Hydropower is not clean energy

Alternet: …Recent reports on methane emissions suggest that dams are anything but carbon-neutral. According to recently published estimates from Ivan Lima and some of his colleagues at Brazil's National Institute for Space Research, the world's 52,000 largest dams release 104 million metric tons of methane annually. If Lima's calculations are correct, then dams would account for about four percent of the total warming impact of human activities -- and would constitute the largest single source of human-related methane emissions.

…In 2004, Philip Fearnside of the National Institute for Research in the Amazon suggested that a massive surge of methane emissions could occur when water is discharged under pressure at hydroelectric dams in a process known in the industry as "degassing."

The problem with dams is that organic matter gets trapped in them when land is first flooded, and more gets flushed in, or grows there, later on. In tropical zones, such as Brazil, this matter quickly decays to form methane and carbon dioxide.

…There is a potential energy upside to the methane emissions equation. Capturing methane in reservoirs and using it to fuel power plants, says Lima, would mean we could "avoid the need to build new dams with their associated human and environmental costs."

McCully agrees that there could be benefits to capturing and burning the methane from reservoirs. "Doing so could significantly reduce the methane emissions. So while it would do away with an argument against the dams-as-clean-energy theory, extracting methane for electricity could help Brazil to not build any more dams. And removing methane reduces the dam's warming impact by 25 times."…