What Is Carbon Sequestration?
Carbon sequestration involves the carbon cycle and carbon capture processes.
The Carbon Cycle
The cycle through which carbon dioxide is released into the atmosphere and absorbed back into Earth is called the carbon cycle. Carbon is stored and released through photosynthesis, decomposition, combustion, and respiration.
The problem is humans are producing too much carbon and storing too little. In 2020, the world set a new record for the average amount of carbon dioxide in the atmosphere: 412.5 parts per million. That’s 12% higher than in 2000. It’s also what’s driving climate change: an increase in greenhouse gases — especially carbon dioxide.
In 2020, the U.S. emitted 4.57 million metric tons of carbon dioxide. The biggest emissions culprit was transportation. Carbon sequestration is one option to help fight those rising emissions.
Carbon Capture and Sequestration
There are two types of carbon sequestration: geologic and biologic.
Geologic sequestration is when carbon is captured from power plants and industrial facilities. The carbon is pressurized into liquid and then stored in porous rock formations underground. While the technology is still in development, it’s mostly being used to offset offshore natural gas production.
Biologic sequestration is when atmospheric carbon is captured by natural processes such as photosynthesis. The carbon is stored in soil, plants, and trees. The process has huge potential to combat climate change. In fact, U.S. forests offset almost 16% of annual U.S. carbon dioxide emissions. That’s 12%-14% of the country’s total greenhouse gas emissions.
Importance of Carbon Sequestration in Forestry
Forests are key to maintaining a good carbon balance. The U.S. has approximately 766 million acres, covering 33% of the country’s land. States with the lowest percentages of forests include Nebraska and North Dakota, while states with the highest percentages of forests include Alaska, Maine, and New Hampshire.
In the past 40 years, forests have absorbed 25% of human carbon emissions, slowing the rate of climate change. In fact, from 1990 to 2020, forests stored 55,933 million metric tons of carbon, and the wood products harvested from forests stored 2,669 million metric tons of carbon.
How It Works
Trees sequester carbon dioxide, acquiring more of it the longer they’re alive. The carbon accumulates in five main pools in forests: aboveground (leaves, trunks, and branches), belowground (roots), and in deadwood, litter (fallen leaves and stems), and soil. As tree parts die, the carbon moves around, cycling from dead tree trunks or branches into deadwood, fallen leaves, and soil. The process can take months to millennia. Afterward, the carbon goes into the product pool through timber harvest or into the atmosphere through respiration, combustion, and decomposition.
How It Helps
Here are five key benefits of carbon sequestration.
1. The longer a forest is alive, the more carbon it can sequester.
The densest carbon is found in living trees, soil, and the forest floor.
2. It purifies air and water.
One tree can take in 10 pounds of pollution and produce enough oxygen for two people.
3. It serves as flood control.
Sequestration helps with moderating runoff and reducing erosion.
4. It protects resources people rely on.
Sequestration helps protect resources such as wild mushrooms, maple syrup, honey, berries, medicinal plants, and landscaping materials.
5. It keeps forests from becoming deserts.
Too few trees equate to too much sun exposure. That can lead to dry soil, dead organisms, and more carbon released.
Why Protecting Forests Requires More Than Just Planting More Trees
Enthusiasm for tree planting is strong, but carbon sequestration requires much more than simply putting more trees in soil. Why? Natural forests store more carbon than human-made forests. Furthermore, their complex ecosystems take centuries to develop, and they store half of carbon aboveground and half belowground.
A Delicate Balance
How much carbon a forest sequesters depends on tree growth, death, and decomposition. If the amount being sequestered is more than the amount being released into the atmosphere, the emissions are negative. If the amount being sequestered is less than the amount being released, the emissions are positive.
Two main types of forces are driving forest carbon dynamics: anthropogenic and ecological.
Ecological forces are unplanned events such as hurricanes and droughts.
Anthropogenic forces are planned activities such as timber harvest or land conversion. Deforestation is turning forests into farms. Globally, from 2000 to 2010, an estimated 32 million acres of forestland disappeared.
These events cause tree mortality, which sets off a cycle wherein carbon moves to deadwood, soil, litter, and product pools. That means the carbon moves — sooner or later — into the atmosphere.
The damage can’t be undone, but bringing a forest back to life can at least begin to offset it.
What Policymakers Can Do to Maximize the Benefits of Carbon Sequestration
Figuring out the right level of offset is a big part of climate policy debates. There’s a lot that policymakers can do. They can restore forests with high carbon density, carefully weigh carbon sequestration versus timber harvesting, and avoid using new forests as an incentive to destroy an existing one. They can also try to put new forests in areas that used to have forests and plant diverse tree species to maximize biodiversity.
Additionally, policymakers can incentivize the use of steel, cement, or aluminum instead of harvested wood. They can divide land into three distinct zones: fully protected original forests, forests that can be carefully harvested, and heavily managed human-made forests. Policymakers can also acknowledge the forest carbon cycle is complex and the science still evolving; for instance, short-term forest management measures that release carbon dioxide could prove a net benefit in the long run by enhancing forest growth.
Ultimately, doing it right requires plenty of data, including information collected from forest life-cycle assessments, environmental impact studies, and carbon emission estimate breakdowns.
Pursuing the Benefits of Carbon Sequestration
Planting trees is a popular strategy to combat climate change, but forests are complex. If policymakers want to maximize the carbon sequestration benefits for forests, they need to pay attention to the evolving science. Still, as complex as forests are, even small forest wins can translate into bigger societal benefits. Planting trees helps buy experts time to develop greener energy technology and transportation options.
Congressional Research Service, “U.S. Forest Carbon Data: In Brief”
EarthHow, “What Is the Carbon Cycle? Photosynthesis, Decomposition, Respiration and Combustion”
The Ecological Society of America Journals, “Carbon Sequestration and Biodiversity Co-Benefits of Preserving Forests in the Western United States”
Food and Agriculture Organization of the United Nations, “Forests and Climate Change”
Frontiers in Forests and Global Change, “Forests and Decarbonization — Roles of Natural and Planted Forests”
Government of Canada, “Forest Carbon”
National Conference of State Legislatures, “The Role of Forests in Carbon Sequestration and Storage”
National Conference of State Legislatures, “State Forest Carbon Incentives and Policies”
Nature, “How Much Can Forests Fight Climate Change?”
NOAA Climate.gov, “Climate Change: Atmospheric Carbon Dioxide”
PNAS, “Tree Planting Has the Potential to Increase Carbon Sequestration Capacity of Forests in the United States”
The Royal Society Publishing, “Mapping Co-Benefits for Carbon Storage and Biodiversity to Inform Conservation Policy and Action”
Sierra Club, “Forest Carbon Sequestration Benefits”
Statista, “Carbon Dioxide Emissions from Energy Consumption in the United States from 1975 to 2020”
United States Geological Survey, “The Concept of Geologic Carbon Sequestration”
United States Geological Survey, “How Much Carbon Dioxide Can the United States Store via Geologic Sequestration?”
United States Geological Survey, “What Is Carbon Sequestration?”
United States Geological Survey, “What’s the Difference Between Geologic and Biologic Carbon Sequestration?”
U.S. Forest Service, “Forest Carbon Science and Reporting”
U.S. Forest Service, “Forest Management for Carbon Benefits”