Creating and Strengthening Carbon Sinks:
Pressure State Response Indicators

In recent years scientists have learned that terrestrial ecosystems may play a significant role in taking up carbon dioxide released from the Earth's surface. Without this "sink" effect, the amount of carbon dioxide in the air would rise more rapidly, and the possibility of more-rapid global warming would be greater. Terrestrial ecosystems may be responsible for taking up about one-third of all the carbon dioxide that is released into the atmosphere. | Pressure State Response Further reading

Concerns about the threat of global change due to the greenhouse effect have caused considerable amounts of attention to be given to the possibility of encouraging the growth of forests as a means of sequestering carbon dioxide. Furthermore, with the advent of the Kyoto Protocol and its recognition of the use of forestry activities and carbon sinks as acceptable tools for addressing the build-up of atmospheric carbon, the potential role of planted forests as a vehicle for carbon sequestration has taken on a new significance. In some countries, e.g. the U.S., this approach has become an explicit element of national policy.

The Kyoto Protocol authorised the creation of an international market in carbon sequestration schemes whereby developed countries can purchase the externally certified reductions in emissions of developing countries and use them to meet their own national emission limits. To date this concept has been applied to forest conservation and reforestation schemes, most notably in Costa Rica, and even there experience is limited. Recent scientific research however, shows that improved deep-rooted pastures, and pasture-tree combinations, can also form significant carbon sinks and may in the future be important in carbon sequestration. Economic analysis has shown that, at least at certain world price levels for carbon, pasture improvement for a combination of carbon sequestration and livestock production could be profitable.

Pressure

The main pressures arise from the increased rates of emission of the greenhouse gas Carbon dioxide to the global atmosphere. Although Carbon dioxide emissions from agricultural activities are estimated to account for approximately 5% of total anthropogenic emissions, agricultural land has a potentially significant role to play in mitigating the effects of Carbon dioxide emissions.

Pressure is therefore characterised by the change in levels of total atmospheric Carbon dioxide, not just that portion for which agriculture is estimated to be directly responsible.

State

Two aspects of "state" can be discerned: one relating to global Carbon dioxide levels and the other relating to the distribution and availability of existing and potential carbon sinks in the form of terrestrial vegetation.

| Atmospheric Concentration of Carbon Dioxide (MaunaLoa Data). (Source: Carbon Dioxide Information Analysis Centre ) Click on the figures to view larger versions
| Atmospheric Concentration of Carbon Dioxide over the last 45,000 years (Source:Carbon Dioxide Information Analysis Centre )

Response

Options to mitigate Carbon Dioxide emissions from agriculture include reducing emissions from present sources, and creating and strengthening carbon sinks. Options for increasing the role of agricultural land as a sink for Carbon dioxide include carbon storage in managed soils and carbon sequestration after reversion of surplus farm lands to natural ecosystems. However, soil carbon sequestration has a finite capacity over a period of 50-100 years, as new equilibrium levels of soil organic matter are established.

Efforts to increase soil carbon levels have additional benefits in terms of improving the productivity and sustainability of agricultural production systems. Soils of croplands taken out of production into permanent set-asides and allowed to revert to natural vegetation could eventually reach carbon levels comparable to their pre-cultivation state.

A large scale restoration of natural vegetation on former agricultural land is only feasible if adequate supplies of food, fibre and other products cab be produced from the remaining area. This is currently possible in the European Union and North America through the intensification of farming systems (see Industrial Systems). However, if farming intensity in these areas changes – perhaps as a result of environmental concerns associated with intensive agriculture – this option may no longer be available.

In tropical areas, significant destruction of forests is taking place. However, it is estimated that only half of the destroyed forest area contributes to an increase in productive agricultural land. The only way to break out of this cycle is through more sustainable use, improved productivity of existing agricultural land and improved protection of undisturbed areas. These practices could assist in reducing agricultural expansion and hence deforestation in humid zones – especially in Latin America and Africa.

Management practices to increase soil carbon stocks include:

- The use of deep-rooted plant species in pastures;
- Pasture – Tree combinations;
- Reduced tillage of cropland;
- Crop residue return;
- The use of perennial crops (including agro-forestry);
- Reduced frequency of bare and fallow land;

However, there are educational, economic and social constraints to improved soil management in many areas of the tropics. For example, crop residues are often required for livestock feed and if the manure is deposited in different areas (e.g. in overnight stock pens), then there is little or no return of this source of organic material to the soil.

Measures that can have a significant effect on the mitigation of greenhouse gas emissions ion the agricultural sector (including both livestock and crop systems) include the following:

- Market based programmes (e.g. reduction and reform of agricultural support policies; taxes on the use of nitrogen based fertiliser; subsidies on the production and use of bio-energy);
- Regulatory measures (e.g. limits on the use of nitrogen based fertilisers; integration and cross compliance of agricultural and environmental support policies);
- Voluntary and "Best Practice" agreements (e.g. soil management practices that enhance carbon sequestration in agricultural soils);
- International programmes (e.g. support for technology transfer in agricultural systems).

The primary objectives of many of these measures are usually not related solely to climate change issues, but rather to such aims as reducing environmental pollution and natural resource degradation. Governments should, for example, promote more efficient fertiliser use by changing commodity programmes to allow greater flexibility and encourage farmers to adopt practices that rely less on commercial fertilisers. Support and encouragement of the best management practices to reduce soil degradation and environmental pollution would be entirely consistent with mitigation measures for reduction of greenhouse gas emissions.

Further Reading

- Carbon Sequestration Schemes on Pasture Land
- Greenhouse Gasses and Global Warming
- Deforestation
- Deforestation: Pressure-State-Response

Watson, R.T., Zinyowera, M.C. & Moss, R.H. 1996. Technologies, Policies and Measures for Mitigating Climate Change. Intergovernmental Panel on Climate Change. pp.87.

Carbon Dioxide Information Analysis Centre (CDIAC). http://cdiac.esd.ornl.gov/home.html

Kyoto Protocol to the United Nations Framework on Climate Change. (click here to view in Acrobat format). |

Grubb, M., Vrolijk, C. & Brack, D. 1999. The Kyoto Protocol: A Guide to Assessment. The Royal Institute of International Affairs and Earthscan Publications. (ISBN 1 85383 580 3).

Forest Trends. Getting It Right: Emerging Markets For Storing Carbon in Forests. http://www.forest-trends.org/resources/getting.htm. (Click here to view in PDF format) |

World Resources Institute. Carbon Sinks and Sequestration. http://www.wri.org/climate/sinks.html

World resources Institute. Climate, Biodiversity, and Forests: Issues and Opportunities Emerging from the Kyoto Protocol (1998). http://www.wri.org/ffi/climate/

Jones, M.H. & Curtis, P.S. 1999. A Database of Herbaceous Vegetation Responses to Elevated Atmospheric CO2. (Click here to view in PDF format) or go to the web site: http://cdiac.esd.ornl.gov/epubs/ndp/ndp073/ndp073.html |

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