Global Carbon Sequestration Potential

Management-induced C sequestration is a temporary solution to greenhouse gas buildup.

Knowing how much water is needed to fill up a drinking glass or a water trough is easy: the empty volume equals the amount of water needed. Ordering the right amount of food for dinner to fill your stomach is a little more difficult since measuring the empty space is not as straightforward and, further, the amount of available space varies with the tastiness of the meal. This is similar to estimating the potential to sequester atmospheric CO in agricultural, range, or forest soils and biomass. Most (but not all) C that can be sequestered is C that was lost from the biosphere due to past management practices -- equivalent to the empty space in your stomach. However, the portion of this potential that might become occupied varies with land managers' appetites for C sequestration policies and practices. The absolute amount that can be sequestered is calculated as the difference between what the biosphere can hold and what it holds now. This calculation is by no means simple, and it is further complicated by our incomplete knowledge of how land managers (those who will actually be deciding how that land is managed and, thus how much C is sequestered) will behave. Therefore, any estimates of C sequestration potential are obligated to carry a number of assumptions and caveats that confine them to a limited number of future scenarios.

Since potential C sequestration is such an important issue for greenhouse gas management, a variety of likely C sequestration policies and practices have been evaluated with the aforementioned issues in mind. The Intergovernmental Panel on Climate Change (IPCC) recently published a special report on Land Use, Land-Use Change, and Forestry (Sampson et al., 2000) that reviewed how various management practices might impact C sequestration worldwide. Carbon sequestration rates were based on review data from published studies, and adoption rates were based on expert opinion. Results from this report are listed in Table 1 (below). In general, C storage potentials for management changes within a particular land use are substantially larger than changes associated with those arising between different types of land use. Within grazing lands, for example, nearly 525 billion lbs C might be sequestered annually by 2010, but only 83 billion lbs C are likely to be sequestered with conversion from cropland to grassland. Of these estimated total potentials, most (71%) is in the developing world, but of the C sequestration likely with changes in management, almost half (45%) is in the developed world.

Within the U.S., it has been estimated that 165-459 billion lbs C can be sequestered annually in croplands (Lal et al., 1998) and between 65-243 billion lbs C yr-1 in grazing lands (Follett et al., 2001a). These calculations, like those presented above, are based on published studies examining changes in soil C with changes in management, and they assume very widespread adoption. Furthermore, these sequestration estimates, again like those done by the IPCC and most others, do not account for management-induced changes in other biogenic greenhouse gases (nitrous oxide and methane) that could increase as a result of some of the practices evaluated.

In the mid 1990s, CO2 emissions in the US were about 11 trillion lbs C yr-1. So compared to emissions, C sequestration in terrestrial ecosystems can account for about 6.4% of 1990 emissions. While a considerable amount of C can be stored in terrestrial ecosystems, management-induced C sequestration is only a temporary and partial solution to the greenhouse gas problem. The degree to which sequestration is applied as a solution depends in large part on the appetite of land managers for C sequestering practices.

Rich Conant
Research Associate
Natural Resources Ecology Laboratory

Table 1
Area, portion of area likely to adopt a new practice or land use, rate of C gain with change, and total potential for area in which improved management practices can be implemented (A) and in which land use changes are likely to occur (B). Within each activity, the top line (unshaded) contains data for developed countries and the bottom line (shaded) contains data for developing countries.