A key climate solution lies under our feet—in soils. Soils naturally remove carbon dioxide from the air and store that carbon underground.
By keeping carbon out of the atmosphere, soils play a major role in balancing the global carbon budget and slowing the rate of warming.
In some ecosystems, carbon can stay in the soil for a long time. But keeping soils healthy is essential for maximum soil carbon storage.
Climate Central’s new report summarizes approaches that can increase the amount of carbon stored in the soils of four major ecosystems: agricultural land, forests, grasslands, and wetlands.
Soils matter tons—billions of tons
A key climate solution lies under our feet—in soils. Soils naturally remove carbon dioxide from the air and store that carbon underground. By keeping carbon out of the atmosphere, soils play a major role in balancing the global carbon budget and slowing the rate of warming.
Globally, burning fossil fuels (coal, oil, and natural gas) releases 9.5 billion metric tons (Gt) of carbon. For reference, 1 Gt is about 800,000 times the mass of the world’s largest tree (a giant sequoia in California), according to the USDA.
That’s a massive amount of carbon. Where does it all go? More than half of the carbon emitted into the atmosphere each year is absorbed by the oceans (26%) and by ecosystems on land (28%). The rest accumulates in the atmosphere, thickening the blanket of heat-trapping gasses that warm the planet.
If it weren’t for the oceans and land absorbing excess carbon from fossil fuel emissions each year, we’d see even more warming than we already have. And of all the carbon absorbed on land, the vast majority goes into soils. Maintaining and increasing carbon storage in soils is therefore a critically important climate solution, and the focus of Climate Central’s latest report.
How soils store carbon
Soils are dynamic living systems, and far more complex than they may seem. Although best known for worms, soils are also home to a vast array of other insects, bacteria, and fungi. These organisms are critical for soil carbon: they break down organic matter (carbon-based plant and animal remains) and release carbon into the soil.
In some ecosystems, that carbon can stay in the soil for a long time. But the amount of carbon that can be stored in soils depends on local ecosystems and land use (for example, whether a location is forested or used for growing crops). The key to soils reaching their full potential to store carbon is keeping soils healthy.
Promoting soil health and carbon storage
Climate Central’s new report summarizes approaches that can maintain or increase the amount of carbon stored in the soils of four major ecosystems: agricultural land, forests, grasslands, and wetlands.
Agricultural soils. Practices that promote soil health and boost carbon storage on croplands and pastures include:
Planting cover crops after harvest can stabilize soil, prevent erosion, and increase water retention.
Moving livestock between pastures (a practice called managed grazing) can prevent overgrazing and soil erosion.
Forest soils. Deforestation is a threat to the carbon stored in forest soils.
Reforestation can increase the carbon in the soil, but this process can take a long time.
Forest management can support carbon storage by reducing erosion, growing more trees, and increasing the diversity of plant species within forests.
Grassland soils. Grassland carbon storage is especially important in the Great Plains and the western U.S.
But grasslands tend to be open and flat, making them vulnerable to development for agriculture and urban expansion. In the U.S., only 4% of native tallgrass prairie remains intact today.
Conservation and restoration of grasslands is critical to ensure their continued carbon storage.
Wetlands. Despite covering a relatively small area, wetland soils can store more carbon per acre than other ecosystems.
But wetlands face habitat destruction, polluted runoff, invasive species and water level changes—all of which reduce their potential to store carbon.
Preserving wetlands and conserving land for coastal wetland migration as sea levels rise can help avoid the loss of wetlands and their dense stores of carbon.
Carbon stored in U.S. soils
According to USGS estimates, the upper 7.9 inches of soils in the contiguous U.S. contain about 22.5 Gt of organic carbon—primarily in forests (36%) and agricultural soils (32%), followed by grasslands (21%) and wetlands (11%).
22.5 Gt of carbon is more than double the amount of carbon released worldwide from fossil fuels each year. And that’s just scratching the surface; the total carbon stored in deeper soils of the U.S. is estimated to be many times greater.
Due to their geographic distribution, forests, agriculture, grasslands and wetlands each play a different role in carbon storage within different U.S. regions. Based on the upper 7.9 inches of soil in each region:
Soils of the eastern U.S. store 10.3 Gt of organic carbon, of which 46% is stored in forests, followed by 31% in agricultural lands, and 21% in wetlands.
Great Plains soils store 7.4 Gt of organic carbon, mainly in agricultural lands (46%) and grasslands (35%).
Soils of the western U.S. store 4.8 Gt of organic carbon, primarily in forests (47%) and grasslands (43%).
These regional differences indicate that a one-size-fits-all approach to promoting soil health and carbon storage isn’t possible. Effective approaches must be tailored to local conditions and ecosystems.
POTENTIAL LOCAL STORY ANGLES
What’s the status of soil health in your local area?
The USDA provides guidance on soil health assessment and indicators to look for. State university extension offices in your area (examples from Cornell University and The Ohio State University) will have more information and resources to understand and assess soil health indicators in your local area—from farms to backyards. The USDA’s Land-Grant University Partner Map provides links to extension offices in all 50 states.
What measures are being taken to improve soil health in your state?
Almost half the states in the U.S. have passed healthy soil legislation or related policies that encourage regenerative agriculture, decrease financial barriers and provide compensation for healthy soil practices. Check the U.S. Healthy Soils Legislation Map to learn about soil-related policies in your state. Sustainable Agricultural Research and Education (SARE) maintains a library of sustainable farming resources, including research and decision tools for soil health. You can search for local innovative sustainable farming projects in their state database.
How much carbon could cropland soils absorb in your state?
A set of graphics from Climate Central show the maximum amount of carbon dioxide that cropland soils in each state could absorb annually through adoption of practices that promote soil health. County-level soil carbon storage estimates for farms using different land management practices can be calculated from COMET-Farm and COMET-Planner tools developed at Colorado State University in collaboration with the USDA’s Natural Resources Conservations Service.
Carbon-rich coastal wetlands face multiple risks. What risks do coastal wetlands face in your area?
The SciLine service, 500 Women Scientists or the press offices of local universities may be able to connect you with local scientists who have expertise on soil carbon and climate change. The American Association of State Climatologists is a professional scientific organization composed of all state climatologists. The USDA provides contact information for state soil scientists in all 50 states as well as a Service Center Locator with contacts for Agency offices, searchable by state and county.
Bianca Moebius-Clune, PhD
Climate Initiative Director
American Farmland Trust
Related expertise: Agricultural soil health and carbon storage
Contact: firstname.lastname@example.org (cc: Lori Sallet, email@example.com)
Deborah S. Page-Dumroese, PhD
Forest Service, U.S. Department of Agriculture
Related expertise: biochar, soil productivity, organic matter, soil disturbance
Estimates of organic carbon stored in the upper 7.9 inches of U.S. soils are based on the following regional USGS reports: Eastern U.S., Zhu and Reed (2014), USGS 1804 (approximately 1.2 million mi2); Western U.S., Zhu and Reed (2012), USGS 1797 (approximately 1.0 million mi2); Great Plains, Zhu (2011), USGS 1787 (approximately 838,000 mi2). Regions are defined in each USGS report based on EPA Level II Ecoregions.