Creating and Strengthening Carbon Sinks

Critical ecosystem processes drive our fundamental life support system. One of the principal links in the system is the transfer of carbon between organisms and the atmosphere. This process is known as the Carbon Cycle. | Environmental Assessment: Pressure State Response Indicators Policy Pressures and Policy Options Further Reading

The great bulk of living matter is water, but the rest is made mainly of carbon based molecules (95% or more), including compounds used in energy transfer and storage. Stored energy is ultimately dissipated when carbon compounds are oxidized to carbon dioxide by metabolic reactions, at all levels of the food chain. Atmospheric carbon dioxide is then recycled into more complex carbon compounds by plants and other autotrophic (self feeding) life forms. Not all carbon, however, is quickly recycled. Some is stored in ocean sediments, and some is stored on land as biomass that accumulates carbon. Forests, for example, store significant amounts of carbon in durable forms.

As a general rule, about half of the weight of a mature tree is in elemental carbon. As long as that tree is alive and productive, more carbon is removed than returned to the atmosphere. Forests are therefore considered carbon sinks. Older forest soils contain deep layers of slowly decaying carbon compounds, layers that gradually build up over time. Living trees add to the soil carbon pool when they lose their leaves, and old trees contribute dead wood when they are damaged or die. The lesson here is simple: Planting trees can help soak up atmospheric carbon, but long term carbon storage requires a system where old plant material can build up over time.

The concentration of atmospheric carbon dioxide has been driven upwards over the last 150 years by human activities. There are two ways in which we affect the carbon cycle.

- First, we add new atmospheric carbon dioxide into the mix. Power generation and other fossil fuel emissions release about 6 billion tons of carbon per year, worldwide, to the atmosphere. Compared to the amount added naturally every year (approximately 100 billion tons) human contribution is small. However, the new carbon is remaining and accumulating in the atmosphere.

- Second, land use changes are converting forested systems, which are carbon sinks, into agricultural and urban zones, which tend to be carbon sources. For example, tropical forest losses are estimated to add 1 billion tons of carbon per year. Perhaps more important, the opportunity to remove carbon dioxide from the atmosphere is greatly reduced when the forests disappear.

Carbon dioxide is a greenhouse gas, which means that it absorbs heat reflected from the earth's surface and prevents the escape of heat into space. A delicate balance has developed on earth, one that permits a wide variety of life forms to coexist. Too little heat trapping results in a cold planet. Too much heat trapping results in a warmer atmosphere, and in a less stable climate (increased number of extreme climatic events). The average surface temperature of the earth has risen along with atmospheric carbon dioxide concentrations in both the distant and the recent past.

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 issue of the build-up of atmospheric carbon, the potential role of planted forests as a vehicle for carbon sequestration has taken on a new significance. Additionally, the emergence of tradable emission permits and now tradable carbon offsets provides a vehicle for financially capturing the benefits of carbon emission reductions and carbon offsetting activities. Carbon sequestration has monetary value. Therefore investment in planted forests (or in forest preservation) can be made in relation to both the timber resources themselves and the carbon sequestration services.

Carbon sinks can also occur in non-forested areas. Recent research has indicated that improved deep-rooted pastures, and pasture-tree combinations, can also be significant 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. (See Carbon Sequestration Schemes on Pasture Land)

Further Reading

Greenhouse Gasses and Global warming

Greenhouse Gas Emissions, Fossil Fuels and Taxes

The Terrestrial Carbon Cycle: Implications for the Kyoto Protocol. Science 280, 1393-1394 May 29th 1998

The Kyoto Protocol. A commentary on the treatment of terrestrial carbon issues in the Protocol http://www.igbp.kva.se/protocol.html

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.

Global carbon budget. http://www.igbp.kva.se/TCTop.html

The Gross-net Issue - A description of the different accounting schemes used in discussions leading to the Kyoto agreement http://www.igbp.kva.se/grossnet.html

Haugland, T. 1993. A Comparison of Carbon Taxes in Selected Countries. OECD Environment Monographs. Click here to view this document in Acrobat format (123KB) |  |
OECD 1997. International Greenhouse Gas Emission trading. Expert Group on the UN Framework Convention on Climate Change. Working Paper No.9. Click here to view this document in Acrobat format (287KB) |  |
OECD 1998. Lessons from Existing Trading Systems for International Greenhouse Gas Emission Trading. Click here to view this document in Acrobat format (162KB) |  |
OECD 1999. International Emissions Trading Under the Kyoto Protocol. OECD Information Paper. Click here to view this document in Acrobat format (128KB) |  |

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