extends from the Rocky Mountains to the Pacific coastal waters, and totals just over 1 million square miles. The major ecosystems evaluated were terrestrial — forests, wetlands, agricultural lands, and shrublands and grasslands — and aquatic — rivers, lakes, estuaries and coastal waters. It includes well-known ecosystems, such as the Rocky Mountains and the Sierra Nevada Mountains, the Mojave and Sonoran deserts, the Pacific Northwest forests and the vast grasslands and shrublands of the Great Basin.

Western Forests Stored the Most Carbon

While the western ecosystems varied widely in their potential for storing carbon now and in the future, forests are by far the largest carbon-storing pools, accounting for about 70 percent of the carbon stored recently in the West.

• Forests cover 28 percent of the land areas of West, contain the most carbon per unit area, and have the second-highest rate of sequestration of ecosystem types.
• Wetlands cover less than 1 percent of the West and had the highest rate of sequestration of all ecosystem types, but because they cover only such a small percentage of land, the amount of carbon they sequester is far less significant than other ecosystem types.
• Grasslands and shrublands cover nearly 60 percent of the West and contain 23 percent of the region’s carbon stored recently.
• Agricultural lands cover about 6 percent of the land areas of the West and contain 4.5 percent of the carbon stored recently.

Significant Greenhouse Gas Emission Sources in Western Ecosystems

Wildland fires in western ecosystems generated significant amounts of greenhouse gas emissions, with such emissions equivalent to 13 percent of the estimated rate of the recent annual carbon sequestration by western terrestrial ecosystems. This amount could increase up to 31 percent in the future.

Water bodies in the West emitted even more CO₂ than fires. Emissions from water bodies are equivalent to more than 30 percent of the recent annual carbon sequestration rate of terrestrial ecosystems in the West.  Basically, the more interaction with the atmosphere, the more CO₂ is released.  So, in fast-moving waters, where the water is churned up, there is a greater loss of CO₂ to the atmosphere.

Land-Use, Land-Cover, and Carbon Stocks

Future changes in the ability of western ecosystems to sequester carbon will depend on future changes in land-use, climate, and wildfires.  Future carbon stocks are tied to these drivers because as ecosystems, forests or agricultural lands are converted for other uses, their ability to capture and store carbon is affected.  Land use by people causes a significant loss of carbon from ecosystems. Specific examples are forest harvesting (nearly 13 million tons of carbon per year) and agricultural harvesting (more than 20 million tons of carbon per year).

To Read More:

Blog on the Report by David Hayes, Deputy Secretary of the Department of the Interior

Department of the Interior News Release on the New Report

The report: Baseline and Projected Carbon Storage and Greenhouse Gas Fluxes in the Ecosystems of the Western United States.

Nest in a Salt Marsh, San Francisco Bay

Salt marshes may help slow the rate of climate change in the future, as rising and warmer oceans will enable them to more quickly capture and remove carbon dioxide from the atmosphere, according to a study published in the journal Nature this week.

Carbon dioxide is the predominant “greenhouse gas” that traps heat and warms the atmosphere.

Marshes and Carbon

“Our research suggests that the value of these ecosystems in capturing atmospheric carbon might become much more important in the future, as the climate warms,” said Matthew Kirwan, a University of Virginia environmental scientist, and the lead author of this USGS-funded and supported research.

In fact, said Kirwan, the research forecasts that under faster sea-level rise rates, salt marshes could bury up to four times as much carbon as they do now. “The study forecasts that marshes will absorb some of that carbon dioxide, and if other coastal ecosystems – such as seagrasses and mangroves – respond similarly, there might be a little less warming,” said Kirwan.

One of the most interesting facets about salt marshes is they are perhaps the best example of an ecosystem that actually depends on carbon accumulation to survive climate change: the accumulation of roots in the soil builds their elevation, keeping the plants above the water, Kirwan noted.

Salt marshes store significant quantities of carbon by taking carbon dioxide out of the atmosphere through their leaves, and then storing it in their roots. As plants die, the carbon becomes part of the soil and helps the marsh survive sea level rise.

“Coastal wetlands are among the most economically and ecologically valuable ecosystems on Earth, with their services estimated worth about $15,000 an acre,” said Matthew Larsen, associate director for climate and land use research at the U.S. Geological Survey. “They provide clean water, abundant food, wildlife habitat, and protection from storms. This and other USGS research aims to understand and forecast the vulnerability of coastal wetland systems to global change and identify ways that managers can effectively respond to global change effects.”

Marshes and Sea Level Rise

Kirwan cautioned that the study also showed that marshes can survive only moderately fast rates of sea level rise. To survive, the elevation of the soil surface has to build vertically through time. If the seas rise more quickly than the marsh can build up, marshes drown and die off.

“At fast levels of sea level rise, no realistic amount of carbon accumulation will help them survive,” Kirwan noted.

And, said Kirwan, if marshes are drowned by fast-rising seas, they no longer would provide a significant carbon storage capacity.

The Value of Marsh Ecosystems

Salt marshes, made up primarily of grasses, are important coastal ecosystems that provide a variety of ecosystem services for wildlife, fisheries, and people. They help protect shorelines from storms, provide diverse wildlife habitat for birds, mammals, fish, and mollusks. They also build up coastal elevations by trapping sediment during floods, producing new soil from roots and decaying organic matter. New Orleans, for example, is separated from the Gulf of Mexico almost entirely by marshes.

Little Blue herons in a Louisiana marsh.

DOI manages 35 million acres of low-lying coastal areas, including marshes and thousands of miles of shoreline. The U.S. Fish and Wildlife Service alone manages about 5 million acres of coastal wetlands.

“This research can help decision makers understand and prepare for how coastal areas may fare in response to climate change,” said Glenn Guntenspergen, a USGS researcher who leads a project on Coastal Marsh Response to Climate and Land Use Change Project that this study was a part of.  Kirwan and his co-author, Simon Mudd, a geosciences researcher at the University of Edinburgh in Scotland, used computer models to predict salt marsh growth rates under different climate change and sea level scenarios.

For more information, visit:

Coastal Marsh response to Climate and Land Use Change Project

Climate and Land Use Change Research and Development Program

USGS scientists Doug Halm, Paul Schuster, and Kathy Kelsey collecting melt water samples from Gulkana Glacier. Results of recent analyses identified old carbonin the Yukon River, but also indicated that the chemical source was not derived from ancient plant material stored in the glacier, but from fossil fuel sources derived from atmospheric deposition. This add new complications to the interpretation of carbon sources and sinks in high latitudes and of the apparent sources of old organic carbon exported by arctic rivers.

A new study concludes that fossil fuel emissions are likely contributors to a substantial amount of organic carbon found on glaciers in Alaska.

Fossil fuel emissions, which contain organic carbon, can speed up the rate of glacier melt when deposited on glacier surfaces. In addition, the organic molecules associated with these deposits can be transported in rivers and streams, affecting downstream aquatic ecosystems. Knowledge of the source and age of organic carbon in glaciers allows for a better understanding of these and other impacts.

Prior research suggested that the main sources of organic carbon in Alaska’s glaciers were from forests and peatlands overrun by glaciers as far back as ten thousand years ago. While old soil and plant material are still possible sources of glacial organic carbon, new research indicates that human-created, or anthropogenic, sources are also important.

“We knew the organic carbon present in Alaska’s glaciers was old, but identifying the sources of this material has been difficult due to the lack of chemical data,” said USGS scientist George Aiken.

While extensive burning of fossil fuels is, geologically speaking, a relatively modern practice, the fuels themselves and the resulting carbon emissions are ancient. This is because the fuels are formed from plants and microorganisms that lived millions of years ago.

“Now we know that a substantial amount of ancient organic matter associated with these and other glaciers is of anthropogenic origin,” continued Aiken.

Why Study Carbon Levels?

When organic matter and other materials from the atmosphere are deposited on the surface of a glacier, less sunlight can be reflected and, therefore, more radiation and heat are absorbed. Having these materials on snow and ice surfaces causes them to melt faster.

Another concern is impacts to ecosystems and species habitats. As an example, organic matter exported to coastal areas is a potential nutrient or food source for aquatic bacteria, phytoplankton, and small grazing zooplankton. Climate warming or other factors may change the amount and quality of organic carbon available to these organisms. These aquatic organisms are also the base of the food web for all aquatic communities.

“When trying to understand climate change and decipher the carbon cycle puzzle, we need to make sure that we are using all of the right pieces,” said USGS scientist Rob Striegl. “As part of that puzzle, we are studying the source and amount of carbon flowing into the Arctic Ocean. An understanding of the complete picture allows for the most informed decisions to protect our environment.”

Melt water stream discharging from Gulkana Glacier, Alaska. USGS research of the Yukon River has had a long term goal of determining the source and fate of organic carbon transported by the river to the Bering Sea and ultimately the Arctic Ocean.

“The Arctic is of special interest because what happens there, such as extensive glacier melt, has impacts on the rest of the world,” continued Striegl. “Glacier environments, especially those in the high latitudes of the Arctic, are also among the most sensitive to climate warming.”

New Twist to Understanding Carbon in Glaciers

“Our new paper describes, for the first time, the detailed chemical composition of dissolved organic matter associated with glaciers and glacial meltwater in coastal Alaska and in Wyoming,” said Aiken.

“This study adds a twist to previous understandings, showing there is another source of organic carbon out there that needs to be considered,” said Striegl.

This study, published in the journal Nature Geosciences, was a collaborative effort of many institutions led primarily by the University of Alaska Southeast, Skidaway Institute of Oceanography, Woods Hole Research Center, and the USGS.

The Role of USGS Science

Earlier studies by the USGS, in collaboration with university researchers, found the presence of ancient organic carbon in the Yukon River and traced it back to meltwater from glaciers. For further analyses, USGS scientists continued those collaborations to sample meltwater from Mendenhall Glacier and Herbert Glacier in southeastern Alaska. The samples were then analyzed at USGS and university laboratories to develop the conclusions outlined in this new study.

“This truly is a collaborative effort, taking the expertise of many scientists to put the story together on the source of the carbon,” said Striegl. “The original work of the USGS in the Yukon basin helped form the questions and lab results contributed to answering the questions; but it took specialized instrumentation and scientific expertise from several other organizations to determine the final answer.”

Additional samples used for age dating and for other chemical characterization of the organic carbon of glaciers from other locations came from Gulkana Glacier in Alaska and from Fremont Glacier in Wyoming.

USGS scientists Doug Halm, Paul Schuster, Peter Murdoch, and Kathy Kelsey collecting melt water samples from Gulkana Glacier.

The Big Picture of Aquatic Carbon

The USGS has a long term goal of determining the source and fate of organic and inorganic carbon transported to coastal areas and oceans across the entire Nation. USGS research on the Yukon and other Arctic rivers is particularly focused on climate warming effects on mobilizing ancient carbon from permafrost to coastal regions and the Arctic Ocean. The USGS participates in the Arctic Great Rivers Observatory project, which is an international effort to study the six largest rivers, including the Yukon, which flow into the Arctic Ocean.

Learn more about USGS Yukon River Basin studies.

Contact: Jessica Robertson

Forest Landscape

Forests play a significant role in removing carbon from the atmosphere by absorbing one-third of carbon emissions annually. This is according to a new U.S. Forest Service study conducted in collaboration with USGS scientists.
Learn more