Terrestrial carbon capture and storage (CCS) involves storing carbon dioxide (CO2) from the atmosphere in soils and plant biomass such as tree trunks, branches, foliage and roots. CCS through soils is done by increasing organic matter combined with reduction in ground disturbance such as tilling, reducing erosion, and moderating the exposure to a microbial environment (e.g. water, air, temps and microbes) that will break down and release the carbon.
Approaches: There are two approaches to storing carbon in terrestrial ecosystems. It can be done by protecting ecosystems that store carbon in order to maintain or increase their carbon stores or managing soils and plants to increase CCS beyond the current conditions through natural processes such as photosynthesis. Putting forest lands into conservation is an example of the first approach, and planting an additional crop during the fallow period is an example of the second approach.
Near-term Solution: Terrestrial CCS is considered a near-term approach to reducing greenhouse gases because it can be implemented today. Other benefits of terrestrial CCS may include: improved soil and water quality, reduced erosion, reduced evaporative water loss, reduced pest problems and overall ecosystem improvement. Opportunities for terrestrial CCS exist in: cropland management, grazing land management, afforestation, restoration of degraded soils or wetlands, and biofuels substitution. The sections below describe approaches in soils and forests.
Land Use Change: Historic land use change from native forests and grasslands to cropland and grazing lands has resulted in a loss of organic carbon from soil to the atmosphere. The organic carbon content in tilled US soils has been reduced approximately 40% from pre-tillage levels. This historic loss is a ‘pool’ that can be refilled by management practices such as cropping systems, conservation tillage, grass buffers, planting forests, conservation reserve programs, and wetland restoration.
Soils provide valuable opportunities for terrestrial CCS. They can store two times as much carbon as the atmosphere and 2.5 times as much as plants. Soil carbon content is increased by carbon rich inputs from plants and by management strategies that limit soil disturbance. Plants use carbon from atmospheric CO2 to live and to grow leaves, stems, branches and roots. When a plant dies, the plant components fall to the ground and begin to decompose. During this natural process, some of the plant’s carbon is released to the atmosphere and some of the carbon is captured within the soil thus increasing the soil’s organic matter.
It is estimated that 20-40% of targeted emission reductions can be met by agricultural soil CCS (CASMGS). There are several methods that can increase soil organic carbon in both grazing and croplands. Grazing lands, comprised of pasture and rangelands, represent the largest most diverse single land resource in the United States. As with croplands, the magnitude of the carbon input to the soil in grazing lands depends on several management approaches. Land management practices for increasing carbon storage in soils include: plant residue management, improving the use of fertilizers, application of organic manure, planting improved species, regular use of prescribed burns to increase forage productivity, and improving grazing practices. Soils under grazing management have more soil organic carbon than those under cropping.
Forests cover about one-third of the United States, totaling about 750 million acres. The growth of forests and their management offers one of the most promising sources of CCS in the biosphere. The concept of offsetting CO2 emissions by capturing and storing CO2 in forests is not new. The International Panel on Climate Change found that globally, changes in forest management could offset an additional 15-20% of global CO2 emissions. Trees can live for hundreds, even thousands of years and can lock CO2 in their wood for their entire lifespan. Sustainable logging programs, reforestation, and conservation of forests are all ways to improve CCS in trees.
Terrestrial CCS also provides the opportunity to trade carbon credits and reduce emissions voluntarily. Carbon sequestered by one party could offset emissions produced by another. The U.S. Department of Agriculture (USDA) and the U.S. Department of Energy (DOE) have looked at developing accounting rules for CCS projects and improving the voluntary GHG registry (1605b) and crediting system. Private sector groups such as the National Carbon Offset Coalition and Big Sky Partnership members have initiated pilot market-based systems to trade CO2. Learn more about carbon markets and economics here.