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Dams Contribute Significantly to Climate Change, WCD Finds
 Dams Contribute Significantly to Climate Change, WCD Finds

By Aviva Imhof
World Rivers Review
Volume 15, Number 6 / December 200

The World Commission on Dams has found that dams are a significant contributor to climate change, and that many hydropower schemes release more greenhouse gases into the atmosphere than large coal–fired power stations. The WCD estimates that gross emissions from reservoirs, as a result of rotting vegetation, may account for between 1% and 28% of the global warming potential of greenhouse gas (GHG) emissions. The WCD states that "all reservoirs emit GHGs" and that "in some circumstances the gross emissions can be considerable, and possibly greater than the thermal alternatives."

The WCD found that decomposing vegetation in the reservoir emits carbon dioxide and methane. Stagnant water produces the worst emissions because the decaying vegetation generates methane, a greenhouse gas that is 20 times more potent than carbon dioxide. In a new discovery, the WCD found that organic matter washed into a reservoir from upstream generates much of these gases. Thus, emissions may continue for the lifetime of the reservoir, long after all vegetation in the reservoir has decomposed. The WCD says that a period of 100 years is appropriate for the initial calculation of the lifecycle emissions from reservoirs.

"Current understanding of emissions suggests that shallow, warm tropical dams are more likely to be major GHG emitters than deep cold boreal dams," the WCD states. "To date, no experience exists with minimizing, mitigating, or compensating these impacts."

The Balbina reservoir in Brazil, which in places is only four meters deep, is expected to produce three million tons of carbon dioxide annually over its first 20 years. A coal–fired power station of the same capacity would produce 0.35 million tons of CO2 a year.

In addition, the WCD states that other land use changes induced by displacement of people, resource extraction and other activities associated with construction of the dam may form part of the net contribution to greenhouse gas emissions.

The WCD’s findings are especially significant in light of the recent failure by the world’s top polluting governments to agree on a strategy for meeting the targets for reducing GHGs set in Kyoto in 1997.

The United States, Australia, Japan and Canada were pushing to allow for pollution increases above 1997 targets through the use of Clean Development Mechanism credits. The key disagreement, which ultimately led to the breakdown of the talks, was over whether forests could be used as carbon sinks to offset greenhouse gas emissions. However, another outstanding issue is whether industrialized countries can get credits for funding dams and nuclear power stations in Southern countries. Countries made no agreements, except to convene another meeting next May.

"From the WCD’s findings, it would appear that dams are a significant contributor to global warming and should not be considered a clean, carbon–free alternative. In any event, dams have other local and regional impacts that make them inappropriate as a so–called "clean development" project," said Richard Sherman, Coordinator for the South African Climate Action Network in Johannesburg.

   
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