Hydro 'emits more carbon than fossil fuels'
A hydroelectric dam in the tropics can release four times as much carbon as a comparable fossil-fuel station in the first ten years of its life, scientists have said.
According to conservation biologist Philip Fearnside from the National Institute for Research in the Amazon in Manaus, the levels of greenhouse gases an average dam releases are many times higher than those released from a fossil fuel plant - suggesting hydroelectricity is far from being a "green"or "renewable" energy source as is often claimed.
"The clean, green image of dams may have been seriously overstated," according to an article in Nature magazine where Dr Fearnside set out his arguments this week.
The problem is mostly confined to the tropics, and is linked to the abrupt pressure change that water goes through as it rises from below the surface of the reservoir, causing massive methane releases, Dr Fearnside believes.
Were he proved right about the levels of methane emanating from hydro-plants, current estimates of global emissions of the gas would have to be revised upwards by 20%.
But some researchers dispute the data and say that Dr Fearnside is exaggerating the amount of methane emitted from reservoirs.
Luiz Pinguelli Rosa of the University of Rio de Janeiro says that Fearnside's theoretical calculations extrapolate data from a dam in French Guiana where organic matter levels are particularly high to encompass all dams in tropical areas.
But "with few data sets available on tropical dams, the debate has increased in acrimony without approaching a conclusion," according to Nature.
Environmental campaigners have questioned Dr Rosa's results, suggesting he may have links with the hydropower industry - a charge he strongly denies.
The outcome of the debate, which continued this week as scientists gathered for a Unesco meeting in Paris, could have a bearing on projects funded through the Kyoto protocol's Clean Development Mechanisms, which still counts some hydro-dam projects as "low-carbon."
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