NCPA - National Center for Policy Analysis


April 16, 2007

Hoping to rally support for California Gov. Arnold Schwarzenegger's $4 billion plan to build two new hydroelectric dams, state Sen. Dave Cogdill (R-Modesto) told the California Farm Bureau Federation on March 1 the dams are needed to counteract potential global warming effects.

However, new research reported in the February 16 Sacramento Bee suggests the governor's scheme may increase the amount of greenhouse gases put into the air:

  • Substantial greenhouse gas emissions will be released when cement is made for the dam, when the dam is under construction and when the land behind it is flooded, causing vegetation to rot, which releases carbon dioxide and methane into the air.
  • According to several recent research projects summarized by the Bee, some reservoirs absorb more carbon dioxide than they emit, while the net effects at other manmade lakes vary according to geology, climate, reservoir operations, and other factors.

To date, only one such study has been carried out in California.  The study, released in 2004 by researchers at the University of Quebec in Montreal, produced mixed results:

  • It found California's Shasta Lake released 224 tons per day of carbon dioxide, equal to about 14,500 average automobiles, each driven 40 miles a day; emissions at California's Lake Oroville equaled about 3,400 cars.
  • By contrast, California's New Melones reservoir, probably because of a difference in water acidity, absorbed carbon dioxide equal to about 975 cars.

Reservoirs also emit methane, a more potent greenhouse gas than carbon dioxide:

  • The Canadian researchers found each of the three California lakes they studied emitted about a ton of methane a day.
  • Methane from reservoirs may boost global methane inventories 20 percent.
  • California has yet to count reservoir emissions in its own greenhouse gas inventory.

Source: Bonner R. Cohen, "Global Warming Creates Need for New Dams: Schwarzenegger," Heartland Institute, May 2007.


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