Heated dispute

"It's not nice to fool Mother Nature" (SN: 8/25/07, p. 125) states that "an increase in the atmospheric concentration of carbon dioxide, not an increase in solar radiation" is responsible for current global warming. What is the scientific—not political—basis for that remark?

Warren Finley
Laguna Beach, Calif.

Increasing solar radiation doesn't affect climate change? Doesn't changing the thermostat change the temperature in a room?

Sean Walton
Orem, Utah.

In February, the Intergovernmental Panel on Climate Change acknowledged that an increase in solar radiation had generated a slight warming of Earth since 1750 (SN: 2/10/07, p. 83). Over that same interval, however, the IPCC reports that warming attributed to human-caused emissions of greenhouse gases such as carbon dioxide and methane has been about 20 times greater.—S. Perkins

Pitch out

"Perfect pitch isn't so perfect in many" (SN: 9/15/07, p. 173) brought to mind the history of pitch through the centuries. In the 17th century, what is now G sharp was an A. Maybe the "perfect" pitch is somewhere else.

Stanton Alger
Bainbridge Island, Wash.

Before the 20th century, the tone that musicians called A ranged widely but was generally between 415 and 432 hertz in frequency. Some people today who play "period" instruments tune them accordingly. Today, 415 Hz is indeed G sharp, and A is 440 Hz. The authors of the study say that this historical movement of A might in part explain why even people with perfect pitch often slip up in identifying G sharp.—N. Seppa

An alternative test for people with perfect pitch is to give them the name of a tone and ask them to produce it by humming, singing, or whistling. It was always nice to have such a person in our choir when I was in college.

Stanley Murphy
Zephyrhills, Fla.

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