A bitter debate has broken out in the scientific community over hydropower’s contribution to global warming. A leading Brazil-based climate scientist calculates that startlingly high levels of greenhouse gases are emitted when water is released from the turbines and spillways of tropical dams. But hydro industry-backed researchers have fiercely attacked his work. In an effort to settle the debate, International Rivers is releasing a report, just prior to the UN Climate Change conference in Nairobi (Nov. 6-25), calling on the UN’s Intergovernmental Panel on Climate Change to determine hydropower’s culpability in global warming.
“It may seem counterintuitive, but tropical hydropower reservoirs can have a far greater impact on global warming than even their dirtiest fossil fuel plant rivals,” says Patrick McCully, International Rivers Executive Director and author of the report. “The big-hydro lobby has consistently underplayed the scale of hydropower emissions and sought to discredit and silence independent scientists researching dams and global warming.”
Philip Fearnside, one of the world’s most frequently cited scientists on global warming, estimates 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.
The debate between Fearnside and the hydro industry-backed researchers pivots on what happens to methane dissolved in reservoir water when it is released at a dam. Imagine a reservoir as a vast bottle of Coke. Everyone knows what happens when you shake a Coke bottle and open it. The same thing happens as water jets out of dam turbines and spillways — as with opening a Coke there is a sudden release of gas bubbles.
The surfaces of reservoirs also emit greenhouse gases. Emissions of carbon dioxide and methane have been measured from the surfaces of over 100 reservoirs around the world. These gases come from the rotting of flooded vegetation and from organic matter that flows into reservoirs over time.
The scientists researching this issue — most of the relevant work is sponsored by Brazilian and Canadian hydropower utilities — agree that reservoir surfaces emit greenhouse gases. But the hydro-backed scientists downplay the significance of “degassing” releases and assert that the overall impact of tropical hydropower on global warming is not significant compared to fossil fuel power plants.
“It is as if Phillip Morris were in control of all lung cancer research, or Exxon Mobil controlled climate research,” declared McCully. “There is far too much at stake in this debate to allow Big Hydro to control the research agenda. Hundreds of millions of dollars in climate subsidies and carbon credits could be spent on projects which would both worsen global warming and destroy valuable ecosystems.”