Fossil fuel combustion and changes in the land use (including deforestation) have resulted in an annual rate of carbon dioxide (CO₂) accumulation in the atmosphere of 3,500 million metric tons. The accumulation of CO₂ and other greenhouse gases (GHG) is expected to cause observable climatic changes in the 21^st century. The Kyoto Protocol to the United Nations Framework Convention for Climate Change identified a goal for participating developed countries to reduce the net GHG emissions in 2008-2012 to less than that emitted in 1990. As a result much effort is being devoted within the scientific community to develop technologies for reducing emissions and to remove CO₂ from the atmosphere.

Regarding the option of removing CO₂ from the atmosphere, the Intergovernmental Panel for Climate Change (IPCC) has estimated that agricultural lands have the potential for removing 40,000 - 80,000 million metric tons of carbon over the next 50-100 years. Thus, soil carbon sequestration in agricultural lands alone might offset the effects of fossil fuel emissions and land use changes for 10-20 years or even longer. Additional carbon can be sequestered in well-managed forests and grassland soils. This strategy cannot be viewed as the permanent solution for the GHG emission problem, but it can be an excellent option for "buying time" and allow for the development and global adoption of new, clean and safe energy sources, which are the main sources of the current emissions.

On the other hand, a significant amount of global GHG emissions is attributed to agricultural production activities, not including the use of fossil fuels or the indirect GHG emissions from fertilizer production. The main sources of GHG in the agricultural sector are N2 O emissions associated primarily with agricultural nitrogen sources (fertilizer and animal manure) and CH4 from ruminants and rice. There is huge variability in the emission of GHG from the agricultural sector, and given this variability there are still many knowledge gaps in the measurement and understanding of agricultural GHG emissions.

Past and recent research has shown that reduction in atmospheric carbon content can be achieved by large-scale applications of land management practices. Among others: reduced tillage, use of rotational crops (e.g., clovers, alfalfa), increased efficiency of animal feed and return of animal waste, improved strategies to enhance plant nutrient use efficiency, establishment of forests and grasslands in former croplands and degraded soils. Most importantly, increasing sequestered carbon in the soils will provide ancillary benefits such as improvements in soil fertility, water-holding capacity and tilth, and reductions in soil erosion. However, although viable agricultural technologies that increase carbon sequestration in soil already exist, research is needed to develop methods that result in larger amounts of sequestered carbon and increased length of time that carbon remains in the soil.

The consideration of carbon sequestration in Kyoto Protocol-type projects is still under discussion. One cause of this discussion is the perception that it is impossible to monitor and verify the amounts of carbon that are supposedly sequestered in such projects. Although it is now possible to monitor the amounts of carbon being sequestered in the soils, the available methods are too expensive and not suited for global studies. However, technology can now provide new applicable methods at reasonable costs. These methods will be based on applications of remote sensing, direct nondestructive sampling, field carbon flux monitoring, and the use of calibrated and validated simulation models (e.g., Century, Decision Support System for Agrotechnology Transfer—DSSAT).

Finally, there is uncertainty about the cost, benefits and risks of technologies to increase carbon sequestration, and this uncertainty could impede the adoption of such technologies. Financial incentives could stimulate the adoption of these technologies and result in additional income for farmers. Mechanisms that could be used to overcome farmer reluctance could include government payments, tax credits, and emission trading with the private sector.

IFDC’s future research on this issue will focus on four research areas:

• Measurement of GHG (mainly N₂O and CH₄) from agricultural soils under different production systems.
   
• Developing management practices to enhance carbon sequestration and increase the length of time that the carbon remains in the soil.
   
• Establish IDSS with the capability of monitoring and verifying carbon sequestration using remote sensing and simulation models.
   
• Policy studies to identify mechanisms to stimulate adoption of technologies, which increase carbon sequestration.

(Contact: baethgen@undp.org.uy)

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