LARGE DAMS contribute heavily to global warming, environmentalists have claimed.
Greenhouse gas emissions from hydropower projects can be up to 38 times greater per unit of electricity produced than from modern coal power stations, says a report from pressure group International Rivers Network (IRN).
The report Flooding the land, warming the earth says huge volumes of methane, a gas closely linked with global warming, are produced as submerged vegetation decomposes when dams fill.
Based on study of 30 reservoirs in Canada and Brazil, the IRN estimates that emissions in temperate regions are roughly half those of a modern gas fired station.
But 'emissions from tropical reservoirs are typically between five and 20 times higher than those in temperate and boreal regions. The worst tropical reservoirs can contribute many times more to global warming than coal plants generating the same amount of power.'
Emissions from the Tucurui reservoir in Brazil were calculated to be up to 38 times greater than those from a coal fired power station.
Including dams built for irrigation, reservoirs release worldwide 70Mt of methane and 1bn tonnes of carbon dioxide per annum. This accounts for 20% of total manmade methane emissions, including farming, and 4% of carbon dioxide emissions.
Combined, the two gases contribute to an estimated 7% of human-created global warming over a 100 year period. The contribution to global warming would be considerably higher if measured over a shorter time span, says the report.
Flooding the land, warming the earth can be found at www. irn. org