Thursday, December 28, 2006

Dams Pollute?

Interesting perspective that needs to be factored in on any major dam project and one assumes the new research around the viability of the Auburn Dam is doing so.

Patrick McCully: Hydropower reservoirs might add to global warming
By Patrick McCully -
Published 12:00 am PST Thursday, December 28, 2006

Except for a handful of fossil-fuel-funded lobbyists who deny the reality of global warming, we all agree that we urgently need to "green" our energy sources. The big-hydropower industry -- under fire for harm to river ecology and the eviction of communities in the way of its reservoirs -- has seized the opportunity to reposition itself as climate-friendly. The problem is, big hydro is nowhere near as climate-friendly as the industry claims.

Although few people are aware of it, the reservoirs behind the world's dams are likely a major source of global-warming pollution. Investors in electricity generation with low greenhouse-gas emissions stand to make a lot of money in the coming green economy. In the case of big reservoirs in the tropics -- where most dams are proposed -- hydropower can emit more greenhouse gases per kilowatt-hour than fossil fuels, including the dirtiest coal plants.

Eminent climate-change scientist Philip Fearnside estimates that hydro projects in the Brazilian Amazon emit at least twice as much as coal plants. The worst example studied, Balbina dam, had a climate effect in 1990 equal to 54 natural gas plants generating the same amount of power.

How is this possible? When a big dam is built, its reservoir floods vegetation and soils that contain vast amounts of carbon. This organic matter rots underwater, creating carbon dioxide, methane and, in at least some cases, the extremely potent global warming gas nitrous oxide. While emissions are particularly high in the first few years after a reservoir is created, they can remain significant for many decades.

This is because the river that feeds the reservoir, and the plants and plankton that grow in it, will continue to provide more organic matter to fuel greenhouse gas production.

Some of the emissions bubble up from the reservoir surface. The rest occur at the dam: When methane-rich water jets out from turbines and spillways, it releases most of its methane, just like the fizz from an opened bottle of soda. Although the scientists working in the field agree that emissions are released from reservoir surfaces, there is a heated dispute between industry-backed and independent researchers on the amount of gases released at dams. Accounting for these "fizz" emissions greatly increases estimates of the global-warming impact of hydropower. (Research published in November by a team of French scientists indicates that conventional estimates of "fizz" emissions understate the problem.)

Although reservoirs in all climate zones emit greenhouse gases, it is only in the tropics that these emissions are likely often to be worse than fossil-fuel pollution. No comprehensive studies have been done on this issue in the United States, but it is likely that the many thousands of U.S. reservoirs cumulatively emit significant greenhouse gases.