What Is CO₂ Sequestration?

Carbon sequestration means capturing CO₂ from the atmosphere or from anthropogenic (human action) CO₂ sources and putting the CO₂ (or the carbon portion of the CO₂) into long-term storage. CO₂ sequestration has the potential to significantly reduce the level of atmospheric carbon as CO₂ and control the release of CO₂ to the atmosphere from major human sources, including power plants and refineries.¹

There are two major types of CO₂ sequestration: terrestrial and geologic.

Terrestrial Sequestration

Click for larger image

Terrestrial (or biologic) sequestration means using plants to capture CO₂ from the atmosphere and then storing it as carbon in the stems and roots of the plants as well as in the soil. In photosynthesis, plants take in CO₂ and give off the O₂ to the atmosphere as a waste gas. The plants retain and use the carbon to live and grow. When the plant winters or dies, part of the carbon from the plant is preserved (stored) in the soil. Terrestrial sequestration is a set of land management practices that maximizes the amount of carbon that remains stored in the soil and plant material for the long term. No-till farming, wetland management, rangeland management, and reforestation are examples of terrestrial sequestration practices that are already in use. It is important to remember that terrestrial sequestration does not store CO₂ as a gas but stores the carbon portion of the CO₂ (the C in the CO₂). If the soil is disturbed and the soil carbon comes in contact with oxygen in the air, the exposed soil carbon can combine with O₂ to form CO₂ gas and reenter the atmosphere, reducing the amount of carbon in storage.

Learn more about the considerations for terrestrial sequestration in the region.
Learn about terrestrial sequestration field projects in the PCOR Partnership region.

Geologic Sequestration
Geologic sequestration, also called carbon capture and storage or CCS, captures CO₂ at anthropogenic sources before it is released to the atmosphere and transports the CO₂ gas to a site where it can be put into long-term, environmentally sound storage deep underground or deep in the ocean.

Before geologic sequestration can be widely used, two issues need to be addressed:

1. Only a handful of specialized facilities like natural gas-processing plants, coal gasification plants, and ethanol plants currently have processes that separate CO₂ and make it available for geologic sequestration. Actions are under way now to develop economical methods of separating CO₂ at other large-scale systems like power plants that produce relatively large quantities of anthropogenic CO₂.
2. Although pure CO₂ has been stored as a gas in natural underground deposits for millions of years and oil field operators have safely pumped millions of tons of CO₂ underground into oil-producing formations to increase production (CO₂ flooding), we need validation demonstrations in geologic and oceanic environments to ensure that we understand the best ways to site the systems as well as monitor the CO₂ in storage over the long term.

References:

1. Pacala, S., and Socolow, R., 2004, Stabilization wedges-solving the climate problem for the next 50 years with current technologies: Science, v. 305, p. 968-972.