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Decision and Policy Analysis Research Area – DAPA

Carbon Sequestration: A Truly Green Revolution

“Continued greenhouse gas emissions at or above current rates would cause further warming and induce many changes in the global climate system during the 21st century that would very likely be larger than those observed during the 20th century” (IPCC, 2007a, p. 13).

Carbon sequestration – the process of removing carbon from the atmosphere or preventing its release altogether by guarding it in a reservoir – is a pivotal facet of climate change mitigation. The Kyoto Protocol recognizes that net carbon emissions may be reduced either by decreasing the rate at which greenhouse gases are emitted to the atmosphere or by increasing the rate at which greenhouse gases are removed from the atmosphere through sinks, both of which can be achieved through sequestration. Agricultural soils are among the planet’s largest reservoirs of carbon and hold potential for expanded carbon sequestration, thus providing a prospect for mitigating the increasing atmospheric concentration of CO2. Within the context of the Kyoto Protocol and subsequent COP discussions, a number of features make carbon sequestration on agricultural and forestry lands an attractive mitigation strategy.

The Challenge: Make an homogenized database for carbon sequestration in the tropics.

DAPA is working to create soil carbon baselines for different tropical soil types, taking into account the climate, location and management (including past and current agroforestry or silvopastoral practices) of each. The eventual goal is to identify tropical locales with strong sequestration potential, ones that could possibly host mitigation projects financed by carbon bonds from the World Bank.

Soil carbon gaps indicate areas with current low soil carbon levels, but high technical potential for sequestration.

Getting a good carbon baseline for  different tropical soils requires the homogenization of a number of different studies using statistical methods. Different sampling methods, farm management systems and objectives must all be integrated to get a unified idea of annual carbon increase. There is some debate within the scientific community as to the viability of this approach. Arguments against it include:

  • Limited or incomplete information about farm management practices
  • The difficulty of unifying disparate carbon sampling methodologies
  • Differing results and high degrees of uncertainty

The first point could in fact be the most important; small changes in agricultural management practices can dramatically accelerate or reverse the degree of sequestration. Planting of cover crops or the integration of mulching, zero tillage, or agro-forestry will increase below-ground carbon sequestration. Inappropriate use of nitrogen soil amendments or high-intensity tilling will do the reverse. The effects of different management practices can also differ considerably by location depending on the biophysical processes in motion.

Ecosystem Services

The economic feasibility of implementing the land-use changes needed to improve carbon sequestration is not yet clear, although there is growing evidence that changes in production systems leading to carbon sequestration could also provide other economic benefits.

Agriculture has the potential to increase significantly the provision of environmental services such as biodiversity conservation, improved soil and water quality and carbon sequestration. Planting new trees and improving forest health through thinning and prescribed burning are some ways to increase forest carbon in the long run. Harvesting and regenerating forests can also result in net carbon sequestration in wood products and new forest growth.

Source: Fao 2007

Agriculture also plays an important role as a carbon “sink” through its capacity to sequester and store greenhouse gases, especially in the form of carbon in soils, plants and trees. Carbon sequestration involves increasing carbon storage in terrestrial systems, either above or below ground. Changes in land- and soil-use practices can trigger a process of soil carbon accumulation over time. Eventually, however, the system will reach a new carbon stock equilibrium or saturation point, and no new carbon will be absorbed.

Carbon sequestration presents both advantages and disadvantages as a means of mitigating climate change. The main advantage is that it is relatively low-cost and can be readily implemented. Moreover, it provides multiple associated benefits as the resultant increase in root biomass and soil organic matter enhances water and nutrient retention, availability and plant uptake and hence land productivity. A major disadvantage is that, unlike other forms of climate change mitigation, carbon sequestration is reversible; indeed, changes in agricultural management practices can accelerate or reverse the degree of sequestration in a relatively short time frame. In any case, we must be optimistic and work for a green future based on eco-logical development.

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