Some may be dirty, some may be clean, so it’s clear that further research is needed.
'Clean' energy dams may be dirty after all
By Matt Weiser - Bee Staff Writer
Published 12:00 am PST Friday, February 16, 2007
Last month, Gov. Arnold Schwarzenegger announced a plan to borrow $4.5 billion to build two massive new reservoirs. He pitched them as a vital response to climate change.
"With the impact that global warming will cause to our snowpacks," he said, "we need more infrastructure ... so the next generation of Californians is not faced with a shortage of this precious resource."
But new research suggests the governor's water plan may instead aggravate climate change. In recent years, scientists have documented that dams and hydropower -- long considered a "clean" energy source -- may actually pump greenhouse gases into the atmosphere in surprising ways.
Emissions occur, first, during cement-making and construction for a dam. More happens when land behind it is flooded, causing vegetation to rot, releasing carbon dioxide and methane.
Emissions continue throughout the dam's life as more organic matter washes in from upstream, and when water is released to make electricity, causing a pressure drop that frees gases locked within the stored water.
"If these are going to be built as a response to climate change, you at least need to convene some people to study the effect it will have," said Danny Cullenward, a research associate at the Program on Energy and Sustainable Development at Stanford University. "The facts are in that it's not a zero-impact source from an emissions standpoint."
Natural lakes may produce emissions in the same way. But the effects could be greater in man-made reservoirs because water levels change more dramatically behind dams. And, like any other man-made energy source, reservoirs would be counted as an addition of greenhouse gases beyond natural levels.
"Obviously, there's some irony if measures supposed to help us adapt to climate change are themselves contributing to the problem," said Patrick McCully, executive director of the International Rivers Network in Oakland.
Research shows that some reservoirs have a positive effect, absorbing more carbon dioxide than they emit. In either case, the effects vary according to geology, climate, reservoir operations and other factors.
