Argument: Dam reservoirs release large amounts of greenhouse gas Methane

Issue Report: Hydroelectric dams


Duncan Graham-Rowe. “Hydroelectric power’s dirty secret revealed”. New Scientist. 24 Feb. 2005 – Contrary to popular belief, hydroelectric power can seriously damage the climate. Proposed changes to the way countries’ climate budgets are calculated aim to take greenhouse gas emissions from hydropower reservoirs into account, but some experts worry that they will not go far enough.

The green image of hydro power as a benign alternative to fossil fuels is false, says Éric Duchemin, a consultant for the Intergovernmental Panel on Climate Change (IPCC). “Everyone thinks hydro is very clean, but this is not the case,” he says.

Hydroelectric dams produce significant amounts of carbon dioxide and methane, and in some cases produce more of these greenhouse gases than power plants running on fossil fuels. Carbon emissions vary from dam to dam, says Philip Fearnside from Brazil’s National Institute for Research in the Amazon in Manaus. “But we do know that there are enough emissions to worry about.”

In a study to be published in Mitigation and Adaptation Strategies for Global Change, Fearnside estimates that in 1990 the greenhouse effect of emissions from the Curuá-Una dam in Pará, Brazil, was more than three-and-a-half times what would have been produced by generating the same amount of electricity from oil.

This is because large amounts of carbon tied up in trees and other plants are released when the reservoir is initially flooded and the plants rot. Then after this first pulse of decay, plant matter settling on the reservoir’s bottom decomposes without oxygen, resulting in a build-up of dissolved methane. This is released into the atmosphere when water passes through the dam’s turbines.

Danielle Knight. “Report Highlights Dams’ Role in Global Warming”. Inter Press Service. June 12, 2002 – WASHINGTON – Dams and their reservoirs are significant sources of heat-trapping greenhouse gases, contrary to hydropower industry assertions, environmentalists said Tuesday.

Industry groups have described dams as “climate-friendly” because they are unlike coal-powered energy plants, which emit large amounts of the air pollutants that most scientists believe cause global warming.

However, a growing body of scientific evidence refutes those assertions, said the International Rivers Network (IRN), a U.S.-based anti-dam group, in its report, “Flooding the Land, Warming the Earth.”

Fred Pearce. “Water-reservoirs and greenhouse emissions”. The Independent. 13 October 2000 – Our reservoirs are plumbing the depths of insanity Once reservoirs and dams were the answer to pollution-free power. Now evidence shows greenhouse gases bubbling up from them at an alarming ratee

Fetid, choked with weeds and swarming with mosquitos, the Balbina reservoir in the Amazon rainforest is a billion-dollar boondoggle. The dam soars 50 metres above the trees. But much of the reservoir behind it, which floods an area the size of Warwickshire, is less than four metres deep. “From the air, you can see brown trees beneath the water across huge areas,” says Philip Fearnside, from Brazil’s National Institute for Research in Amazonia. He has counted 1500 islands and “so many bays and inlets it looks rather life a cross-section of a human lung”. Even the introduction of a herd of grazing manatees has failed to staunch the spread of weeds across the surface. Water stagnates in the reservoir’s backwaters for years before reaching the dam’s hydroelectric turbines, which have a piffling generating capacity of 112 megawatts. That means the reservoir needs to flood the equivalent of two football pitches to power a one-kilowatt air conditioner in the Amazonian capital, Manaus. The depth of the insanity of this hydroelectric dam has only recently emerged. Built 13 years ago to provide “green”, pollution-free electricity, it in fact produces eight times more greenhouse gas than a typical coal-fired power station with a similar generating capacity. The rotting vegetation has generated millions of tonnes of two greenhouse gases. These are carbon dioxide and methane – a gas that, molecule for molecule, is 20 times more potent at warming the planet than carbon dioxide.

Jim Giles. “Methane quashes green credentials of hydropower”. Nature. 29 Nov. 2006 – “Emissions from tropical dams can exceed fossil-fuel plants.”

Jessica Marszalek. “World’s dams are ‘contributing to global warming'”. 4 Sept 2007 – THE world’s dams are contributing millions of tonnes of harmful greenhouse gases and spurring on global warming, according to a US environmental agency.

International Rivers Network executive director Patrick McCully said in 2007 to Brisbane’s Riversymposium that rotting vegetation and fish found in dams produced large amounts of methane, which is 25 times stronger than carbon dioxide: “Often it’s accepted that hydropower is a climate friendly technology but in fact probably all reservoirs around the world emit greenhouse gases and some of them, especially some of the ones in the tropics, emit very high quantities of greenhouse gases even comparable to, in some cases even much worse than, fossil fuels like coal and gas.”[1]

Emma Graham-Harrison. “China’s hydropower may be global warming time bomb”. USA Today. 26 Sept. 2007 – BEIJING — China is scrambling to build massive hydropower dams to curb pollution and slake its thirst for energy, but scientists warn that reservoirs can also worsen global warming by emitting a powerful greenhouse gas.
Methane, which traps heat much more efficiently than carbon dioxide, is produced by plants and animals rotting underwater and released when that water rushes through hydropower turbines.