Fizzy Science: Big Hydro’s Role in Global Warming

Patrick McCully
Friday, November 17, 2006

This op-ed first appeared in the San Francisco Chronicle, November 17, 2006

It comes as a surprise to most people, but the reservoirs behind the world’s dams are likely a major source of global warming pollution. In the case of big reservoirs in the tropics -- where most new dams are proposed -- hydropower can actually emit more greenhouse gases per kilowatt-hour than fossil fuels, including dirty coal.

Climate change scientist Philip Fearnside estimates that hydro projects in the Brazilian Amazon emit at least twice as much greenhouse gas as coal plants. The worst example studied, Balbina Dam, had a climate impact in 1990 equal to an astonishing 54 natural gas plants generating the same amount of power, according to Fearnside.

How is this possible? When a big dam is built, its reservoir floods vast amounts of carbon in vegetation and soils. This organic matter rots underwater, creating carbon dioxide, methane and, in at least some cases, the extremely potent warming gas, nitrous oxide. While emissions are particularly high in the first few years after a reservoir is filled, 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’s surface. The rest occur at the dam: When methane-rich water jets out from turbines and spillways, it suddenly releases most of its methane, just like the fizz from a newly opened bottle of Coke. While the scientists working in the field agree on the emissions 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.

It is not surprising that the hydropower industry is alarmed that it would be considered another global-warming culprit. In the coming green economy, energy technologies with the lowest greenhouse-gas emissions will dominate. There’s a lot of money to be made in this energy transformation, and the Big Hydro lobby is pushing hard to be seen as climate-friendly.

Canadian and Brazilian hydro interests dominate funding for reservoir emission science, and have tried hard to control the interpretation of the results. In Canada, industry giant Hydro-Quebec has cut funding to scientists whose work was leading to conclusions the utility considered inconvenient. Hydro-Quebec also tried, unsuccessfully, to pressure a scientific journal (Lakes and Reservoirs Management) into not publishing an article by these scientists.

In hydropower-dependent Brazil, the hydro utilities and government have backed a group of scientists who Fearnside charges have "made a career out of trying to prove me wrong." The industry-backed scientists accuse Fearnside, a rigorously independent researcher, of being seduced by the "lures" of the fossil fuel and nuclear lobbies.

Fearnside’s findings were supported in a recent editorial in the scientific journal Climatic Change written by Danny Cullenward and David Victor from Stanford University. Cullenward and Victor criticize the hydro industry’s control of the reservoir emissions research agenda and call for an independent analysis of the data and their interpretation by the U.N.’s Intergovernmental Panel on Climate Change (IPCC). This is an eminently sensible suggestion.

Given the high stakes -- the billions of dollars that will be directed to reducing climate change and the importance that these investments be as effective as possible -- it is vital that decisions on climate policy are not made based on evidence produced by self-interested industry lobby groups. This is why an independent review of reservoir emission science is essential. Only the IPCC has the resources and reputation needed to clear the fog of confusion created by the hydro industry and its control of the reservoir emissions research agenda.

    More information: