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Reservoir Emissions & Climate Change
Greenhouse Gas Emissions from Reservoirs
Scientists have found greenhouse gases are emitted from all of the dozens of reservoirs where measurements have been made. Gases are emitted from the reservoir itself and when water is discharged through turbines and spillways. Emission levels vary widely among reservoirs depending upon such factors as the area and type of ecosystems flooded, reservoir depth and shape, the local climate, and the way in which the dam is operated. In tropical countries, several of the hydropower plants studied appear to have a much greater impact on global warming than natural gas plants generating equivalent amounts of electricity.
Reservoirs emit greenhouse gases due to the rotting of organic matter, including submerged vegetation and soils and the detritus that flows into the reservoir from upstream. The diffusion of carbon dioxide into the atmosphere from reservoir surfaces accounts for most of the global warming impact of dams in boreal and temperate regions, as well as deep tropical reservoirs. For shallow tropical reservoirs, however, methane bubbling up from the reservoir bottom appears to contribute most to their climate impact. Some researchers believe that releases of dissolved methane from water discharged at turbines and spillways may prove to be the largest component of the warming impact of tropical hydropower.
While there is clearly a huge need for further research on this issue, there is already a preponderance of evidence showing that the UN’s Intergovernmental Panel on Climate Change (IPCC) should incorporate dams and reservoirs into their analysis of global sources of greenhouse gases. Countries should include reservoir emissions in their climate treaty-mandated inventories of sources of greenhouse gases. Estimates of greenhouse gas emissions from proposed dam projects should be required by regulatory agencies and funders as part of the project approval process, as recommended by the World Commission on Dams.
A bitter debate has broken out in the scientific community over hydropower’s contribution to global warming. A leading climate scientist calculates that there are startlingly high levels of greenhouse gas emissions when water is released from the turbines and spillways of dams in the tropics. But hydro industry-backed researchers have sharply attacked his work. An IRN report, "Fizzy Science: Loosening the Hydro Industry’s Grip on Reservoir Greenhouse Gas Emissions Research," calls for a UN scientific panel to review the issue.
This report documents the growing evidence for the global significance of greenhouse gas emissions from dams and reservoirs. It also provides an overview of the likely impacts of climate change upon dams and the implications of climate change for already stressed freshwater ecosystems. The report makes a number of relevant policy recommendations.