Needless to say, this and other similar reports have generated denial on the part of hydro industry-backed researchers. As a result, the International Rivers Network is calling on the United Nations and the Intergovernmental Panel on Climate Change to develop more definitive research on this topic. This issue is of particular concern as hundreds of millions of dollars in climate subsidies and carbon credits could be spent on hydroelectric projects, which might actually serve to intensify global warming while also destroying ecosystems.
Although large-scale hydroelectric facilities fail to qualify under most definitions of renewable energy, hydropower is generally agreed to be a relatively low carbon intensity form of electricity generation. However, a recent report by the International Rivers Network may change the collective perception of hydroelectricity, in particular tropical hydropower. According to 'Battling Over Bubbles: Big Hydro Hides its Role in Global Warming', "tropical hydropower reservoirs can have a greater impact on global warming than even their dirtiest fossil fuel plant rivals". The report indicates that the greenhouse gases in question, carbon dioxide and methane, are emitted from the rotting of flooded vegetation and other organic matter that is present in hydroelectric reservoirs. The release of water at a dam is subsequently compared to the opening of a "vast coke bottle". More specifically, the report suggests that as water is released from turbines there is an associated large and sudden release of gas bubbles. This has led some to estimate that "in 1990 hydropower dams in the Amazon caused between 3 and 54 times more global warming than modern natural gas plants generating the same amount of energy".