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See Inside May 2008

Mailbag: Is Fluoride Dangerous? Is a Solar Grand Plan a Good Idea?

Fluoridation; Solar Power; Congress and Science

Fluoride Findings
A report by the National Research Council (NRC) is cited as suggesting negative effects of fluoride in “Second Thoughts about Fluoride,” by Dan Fagin. But the NRC notes that its report was not initiated because of concerns about the low levels of fluoride used in community water fluoridation, nor did it examine that issue. Instead the report is part of a routine review by the Environmental Protection Agency to address whether the higher levels of naturally occurring fluoride currently allowed in drinking water pose a health risk. The EPA is evaluating the report.

The article rightly points out that enamel fluorosis only has a health impact in the severest cases, yet Fagin incorrectly refers to it as a “disease.” It is rather a disruption in enamel formation that affects the way teeth look. The American Dental Association (ADA) offers information on reducing the risk of fluorosis at www.ada.org.

The ADA’s support for fluoridation is based on more than six decades of research, thousands of studies, and the experience of more than 170 million Americans. We welcome additional peer-reviewed scientific studies that will add to the body of knowledge on the use of fluoride.

Mark Feldman
President, American Dental Association

Cosmic Growth Spurt
In “Making Space for Time” [News Scan], Scott Dodd explains that cosmic microwave background radiation shows that 380,000 years after its birth, the universe was filled with hot gas. He then writes,

“Eventually the early cosmos underwent inflation....” This statement is misleading. It implies that the exponential expansion of the universe called inflation occurred hundreds of thousands of years after the big bang. According to inflationary cosmology, inflation occurred around 10^–35 second after the big bang.

Mark Egdall
Hollywood, Fla.

Sunlit Path?
A Solar Grand Plan,” by Ken Zweibel, James Mason and Vasilis Fthenakis, calls for the conversion of 30,000 square miles of pristine desert into photovoltaic farms. A better alternative exists: utilize rooftops. Although this strategy will not take advantage of the concentrated sunshine of the Southwest and will not be as efficient, it will distribute power generation across all time zones and weather conditions, without paving over additional land.

Mathieu Federspiel
via e-mail

Has anyone looked into the effects of installing 30,000 square miles of low-albedo surface material? Solar panels, by design, have a much lower albedo than most flat ground in the Southwest. How would their greater heat absorption affect the local environment?

Talon Swanson
Seattle

THE AUTHORS REPLY: In regard to the first letter, a common and valid criticism of our solar plan is that we undermodeled distributed energy systems, such as rooftop photovoltaics (PVs) and solar hot-water systems. If the price of residential systems is drastically reduced and local storage is provided, dispersed installations can play a much larger role than our article describes.

As to the second letter, locally we would experience differences in temperature and air movements because of albedo change. Although studies on this effect have not yet been conducted for large PV plants, observations and global models suggest some tentative conclusions. Tom Hansen, manager of Tucson Electric Power Company’s PV plant in Springerville, Ariz., has measured a two- to three-degree-Fahrenheit increase at the center of the PV field and a wind vortex from its periphery toward its center. An area of 50,000 square kilometers would receive about 3 x 10^14 watt-hours of solar energy daily. With a 20 percent albedo differential between desert and PV surfaces, this would amount to a net excess of 6 x 10^13 watt-hours per day. Similar albedo changes have also been caused by the major cities of the Southwest with no apparent effects. One should also consider that albedo heating will, nationally, be counterbalanced by avoidance of the heating caused by thermoelectric plants. Greg Nemet of the University of Wisconsin–Madison has studied global net radiative forcing by supplying 50 percent of the world’s energy with PVs, taking into account the albedo effect, and concludes that they are one of the most effective solutions to anthropogenic global warming.

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